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Silva Fennica 1926-1997
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Acta Forestalia Fennica
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Articles containing the keyword 'model'

Category: Article

article id 5632, category Article
Annikki Mäkelä, Veli-Pekka Ikonen, Petteri Vanninen. (1997). An application of process-based modelling to the development of branchiness in Scots pine. Silva Fennica vol. 31 no. 3 article id 5632. https://doi.org/10.14214/sf.a8534
Original keywords: puutavara; mänty; kasvu; hiili; läpimitta; biomassa; oksat; laatu; latvus; simulointi; kasvumallit; mallit; hiilitase; oksaisus
English keywords: Pinus sylvestris; carbon balance; simulation; pipe model; timber quality; growth model; branching; crown structure; whorl
Abstract | View details | Full text in PDF | Author Info

A process-oriented tree and stand growth model is extended to be applicable to the analysis of timber quality, and how it is influenced by silvicultural treatments. The tree-level model is based on the carbon balance and it incorporates the dynamics of five biomass variables as well as tree height, crown base, and breast height diameter. Allocation of carbon is based on the conservation of structural relationships, in particular, the pipe model. The pipe-model relationships are extended to the whorl level, but in order to avoid a 3-dimensional model of entire crown structure, the branch module is largely stochastic and aggregated. In model construction, a top-down hierarchy is used where at each step down, the upper level sets constraints for the lower level. Some advantages of this approach are model consistency and efficiency of calculations, but probably at the cost of reduced flexibility. The detailed structure related with the branching module is preliminary and will be improved when more data becomes available. Model parameters are identified for Scots pine (Pinus sylvestris L.) in Southern Finland, and example simulations are carried out to compare the development of quality characteristics in different stocking densities.

  • Mäkelä, E-mail: am@mm.unknown (email)
  • Ikonen, E-mail: vi@mm.unknown
  • Vanninen, E-mail: pv@mm.unknown
article id 5631, category Article
Christophe Godin, Yves Caraglio, Evelyne Costes. (1997). Exploring plant topological structure with the AMAPmod software: an outline. Silva Fennica vol. 31 no. 3 article id 5631. https://doi.org/10.14214/sf.a8533
Keywords: models; plant structure; architectural models; plant development; coding; analysis
Abstract | View details | Full text in PDF | Author Info

In the last decades, architectural analysis has been used to understand and to model plant development. These studies have led us to reconsider the problem of measuring plants while taking into account their topological structure at several scales of detail. A computational platform, called AMAPmod, was created to work on such plant representations. This paper outlines the general methodology used in AMAPmod to represent plant topological structures and to explore these special types of databases. Plant structures are first encoded in order to build corresponding formal representations. Then, a dedicated language, AML, enables the user to extract various types of information from the plant databases and provides appropriate analysing tools.

  • Godin, E-mail: cg@mm.unknown (email)
  • Caraglio, E-mail: yc@mm.unknown
  • Costes, E-mail: ec@mm.unknown
article id 5630, category Article
John H. M. Thornley. (1997). Modelling allocation with transport/conversion processes. Silva Fennica vol. 31 no. 3 article id 5630. https://doi.org/10.14214/sf.a8532
Keywords: simulation; modelling; partitioning; shoot-root ratio; plant growth
Abstract | View details | Full text in PDF | Author Info

A shoot-root carbon:nitrogen allocation model, based on the two processes of transport and chemical conversion, is described and explored. The view is proposed that all allocation models, whether built for the purposes of theoretical investigation or practical application, should start with this irreducible framework. In the present implementation, the processes operate according to: for substrate sources, dependence on shoot and root sizes, with possible product inhibition; for transport, movement down a substrate concentration gradient; for substrate sinks or utilization, linear bisubstrate kinetics. The dynamic and equilibrium properties of the model are explored. Failure of this approach to allocation will indicate to the modeller that additional mechanisms to control the processes are needed, and the mode of failure will indicate the type of mechanisms required. Additional mechanisms are discussed which may involve hormones or teleonomic (goal-seeking) controls, and may be added to the irreducible framework. However, these additions should not replace the irreducible framework of transport and chemical conversion, because they do not in reality. Modifications to the basic model to reflect some possibilities such as ontogenesis with the transition from exponential growth towards a steady state or with the scaling of within-plant transport resistances, the influence of hormones, and active transport, are described.

  • Thornley, E-mail: jt@mm.unknown (email)
article id 5629, category Article
Risto Sievänen, Eero Nikinmaa, Jari Perttunen. (1997). Evaluation of importance of sapwood senescence on tree growth using the model Lignum. Silva Fennica vol. 31 no. 3 article id 5629. https://doi.org/10.14214/sf.a8531
Keywords: Pinus sylvestris; growth; growth model; pipe-model theory; sapwood senescence; open-grown trees
Abstract | View details | Full text in PDF | Author Info

The effects of two alternative formulations of sapwood senescence on the behaviour of model LIGNUM (with parameter values adjusted for Scots pine (Pinus sylvestris L.) growing southern Finland) were studied. The two alternatives were autonomous sapwood senescence assuming a maximum age for the tree ring, and sapwood senescence that is controlled by the mortality of foliage. For the latter alternative two hypothetical further mechanisms were stipulated. All the formulations were implemented in LIGNUM. Simulations were made with all model variants for fertile and poor soil conditions using high, normal and low rates of foliage mortality. The simulation results were compared against of a data set consisting of 11 open grown Scots pine trees from southern Finland. Observations of heartwood proportion were used in this study. They show that heartwood starts to increase in trees from age of approximately 20 years onwards. The simulation results showed no differences between fertile and poor soil conditions as regards heartwood formation. Of the variants of foliage-controlled sapwood senescence the one where death of sapwood in a tree segment induces sapwood senescence in the tree parts below only slightly was the best. This and the autonomous sapwood senescence corresponded equally well to the observations. In order to make more refined conclusions additional data and simulations are necessary.

  • Sievänen, E-mail: rs@mm.unknown (email)
  • Nikinmaa, E-mail: en@mm.unknown
  • Perttunen, E-mail: jp@mm.unknown
article id 5627, category Article
Philippe de Reffye, Daniel Barthélémy, Frédéric Blaise, Thierry Fourcaud, François Houllier. (1997). A functional model of tree growth and tree architecture. Silva Fennica vol. 31 no. 3 article id 5627. https://doi.org/10.14214/sf.a8529
Keywords: growth; water transport; ecophysiology; plant architecture; assimilate production; mathemetical models; computer simulations; growth simulation
Abstract | View details | Full text in PDF | Author Info

A new approach for modelling plant growth using the software AMAPpara is presented. This software takes into consideration knowledge about plant architecture which has been accumulated at the Plant Modelling Unit of CIRAD for several years, and introduces physiological concepts in order to simulate the dynamic functioning of trees. The plant is considered as a serial connection of vegetative organs which conduct water from the roots to the leaves. Another simple description of the plant as a network of parallel pipes is also presented which allows an analytical formulation of growth to be written. This recurring formula is used for very simple architectures and is useful to understand the role of each organ in water transport and assimilate production. Growth simulations are presented which show the influence of modifications in architecture on plant development.

  • de Reffye, E-mail: pd@mm.unknown (email)
  • Barthélémy, E-mail: db@mm.unknown
  • Blaise, E-mail: fb@mm.unknown
  • Fourcaud, E-mail: tf@mm.unknown
  • Houllier, E-mail: fh@mm.unknown
article id 5625, category Article
Thomas Früh. (1997). Simulation of water flow in the branched tree architecture. Silva Fennica vol. 31 no. 3 article id 5625. https://doi.org/10.14214/sf.a8526
Keywords: drought stress; modelling; branches; tree architecture; water flow; finite difference method; hydraulic network; numerical model; hydraulic system
Abstract | View details | Full text in PDF | Author Info

The model HYDRA, which simulates water flow in the branched tree architecture, is characterized. Empirical studies of the last decades give strong evidence for a close structure-function linkage in the case of tree water flow. Like stomatal regulation, spatial patterns of leaf specific conductivity can be regarded as a strategy counteracting conductivity losses, which may arise under drought. Branching-oriented water flow simulation may help to understand how damaging and compensating mechanisms interact within the hydraulic network of trees. Furthermore, a coupling of hydraulic to morphological modelling is a prerequisite if water flow shall be linked to other processes. Basic assumptions of the tree water flow model HYDRA are mass conservation, Darcy's law and the spatial homogeneity of capacitance and axial conductivity. Soil water potential is given as a one-sided border condition. Water flow is driven by transpiration. For unbranched regions these principles are condensed to a nonlinear diffusion equation, which serves as a continuous reference for the discrete method tailored to the specific features of the hydraulic network. The mathematical derivation and model tests indicate that the realization of the basic assumptions is reproducible and sufficiently exact. Moreover, structure and function are coupled in a flexible and computationally efficient manner. Thus, HYDRA may serve as a tool for the comparative study of different tree architectures in terms of hydraulic function.

  • Früh, E-mail: tf@mm.unknown (email)
article id 5623, category Article
Harry T. Valentine. (1997). Height growth, site index, and carbon metabolism. Silva Fennica vol. 31 no. 3 article id 5623. https://doi.org/10.14214/sf.a8524
Keywords: height growth; carbon balance; carbon allocation; carbon dioxide; Bertalanffy model; Mitscherlich model; pipe-model theory; site inxed
Abstract | View details | Full text in PDF | Author Info

A metabolic model of height growth and site index is derived from a parametrization of the annual carbon balance of a tree. The parametrization is based on pipe-model theory. Four principal variants of the height-growth model correspond to four combinations of assumptions regarding carbon allocation: (a) the apical shoot is autonomous or (b) it is not; and (A) the specific rate of elongation of a shoot equals that of a woody root or (B) it does not. The bB model is the most general as it includes the aA, bA, and aB models as special cases. If the physiological parameters are constant, then the aA model reduces to the form of the Mitscherlich model and the bA model to the form of a Bertalanffy model. Responses of height growth to year-to-year variation in atmospheric conditions are rendered through adjustments of a subset of the model's parameters, namely, the specific rate of production of carbon substrate and three specific rates of maintenance respiration. As an example, the effect of the increasing atmospheric concentration of CO2 on the time-course of tree height of loblolly pine (Pinus taeda) is projected over 50-year span from 1986. Site index is predicted to increase and, more importantly, the shape of the site-index curve is predicted to change.

  • Valentine, E-mail: hv@mm.unknown (email)
article id 5622, category Article
Christine Deleuze, François Houllier. (1997). A transport model for tree ring width. Silva Fennica vol. 31 no. 3 article id 5622. https://doi.org/10.14214/sf.a8523
Keywords: carbon; optimization; tree growth; stem taper; allocation; environment; wood distribution; functional balance; Münch’s theory; partitioning; process-model; reaction-diffusion; Thornley's model; silvicultural treatments
Abstract | View details | Full text in PDF | Author Info

Process-based tree growth models are recognized to be flexible tools which are valuable for investigating tree growth in relation to changing environment or silvicultural treatments. In the context of forestry, we address two key modelling problems: allocation of growth which determines total wood production, and distribution of wood along the stem which determines stem form and wood quality. Growth allocation and distribution are the outcome of carbon translocation, which may be described by the Munch theory. We propose a simpler gradient process to describe the carbon distribution in the phloem of conifers. This model is a reformulation of a carbon diffusion-like process proposed by Thornley in 1972. By taking into account the continuity of the cambium along the stem, we obtain a one-dimensional reaction-diffusion model which describes both growth allocation between foliage, stem and roots, and growth distribution along the stem. Distribution of wood along the stem is then regarded as an allocation process at a smaller scale. A preliminary sensitivity analysis is presented. The model predicts a strong relationship between morphology and foliage-root allocation. It also suggests how empirical data, such as stem analysis, could be used to calibrate and validate allocation rules in process-based growth models.

  • Deleuze, E-mail: cd@mm.unknown (email)
  • Houllier, E-mail: fh@mm.unknown
article id 5618, category Article
Marja-Leena Nykänen, Marianne Broadgate, Seppo Kellomäki, Heli Peltola, Christopher Quine. (1997). Factors affecting snow damage of trees with particular reference to European conditions. Silva Fennica vol. 31 no. 2 article id 5618. https://doi.org/10.14214/sf.a8519
Keywords: stem breakage; stand management; snow accumulation; topography; risk assessment; snow damage; snowfall; risk model
Abstract | View details | Full text in PDF | Author Info

Within the European Community snow damage affects an estimated 4 million m3 of timber every year, causing significant economic losses to forest owners. In Northern Europe, for example, the occurrence of snow damage has increased over the last few decades mainly due to the increase in total growing stock. The most common form of damage is stem breakage, but trees can also be bent or uprooted. Trees suffering snow damage are also more prone to consequential damage through insect or fungal attacks.

Snow accumulation on trees is strongly dependent upon weather and climatological conditions. Temperature influences the moisture content of snow and therefore the degree to which it can accumulate on branches. Wind can cause snow to be shed, but can also lead to large accumulations of wet snow, rime or freezing rain. Wet snow is most likely in late autumn or early spring. Geographic location and topography influence the occurrence of damaging forms of snow, and coastal locations and moderate to high elevations experience large accumulations. Slope plays a less important role and the evidence on the role of aspect is contradictory. The occurrence of damaging events can vary from every winter to once every 10 years or so depending upon regional climatology. In the future, assuming global warming in northern latitudes, the risk of snow damage could increase, because the relative occurrence of snowfall near temperatures of zero could increase.

The severity of snow damage is related to tree characteristics. Stem taper and crown characteristics are the most important factors controlling the stability of trees. Slightly tapering stems, asymmetric crowns, and rigid horizontal branching are all associated with high risk. However, the evidence on species differences is less clear due to the interaction with location. Management of forests can alter risk through choice of regeneration, tending, thinning and rotation. However, quantification and comparison of the absolute effect of these measures is not yet possible. An integrated risk model is required to allow the various locational and silvicultural factors to be assessed. Plans are presented to construct such a model, and gaps in knowledge are highlighted.

  • Nykänen, E-mail: mn@mm.unknown (email)
  • Broadgate, E-mail: mb@mm.unknown
  • Kellomäki, E-mail: sk@mm.unknown
  • Peltola, E-mail: hp@mm.unknown
  • Quine, E-mail: cq@mm.unknown
article id 5616, category Article
Hannu Hökkä, Virpi Alenius, Timo Penttilä. (1997). Individual-tree basal area growth models for Scots pine, pubescent birch and Norway spruce on drained peatlands in Finland. Silva Fennica vol. 31 no. 2 article id 5616. https://doi.org/10.14214/sf.a8517
Keywords: Pinus sylvestris; site quality; Picea abies; Betula pubescens; forest drainage; mixed models; peatlands; growth models
Abstract | View details | Full text in PDF | Author Info

Models for individual-tree basal area growth were constructed for Scots pine (Pinus sylvestris L.), pubescent birch (Betula pubescens Ehrh.) and Norway spruce (Picea abies (L.) Karst.) growing in drained peatland stands. The data consisted of two separate sets of permanent sample plots forming a large sample of drained peatland stands in Finland. The dependent variable in all models was the 5-year basal area growth of a tree. The independent tree-level variables were tree dbh, tree basal area, and the sum of the basal area of trees larger than the target tree. Independent stand-level variables were stand basal area, the diameter of the tree of median basal area, and temperature sum. Categorical variables describing the site quality, as well as the condition and age of drainage, were used. Differences in tree growth were used as criteria in reclassifying the a priori site types into new yield classes by tree species. All models were constructed as mixed linear models with a random stand effect. The models were tested against the modelling data and against independent data sets.

  • Hökkä, E-mail: hh@mm.unknown (email)
  • Alenius, E-mail: va@mm.unknown
  • Penttilä, E-mail: tp@mm.unknown
article id 5607, category Article
Paola Virgilietti, Joseph Buongiorno. (1997). Modeling forest growth with management data: A matrix approach for the Italian Alps. Silva Fennica vol. 31 no. 1 article id 5607. https://doi.org/10.14214/sf.a8508
Keywords: forest dynamics; succession; growth models; matrix models; Italian Alps; Italy
Abstract | View details | Full text in PDF | Author Info

This paper reports on the possibility and difficulties in building growth models from past Forest Administration records on cut and growth in the Italian Alps. As a case study, a matrix model was calibrated for uneven-aged forests in the Valsugana valley of the Trentino province. The model gave reliable predictions over 30 years, and plausible long-term forest dynamics, including steady-states that are similar to virgin forests. The results support the view that the current forests are deeply altered as to composition, relative to what would obtain from natural growth. They also support the concept of long cyclic changes in natural stands, gradually approaching a climax state. Shortcomings of the data are that they do not come from an experimental design, they are not always accurate, and they must be supplemented with other information, especially concerning mortality. Still, these cheap and available data can lead to workable models adapted to local conditions, with many management applications.

  • Virgilietti, E-mail: pv@mm.unknown (email)
  • Buongiorno, E-mail: jb@mm.unknown
article id 5593, category Article
Malle Mandre, Jaan Klõseiko, Vaike Reisner, Hardi Tullus. (1996). Assessment of CO2 fluxes and effects of possible climate changes on forests in Estonia. Silva Fennica vol. 30 no. 2–3 article id 5593. https://doi.org/10.14214/sf.a9238
Keywords: climate change; CO2; forestry; Estonia; carbon dioxide; forest composition; Forest Gap model
Abstract | View details | Full text in PDF | Author Info

The present study is the first attempt to carry out an inventory of greenhouse gas (GHG) fluxes in the forests of Estonia. The emission and uptake of CO2 as a result of forest management, forest conversion and abandonment of cultivated lands in Estonia was estimated. The removal of GHG by Estonian forests in 1990 exceeded the release about 3.3 times. Changes in the species composition and productivity of forest sites under various simulated climate change scenarios have been predicted by using the Forest Gap Model for the central and coastal areas of Estonia. The computational examples showed that the changes in forest community would be essential.

  • Mandre, E-mail: mm@mm.unknown (email)
  • Klõseiko, E-mail: jk@mm.unknown
  • Reisner, E-mail: vr@mm.unknown
  • Tullus, E-mail: ht@mm.unknown
article id 5592, category Article
Ari Talkkari. (1996). Regional predictions concerning the effects of climate change on forests in southern Finland. Silva Fennica vol. 30 no. 2–3 article id 5592. https://doi.org/10.14214/sf.a9237
Keywords: climate change; Finland; simulation; growing stock; wood production; Gap model; regional predictions; cutting yield
Abstract | View details | Full text in PDF | Author Info

A gap-model was used with forest inventory data in taking ground-true site, soil and tree characteristics into account in predicting the effects of climate change on forests. A total of 910 permanent sample plots established in the course of national forest inventory (NFI) in Finland and located on mineral soil sites in southern Finland were selected as the input data. The climatological input used in the simulations consisted of interpolated means of and deviations from long-term local temperature and precipitation records. The policy-oriented climate scenarios of SILMU (Finnish Research Programme on Climate Change) were used to describe the climate change. The temperature changes in the climate scenarios were increases of ca. +1.1 °C (low), +4.4 °C (medium) and +6.6 °C (high) compared to the current climate in 110 years. The simulation period was 110 years covering the time years 1990–2100.

Southern Finland, divided into fifteen forestry board districts, was used as the study region. Regional development of stand volume, cutting yield, and total wood production of forests under different climate scenarios were examined. The annual average growth in simulations under current climate was close to that observed in NFL Forests benefited from a modest temperature increase (Scenario 2), but under Scenario 1 the growing stock remained at a lower level than under the current climate in all parts of the study region. In wood production and cutting yield there were regional differences. In the southern part of the study regional wood production under Scenario 1 was ca. 10% lower than under the current climate, but in the eastern and western parts wood production was 5–15% higher under Scenario 1 than under the current climate. The relative values of total wood production and cutting yield indicated that the response of forests to climate change varied by geographical location and the magnitude of climate change. This may be a consequence of not just varying climatic (e.g. temperature and precipitation) and site conditions, but of varying responses by different kind of forests (e.g. forests differing in tree species composition and age).

  • Talkkari, E-mail: at@mm.unknown (email)
article id 5591, category Article
Egbert Beuker, Seppo Kellomäki, Marja Kolström. (1996). Changes in wood production of Picea abies and Pinus sylvestris under a warmer climate: comparison of field measurements and results of a mathematical model. Silva Fennica vol. 30 no. 2–3 article id 5591. https://doi.org/10.14214/sf.a9236
Keywords: Pinus sylvestris; climate change; Picea abies; simulation model; global warming; provenance trials
Abstract | View details | Full text in PDF | Author Info

To project the changes in wood production of Norway spruce (Picea abies (L.) H. Karst.) and Scots pine (Pinus sylvestris L.) in Finland as a result of climate change, two separate studies were made. The first study, at the Faculty of Forestry, University of Joensuu, based its projections on mathematical models; the second one, at the Finnish Forest Research Institute, based projections on measurements of wood production in two series of aged provenance experiments. The results of the two studies were similar for both species: after a 4°C increase of the annual mean temperature a drastic increase in wood production in northern Finland, but little effect, or even some decrease in the southern part of the country. However, the assumptions used in the two studies differed. One important difference was that in the models the temperature is assumed to be increasing gradually over the years, whereas in the provenance experiments, climate changed immediately when the seedlings were transferred to the planting sites. Another problem with the provenance experiments is that when material is moved in a north-south direction in Finland, not only temperature but also photoperiod changes markedly. To compare these two studies, site factors (e.g. soil type, temperature, precipitation) and silvicultural factors (e.g. plant spacing, survival, time of thinning, thinning intensity) from the provenance experiments were included a variable in the mathematical models.

  • Beuker, E-mail: eb@mm.unknown (email)
  • Kellomäki, E-mail: sk@mm.unknown
  • Kolström, E-mail: mk@mm.unknown
article id 5590, category Article
Heikki Hänninen, Seppo Kellomäki, Ilkka Leinonen, Tapani Repo. (1996). Overwintering and productivity of Scots pine in a changing climate. Silva Fennica vol. 30 no. 2–3 article id 5590. https://doi.org/10.14214/sf.a9235
Keywords: Pinus sylvestris; climate change; ecosystems; frost damage; phenology; forest ecology; gap-type model; model accuracy; model realism; overvintering
Abstract | View details | Full text in PDF | Author Info

The productivity of Scots pine (Pinus sylvestris L.) under changing climatic conditions in the southern part of Finland was studied by scenario analysis with a gap-type forest ecosystem model. Standard simulations with the model predicted an increased rate of growth and hence increased productivity as a result of climatic warming. The gap-type model was refined by introducing an overwintering sub-model describing the annual growth cycle, frost hardiness, and frost damage of the trees. Simulations with the refined gap-type model produced results conflicting with those of the standard simulation, i.e., drastically decreased productivity caused by mortality and growth-reducing damage due to premature dehardening in the changing climate. The overwintering sub-model was tested with frost hardiness data from Scots pine saplings growing at their natural site 1) under natural conditions and 2) under elevated temperature condition, both in open-top chambers. The model predicted the frost hardiness dynamics quite accurately for the natural conditions while underestimating the frost hardiness of the saplings for the elevated temperature conditions. These findings show that 1) the overwintering sub-model requires further development, and 2) the possible reduction of productivity caused by frost damage in a changing climate is less drastic than predicted in the scenario analysis. The results as a whole demonstrated the need to consider the overwintering of trees in scenario analysis carried out with ecosystem model for boreal conditions. More generally, the results revealed a problem that exists in scenario analysis with ecological models: the accuracy of a model in predicting the ecosystem functioning under present climatic condition does not guarantee the realism of the model, nor for this reason the accuracy for predicting the ecosystem functioning under changing climatic conditions. This finding calls for the continuous rigorous experimental testing of ecological models used for assessing the ecological implications of climatic change.

  • Hänninen, E-mail: hh@mm.unknown (email)
  • Kellomäki, E-mail: sk@mm.unknown
  • Leinonen, E-mail: il@mm.unknown
  • Repo, E-mail: tr@mm.unknown
article id 5587, category Article
Dina I. Nazimova, N.P. Polikarpov. (1996). Forest zones of Siberia as determined by climatic zones and their possible transformation trends under global change. Silva Fennica vol. 30 no. 2–3 article id 5587. https://doi.org/10.14214/sf.a9232
Keywords: climate change; boreal forests; modelling; Siberia; climatic zones; Russian Federation; zonal forest types; climatic ordination
Abstract | View details | Full text in PDF | Author Info

A system of zonality in Siberia has been formed under the control of continentality, which provides the heat and humidity regimes of the forest provinces. Three sectors of continentality and four to six boreal sub-zone form a framework for the systematization of the different features of land cover in Siberia. Their climatic ordination provides the fundamental basis for the principal potential forest types (composition, productivity) forecasting the current climate. These are useful in predicting the future transformations and succession under global change.

  • Nazimova, E-mail: dn@mm.unknown (email)
  • Polikarpov, E-mail: np@mm.unknown
article id 5586, category Article
Robert A. Monserud, Olga V. Denissenko, Tatyana P. Kolchugina, Nadja M. Tchebakova. (1996). Change in Siberian phytomass predicted for global warming. Silva Fennica vol. 30 no. 2–3 article id 5586. https://doi.org/10.14214/sf.a9231
Keywords: climate change; Siberia; taiga; phytomass; global warming; carbon cycle; vegetation modelling; bioclimatology; vegetation zone
Abstract | View details | Full text in PDF | Author Info

An equilibrium model driven by climatic parameters, the Siberian Vegetation Model, was used to estimate changes in the phytomass of Siberian vegetation under climate change scenarios (CO2 doubling) from four general circulation models (GCM's) of the atmosphere. Ecosystems were classified using a three-dimensional climatic ordination of growing degree days (above a 5 °C threshold), Budyko's dryness index (based on radiation balance and annual precipitation), and Conrad's continentality index. Phytomass density was estimated using published data of Bazilevich covering all vegetation zones in Siberia. Under current climate, total phytomass of Siberia is estimated to be 74.1 ± 2.0 Pg (petagram = 1,015 g). Note that this estimate is based on the current forested percentage in each vegetation class compiled from forest inventory data.

Moderate warming associated with the GISS (Goddard Institute for Space Studies) and OSU (Oregon State Univ.) projections resulted in a 23–26 % increase in phytomass (to 91.3 ± 2.1 Pg and 93.6 ± 2.4 Pg, respectively), primarily due to an increase in the productive Southern Taiga and Sub-taiga classes. Greater warming associated with the GFDL (General Fluid Dynamics Laboratory) and UKMO (United Kingdom Meteorological Office) projections resulted in a small 3–7 % increase in phytomass (to 76.6 ± 1.3 Pg and 79.6 ± 1.2 Pg, respectively). A major component of predicted change using GFDL and UKMO is the introduction of a vast Temperate Forest-Steppe class covering nearly 40% of the area of Siberia, at the expense of Taiga; with current climate, this vegetation class is nearly non-existent in Siberia. In addition, Sub-boreal Forest-Steppe phytomass double with all GCM predictions. In all four climate change scenarios, the predicted phytomass stock of all colder, northern classes is reduced considerably (viz., Tundra, Fore Tundra, northern Taiga, and Middle Taiga). Phytomass in Sub-taiga increases greatly with all scenarios, from a doubling with GFDL to quadrupling with OSU and GISS. Overall, phytomass of the Taiga biome (Northern, Middle, Southern and Sub-taiga) increased 15% in the moderate OSU and GISS scenarios and decreased by a third in the warmer UKMO and GFDL projections. In addition, a sensitivity analysis found that the percentage of a vegetation class that is forested is a major factor determining phytomass distribution. From 25 to 50% more phytomass is predicted under climate change if the forested proportion corresponding to potential rather than current vegetation is assumed.

  • Monserud, E-mail: rm@mm.unknown (email)
  • Denissenko, E-mail: od@mm.unknown
  • Kolchugina, E-mail: tk@mm.unknown
  • Tchebakova, E-mail: nt@mm.unknown
article id 5583, category Article
Ilkka Leinonen, Heikki Hänninen, Tapani Repo. (1996). Testing of frost hardiness models for Pinus sylvestris in natural conditions and in elevated temperature. Silva Fennica vol. 30 no. 2–3 article id 5583. https://doi.org/10.14214/sf.a9228
Keywords: Pinus sylvestris; climate change; frost hardiness; Scots pine; temperature; dynamic models; photoperiod; climatic warming
Abstract | View details | Full text in PDF | Author Info

Two dynamic models predicting the development of frost hardiness of Finnish Scots pine (Pinus sylvestris L.) were tested with frost hardiness data obtained from trees growing in the natural conditions of Finland and from an experiment simulating the predicted climatic warming. The input variables were temperature in the first model, and temperature and night length in the second. The model parameters were fixed on the basis of previous independent studies. The results suggested that the model which included temperature and photoperiod as input variables was more accurate than the model using temperature as the only input variable to predict the development of frost hardiness in different environmental conditions. Further requirements for developing the frost hardiness models are discussed.

  • Leinonen, E-mail: il@mm.unknown (email)
  • Hänninen, E-mail: hh@mm.unknown
  • Repo, E-mail: tr@mm.unknown
article id 5574, category Article
Jouni Vettenranta. (1996). Effect of species composition on economic return in a mixed stand of Norway spruce and Scots pine. Silva Fennica vol. 30 no. 1 article id 5574. https://doi.org/10.14214/sf.a9219
Keywords: Pinus sylvestris; Picea abies; net present value; mixed forests; growth models; tree species composition; forest management practices; felling methods; valuation; soil expectation value; treatment programme
Abstract | View details | Full text in PDF | Author Info

The effect of species mixture was studied in a mixed stand of Norway spruce (Picea abies (L.) H. Karst.) and Scots pine (Pinus sylvestris L.) by simulating around 100 different treatment schedules during the rotation in a naturally regenerated even-aged stand located on a site of medium fertility in North Karelia, Finland. Both thinning from below and thinning from above were applied. Optimum rotations were determined by maximising the net present value calculated to infinity and different treatment schedules were compared with the net present value over one rotation as per rotation applied. In the optimum treatment programme, the proportion of pines was decreased by half of the basal area in the first thinning stage and by the end of the rotation to about one third. In thinning from above, the proportion of pines can be maintained at a slightly higher level. It is economically profitable to maintain the growing stock capital at approximately the level recommended by Forest Centre Tapio, a semi-governmental forestry authority. With non-optimum species composition, the loss in net present value over one rotation can be about 10 % in thinning from below and about 20 % in thinning from above.

  • Vettenranta, E-mail: jv@mm.unknown (email)
article id 5573, category Article
Ilkka Vanha-Majamaa, Raili Suominen, Tiina Tonteri, Eeva-Stiina Tuittila. (1996). Seedling establishment after prescribed burning of a clear-cut and a partially cut mesic boreal forest in southern Finland. Silva Fennica vol. 30 no. 1 article id 5573. https://doi.org/10.14214/sf.a9218
Keywords: Pinus sylvestris; Betula pendula; Picea abies; Betula pubescens; natural regeneration; seedling establishment; prescribed burning; controlled burning; Sorbus aucuparia; seed dispersal; mesic forest; seed rain; autoregression model; GLM
Abstract | View details | Full text in PDF | Author Info

The prescribed burning of a 7.3 ha clear-cut and a 1.7 ha partially cut forest (volume 150 m3/ha) was carried out in Evo (61 °12'N, 25°07'E) on 1 June 1992. The forest was a mesic Myrtillus site type forest dominated by Norway spruce (Picea abies (L.) H. Karst.). Practically all the trees and the above-ground parts of the understorey vegetation died in the fire, while the mor layer was thinned by an average of 1.5 cm.

A study was made on the change of germinated seedling population in time and their dependence on environmental factors. Seedlings of Norway spruce, Scots pine (Pinus sylvestris L.), silver birch (Betula pendula Roth), pubescent birch (B. pubescens Ehrh.) and rowan (Sorbus aucuparia L.) were inventoried in 1993 and in 1994 on permanent plots, four times per growing season. Autoregression models were used to compare regeneration of tree species in the burned forest with regeneration in the burnt clear-cut area, and to study the effect of distance from nearest seed source to regeneration.

The average number of seedlings germinating in 1993 was higher than in 1994, probably because of differences between these consecutive years in regard to the amount of seed rain and weather conditions. The number of Norway spruce and rowan seedling was higher inside the forest area than in the clear-cut area. The distance to the bordering forest and to the closest seed tree did not explain the result. It is suggested that the more stable microclimatic conditions under the shade of dead tree promote germination and seedling establishment in the forest area. As rowan is a bird-dispersed species, it is likely that dead trees help the dispersal of rowan seed by providing birds place to sit and defecate. The shade provided by dead trees may influence the further succession of the tree stand and vegetation composition and diversity.

  • Vanha-Majamaa, E-mail: iv@mm.unknown (email)
  • Suominen, E-mail: rs@mm.unknown
  • Tonteri, E-mail: tt@mm.unknown
  • Tuittila, E-mail: et@mm.unknown
article id 5559, category Article
Jari Hynynen. (1995). Predicting the growth response to thinning for Scots pine stands using individual-tree growth models. Silva Fennica vol. 29 no. 3 article id 5559. https://doi.org/10.14214/sf.a9210
Keywords: Pinus sylvestris; thinnings; height; diameter; stem form; growth models; individual-tree; distance-dependent
Abstract | View details | Full text in PDF | Author Info

Individual tree-growth models for diameter and height, and a model for the cylindrical stem form factor are presented. The aims of the study were to examine modelling methods in predicting growth response to thinning, and to develop individual-tree, distance-independent growth models for predicting the development of thinned and unthinned stands of Scots pine (Pinus sylvestris L.). The models were constructed to be applicable in simulation systems used in practical forest management planning. The models were based on data obtained from eleven permanent thinning experiments located in even-aged Scots pine stands in Southern and Central Finland.

Two alternative models were developed to predict tree diameter growth in thinned and unthinned stands. In the first model, the effect of stand density was described using stand basal area. In the alternative model, an explicit variable was incorporated referring to the relative growth response due to thinning. The magnitude of the growth response was expressed as a function of thinning intensity. The Weibull function was employed to describe the temporal distribution of the thinning response. Both models resulted in unbiased predictions in unthinned and in moderately thinned stands. An explicit thinning variable was needed for unbiased growth prediction in heavily thinned stands, and in order to correctly predict the dynamics of the growth response.

In the height growth model, no explicit thinnning variable referring thinning was necessary for growth prediction in thinned stands. The stem form factor was predicted using the model that included tree diameter and tree height as regressor variables. According to the results obtained, the information on the changes in the diameter/height ratio following the thinning is sufficient to predict the change in stem form.

  • Hynynen, E-mail: jh@mm.unknown (email)
article id 5553, category Article
Annika Kangas, Kari T. Korhonen. (1995). Generalizing sample tree information with semiparametric and parametric models. Silva Fennica vol. 29 no. 2 article id 5553. https://doi.org/10.14214/sf.a9204
Keywords: forest inventories; mixed models; volume; nonparametric models; semiparametric models
Abstract | View details | Full text in PDF | Author Info

Semiparametric models, ordinary regression models and mixed models were compared for modelling stem volume in National Forest Inventory data. MSE was lowest for the mixed model. Examination of spatial distribution of residuals showed that spatial correlation of residuals is lower for semiparametric and mixed models than for parametric models with fixed regressors. Mixed models and semiparametric models can both be used for describing the effect of geographic location on stem form.

  • Kangas, E-mail: ak@mm.unknown (email)
  • Korhonen, E-mail: kk@mm.unknown
article id 5546, category Article
Oliver Schabenberger, Timothy G. Gregoire. (1995). A conspectus on Estimating Function theory and its applicability to recurrent modeling issues in forest biometry. Silva Fennica vol. 29 no. 1 article id 5546. https://doi.org/10.14214/sf.a9197
Keywords: modelling; mixed models; statistical methods; longitudinal data; generalized linear models; optimality
Abstract | View details | Full text in PDF | Author Info

Much of forestry data is characterized by a longitudinal or repeated measures structure where multiple observations taken on some units of interest are correlated. Such dependencies are often ignored in favour of an apparently simpler analysis at the cost of invalid inferences. The last decade has brought to light many new statistical techniques that enable one to successfully deal with dependent observations. Although apparently distinct at first, the theory of Estimating Functions provides a natural extension of classical estimation that encompasses many of these new approaches. This contribution introduces Estimating Function Theory as a principle with potential for unification and presents examples covering a variety of modelling issues to demonstrate its applicability.

  • Schabenberger, E-mail: os@mm.unknown (email)
  • Gregoire, E-mail: tg@mm.unknown
article id 5525, category Article
Jari Miina. (1994). Spatial growth model for Scots pine on drained peatland. Silva Fennica vol. 28 no. 1 article id 5525. https://doi.org/10.14214/sf.a9159
Keywords: Pinus sylvestris; drained peatlands; growth models; linear models
Abstract | View details | Full text in PDF | Author Info

A spatial growth model is presented for Scots pine (Pinus sylvestris L.) on a dwarf-shrub pine mire drained 14 years earlier. The growth model accounts for the variation in tree diameter growth owing to the competition between trees, the distance between tree and ditch, and the time passed since drainage. The model was used to study the effect of tree arrangement on the post-drainage growth of a pine stand. Clustering of trees decreased the volume growth by 9–20% as compared to a regular spatial distribution. Stand volume growth, for a given number of stems, was at its maximum and variation in diameter growth at its minimum when the stand density on the ditch border was 1.5–5 higher than midway between two adjacent ditches.

  • Miina, E-mail: jm@mm.unknown (email)
article id 5524, category Article
Annika Kangas. (1994). Classical and model based estimators for forest inventory. Silva Fennica vol. 28 no. 1 article id 5524. https://doi.org/10.14214/sf.a9158
Keywords: models; forest inventories; estimation; systematic cluster sampling; covariance structure
Abstract | View details | Full text in PDF | Author Info

In this study, model-based and design-based inference methods are used for estimating mean volume and its standard error for systematic cluster sampling. Results obtained with models are compared to results obtained with classical methods. The data are from the Finnish National Forest Inventory. The variation of volume in ten forestry board districts in Southern Finland is studied. The variation is divided into two components: trend and correlated random errors. The effect of the trend and the covariance structure on the obtained mean volume and standard error estimates is discussed. The larger the coefficient of determination of the trend model, the smaller the model-based estimates of standard error, when compared to classical estimates. On the other hand, the wider the range and level of autocorrelation between the sample plots, the larger the model-based estimates of standard error.

  • Kangas, E-mail: ak@mm.unknown (email)
article id 5520, category Article
Kari T. Korhonen. (1993). Mixed estimation in calibration of volume functions of Scots pine. Silva Fennica vol. 27 no. 4 article id 5520. https://doi.org/10.14214/sf.a15681
Keywords: Pinus sylvestris; models; forest inventories; volume; estimation
Abstract | View details | Full text in PDF | Author Info

Regression models for estimating stem volume of Scots pine (Pinus sylvestris L.) were constructed using sample tree data measured in the 7th and 8th National Forest Inventory of Finland. Stem volume were regressed on diameter, basal area of growing stock, and geographic location. The results of the study show that using second order trend surface to describe the geographic variation of the residuals gives satisfactory results. Using mixed estimation for combining old and new sample tree data improves the efficiency of an inventory. The weight of the prior information must be low, because remarkable differences in stem form was found in the two inventories.

The PDF includes an abstract in Finnish.

  • Korhonen, E-mail: kk@mm.unknown (email)
article id 5519, category Article
Jyrki Kangas, Jari Karsikko, Laura Laasonen, Timo Pukkala. (1993). A method for estimating the suitability function of wildlife habitat for forest planning on the basis of expertise. Silva Fennica vol. 27 no. 4 article id 5519. https://doi.org/10.14214/sf.a15680
Keywords: forest management; models; wildlife management; black grouse; production functions; multiple use; Lururus tetrix
Abstract | View details | Full text in PDF | Author Info

In the method presented in this study, a group of experts evaluate, in a pairwise manner, a set of forest areas with respect to the game species considered. On the basis of these comparisons, relative priorities of forest areas are estimated using the eigenvalue technique. Using regression analysis, a habitat suitability function is estimated in which the priority is predicted by measures already familiar in forest planning. As a case study, a habitat suitability function was estimated for black grouse (Tetrao tetrix, Lururus tetrix L.). The function is applicable in forestry planning carried out using modern planning techniques.

The PDF includes an abstract in Finnish.

  • Kangas, E-mail: jk@mm.unknown (email)
  • Karsikko, E-mail: jk@mm.unknown
  • Laasonen, E-mail: ll@mm.unknown
  • Pukkala, E-mail: tp@mm.unknown
article id 5511, category Article
Veli Pohjonen, Timo Pukkala. (1993). Cupressus lusitanican tuotos Etiopiassa. Silva Fennica vol. 27 no. 3 article id 5511. https://doi.org/10.14214/sf.a15672
English title: Yield of Cupressus lusitanica in Ethiopia.
Keywords: distribution; plantation; diameter; yield, models; yield tables; Cupressus lusitanica; thinning regimes
Abstract | View details | Full text in PDF | Author Info

Yield of Cupressus lusitanica Mill. was modelled by predicting the diameter distribution of trees at given stand ages. The beta distribution was used as a theoretical distribution. The models used for the calculation of diameter distribution were based on 66 temporal sample plots with varying age, site and stand density. The growing sites of Cupressus lusitanica were divided into four classes on the basis of age and dominant height. Using the stand models developed in the study, the yield and profitability of different thinning schedules was evaluated by a simulation technique. In the simulated treatment regimes, the mean annual increment varied from 6.6 m3/ha in the poorest site class to 16.6 m3/ha in the best class with rotation lengths ranging from 25 years (best sites) to 34 years (poorest sites). With typical planting densities (1,600 trees/ha), thinnings increase the total harvest by a few percentage points and improved the profitability of plantation forestry.
The PDF includes an abstract in Finnish.

  • Pohjonen, E-mail: vp@mm.unknown (email)
  • Pukkala, E-mail: tp@mm.unknown
article id 5510, category Article
Esa Koistinen, Sauli Valkonen. (1993). Models for height development of Norway spruce and Scots pine advance growth after release in southern Finland. Silva Fennica vol. 27 no. 3 article id 5510. https://doi.org/10.14214/sf.a15671
Keywords: Pinus sylvestris; Picea abies; Finland; growth models; advance growth; release cut
Abstract | View details | Full text in PDF | Author Info

Mixed linear models were constructed to describe the height development of Norway spruce (Picea abies (L.) H. Karst.) and Scots pine (Pinus sylvestris L.) advance growth after release cutting. The models related density of the overstory, time elapsed since release cutting and tree size with annual height increment. Parameters of preliminary models were estimated from a limited data set to judge the feasibility of the approach for further studies.

The PDF includes an abstract in Finnish.

  • Koistinen, E-mail: ek@mm.unknown (email)
  • Valkonen, E-mail: sv@mm.unknown
article id 5504, category Article
Heli Peltola, Seppo Kellomäki. (1993). A mechanistic model for calculating windthrow and stem breakage of Scots pines at stand age. Silva Fennica vol. 27 no. 2 article id 5504. https://doi.org/10.14214/sf.a15665
Keywords: Pinus sylvestris; wind; stems; breakage; windspeed; breaking stress; bending models
Abstract | View details | Full text in PDF | Author Info

A model for the mechanism of windfall and stem breakage was constructed for single Scots pine (Pinus sylvestris L.) at the stand edge. The total turning moment arising from the wind drag and from the bending of stem and crown was calculated along with the breaking stress of the stem. Similarly, the support given by the root -soil plate anchorage was calculated. Windspeed variation within the crown and the vertical distribution of stem and crown weight were taken into account. Model computations showed that trees having a large height to diameter ratio were subjected to greater risk of falling down or breaking than trees with a small height to diameter ratio. The windspeed required to blow down a tree or break the stem of a tree decreased if the height to diameter ratio or the crown to stem ratio of trees increased.
The PDF includes an abstract in Finnish.

  • Peltola, E-mail: hp@mm.unknown (email)
  • Kellomäki, E-mail: sk@mm.unknown
article id 5491, category Article
Kari T. Korhonen. (1992). Calibration of upper diameter models in large scale forest inventory. Silva Fennica vol. 26 no. 4 article id 5491. https://doi.org/10.14214/sf.a15652
Keywords: models; forest inventories; simulation; diameter; estimation
Abstract | View details | Full text in PDF | Author Info

Models for estimating the upper diameter of trees were constructed using sample tree data measured in the 7th National Forest Inventory in Finland. Calibration of the models was tested with data from the 8th National Forest Inventory. The results showed that using mixed estimation for combining the two data sets improves the reliability of the models. Models and methods used in this study can be recommended for use in forest inventories.

The PDF includes an abstract in Finnish.

  • Korhonen, E-mail: kk@mm.unknown (email)
article id 5484, category Article
Jyrki Kangas, Timo Pukkala. (1992). A decision theoretic approach applied to goal programming of forest management. Silva Fennica vol. 26 no. 3 article id 5484. https://doi.org/10.14214/sf.a15645
Keywords: forest management; models; forest planning; decision analysis; goal programming; optimization methods
Abstract | View details | Full text in PDF | Author Info

An alternative approach to formulating a forestry goal programming problem is presented. First, single objective optima levels are solved. The Analytical Hierarchy Process is applied in the estimation of a priori weights of deviations from the goal target levels. The ratios of the weights can be interpreted as relative importance of the goals, respectively. The sum of the weighted deviations from all single optima levels associated with the management goals is minimized. Instead of absolute deviations, relative ones are used. A case study problem of forest management planning with several objectives, measured in different units, is analysed.

The PDF includes an abstract in Finnish.

  • Kangas, E-mail: jk@mm.unknown (email)
  • Pukkala, E-mail: tp@mm.unknown
article id 5478, category Article
Seppo Kellomäki, Marja Kolström. (1992). Computations on the management of seedling stands of Scots pine under the influence of changing climate in southern Finland. Silva Fennica vol. 26 no. 2 article id 5478. https://doi.org/10.14214/sf.a15639
Keywords: Pinus sylvestris; forest management; models; Betula pendula; Scots pine; silver birch; simulation; climatic change; seedling stands
Abstract | View details | Full text in PDF | Author Info

Model computations on the management of Scots pine (Pinus sylvestris L.) at the seedling stage showed that a rising temperature due to the suggested climate change could increase the competition capacity of birch species (Betula pendula) more than Scots pine, whose growth could even decline during the course of a rise in temperature. A temperature rise could, thus, bring the time of removal of birches forward when aiming at Scots pine timber stands composed of these tree species. The increasing proportion of birches makes the removal of birches even more urgent and emphasizes the need for careful management of Scots pine stands under rising temperatures. The first thinning of Scots pine is generally brought forward; this is particularly the case when wide spacing is applied in planting. A furthrer rise in temperature magnifies the above patterns by reducing further the competitive capacity of Scots pine in relation to birches.
The PDF includes an abstract in Finnish.

  • Kellomäki, E-mail: sk@mm.unknown (email)
  • Kolström, E-mail: mk@mm.unknown
article id 5468, category Article
Seppo Kellomäki, Heikki Hänninen, Taneli Kolström, Risto Lauhanen, Ulla Mattila, Brita Pajari, Hannu Väisänen. (1992). A simulation model for the succession of the boreal forest ecosystem. Silva Fennica vol. 26 no. 1 article id 5468. https://doi.org/10.14214/sf.a15626
Keywords: succession; gap dynamics; ecosystems; simulation models; forest ecology
Abstract | View details | Full text in PDF | Author Info

A model for the succession of the forest ecosystem is described. The growth and development of trees and ground cover are controlled by temperature and light conditions and the availability of nitrogen and water. In addition, the effects of the annual cycle of trees including the risk of frost damage, wild fire, and wind damages are contained in the model as factors which control the survival and productivity of trees. The model also makes it possible to evaluated the risk of insect attack assuming that this risk is inversely related to the growth efficiency of trees.

The PDF includes an abstract in Finnish.

  • Kellomäki, E-mail: sk@mm.unknown (email)
  • Hänninen, E-mail: hh@mm.unknown
  • Kolström, E-mail: tk@mm.unknown
  • Lauhanen, E-mail: rl@mm.unknown
  • Mattila, E-mail: um@mm.unknown
  • Pajari, E-mail: bp@mm.unknown
  • Väisänen, E-mail: hv@mm.unknown
article id 5453, category Article
Annika Kangas. (1991). Updated measurement data as prior information in forest inventory. Silva Fennica vol. 25 no. 3 article id 5453. https://doi.org/10.14214/sf.a15611
Keywords: forest inventories; mixed estimator; prior information; model-based inference
Abstract | View details | Full text in PDF | Author Info

Old inventory data has widely been used as prior information in forest inventory using the method of sampling with partial replacement (SPR). In this method knowledge about forest growth has not been utilized. However, the accuracy of the inventory results can be improved if this knowledge is utilized. The usability of the inventory results can be improved if the prior information is updated by treewise growth models. In this paper a statistical basis is presented for a method in which such information can be used. The applicability of the method is also discussed. An example is given to demonstrate the method.

The PDF includes an abstract in Finnish.

  • Kangas, E-mail: ak@mm.unknown (email)
article id 5449, category Article
Timo Pukkala, Taneli Kolström. (1991). Effect of spatial pattern of trees on the growth of Norway spruce stand. Silva Fennica vol. 25 no. 3 article id 5449. https://doi.org/10.14214/sf.a15603
Keywords: Picea abies; thinnings; growth; spatial distribution; simulation models; biological competition
Abstract | View details | Full text in PDF | Author Info

The simulation model consists of a method to generate theoretical Norway spruce (Picea abies (L.) H. Karst.) stands, and a spatial growth model to predict the growth of these stands. The stand generation procedure first predicts the tree diameters from a few stand characteristics and from tree locations. Tree age and height are predicted using spatial models. Spatial growth models were made for both diameter growth and basal area growth. Past growth was used as a predictor in one pair of models and omitted in another pair. The stand generation method and the growth models were utilized in studying the effect of tree arrangement and thinning method on the growth of a Norway spruce stand.

The PDF includes an abstract in Finnish.

  • Pukkala, E-mail: tp@mm.unknown (email)
  • Kolström, E-mail: tk@mm.unknown
article id 5425, category Article
Hannu Saarenmaa. (1990). Frame- and rule-based knowledge representation in an expert system for integrated management of bark beetles. Silva Fennica vol. 24 no. 2 article id 5425. https://doi.org/10.14214/sf.a15579
Keywords: modeling; Scolytidae; expert systems; frame-based knowledge representation; integrated pest management
Abstract | View details | Full text in PDF | Author Info

Decision making in the forest protection involves diagnosing the pest, making predictions of the effects of the pest on forest, knowing the possible control tactics, and cost/benefit integration. To cope with all that, a generalist forest manager needs a tool like an expert system to support decisions.

This paper presents an expert system that approaches the goals of integrated pest management. With the systm, the user can make diagnosis and predictions of 12 North European bark beetles. Written in Common LISP and Flavors, the expert system has a combined frame- and rule-based knowledge representation. Frames are used to represent the hierarchy of insect taxonomy in diagnosis. Prediction is made with qualitative reasoning with rules. The interface engine applies both forward and backward chaining. The system has a graphical user interface that supports exploring the sensitivity of advice on input.

It is concluded that expert systems and artificial intelligence have high applicability everywhere in forestry where complicated decisions have to be made. Especially, an integrated pest management system in forestry is largely equivalent to a computerized decision-making aid.

The PDF includes an abstract in Finnish.

  • Saarenmaa, E-mail: hs@mm.unknown (email)
article id 5424, category Article
Timo Pukkala, Veli Pohjonen. (1990). Use of linear programming in land use planning in the Ethiopian highlands. Silva Fennica vol. 24 no. 2 article id 5424. https://doi.org/10.14214/sf.a15578
Keywords: plantations; fuelwood; mathematical models; grazing; Eucalyptus globulus; arable crops
Abstract | View details | Full text in PDF | Author Info

Linear programming was used to analyse the land use alternatives in the Debre Birhan Fuelwood Plantation area, in the central highlands of Ethiopia. The region represents a rural, high-altitude area, where the main land uses are grazing and cultivation of barley, wheat and pulses. To alleviate fuelwood shortage, large plantations of Eucalyptus globulus Labill. have been established. Livestock has traditionally used the major part of the production capacity of the sites. A decrease in the number of cattle would facilitate a considerable increase in the production of cereals, pulses, fuelwood and construction timber. The optimal share of the land for arable crops, grazing and tree plantations would be about 40, 45 and 15% respectively.

The PDF includes an abstract in Finnish.

  • Pukkala, E-mail: tp@mm.unknown (email)
  • Pohjonen, E-mail: vp@mm.unknown
article id 5419, category Article
Timo Pukkala, Owen Mubita, Jussi Saramäki. (1990). Management planning system for tree plantations. Silva Fennica vol. 24 no. 2 article id 5419. https://doi.org/10.14214/sf.a15573
Keywords: diameter distribution; plantations; yield model; Zambia; simulation model; Pinus kesiya; timber management planning; multiobjective optimization
Abstract | View details | Full text in PDF | Author Info

The paper presents a simple model of long-term forest management planning in tree plantations. The model is particularly suitable for developing countries where the research resources are limited. The management plan is prepared in two steps. First, one or several treatment schedules are simulated for each calculation unit (age class, compartment, etc.) over the selected planning period. Second, an optimal combination treatment schedules according to the selected objectives and constraints is searched by mathematical programming. The simulation of growth is based on the prediction of the diameter distribution at the desired time point. All stand characteristics are derived from this distribution. The models needed in the yield simulation can be estimated from temporary sample plots. A case study management plan for 13,000 ha of Pinus kesiya (Royle ex Gordon) plantations in Zambia is presented to demonstrate the system.

The PDF includes an abstract in Finnish.

  • Pukkala, E-mail: tp@mm.unknown (email)
  • Mubita, E-mail: om@mm.unknown
  • Saramäki, E-mail: js@mm.unknown
article id 5388, category Article
Martti Varmola. (1989). Männyn istutustaimikoiden lustonleveysmalli. Silva Fennica vol. 23 no. 4 article id 5388. https://doi.org/10.14214/sf.a15546
English title: A model for ring width of planted Scots pine.
Original keywords: mänty; taimikot; lustonleveys; kasvumallit; puuaineen laatu
English keywords: Pinus sylvestris; wood quality; spacing; ring width; growth models
Abstract | View details | Full text in PDF | Author Info

Ring width at breast height is presented as a function of stem radius at breast height, the ratio between the diameter of a tree and the basal area median diameter, site index, and density of stand. By means of a conversion model ring width at stump height can be estimated as a function of ring width at breast height.

According to previous studies substantially better wood quality can be expected if mean width near the pith at stump height decreases from 3 to 2 mm. According to the present study only on the poorest sites suitable for Scots pine (Pinus sylvestris L.) planting (poor Vaccinium type) the ring width is less than 3 mm at stump height even in the thickest trees. On more fertile sites a substantial increase in the recommended planting density is required, if the mean ring width is aimed to be less than 3 mm. On the best sites it is impossible to reach mean ring width of less than 2 mm, when the density is less than 4,000 stems/ha. Only the thinnest trees on the poorest sites can have a mean ring width less than 2mm.

The PDF includes an abstract in English.

  • Varmola, E-mail: mv@mm.unknown (email)
article id 5379, category Article
Timo Kuuluvainen, Timo Pukkala. (1989). Effect of Scots pine seed trees on the density of ground vegetation and tree seedlings. Silva Fennica vol. 23 no. 2 article id 5379. https://doi.org/10.14214/sf.a15536
Keywords: Pinus sylvestris; natural regeneration; spatial variation; ground vegetation; seedlings; seed trees; regeneration models; ecological fields; resource consumption; competitive interface
Abstract | View details | Full text in PDF | Author Info

The study uses the methodology of ecological field theory to model the effect of Scots pine (Pinus sylvestris L.) seed trees on the density of tree seedlings and other plants in the field layer. The seed trees had a clear effect on the expected value of the amount and distribution of the ground vegetation. The vicinity of seed trees had an adverse effect on the growth of grasses, herbs and seedlings, while mosses were most abundant near the trees. Models based on the ecological field approach were derived to describe the effect of seed trees on the ground vegetation.

The PDF includes an abstract in Finnish.

  • Kuuluvainen, E-mail: tk@mm.unknown (email)
  • Pukkala, E-mail: tp@mm.unknown
article id 5376, category Article
Timo Pukkala. (1989). Predicting diameter growth in even-aged Scots pine stands with a spatial and non-spatial model. Silva Fennica vol. 23 no. 2 article id 5376. https://doi.org/10.14214/sf.a15533
Keywords: Pinus sylvestris; growth prediction; spatial distribution; growth models; tree models
Abstract | View details | Full text in PDF | Author Info

The single tree growth models presented in this study were based on about 4,000 trees measured in 50 even-aged Scots pine (Pinus sylvestris L.) sample plots with varying density, spatial pattern of trees and stand age. Predictors that used information about tree locations decreased the relative standard error of estimate by 10 percentage points (15%), if past growth was not used as a predictor, and about 15 percentage points (30%) when past growth was one of the predictors. When ranked according to the degree of determination, the best growth models were obtained for the basal area increment, the next best for relative growth, and the poorest for diameter increment. The past growth decreased the relative standard error of estimate by 15–20 percentage points, but did not make the spatial predictors unnecessary. The degree of determination of the spatial basal area growth model was almost 80% if the past growth was unknown and almost 90% if the past growth was known. Variables that described the amount of removed competition did not improve the growth models.

The PDF includes an abstract in Finnish.

  • Pukkala, E-mail: tp@mm.unknown (email)
article id 5375, category Article
Timo Pukkala. (1989). Prediction of tree diameter and height in a Scots pine stand as a function of the spatial pattern of trees. Silva Fennica vol. 23 no. 2 article id 5375. https://doi.org/10.14214/sf.a15532
Keywords: Pinus sylvestris; diameter distribution; competition; spatial distribution; simulations studies; tree models
Abstract | View details | Full text in PDF | Author Info

The study presents two methods of predicting tree dimensions in a Scots pine (Pinus sylvestris L.) stand if only the location of trees is known. The first method predicts the tree diameter from the spatial location of neighbours. In the second method the diameter distribution of a subarea is estimated from the local stand density. This distribution is then sampled to obtain diameters. In both methods the tree height is predicted with a spatial model on the basis of diameters and locations of trees. The main purpose of the presented models is to generate realistic stands for simulation studies.

The PDF includes an abstract in Finnish.

  • Pukkala, E-mail: tp@mm.unknown (email)
article id 5357, category Article
Heikki Hänninen, Paavo Pelkonen. (1988). Effects of temperature on dormancy release in Norway spruce and Scots pine seedlings. Silva Fennica vol. 22 no. 3 article id 5357. https://doi.org/10.14214/sf.a15514
Keywords: Pinus sylvestris; Norway spruce; Picea abies; Scots pine; bud burst; dormancy release; annual cycle of development; chilling requirement; rest period; simulation model
Abstract | View details | Full text in PDF | Author Info

Models concerning the effects of temperature on dormancy release in woody plants were tested using two-year old seedlings of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) H. Karst.). Chilling experiments suggest that the rest period has a distinct end point. Before the attainment of this end point high temperatures do not promote bud development towards dormancy release, and after it further chilling does not affect the subsequent bud development. A new hypothesis of dormancy release is suggested on the basis of a comparison between present and earlier findings. No difference in the proportion of growth commencing seedlings were detected between the forcing temperatures of 17°C and 22°C. The rest break of 50% of Norway spruce and Scots pine seedlings required six and eight weeks of chilling, respectively. Great variation in the chilling requirement was found, especially for Scots pine.

The PDF includes an abstract in Finnish.

  • Hänninen, E-mail: hh@mm.unknown (email)
  • Pelkonen, E-mail: pp@mm.unknown
article id 5338, category Article
Timo Pukkala. (1988). Effect of spatial distribution of trees on the volume increment of a young Scots pine stand. Silva Fennica vol. 22 no. 1 article id 5338. https://doi.org/10.14214/sf.a15495
Keywords: Pinus sylvestris; simulation; competition; spatial distribution; growth model; spatial pattern
Abstract | View details | Full text in PDF | Author Info

The effect of grouping on 5-year old volume increment was studied by a simulation technique using spatial growth models estimated in Scots pine (Pinus sylvestris L.) stands in the phase of the first commercial thinning. A total of 24 model stands were regenerated by applying 12 spatial processes for two different diameter distributions. In addition to model stands, 6 different thinnings were simulated in two real stands. The clustering of trees was described with Fisher’s grouping index and by estimating the relative interception of diffuse radiation. In model stands with constant diameter distribution the correlation between the grouping index and volume increment ranged from -0.81 to -0.91. The correlation between volume increment and interception was 0.81–0.83 with one diameter distribution and 0.70 if both distributions were combined. In one thinned stand the correlation between the growth estimate and grouping index varied between -0.33 and 0.76. The correlation between interception and growth was about 0.30 in one stand and 0.72 if both stands were combined. Small irregularities do not decrease the volume production of a young Scots pine stand, but if the clustering is considerable or there are reasonably wide harvest strips, growth will be reduced by 10–20%.

The PDF includes a summary in Finnish.

  • Pukkala, E-mail: tp@mm.unknown (email)
article id 5319, category Article
Heikki Hänninen. (1987). Effects of temperature on dormancy release in woody plants. Silva Fennica vol. 21 no. 3 article id 5319. https://doi.org/10.14214/sf.a15476
Keywords: temperature; bud burst; dormancy; annual cycle of development; dormancy breaking; chilling requirement; rate of development; rest period; simulation model; stage of development
Abstract | View details | Full text in PDF | Author Info

Logical structure of three simulation models and one conceptual model concerning effects of temperature on dormancy release in woody plants was examined. The three basic types of simulation models differed in their underlying assumptions. Contrasting implications of the models were inferred by deduction. With the aid of these implications, the model types can be tested using experiments with continuous and interrupted chilling. Similarly, implications of the conceptual model of rest phases were inferred, by which the model can be tested using experiments with continuous chilling and forcing in multiple temperatures. The possibilities to synthetize the conceptual model with any of the three simulation model types, as well as the biological interpretation of the model variables, were discussed.

The PDF includes an abstract in Finnish.

  • Hänninen, E-mail: hh@mm.unknown (email)
article id 5311, category Article
Timo Pukkala. (1987). Kuusen ja männyn siemensadon ennustemalli. Silva Fennica vol. 21 no. 2 article id 5311. https://doi.org/10.14214/sf.a15468
English title: Model for predicting the seed crop of Picea abies and Pinus sylvestris.
Original keywords: kuusi; mänty; luontainen uudistaminen; Lappi; siemensato; lämpötila; kukinnan aloitus; ennustemalli
English keywords: Pinus sylvestris; Norway spruce; Picea abies; natural regeneration; Scots pine; Finland; Lapland; predictive modelling; seed crop; flowering initiation; influence of temperature
Abstract | View details | Full text in PDF | Author Info

The seed crop of Norway spruce (Picea abies (L.) H. Karst.) and Scots pine (Pinus sylvestris L.) is predicted with the help of mean monthly temperatures during May–August one and two years before the flowering year. The prediction models were made separately for Lapland and for the rest of Finland. The models are based on 10-year periods of seed crop measurements and climatic data. The total number of time series was 59.

In Lapland, Norway spruce flowered abundantly and produced an abundant seed crop after warm July–August and two years after cool July–August. In other parts of Finland, warm June and July produced a good flowering year, especially if these months were cool two years before the flowering year.

In Lapland, Scots pine flowered abundantly if the whole previous growing season was warm. Elsewhere in Finland, a cool June preceded prolific flowering in the coming year if the rest of the growing season was considerably warmer than the average.

The prediction models explained 37–49 % of the variation in the size of the seed crop. The occurrence of good and poor seed years was usually predicted correctly. Using the presented models, the prediction of the seed crop is obtainable 1.5 year for Norway spruce and 2.5 year for Scots pine before the year of seed fall.

The PDF includes an abstract in English.

  • Pukkala, E-mail: tp@mm.unknown (email)
article id 5305, category Article
Timo Pukkala. (1987). Simulation model for natural regeneration of Pinus sylvestris, Picea abies, Betula pendula and Betula pubescens. Silva Fennica vol. 21 no. 1 article id 5305. https://doi.org/10.14214/sf.a15462
Keywords: Pinus sylvestris; Betula pendula; Picea abies; germination; Betula pubescens; mortality; seed crop; computer model; stochastic simulation; birth model
Abstract | View details | Full text in PDF | Author Info

In the model the regeneration process is derived into three subprocesses: birth, growth and mortality of seedlings. The main emphasis is on the birth process where the following phases are simulated: seed crop, quality of seeds, maturity of seeds, predation of seeds and germination. The parameters are based on data published in Finland. Part of the parameters are obtained directly from the investigations and part is proposed by the author. The model can be calibrated by changing parameter values. The simulation is made with the help of random numbers which have the same means as the estimates and the same distributions as the residuals of the equations used in simulation. The time step of the model is one year. The number of emerged seedlings in one year is obtained by multiplying the seed crop with the probabilities that the seed passes different phases of the birth process. Because of stochasticity the regeneration period is simulated several times. From the results it is possible to evaluate the risk and succeeding probability of the regeneration. The main drawbacks of the simulation method are the lack of empirical parameters and the difficulty of testing. The model could be further developed by including spatiality into the model.

The PDF includes an abstract in Finnish.

  • Pukkala, E-mail: tp@mm.unknown (email)
article id 5304, category Article
Jimin Tan. (1987). A method to evaluate productivity of logging machines. Silva Fennica vol. 21 no. 1 article id 5304. https://doi.org/10.14214/sf.a15461
Keywords: productivity; processor; time studies; evaluation of logging machines; Pika 35; mathematical model
Abstract | View details | Full text in PDF | Author Info

This study deals with the evaluation of logging machines. The analyses were based on the results of a productivity study with special reference to a PIKA 35 processor, a delimber-bucker, working in Kyröskoski forest area in Finland. Factors affecting the productivity of the machine were surveyed. Mathematical models for determining the productivity were developed and their practical applications to the particular problem under study was demonstrated.

The PDF includes an abstract in Finnish.

  • Tan, E-mail: jt@mm.unknown (email)
article id 5302, category Article
Seppo Kellomäki, Heikki Hänninen, Taneli Kolström, Ahti Kotisaari, Timo Pukkala. (1987). A tentative model for describing the effects of some regenerative process on the properties of natural seedling stands. Silva Fennica vol. 21 no. 1 article id 5302. https://doi.org/10.14214/sf.a15459
Keywords: Pinus sylvestris; natural regeneration; Scots pine; modelling; stand density; seed crop; seed dispersal; parent tree
Abstract | View details | Full text in PDF | Author Info

The effect of the size of seed crop, dispersal of seeds and the early development of seedlings on the density and spatial distribution of young Scots pine (Pinus sylvestris L.) stands are evaluated on the basis of theoretical models. The models include (i) number and spatial distribution of parent trees on the regeneration area, (ii) size of annual seed crop, (iii) seed dispersal from a particular parent tree, (iv) germination of the seeds (germination percentage), (v) death of ageing seedlings after the establishment process, and (vi) height growth of the seedlings.

As expected, stand density and spatial distribution varied within a large range in relation to the density of the parent trees and the distance from them. The simulations also showed that natural seedling stands can be expected to be heterogenous due to the geometry of seed dispersal, emphasizing the frequency of young and small trees. The properties of the seedling stands were, however, greatly dependent on the density of the parent trees and the length of the regeneration period.

The PDF includes an abstract in Finnish.

  • Kellomäki, E-mail: sk@mm.unknown (email)
  • Hänninen, E-mail: hh@mm.unknown
  • Kolström, E-mail: tk@mm.unknown
  • Kotisaari, E-mail: ak@mm.unknown
  • Pukkala, E-mail: tp@mm.unknown
article id 5301, category Article
Birger Solberg. (1986). Forest sector simulation models as methodological tools in forest policy analysis. Silva Fennica vol. 20 no. 4 article id 5301. https://doi.org/10.14214/sf.a27757
Keywords: forest policy; Norway; simulation models; forest sector models; forest policy analysis
Abstract | View details | Full text in PDF | Author Info

The usefulness of forest sector models in forest policy analysis is discussed, mainly based on experiences from Norway. Forest sector modelling is contrasted to two alternative approaches: (i) Intuitive, verbal analysis, and (ii) econometric models. It is concluded that forest sector models, properly developed in contact with the policy makers, should be of considerable value in forest policy analysis.

  • Solberg, E-mail: bs@mm.unknown (email)
article id 5300, category Article
Takuro Kishine. (1986). Optimizing simulation model on forest policy. Silva Fennica vol. 20 no. 4 article id 5300. https://doi.org/10.14214/sf.a27756
Keywords: forest policy; forestry; welfare; environment; Japan; simulation system model; policy formation
Abstract | View details | Full text in PDF | Author Info

This paper designs an Economy-Welfare-Environment Adjustment System model (EWEAS model or EWE model in short) which consists of the circular flow of the economic, the welfare, and the environment system of forestry. That is, this model builds the relationship between the systems for material wealth and that for mental wealth.

The EWE model is designed as a complete open system model which describes the economy-welfare-environment circular system in forestry by linking up the internal system of forestry with the surrounding external systems. The EWE model can be manipulated as a policy formation or a policy decision model, and it is available for policy evaluation in the economic, the welfare and the environmental phase of forestry. The model is a basic simulation system model which is reliable in its reproductive fitness, stability and universality. Thus, this model ought to be useful in any country in the world as well as in Japan.

  • Kishine, E-mail: tk@mm.unknown (email)
article id 5279, category Article
Ilpo Tikkanen. (1986). Analysis and evaluation of public forest policies. Silva Fennica vol. 20 no. 4 article id 5279. https://doi.org/10.14214/sf.a27716
Keywords: forest policy; IUFRO; forest policy programs; forest sector models; World Congress
Abstract | View details | Full text in PDF | Author Info

The issue of Silva Fennica comprises 22 papers on forest policy and program analysis, and evaluation presented at the XVIII IUFRO World Congress in 1986 arranged in Ljubljana. The papers discuss the future and role of policy and program analysis, the effectiveness of policy programs on timber supply and private forestry investments as well as the application of forest sector models to policy analysis.

The PDF includes the preface and list of authors in English and an abstract in Finnish.

  • Tikkanen, E-mail:
article id 5244, category Article
Juha Lappi, Markku Siitonen. (1985). A utility model for timber production based on different interest rates for loans and savings. Silva Fennica vol. 19 no. 3 article id 5244. https://doi.org/10.14214/sf.a15423
Keywords: linear programming; timber production; forest economics; income from fellings; utility model; income flow; present discounted value
Abstract | View details | Full text in PDF | Author Info

The paper discusses the evaluation of timber production policies with different income (timber drain) schedules. Special attention is given to the temporal smoothness of the income flow. A utility model is formulated in which the objective is to maximize a fixed consumption pattern, and money can be saved and borrowed at different interest rates. We thus have smoothness requirements only for consumption, the capital market then determines the smoothness of the optimal income flow. Present discounted value and maximization of even income flow criteria are special cases of the utility model. Consumption can be maximized by linear programming. A sample problem is presented.

The PDF includes a summary in Finnish.

  • Lappi, E-mail: jl@mm.unknown (email)
  • Siitonen, E-mail: ms@mm.unknown
article id 5235, category Article
Pekka Kilkki, Tapani Pohjola, Eljas Pohtila. (1985). Puiden ryhmittäisyyden huomioonottaminen harvennusmalleissa. Silva Fennica vol. 19 no. 2 article id 5235. https://doi.org/10.14214/sf.a15414
English title: Use of the spatial distribution of trees in thinning models.
Original keywords: harvennus; harvennusmallit; mallinnus; puiden ryhmittäisyys
English keywords: thinnings; spatial distribution; relascope plots; thinning models; basal area classes
Abstract | View details | Full text in PDF | Author Info

Thinning models are generally based on the density of the stand measured by the average basal area per hectare, for instance. These models are handicapped by the uneven structure of the stands. In uneven stands the averages are inadequate indicators for the need and amount of thinnings.

Small relascope plots were tested in the measurement of the spatial distribution of trees and in the determination of the need and amount of thinnings. The thinning quantity was determined as the difference between the actual distribution of the relascope plots into basal area classes and the ideal distribution after thinning. Sequential sampling was used in the derivation of the decision equations. A respective BASIC-program for a programmable pocket calculator is given.

The PDF includes a summary in English.

  • Kilkki, E-mail: pk@mm.unknown (email)
  • Pohjola, E-mail: tp@mm.unknown
  • Pohtila, E-mail: ep@mm.unknown
article id 5200, category Article
Seppo Kellomäki, Timo Nevalainen. (1983). Näkökohtia puuston tiheyden ja puiden koon välisestä suhteesta. Silva Fennica vol. 17 no. 4 article id 5200. https://doi.org/10.14214/sf.a15183
English title: Relationship between stand density on tree size.
Original keywords: kilpailu; metsikön tiheys; puiden koko
English keywords: tree size; modelling; stand density; within-stand competition
Abstract | View details | Full text in PDF | Author Info

Two Japanese models regarding the within-stand competition have been reviewed on the basis of relevant literature. Competition-density and 3/2 th power models seem to be applicable also into tree stands. The latter model has been applied into the material obtained from literature. Computations showed consistancy with the results obtained elsewhere in the world. It is concluded that also in Finnish conditions the 3/2 th power law may have great potentials in describing the effects of stand density on tree size.

The PDF includes a summary in English.

  • Kellomäki, E-mail: sk@mm.unknown (email)
  • Nevalainen, E-mail: tn@mm.unknown
article id 5187, category Article
Fuhe Luo. (1983). Determination of stem value. Silva Fennica vol. 17 no. 3 article id 5187. https://doi.org/10.14214/sf.a15170
Keywords: Pinus sylvestris; Scots pine; modelling; pulpwood; saw log; stem value; taper curve model; bark model; cubic spline interpolation
Abstract | View details | Full text in PDF | Author Info

A dynamic programming approach toward stem value estimation for standing Scots pine (Pinus sylvestris L.) trees was developed. The determination of the saw log value was based on the sawing pattern and on the final products composition. The combination of taper curve models and bark models providing taper curves both over bark and under bark, which constituted the basis of the optimum stem scaling. A computer program was developed to determine the optimum log sequence of the stem aiming at maximizing the value of the final products. To examine the reliability of the computation system, 445 Scots pine sample trees from 29 stands were used as a test material. The stem values of sample trees were calculated in two ways: 1) with 12 measured diameters, and 2) with 12 estimated diameters derived from measured tree characteristics. In both cases the values of the intermediate diameters were calculated via cubic spline interpolation.

The PDF includes a summary in Finnish.

  • Luo, E-mail: fl@mm.unknown (email)
article id 5183, category Article
Risto Ojansuu, Helena Henttonen. (1983). Kuukauden keskilämpötilan, lämpösumman ja sademäärän paikallisten arvojen johtaminen Ilmatieteen laitoksen mittaustiedoista. Silva Fennica vol. 17 no. 2 article id 5183. https://doi.org/10.14214/sf.a15099
English title: Estimation of the local values of monthly mean temperature, effective temperature sum and precipitation sum from the measurements made by the Finnish Meteorological Office.
Original keywords: sademäärä; lämpösumma; paikallisilmasto; laskentamenetelmä; keskilämpötila; ilmastotekijät; trendipintamenetelmä
English keywords: modelling; effective temperature sum; local climate; monthly mean temperature; precipitation sum; trend surface method; climatic factors
Abstract | View details | Full text in PDF | Author Info

Methods involving the use of moving averages, trend surfaces and their combination are compared in deriving local values of monthly mean temperatures and precipitation sums from the observations made by the Finnish Meteorological Office. Correlation between meteorological variables and sea index, lake index and height above sea level were used in the trend surface method and in the combined method. Combined method, with a trend surface calculated from means of a long time period, was the most reliable method to estimate long local time series.

A method to calculate unbiased estimates of effective temperature sums from monthly mean temperatures is presented.

The PDF includes a summary in English.

  • Ojansuu, E-mail: ro@mm.unknown (email)
  • Henttonen, E-mail: hh@mm.unknown
article id 5151, category Article
A. Mäkelä, P. Hari, Seppo Kellomäki. (1981). A model for the effect of air pollutants on forest growth. Silva Fennica vol. 15 no. 4 article id 5151. https://doi.org/10.14214/sf.a15378
Keywords: photosynthesis; growth; modelling; air pollution; environmental impact; allocation of photosynthates
Abstract | View details | Full text in PDF | Author Info

A model was constructed, the aim of which was to predict growth under conditions where air pollutants are present. The model is based on photosynthesis and on the allocation of photosynthetic products for growth. It is assumed that air pollutants released during energy production mainly affect photosynthesis in two ways: 1) directly by injuring the photosynthetic mechanism, and 2) indirectly by leaching nutrients. The two ways were studied empirically in order to identify a sub-model for the photosynthesis of a plant exposed to air pollutants. 

The stand model will be applied to two purposes. The present stage of forests in Finland is compared with the simulated state based on the assumption that no pollutants are present. In addition, the decrease in forest yield under different conditions derived from predictions about long-range pollutant transport in Europe is analysed.

  • Mäkelä, E-mail: am@mm.unknown (email)
  • Hari, E-mail: ph@mm.unknown
  • Kellomäki, E-mail: sk@mm.unknown
article id 5142, category Article
Lars Moseholm. (1981). Responses of transplanted lichens to sulphur dioxide dosages - a new semi-statistical dosage/injury model. Silva Fennica vol. 15 no. 4 article id 5142. https://doi.org/10.14214/sf.a15369
Keywords: lichen; modelling; methods; air pollution; sulphur dioxide; bioindicators; indicator plants; plant injury; air pollutant concentration; monitoring method
Abstract | View details | Full text in PDF | Author Info

A semi-statistical model is suggested for monitoring injuries of plants for long-time field exposures (months). The model is based on the following assumptions:

1. The concentrations of air pollutants in the atmosphere follow the Johnson SB distribution.

2. The degree of plant injury is proportional to the logarithm of air pollutant dose.

3. No injuries occur below a certain dose level.

4. A dose is defined as the air pollutant concentration multiplied by the duration of exposure raised to an exponent.

Based on the air pollutant frequency distribution a total dose for the exposure period is calculated by integration, and the total dose is related to the observed plant injury by non-linear regression. The model is tested for long-time exposures of sulphur dioxide to transplant lichen in natural environment.

  • Moseholm, E-mail: lm@mm.unknown (email)
article id 5054, category Article
Pekka Kilkki. (1979). Outline for a data processing system in forest mensuration. Silva Fennica vol. 13 no. 4 article id 5054. https://doi.org/10.14214/sf.a14911
Keywords: forest mensuration; methods; data processing; multi-equation model
Abstract | View details | Full text in PDF | Author Info

This paper presents the principles of a unified data processing system suitable for derivation of the most variables of interest in forest mensuration. The precedence (succedence) relations between the tree and forest stand variables are analysed and a block-wise simultaneous recursive multi-equation model is suggested to describe these relations. Regression analysis is used in the estimation of the model parameters and Taylor’s series and Monte Carlo simulation are available in the derivation of the unbiased results.

The PDF includes a summary in Finnish.

  • Kilkki, E-mail: pk@mm.unknown (email)
article id 5047, category Article
Pekka Kilkki, Martti Varmola. (1979). A nonlinear simultaneous equation model to determine taper curve. Silva Fennica vol. 13 no. 4 article id 5047. https://doi.org/10.14214/sf.a14904
Keywords: Pinus sylvestris; diameter; mathematical models; taper curve
Abstract | View details | Full text in PDF | Author Info

In the original set of equations derived by regression analysis, relative-height diameters (endogenous variables) are presented as nonlinear functions of the other relative-height diameters and of the height of the tree (an exogenous variable). Any of the original equations can be replaced by an interpolation formula which links a measured diameter to the four closest relative-height diameters. The solution of the simultaneous equation model yields 10 relative-height diameters. Intermediate values are obtained to avoid biases due to the nonlinearity of the simultaneous model equations.

The PDF includes a summary in Finnish.

  • Kilkki, E-mail: pk@mm.unknown (email)
  • Varmola, E-mail: mv@mm.unknown
article id 4995, category Article
Pekka Kilkki, Matti Saramäki, Martti Varmola. (1978). A simultaneous equation model to determine taper curve. Silva Fennica vol. 12 no. 2 article id 4995. https://doi.org/10.14214/sf.a14849
Keywords: Pinus sylvestris; Scots pine; diameter; mathematical models; taper curve
Abstract | View details | Full text in PDF | Author Info

A simultaneous equation model to determine taper curve for Scots pine is presented. The diameters at relative heights are endogenous variables and height an exogenous variable. Any equations may be substituted by the measured value of diameter. Solution of the system of equations yields 11 diameters at relative heights. Intermediate values are obtained by interpolation. Interpolation allows the use of diameters measured at absolute heights, too.

The PDF includes a summary in Finnish.

  • Kilkki, E-mail: pk@mm.unknown (email)
  • Saramäki, E-mail: ms@mm.unknown
  • Varmola, E-mail: mv@mm.unknown

Category: Article

article id 7139, category Article
Päiviö Riihinen. (1963). Economic models underlying forest policy programs : an evaluation of ends and means. Silva Fennica vol. 75 no. 5 article id 7139. https://doi.org/10.14214/aff.7139
Keywords: forest policy; economic models; economic theories; marketing models; policy models; static models
Abstract | View details | Full text in PDF | Author Info

The purpose of this study was to analyse economic models used in certain studies and to evaluate whether the economic theory envisaged by a model is consistent with its aims in forest policy. Second, the paper will point out assumed improvements for models that can be used as a basis for forest policy.

There are two types of economic models according to their purpose. One type, the marketing models, can be used for explaining or forecasting the consumer’s behaviour with no intension to affect the economies to be gained from the alternative patterns of behaviour explained. Others, the policy models, are meant to serve as guideposts which by means of normative forecasts point out the programme to be followed in order to attain certain aims. The majority of the policy models are static. The paper assesses the static models, and evaluates how well they fit their purpose. Special attention is given to dynamic economic models. A dynamic model can, at least in principle, be used to explain the course of events during the adjustment period required to achieve a production goal.

The PDF includes a summary in Finnish.

  • Riihinen, E-mail: pr@mm.unknown (email)
article id 7197, category Article
Erik Lönnroth. (1926). The stereometric mean tree of the stand. Silva Fennica vol. 30 no. 2 article id 7197. https://doi.org/10.14214/aff.7197
Keywords: mean tree; average tree; stereometry; stereometric; statistical numbers
Abstract | View details | Full text in PDF | Author Info

The mean has a great importance in statistics in general and also in forest statistical calculations. The meaning of the average tree and its characteristics is important also for the practical forest mensuration work. However, the question is how are the statistical numbers of a mean tree related to the statistical numbers of the stand.   

Study is based on the strip-wise survey of forests in southern Finland. From that information the 30 sample plots were chosen, 10 of each of most typical forest site types, MT, VT and CT. The stands are of different ages and development classes, varying from 14 to 159 years.

For the determination of the average tree are the statistical numbers of five characteristics needed: volume, basal area, diameter, height and form factor. The stereometric mean tree of the stand can be calculated with only one statistical method and that solution is absolute.

Theoretically and statistically absolute solution for the problem is the continuous solution by the mean that is weighted with the number of stems. This solution however is not very useful in practical sense.

A simple, practical and adequately exact solution for determining the average tree by approximation procedure of a certain arithmetic mean. 

  • Lönnroth, E-mail: el@mm.unknown (email)
article id 7522, category Article
Timo Kareinen, Ari Nissinen, Hannu Ilvesniemi. (1998). Analysis of forest soil chemistry and hydrology with a dynamic model ACIDIC. Silva Fennica vol. 0 no. 262 article id 7522. https://doi.org/10.14214/aff.7522
Keywords: simulation; modelling; aluminium; leaching; water flow; cation exchange; macropores; micropores; flow paths
Abstract | View details | Full text in PDF | Author Info

In this study we analyse how the ion concentrations in forest soil solution are determined by hydrological and biogeochemical processes. A dynamic mode ACIDIC was developed, including processes common to dynamic soil acidification models. The model treats one to eight interacting layers and simulates soil hydrology, transpiration, root water and nutrient uptake, cation exchange, dissolutions and reaction of Al hydroxides in solution, and the formation of carbonic acid and its dissociation products. It includes also a possibility to a simultaneous use of preferential and matrix flow paths, enabling the throughfall water to enter the deeper soil layers in macropores without first reacting with the upper layers. Three different combinations of routing the throughfall water via macro- and micropores through the soil profile is presented. The large vertical gradient in the observed total charge was simulated successfully. According to the simulations, gradient is mostly caused by differences in the intensity of water uptake, sulphate adsorption and organic anion retention at the various depths. The temporal variations in Ca and Mg concentrations were simulated fairly well in all soil layers. For H+, Al and K there were much more variation in the observed than in the simulated concentrations. Flow in macropores is a possible explanation for the apparent disequilibrium of the cation exchange for H+ ad K, as the solution H+ and K concentrations have great vertical gradients in soil. The amount of exchangeable H+ increased in O and E horizons and decreased in the Bs1 and Bs2 horizons, the net change in whole soil profile being a decrease. A large part of the decrease of the exchangeable H+ in the illuvial B horizon was caused by sulphate adsorption. The model produces soil water amounts and solution ion concentrations which are comparable to the measured values, and it can be used in both hydrological and chemical studies of soils.

  • Kareinen, E-mail: tk@mm.unknown (email)
  • Nissinen, E-mail: an@mm.unknown
  • Ilvesniemi, E-mail: hi@mm.unknown
article id 7520, category Article
Wending Huang. (1998). Productive coexistence and gain in agroforestry systems. Silva Fennica vol. 0 no. 260 article id 7520. https://doi.org/10.14214/aff.7520
Keywords: agroforestry; coexistence gain; facilitation; interaction model; productive coexistence; resource sharing; Taxodium ascendens
Abstract | View details | Full text in PDF | Author Info

Productive coexistence and gain of populations were studied using nine years’ data from field experiments of Taxodium ascendens-intercrop systems in Lixiahe, Jiangsu province, China. A theoretical framework for productive coexistence in agroforestry was developed. Interaction patterns between trees and intercrops were presented within the framework. A model framework was developed to describe the coexistence gain and interaction of populations in T. ascedens-intercrop systems. Facilitation and resource sharing were identified as main contribution to the advantage of species combination in agroforestry. The model of population interaction developed in the present study was accepted for describing the interaction of populations in T. ascendens -intercrop system, because it explained a high proportion of the variance of experimental data and fitted well the observations in most intercropping types. The model provides flexibility for describing different patterns of intra- and inter-specific interactions. Model coefficients were applied to the determination of the ecological compatibility of species.

Managed T. ascendens-intercrop systems were advantageous as compared to a monoculture of trees or arable crops. In T. ascendens stands up to the age of three, arable crops contributed about 50–80% of the total biomass yield of agroforestry. The diameter height growth of T. ascendens was not significantly influenced by intercrops. When the trees were young (during the first three years), T. ascendens did not depress the crop yields, and a land equivalent ratio greater than unity was obtained together with a high yield of both components. The diameter and height of the trees were similar in four spacing configurations with an equal number of trees per hectare up to the age of 8, but wider between-rows open range were beneficial for the intercrops. The relationship between open-ranges and species coexistence was also analysed and the distribution of soil nutrients studied.

  • Huang, E-mail: wh@mm.unknown (email)
article id 7519, category Article
Jori Uusitalo. (1997). Pre-harvest measurement of pine stands for sawing production planning. Silva Fennica vol. 0 no. 259 article id 7519. https://doi.org/10.14214/aff.7519
Keywords: Pinus sylvestris; diameter distribution; height models; crown height estimation; forest sampling; lumber quality prediction
Abstract | View details | Full text in PDF | Author Info

To enhance the utilization of the wood, the sawmills are forced to place more emphasis on planning to master the whole production chain from the forest to the end product. One significant obstacle to integrating the forest-sawmill-market production chain is the lack of appropriate information about forest stands. Since the wood procurement point of view in forest planning systems has been almost totally disregarded there has been a great need to develop an easy and efficient pre-harvest measurement method, allowing separate measurement of stands prior to harvesting. The main purpose of this study was to develop a measurement method for Scots pine (Pinus sylvestris L.) stands which forest managers could use in describing the properties of the standing trees for sawing production planning.

Study materials were collected from ten Scots pine stands located in North Häme and South Pohjanmaa, in Southern Finland. The data comprise test sawing data on 314 pine stems, diameter at breast height (dbh) and height measures of all trees and measures of the quality parameters of pine sawlog stems in all ten study stands as well as the locations of all trees in six stands. The study was divided into four sub-studies which deal with pine quality prediction, construction of diameter and dead branch height distributions, sampling designs and applying height and crown height models. The final proposal for the pre-harvest measurement method is a synthesis of the individual sub-studies.

Quality analysis resulted in choosing dbh, distance from stump height to the first dead branch, crown height and tree height as the most appropriate quality characteristics of Scots pine. Dbh and dead branch height are measured from each pine sample tree while height and crown height are derived from dbh measures by aid of mixed height and crown height models. Pine and spruce diameter distribution as well as dead branch height distribution are most effectively predicted by the kernel function. Roughly 25 sample trees seem to be appropriate in pure pine stands. In mixed stands the number of sample trees needs to be increased in proportion to the intensity of pines in order to attain the same level of accuracy.

  • Uusitalo, E-mail: ju@mm.unknown (email)
article id 7516, category Article
Euan G. Mason, A. Graham D. Whyte. (1997). Modelling initial survival and growth of radiata pine in New Zealand. Silva Fennica vol. 0 no. 255 article id 7516. https://doi.org/10.14214/aff.7516
Keywords: Pinus radiata; New Zealand; growth modelling; young corps; radiata pine
Abstract | View details | Full text in PDF | Author Info

A sensitive framework has been developed for modelling young radiata pine (Pinus radiata D. Don) survival, its growth and size class distribution, from time of planting to age 5 or 6 years. The data and analysis refer to the Central North Island region of New Zealand. The survival function is derived from a Weibull probability density function, to reflect diminishing mortality with the passage of time in young stands. An anamorphic family of trends was used, as very little between-tree competition can be expected in young stands. An exponential height function was found to fit best the lower portion of its sigmoid form. The most appropriate basal area/ha exponential function included an allometric adjustment which resulted in compatible mean height and basal area/ha models. Each of these equations successfully represented the effects of several establishment practices by making coefficients linear functions of site factors, management activities and their interactions. Height and diameter distribution modelling techniques that ensured compatibility with stand values were employed to represent the effects of management practices on crop variation. Model parameters for this research were estimated using data from site preparation experiments in the region and were tested with some independent data sets.

  • Mason, E-mail: em@mm.unknown (email)
  • Whyte, E-mail: aw@mm.unknown
article id 7525, category Article
Pertti Hari, Johan Ross, Marja Mecke. (1996). Production process of Scots pine. Silva Fennica vol. 0 no. 254 article id 7525. https://doi.org/10.14214/aff.7525
Keywords: Pinus sylvestris; photosynthesis; Scots pine; allocation; structure; annual cycle; irradiance; stand models; geographical features
Abstract | View details | Full text in PDF | Author Info

The accompanying collective research report is the result of the research project in 1986–90 between the Finnish Academy and the former Soviet Academy of Sciences. The project was organized around common field work in Finland and in the former Soviet Union, and theoretical analyses of tree growth determining processes. Based on theoretical analyses, dynamic stand growth models were made and their parameters were determined utilizing the field results.

Annual cycle effects the tree growth. Our theoretical approach was based on adaptation to local climate conditions from Lapland to South Russia. The initiation of growth was described as a simple low and high temperature accumulation driven model. The model was linked with long-term temperature data.

Analysis of field measurements of CO2 exchange showed that irradiance is the dominating factor causing variation in photosynthetic rate in natural conditions during summer. The penetration of irradiance into Scots pine (Pinus sylvestris L.) canopy is a complicated phenomenon. A moderately simple but balanced forest radiation regime sub-model was constructed.

The common field excursions in different geographical regions resulted in a lot of experimental data of regularities of woody structure. The water transport seems to be a good common factor to analyse these properties of tree structure. The produced theoretical and experimental material was utilized in the development of stand growth model that describes the growth and development of Scots pine stands in Finland and the former Soviet Union. The core of the model is carbon and nutrient balances. This means that carbon obtained in photosynthesis is consumed or growth and maintenance and nutrients are taken according to the metabolic need. Since the fundamental metabolic processes are the same in all locations, the same growth model structure can be applied in the large range of Scots pine. The model enables the analysis of geographical differences in the growth of Scots pine. The present approach enables utilization of structural and functional knowledge gained in places of intensive research, in the analysis of growth and development of any stand.

  • Hari, E-mail: ph@mm.unknown (email)
  • Ross, E-mail: jr@mm.unknown
  • Mecke, E-mail: ph@mm.unknown
article id 7505, category Article
Rauno Väisänen, Kari Heliövaara. (1994). Assessment of insect occurrence in boreal forests based on satellite imagery and field measurements. Silva Fennica vol. 0 no. 243 article id 7505. https://doi.org/10.14214/aff.7505
Keywords: biodiversity; remote sensing; insect pests; geological maps; Scolytids; logistic regression models
Abstract | View details | Full text in PDF | Author Info

The presence/absence data of 27 forest insect taxa (Retinia resinella, Formica spp., Pissodes spp., several scolytids) and recorded environmental variation were used to investigate the applicability of modelling insect occurrence based on satellite imagery. The sampling was based on 1,800 sample plots (25 m by 25 m) placed along the sides of 30 equilateral triangles (side 1 km) in a fragmented forest area (approximately 100 km2) in Evo, Southern Finland. The triangles were overlaid on land use maps interpreted from satellite images (Landsat TM 30 m multispectral scanner imagery 1991) and digitized geological maps. Insect occurrence was explained using either environmental variables measured in the field or those interpreted from the land use and geological maps. The fit of logistic regression models carried between species, possibly because some species may be associated with characteristics of single trees while other species with stand characteristics. The occurrence of certain insect species at least, especially those associated with Scots pine, could be relatively accurately assessed indirectly on the basis of satellite imagery and geological maps. Models based on both remotely sensed and geological data better predicted the distribution of forest insects except in the case of Xylechinus pilosus, Dryocetes sp. and Trypodendron lineatum, where the differences were relatively small in favour of the models based on field measurements. The number of species was related to habitat compartment size and distance from the habitat edge calculated from the land use maps, but logistic regressions suggested that other environmental variables in general masked the effect of these variables in species occurrence at the present scale.

  • Väisänen, E-mail: rv@mm.unknown (email)
  • Heliövaara, E-mail: kh@mm.unknown
article id 7685, category Article
Risto Ojansuu. (1993). Prediction of Scots pine increment using a multivariate variance component model. Silva Fennica vol. 0 no. 239 article id 7685. https://doi.org/10.14214/aff.7685
Keywords: Pinus sylvestris; crown height; volume increment; bark volume; variance component models; multivariate models; stem curve models; tree form change
Abstract | View details | Full text in PDF | Author Info

Diameter and volume increment as well as change in stem form of Scots pine (Pinus sylvestris L.) were analysed to predict tree increment variables. A stem curve set model is presented, based on prediction of the diameters at fixed angles in a polar coordinate system. This model consists of three elementary stem curves: 1) with bark, 2) without bark, and 3) without bark five years earlier. The differences between the elementary stem curves are the bark curve and the increment curve. The error variances at fixed angles and covariances between the fixed angles are divided into between-stand and within-stand components. Using principal components, the between-stand and within-stand covariance matrices are condensed separately for stem curve with bark, bark curve and increment curve. The two first principal components of the bark curve describe the vertical change in Scots pine bark type and the first principal component of the increment curve describes the increment rate. The elementary stem curves, bark curve and increment curve as well as corresponding stem volumes, bark volume and volume increment can be predicted for all trees in the stand with free choice of sample tree measurements. When only a few sample trees are measured, the stem curve set model gives significantly more accurate predictions of bark volume and volume increment for tally trees than does the volume method, which is based on the differences between two independent predictions of volume. The volume increment of tally trees can be predicted as reliably with as without measurement of sample tree height increment.

The PDF includes a summary in English.

  • Ojansuu, E-mail: ro@mm.unknown (email)
article id 7681, category Article
Eero Nikinmaa. (1992). Analyses of the growth of Scots pine: matching structure with function. Silva Fennica vol. 0 no. 235 article id 7681. https://doi.org/10.14214/aff.7681
Keywords: Pinus sylvestris; Scots pine; pipe model; nutrients; heartwood; growth models; carbon budget; structure; partitioning of growth; growht
Abstract | View details | Full text in PDF | Author Info

A theoretical framework to analyse the growth of Scots pine (Pinus sylvestris L.) is presented. Material exchange processes and internal processes that transport, transform and consume materials are identified as the components of growth. Hierarchical system is lined out. Momentary uptake of material at a single exchange site depends on the environmental condition next to the exchange site, the internal state of the biochemical system of the plant and the structure of the plant. The internal state depends on the exchange flows over period of time and the structural growth depends on the internal state. The response of these processes to the fluxes is controlled by the genetic composition of the plant.

The theoretical framework is formulated into a mathematical model. A concept of balanced internal state was applied to describe the poorly known internal processes. Internal substrate concentrations were assumed to remain constant but tissue-specific. A linear relationship between the quantity of foliage and wood cross-sectional area was assumed to describe balanced formation of structure. The exchange processes were thus described as a function of external conditions. The stand level interactions were derived from shading and effects of root density on nutrient uptake.

The approach was tested at different levels of hierarchy. Field measurements indicated that the hypothesis of the linear relationship described well the regularities between foliage and sapwood of a tree within a stand when measured at functionally corresponding height. There was considerable variation in the observed regularities in the range of geographic occurrence of Scots pine. Model simulations gave a realistic description of stand development in Southern Finland. The same model was also able to describe growth differences in Lapland after considering the effect of growing season length in the parameter values. Simulations to South Russia indicate stronger deviation from the observed patterns.

The simulations suggest interesting features of stand development. They indicate strong variability in the distribution of carbohydrates between tree parts during stand development. Internal circulation of nutrients and the reuse of the same transport structure by various needle generations had a strong influence on the simulation results.

The PDF includes a summary in Finnish.

  • Nikinmaa, E-mail: en@mm.unknown (email)
article id 7679, category Article
Ville Ovaskainen. (1992). Forest taxation, timber supply, and economic efficiency. Silva Fennica vol. 0 no. 233 article id 7679. https://doi.org/10.14214/aff.7679
Keywords: timber supply; economic efficiency; forest taxation; two-period model; comparative static analysis
Abstract | View details | Full text in PDF | Author Info

The effects and relative efficiency of alternative forest taxes are analysed theoretically. The Fisherian two-period model of consumption, savings and timber harvesting is extended by incorporating the management intensity decision and deriving the concept of long-run timber supply. The effects of lump-sum (site productivity), realized income (yield) and ad valorem property taxes on short-run timber supply, management intensity, and long-run timber supply are established. As the core of the study, the alternative taxes are compared in order to determine the appropriate forest tax regime in terms of production efficiency. The efficiency criterion generally requires that the excess burden of taxation at any given tax revenue should be kept to a minimum. The study distinguishes between an initially undistorted economy and an economy with pre-existing distortions due to capital income taxation (interest charge deductions). When the effects on forest management decisions of forest and capital income taxes are considered as a whole, a neutral forest taxation is no longer efficient. The non-timber benefits of a forest are incorporated to examine the robustness of the tax results with respect to the objective function. Finally, forest tax issues specific to Finland are considered, and administrational and equity aspects are discussed.

The PDF includes a summary in Finnish.

  • Ovaskainen, E-mail: vo@mm.unknown (email)
article id 7676, category Article
Jussi Saramäki. (1992). A growth and yield prediction model of Pinus kesiya (Royle ex Gordon) in Zambia. Silva Fennica vol. 0 no. 230 article id 7676. https://doi.org/10.14214/aff.7676
Keywords: diameter distribution; Weibull function; simulation models; Pinus kesiya; thinning reaction
Abstract | View details | Full text in PDF | Author Info

The study presents a growth and yield prediction model for a Pinus kesiya (Royle ex Gordon) stand by diameter classes. The material consists of temporary sample plots taken from a plantation inventory, of permanent sample plots established in commercial compartments and of an espacement trial. The mean basal area of the stand, variance and skewness of the diameter distribution are predicted. From these variables the parameters of the Weibull function are derived. Site class is assumed to be known or is calculated from measured information. Mortality is also predicted by estimating the number and mean size of dead trees. Thinnings are defined by the number of trees removed and by their relative size. If measured tree level data at the initial situation is available it can be utilized in the predictions, however, simulations can also be performed with stand level information. The minimum information needed for the prediction is planting density, site class as well as the times and removals of thinnings.

The calculations show that by decreasing the planting density of P. Kesiya from the present 1,330 stems/ha or by conducting early precommercial thinning both the relative and absolute amount of large sawlogs in the total production increase. An increase in the present planting density only slightly increases total yield. It is obvious that the presently recommended rotation of 25 years is too short for producing large sawlogs, especially on poor sites. This rotation period is suitable for small sawlog production while for pulpwood regimes shorter rotation periods can be used. If thinnings are done before the maximum current annual growth is reached stands will react well, but later on the ability to respond to thinnings decreases rapidly. Thinnings from below accelerates the production of large sawlogs more than thinning from above or systematic thinning. If all sawlog sizes are considered no great differences between thinning type exist. The study recommends different thinning regimes according to site class. Separate programs are recommended for the production of sawlogs and pulpwood.

The used thinning reaction model needs refinement and further studies with annual measured thinning trial material.

The PDF includes a summary in Finnish.

  • Saramäki, E-mail: js@mm.unknown (email)
article id 7606, category Article
Kari Heliövaara, Rauno Väisänen, Auli Immonen. (1991). Quantitative biogeography of the bark beetles (Coleoptera, Scolytidae) in northern Europe. Silva Fennica vol. 0 no. 219 article id 7606. https://doi.org/10.14214/aff.7606
Keywords: climate change; boreal forests; biodiversity; Nordic countries; multivariate methods; insect pests; biogeography; Scolytids; logistic regression models; faunal changes; Fennoscandia
Abstract | View details | Full text in PDF | Author Info

Biogeographical patterns of the Scolytidae in Fennoscandia and Denmark, based on species incidence data from the approximately 70 km x 70 km quadrats (n = 221) used by Lekander et al. (1977), were classified to environmental variables using multivariate methods (two-way indicator species analysis, detrended correspondence analysis, canonical correspondence analysis).

The distributional patterns of scolytid species composition showed similar features to earlier presented zonations based on vegetation composition. One major difference, however, was that the region was more clearly divided in an east-west direction. Temperature variables associated with the location of the quadrat had the highest canonical coefficient values on the first axis of the CCA. Although these variables were the most important determinants of the biogeographical variation in the beetle species assemblages, annual precipitation and the distribution of Picea abies also improved the fit of the species data.

Samples with the most deviant rarity and typicality indices for the scolytid species assempblages in each quadrat were concentrated in several southern Scandinavian quadrats, in some quadrats in northern Sweden, and especially on the Swedish islands (Öland, Gotland, Gotska Sandön) in the Baltic Sea. The use of rarity indices which do not take the number of species per quadrat, also resulted high values for areas near Stockholm and Helsinki with well-known faunas. Methodological tests in which the real changes in the distribution of Ips acuminatus and I. amitinus were used as indicators showed that the currently available multivariate methods are sensitive to small faunal shifts even, and thus permit analysis of the fauna in relation to environmental changes. However, this requires more detailed monitoring of the species’ distributions over longer time spans.

Distribution of seven species (Scolytus intricatus, S. laevis, Hylurgops glabratus, Crypturgus cinereus, Pityogenes salasi, Ips typographus, and Cyleborus dispar) were predicted by logistic regression models using climatic variables. In spite of the deficiencies in the data and the environmental variables selected, the models were relatively good for several but not for all species. The potential effects of climate change on bark beetles are discussed.

The PDF includes a summary in Finnish.

  • Heliövaara, E-mail: kh@mm.unknown (email)
  • Väisänen, E-mail: rv@mm.unknown
  • Immonen, E-mail: ai@mm.unknown
article id 7664, category Article
Marko Katila, Päiviö Riihinen. (1990). Modeling newsprint consumption: a Finnish case study for the period 1960-1986. Silva Fennica vol. 0 no. 217 article id 7664. https://doi.org/10.14214/aff.7664
Keywords: Finland; advertising; newspaper industry; demand modelling; newsprint industry; recursive models
Abstract | View details | Full text in PDF | Author Info

Factors determining newsprint consumption in Finland in 1960–1986 were analysed. An econometric recursive multi-equation model describing the structure of the newspaper industry was formulated and estimated to obtain information on direct factors influencing newsprint demand. Short-term and long-term demand elasticities for newspapers and newspaper advertising were estimated.

The results indicate that the main factors affecting newsprint consumption are total circulation of newspapers, volume of newspaper advertising and the change in newsprint substance weight. Total newspaper circulation was found to depend on the rate of household formation and real household income changes. Demand for newspapers was shown to be price-inelastic. Structural analysis indicates that income elasticity of newspaper demand has increased slightly over time.

The volume of newspaper advertising was shown to affect newsprint consumption via the effects on pagination. Newspaper and television advertising were found to be independent of each other. The impact of the reduction in the basis weight was found to be substantial. The estimation of long-term elasticities of demand for newspapers and newspaper advertising using dynamic models revealed that demand rigidities exist.

The case study of Finland proposes three reasons why newsprint demand has not shown clear signs of reaching a saturation level. First, although population growth has stagnated in major consuming countries, the number of households has been increasing continuously. Second, income elasticity of newspaper demand does not show a declining trend. Third, the main driving force behind the buoyant demand is the resurgence of demand for newspaper as an advertising medium. In forecasting newsprint consumption, in addition to projections of economic growth, attention must be paid to the rate of household formation, the development of the advertising sector, the factors affecting competition between alternative media and the resulting media-mix in advertising, and changes in the substantial weight.

The PDF includes a summary in Finnish

  • Katila, E-mail: mk@mm.unknown (email)
  • Riihinen, E-mail: pr@mm.unknown
article id 7655, category Article
Leena Finér. (1989). Biomass and nutrient cycle in fertilized and unfertilized pine, mixed birch and pine and spruce stands on a drained mire. Silva Fennica vol. 0 no. 208 article id 7655. https://doi.org/10.14214/aff.7655
Keywords: fertilization; Picea abies; Betula pubescens; peatland; biomass allocation; nutrient cycle; stand modelling
Abstract | View details | Full text in PDF | Author Info

At the beginning of the investigation period the total biomass of the Scots pine (Pinus sylvestris L.) stands on the ordinary sedge pine mire was 48 t/ha. The biomass of the mixed stands of Scots pine and birch (Betula pubescens Erhr.) on the herbrich sedge pine mire was 91 t/ha, out of which 60% was from pine. The biomass of the Norway spruce (Picea abies (L.) H. Karst.) on the Vaccinium-Myrtillus spruce mire was 148 t/ha. The average annual net increment of the stand biomass was 5.8 t/ha in the unfertilized pine stand and 6.7 t/ha in the NPK and micronutrient fertilized one during the six-year investigation period. The corresponding figures in the mixed stand were 7.2 t/ha and 7.6 t/ha. The net increment of the biomass in the unfertilized spruce stand was 6.9 t/ha and in the fertilized 8.4 t/ha. A considerable proportion of the net increment was lost to the ground as litter in all stands.

The nitrogen, phosphorus, potassium, magnesium, iron, manganese, zinc, copper and boron cycles were investigated. The annual nitrogen uptake from the soil was 26–42 kg/ha, that of phosphorus 2.5–3.4 kg/ha, potassium 4.5–12 kg/ha, calcium 12–29 kg/ha, magnesium 2–4 kg/ha, iron 1.4–6.6 kg/ha, manganese less than 2 kg/ha and the other nutrients only some grams. Only part of the fertilized nutrients was fixed in the stand.

The PDF includes a summary in Finnish.

  • Finér, E-mail: lf@mm.unknown (email)
article id 7643, category Article
Pauline Oker-Blom. (1986). Photosynthetic radiation regime and canopy structure in modeled forest stands. Silva Fennica vol. 0 no. 197 article id 7643. https://doi.org/10.14214/aff.7643
Keywords: spatial variation; radiation models; penumbra; grouping effect; photosynthetic radiation
Abstract | View details | Full text in PDF | Author Info

The relationship between canopy structure and photosynthetic radiation regime are studied in a theoretical basis. In modelling the canopy structure, a statistical approach is applied and the radiation field inside a stand is described in terms of random variables and their distribution. A comparison is made between horizontally homogenous stands and grouped forest stands in order to assess the influence of grouping of foliage on the irradiance distribution in a forest stand. Results show that grouping considerably reduces the interception of radiation and causes a large spatial variation. In coniferous stands the grouping of needles into shoots and the effect of penumbra are shown to have an important influence on the distribution of radiation on the needle area.

The PDF includes a summary in Finnish.

  • Oker-Blom, E-mail: po@mm.unknown (email)
article id 7621, category Article
Pekka Kilkki, Martti Varmola. (1981). Taper curve models for Scots pine and their applications. Silva Fennica vol. 0 no. 174 article id 7621. https://doi.org/10.14214/aff.7621
Keywords: Scots pine; taper curve; methods; taper curve model
Abstract | View details | Full text in PDF | Author Info

Taper curve models based on simultaneous equations were derived. The data consisted of 492 Scots pines (Pinus sylvestris L.) from Southern Finland. Two systems of simultaneous equations were constructed, one without the crown ratio and the other with the crown ratio as an exogenous variable. The endogenous variables consisted of 24 relative-height diameters and the height of the tree. The parameters of the model were derived by the ordinary least squares method.

In most applications, the height of the tree was exogenised. The logarithmically linear relationships between the relative-height diameters were utilized in the solution algorithm. The algorithm included both standard matrix operations and an iterative part in which the taper curve was fitted to any measured diameters by the natural cubic spline interpolation formula.

The models were applied to the derivation of taper curves, stem volumes, timber assortment percentages, and stem values. An experiment was also made to derive diameter and height increments from the taper curve model.

The reliability of the models was tested on the original data.

The PDF includes a summary in Finnish.

  • Kilkki, E-mail: pk@mm.unknown (email)
  • Varmola, E-mail: mv@mm.unknown
article id 7577, category Article
Pekka Kilkki, Raimo Pökälä. (1975). A long-term timber production model and its application to a large forest area. Silva Fennica vol. 0 no. 143 article id 7577. https://doi.org/10.14214/aff.7577
Keywords: forest management; forestry; timber production; methods; timber production model
Abstract | View details | Full text in PDF | Author Info

A long-term timber production model was developed. The model is based upon numerical simulation and it is viewed only as a means of providing the decision-maker with values of the predicting variables in his utility function. Special attention was paid to the development of automatic cutting decision rules. The model was applied to the area of 2,752,000 hectares of forest land in Central Finland. The measurement data were extracted from the Sixth National Forest Inventory, which was made in 1973. Utilities from a hypothetical utility function were attained to a number of feasible timber production policies. The Bayes and maximin criteria were employed to evaluate these policies.

The PDF includes a summary in Finnish.

  • Kilkki, E-mail: pk@mm.unknown (email)
  • Pökälä, E-mail: rp@mm.unknown
article id 7190, category Article
Yrjö Kangas. (1968). Describing the growth of a tree as a function of its age: a contribution to the methodological basis of mathematical analysis of the growth. Silva Fennica vol. 0 no. 90 article id 7190. https://doi.org/10.14214/aff.7190
Keywords: dynamic model; methodology; method development; growth analysis
Abstract | View details | Full text in PDF | Author Info

With developing possibilities to analyse data automatically there is a need to develop the mathematical and statistical practices for calculations. The article presents the basis about the growth of trees and the existing models of growth, the basics on growth functions,   and the construction of a regression model to analysis the growth. The theoretical model development has been tested with three existing data sets.

The analysis of growth should be considered with dynamic models. The model need to take into account various aspects and growth factors. The model should have practical implications.

The PDF contains a summary in German. 

  • Kangas, E-mail: yk@mm.unknown (email)

Category: Special section

article id 290, category Special section
Mikko Peltoniemi, Esther Thürig, Stephen Ogle, Taru Palosuo, Marion Schrumpf, Thomas Wutzler, Klaus Butterbach-Bahl, Oleg Chertov, Alexander Komarov, Aleksey Mikhailov, Annemieke Gärdenäs, Charles Perry, Jari Liski, Pete Smith, Raisa Mäkipää. (2007). Models in country scale carbon accounting of forest soils. Silva Fennica vol. 41 no. 3 article id 290. https://doi.org/10.14214/sf.290
Keywords: National Forest Inventory; soil carbon; greenhouse gas inventory; decomposition; IPCC; regional and national modeling; soil model
Abstract | View details | Full text in PDF | Author Info
Countries need to assess changes in the carbon stocks of forest soils as a part of national greenhouse gas (GHG) inventories under the United Nations Framework Convention on Climate Change (UNFCCC) and the Kyoto Protocol (KP). Since measuring these changes is expensive, it is likely that many countries will use alternative methods to prepare these estimates. We reviewed seven well-known soil carbon models from the point of view of preparing country-scale soil C change estimates. We first introduced the models and explained how they incorporated the most important input variables. Second, we evaluated their applicability at regional scale considering commonly available data sources. Third, we compiled references to data that exist for evaluation of model performance in forest soils. A range of process-based soil carbon models differing in input data requirements exist, allowing some flexibility to forest soil C accounting. Simple models may be the only reasonable option to estimate soil C changes if available resources are limited. More complex models may be used as integral parts of sophisticated inventories assimilating several data sources. Currently, measurement data for model evaluation are common for agricultural soils, but less data have been collected in forest soils. Definitions of model and measured soil pools often differ, ancillary model inputs require scaling of data, and soil C measurements are uncertain. These issues complicate the preparation of model estimates and their evaluation with empirical data, at large scale. Assessment of uncertainties that accounts for the effect of model choice is important part of inventories estimating large-scale soil C changes. Joint development of models and large-scale soil measurement campaigns could reduce the inconsistencies between models and empirical data, and eventually also the uncertainties of model predictions.
  • Peltoniemi, Finnish Forest Research Institute, Vantaa Research Unit, P.O. Box 18, FI-01301 Vantaa, Finland E-mail: mikko.peltoniemi@metla.fi (email)
  • Thürig, Swiss Federal Institute for Forest, Snow and Landscape Research (WSL), Birmensdorf, Switzerland; European Forest Institute, Joensuu, Finland E-mail: et@nn.ch
  • Ogle, Natural Resources Ecology Laboratory, Colorado State University, Fort Collins, USA E-mail: so@nn.us
  • Palosuo, European Forest Institute, Joensuu, Finland E-mail: tp@nn.fi
  • Schrumpf, Max-Planck-Institute for Biogeochemistry, Jena, Germany E-mail: ms@nn.de
  • Wutzler, Max-Planck-Institute for Biogeochemistry, Jena, Germany E-mail: tw@nn.de
  • Butterbach-Bahl, Institute for Meteorology and Climate Research, Forschungszentrum Karlsruhe GmbH, Garmisch-Partenkirchen, Germany E-mail: kbb@nn.de
  • Chertov, St. Petersburg State University, St. Petersburg-Peterhof, Russia E-mail: oc@nn.ru
  • Komarov, Institute of Physicochemical and Biological Problems in Soil Science of Russian Academy of Sciences, Pushchino, Russia E-mail: ak@nn.ru
  • Mikhailov, Institute of Physicochemical and Biological Problems in Soil Science of Russian Academy of Sciences, Pushchino, Russia E-mail: am@nn.ru
  • Gärdenäs, Dept. of Soil Sciences, Swedish University of Agricultural Sciences, Uppsala, Sweden E-mail: ag@nn.se
  • Perry, USDA Forest Service, Northern Research Station, St. Paul, MN USA E-mail: cp@nn.us
  • Liski, Finnish Environment Institute, Helsinki, Finland E-mail: jl@nn.fi
  • Smith, School of Biological Sciences, University of Aberdeen, Aberdeen, UK E-mail: ps@nn.uk
  • Mäkipää, Finnish Forest Research Institute, Vantaa Research Unit, P.O. Box 18, FI-01301 Vantaa, Finland E-mail: raisa.makipaa@metla.fi

Category: Research article

article id 10732, category Research article
Ana Aza, A. Maarit I. Kallio, Timo Pukkala, Ari Hietala, Terje Gobakken, Rasmus Astrup. (2022). Species selection in areas subjected to risk of root and butt rot: applying Precision forestry in Norway. Silva Fennica vol. 56 no. 3 article id 10732. https://doi.org/10.14214/sf.10732
Keywords: Norway spruce; Scots pine; growth modelling; precision forestry; root and butt rot severity; tree species selection
Abstract | Full text in HTML | Full text in PDF | Author Info

Norway’s most common tree species, Picea abies (L.) Karst. (Norway spruce), is often infected with Heterobasidion parviporum Niemelä & Korhonen and Heterobasidion annosum (Fr.) Bref.. Because Pinus sylvestris L. (Scots pine) is less susceptible to rot, it is worth considering if converting rot-infested spruce stands to pine improves economic performance. We examined the economically optimal choice between planting Norway spruce and Scots pine for previously spruce-dominated clear-cut sites of different site indexes with initial rot levels varying from 0% to 100% of stumps on the site. While it is optimal to continue to plant Norway spruce in regions with low rot levels, shifting to Scots pine pays off when rot levels get higher. The threshold rot level for changing from Norway spruce to Scots pine increases with the site index. We present a case study demonstrating a practical method (“Precision forestry”) for determining the tree species in a stand at the pixel level when the stand is heterogeneous both in site indexes and rot levels. This method is consistent with the concept of Precision forestry, which aims to plan and execute site-specific forest management activities to improve the quality of wood products while minimising waste, increasing profits, and maintaining environmental quality. The material for the study includes data on rot levels and site indexes in 71 clear-cut stands. Compared to planting the entire stand with a single species, pixel-level optimised species selection increases the net present value in almost every stand, with average increase of approximately 6%.

  • Aza, Norwegian University of Life Sciences, Department of Ecology and Natural Resource Management, PO Box 5003, NO-1432, Ås, Norway ORCID https://orcid.org/0000-0002-6416-6697 E-mail: anfe@nmbu.no (email)
  • Kallio, Norwegian University of Life Sciences, Department of Ecology and Natural Resource Management, PO Box 5003, NO-1432, Ås, Norway E-mail: maarit.kallio@nmbu.no
  • Pukkala, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: timo.pukkala@uef.fi
  • Hietala, Norwegian Institute of Bioeconomy Research, PO Box 115, NO-1431 Ås, Norway E-mail: ari.hietala@nibio.no
  • Gobakken, Norwegian University of Life Sciences, Department of Ecology and Natural Resource Management, PO Box 5003, NO-1432, Ås, Norway E-mail: terje.gobakken@nmbu.no
  • Astrup, Norwegian Institute of Bioeconomy Research, PO Box 115, NO-1431 Ås, Norway E-mail: rasmus.astrup@nibio.no
article id 10698, category Research article
Constança Camilo-Alves, Jose Antonio Nunes, Ana Patricia Poeiras, Joao Ribeiro, Cati Dinis, Joao M. Barroso, Margarida Vaz, Nuno Almeida-Ribeiro. (2022). Influence of water and nutrients on cork oak radial growth – looking for an efficient fertirrigation regime. Silva Fennica vol. 56 no. 3 article id 10698. https://doi.org/10.14214/sf.10698
Keywords: irrigation; mixed models; Quercus suber; climate–growth relationship; increments; stem radius
Abstract | Full text in HTML | Full text in PDF | Author Info

The widespread cork oak (Quercus suber L.) mortality and reduced afforestation /regeneration are causing an overall reduction in cork production. To enhance trees’ growth and vitality, afforestation techniques using fertirrigation were tested. The main objective was the promotion of trees’ growth on new dense plantations using minimum water requirements until reaching productive forests. The experimental plot – Irricork – was installed in 2017 in a ≈1 ha stand with 14 years’ age cork oaks summer-fertirrigated since plantation. Four fertirrigation treatments were applied during fertirrigation campaigns. Radial growth, meteorological parameters and fertirrigation volume were measured every 15–30 days over four years. It was observed that weather, tree size, debarking and trees’ intra-competition had a significant effect on radial increments. Fertirrigation significantly enhanced growth during summer drought and decoupled increments from air vapor pressure deficit constraints. There was a linear relationship between trees’ radial increments and fertirrigation volume up to 140 m3 week–1. Above this value, increments were smoother. In conclusion, summer fertirrigation of 140 m3 week–1 efficiently enhanced the radial growth of trees with 50–75 circumference at breast height, under the particular edaphoclimatic conditions of the stand. This study showed to be, therefore, promising in the use of efficient fertirrigation the enhance cork oaks’ radial growth.

  • Camilo-Alves, MED – Mediterranean Institute for Agriculture, Environment and Development & CHANGE – Global Change and Sustainability Institute, Institute for Advanced Studies and Research, University of Evora, Pólo da Mitra, Ap. 94, 7006-554 Évora, Portugal ORCID https://orcid.org/0000-0001-5156-172X E-mail: calves@uevora.pt (email)
  • Nunes, Department of Plant Science, School of Science and Technology, University of Evora, Pólo da Mitra, Ap. 94, 7006-554 Évora, Portugal ORCID https://orcid.org/0000-0002-6144-3484 E-mail: jain@uevora.pt
  • Poeiras, MED – Mediterranean Institute for Agriculture, Environment and Development & CHANGE – Global Change and Sustainability Institute, Institute for Advanced Studies and Research, University of Evora, Pólo da Mitra, Ap. 94, 7006-554 Évora, Portugal ORCID https://orcid.org/0000-0002-6049-807X E-mail: apcp@uevora.pt
  • Ribeiro, Department of Plant Science, School of Science and Technology, University of Evora, Pólo da Mitra, Ap. 94, 7006-554 Évora, Portugal ORCID https://orcid.org/0000-0001-7242-5866 E-mail: jmrpr@uevora.pt
  • Dinis, ORCID https://orcid.org/0000-0001-6984-1033 E-mail: dinis.cati@gmail.com
  • Barroso, MED – Mediterranean Institute for Agriculture, Environment and Development & CHANGE – Global Change and Sustainability Institute, and Department of Plant Science, School of Science and Technology, University of Evora, Pólo da Mitra, Ap. 94, 7006-554 Évora, Portugal ORCID https://orcid.org/0000-0002-0160-3845 E-mail: jmmb@uevora.pt
  • Vaz, MED – Mediterranean Institute for Agriculture, Environment and Development & CHANGE – Global Change and Sustainability Institute, and Department of Biology, School of Science and Technology, University of Evora. Pólo da Mitra, Ap. 94, 7006-554 Évora, Portugal ORCID https://orcid.org/0000-0002-3368-757X E-mail: mvaz@uevora.pt
  • Almeida-Ribeiro, ICT – Institute of Earth Sciences and Department of Plant Science, School of Science and Technology, University of Evora, Pólo da Mitra, Ap. 94, 7006-554 Évora, Portugal ORCID https://orcid.org/0000-0002-0160-3845 E-mail: nmcar@uevora.pt
article id 10550, category Research article
Miro Demol, Phil Wilkes, Pasi Raumonen, Sruthi M. Krishna Moorthy, Kim Calders, Bert Gielen, Hans Verbeeck. (2022). Volumetric overestimation of small branches in 3D reconstructions of Fraxinus excelsior. Silva Fennica vol. 56 no. 1 article id 10550. https://doi.org/10.14214/sf.10550
Keywords: aboveground biomass; crown architecture; LIDAR; quantitative structure models; common ash; woody tree volume
Highlights: We compare branch diameter and tree woody volume estimates from terrestrial laser scanning data with manual measurements of two Fraxinus excelsior trees; Smaller branch diameters are generally overestimated due to scattering and misalignment errors in the point cloud; Consequently, tree woody volume is overestimated by 38% to 52%; Filtering by reflectance and improved alignment partly mitigate this effect.
Abstract | Full text in HTML | Full text in PDF | Author Info

Terrestrial laser scanning (TLS) has been applied to estimate forest wood volume based on detailed 3D tree reconstructions from point cloud data. However, sources of uncertainties in the point cloud data (alignment and scattering errors, occlusion, foliage...) and the reconstruction algorithm type and parameterisation are known to affect the reconstruction, especially around finer branches. To better understand the impacts of these uncertainties on the accuracy of TLS-derived woody volume, high-quality TLS scans were collected in leaf-off conditions prior to destructive harvesting of two forest-grown common ash trees (Fraxinus excelsior L.; diameter at breast height ~28 cm, woody volume of 732 and 868 L). We manually measured branch diameters at 265 locations in these trees. Estimates of branch diameters and tree volume from Quantitative Structure Models (QSM) were compared with these manual measurements. The accuracy of QSM branch diameter estimates decreased with smaller branch diameters. Tree woody volume was overestimated (+336 L and +392 L) in both trees. Branches measuring < 5 cm in diameter accounted for 80% and 83% of this overestimation respectively. Filtering for scattering errors or improved coregistration approximately halved the overestimation. Range filtering and modified scanning layouts had mixed effects. The small branch overestimations originated primarily in limitations in scanner characteristics and coregistration errors rather than suboptimal QSM parameterisation. For TLS-derived estimates of tree volume, a higher quality point cloud allows smaller branches to be accurately reconstructed. Additional experiments need to elucidate if these results can be generalised beyond the setup of this study.

  • Demol, CAVElab – Computational and Applied Vegetation Ecology, Department of Environment, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium; PLECO – Plants and Ecosystems, Faculty of Science, Antwerp University, Universiteitsplein 1, B-2610 Wilrijk, Belgium ORCID https://orcid.org/0000-0002-5492-2874 E-mail: miro.demol@ugent.be (email)
  • Wilkes, UCL Department of Geography, Gower Street, London WC1E 6BT, UK; NERC National Centre for Earth Observation (NCEO), UK ORCID https://orcid.org/0000-0001-6048-536X E-mail: p.wilkes@ucl.ac.uk
  • Raumonen, Mathematics, Tampere University, FI-33101 Tampere, Finland ORCID https://orcid.org/0000-0001-5471-0970 E-mail: pasi.raumonen@tuni.fi
  • Krishna Moorthy, CAVElab – Computational and Applied Vegetation Ecology, Department of Environment, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium ORCID https://orcid.org/0000-0002-6838-2880 E-mail: Sruthi.KrishnaMoorthyParvathi@ugent.be
  • Calders, CAVElab – Computational and Applied Vegetation Ecology, Department of Environment, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium ORCID https://orcid.org/0000-0002-4562-2538 E-mail: kim.calders@ugent.be
  • Gielen, PLECO – Plants and Ecosystems, Faculty of Science, Antwerp University, Universiteitsplein 1, B-2610 Wilrijk, Belgium ORCID https://orcid.org/0000-0002-4890-3060 E-mail: bert.gielen@uantwerpen.be
  • Verbeeck, CAVElab – Computational and Applied Vegetation Ecology, Department of Environment, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, B-9000 Ghent, Belgium ORCID https://orcid.org/0000-0003-1490-0168 E-mail: hans.verbeeck@ugent.be
article id 10544, category Research article
Lars Sprengel, Heinrich Spiecker, Shuirong Wu. (2022). Two subject specific modelling approaches to construct base-age invariant polymorphic site index curves with varying asymptotes. Silva Fennica vol. 56 no. 1 article id 10544. https://doi.org/10.14214/sf.10544
Keywords: generalized algebraic difference approach; stem analysis; dummy variable approach; gnls; nonlinear mixed-effects models; nlme; Zhongtiaoshan forest region
Highlights: Base-age invariant families of height growth curves with polymorphism and varying asymptotes are presented for the seven economically most important tree species in Zhongtiaoshan forest region, China; The nonlinear fixed-effects approach outperforms the nonlinear mixed-effects approach according to the AIC, but according to RMSE and bias these results are not fully supported.
Abstract | Full text in HTML | Full text in PDF | Author Info

For constructing growth and yield models the concept of site index as measure of productivity is crucial. Here, we use nonlinear mixed-effects models (NLME) with random individual effects and nonlinear models with dummy variables as fixed individual effects (NLFE) to fit mechanistic growth functions to stem analysis data of the economically most important tree species in Zhongtiaoshan forest region, China. The Richards and Lundqvist function are formulated into five dynamic equations (R1, R2, L1, L2 and L3) applying the generalized algebraic difference approach (GADA), which inherit polymorphism, varying asymptotes and base-age invariance. According to Akaike information criterion the R1 model as NLFE fits height growth data of Pinus tabuliformis Carrière, Pinus armandii Franch., Quercus liaotungensis Koidz., Quercus aliena Blume and Betula platyphylla Sukaczev best, while for Quercus variabilis Blume R2 as NLFE fits height growth data best. For Larix principis-rupprechtii Mayr L1 as NLME has been selected as best model, as R1 and R2 both as NLFE and NLME are not extrapolating the comparably short length of height growth data well enough. However, according to the root mean square error and bias differences between model fits of both the selected equation and the chosen model fitting approach are not so clear. Presented families of height growth curves serve as planning tools to identify site index and therefore assess productivity of forest stands in the studied region. A direct comparison of the productivity of forest stands of the same tree species is possible due to base-age invariance of the selected models.

  • Sprengel, Chair of Forest Growth and Dendroecology, Albert-Ludwigs-University Freiburg, Tennenbacher Str. 4, 79106 Freiburg, Germany ORCID https://orcid.org/0000-0002-6332-7911 E-mail: lars.sprengel@iww.uni-freiburg.de (email)
  • Spiecker, Chair of Forest Growth and Dendroecology, Albert-Ludwigs-University Freiburg, Tennenbacher Str. 4, 79106 Freiburg, Germany E-mail: instww@uni-freiburg.de
  • Wu, Research Institute of Forest Policy and Information, Chinese Academy of Forestry, No. 1 Dongxiaofu, Haidian District, Beijing 100091, China E-mail: shuirongwu@126.com
article id 10612, category Research article
Daesung Lee, Jouni Siipilehto, Jari Hynynen. (2021). Models for diameter distribution and tree height in hybrid aspen plantations in southern Finland. Silva Fennica vol. 55 no. 5 article id 10612. https://doi.org/10.14214/sf.10612
Keywords: Näslund’s height curve; Weibull distribution; parameter recovery; Populus tremula × P. tremuloides; clonal plantation; nonlinear mixed-effects model
Highlights: Parameter recovery method for the Weibull function fitted diameter distributions well by means of sum and mean forest stand characteristics for hybrid aspen plantations; Arithmetic and weighted mean diameters performed better for the recovery method than the corresponding median diameters; Two alternative Näslund’s height curve models with stand characteristics and tree dbh predictors provided unbiased tree height predictions.
Abstract | Full text in HTML | Full text in PDF | Author Info

Hybrid aspen (Populus tremula L. × P. tremuloides Michx.) is known with outstanding growth rate and some favourable wood characteristics, but models for stand management have not yet been prepared in northern Europe. This study introduces methods and models to predict tree dimensions, diameter at breast height (dbh) and tree height for a hybrid aspen plantation using data from repeatedly measured permanent sample plots established in clonal plantations in southern Finland. Dbh distributions using parameter recovery method for the Weibull function was used with Näslund’s height curve to model tree heights. According to the goodness-of-fit statistics of Kolmogorov-Smirnov and the Error Index, the arithmetic mean diameter (D) and basal area-weighted mean diameter (DG) provided more stable parameter recovery for the Weibull distribution than the median diameter (DM) and basal area-weighted median diameter (DGM), while DG showed the best overall fit. Thus, Näslund’s height curve was modelled using DG with Lorey’s height (HG), age, basal area (BA), and tree dbh (Model 1). Also, Model 2 was tested using all predictors of Model 1 with the number of trees per ha (TPH). All predictors were shown to be significant in both Models, showing slightly different behaviour. Model 1 was sensitive to the mean characteristics, DG and HG, while Model 2 was sensitive to stand density, including both BA and TPH as predictors. Model 1 was considered more reasonable to apply based on our results. Consequently, the parameter recovery method using DG and Näslund’s models were applicable for predicting tree diameter and height.

  • Lee, Natural Resources Institute Finland (Luke), Natural resources, Latokartanonkaari 9, FI-00790 Helsinki, Finland ORCID https://orcid.org/0000-0003-1586-9385 E-mail: daesung.lee@luke.fi (email)
  • Siipilehto, Natural Resources Institute Finland (Luke), Natural resources, Latokartanonkaari 9, FI-00790 Helsinki, Finland E-mail: jouni.siipilehto@luke.fi
  • Hynynen, Natural Resources Institute Finland (Luke), Natural resources, Vipusenkuja 5, FI-57200 Savonlinna, Finland ORCID https://orcid.org/0000-0002-9132-8612 E-mail: jari.hynynen@luke.fi
article id 10573, category Research article
Jari Miina, Inka Bohlin, Torgny Lind, Jonas Dahlgren, Kari Härkönen, Tuula Packalen, Anne Tolvanen. (2021). Lessons learned from assessing the cover and yield of bilberry and lingonberry using the national forest inventories in Finland and Sweden. Silva Fennica vol. 55 no. 5 article id 10573. https://doi.org/10.14214/sf.10573
Keywords: forest management planning; berry models; field measurements; predictions
Highlights: Model-based predictions of the berry yields of an average crop year are produced using the Finnish National Forest Inventory (NFI); Inventory-based estimates of seasonal berry yields are produced using the Swedish NFI observations; The inventory-based method provides seasonal estimates, whereas models can be utilised to integrate vegetation cover and berry yields in numerical multi-objective forest planning.
Abstract | Full text in HTML | Full text in PDF | Author Info

Bilberry (Vaccinium myrtillus L.) and lingonberry (V. vitis-idaea L.) can be a part of healthy diet and are important for many animals. Two approaches are described to assessing their vegetation cover and berry yield via national forest inventory (NFI) observations. The aim was to provide estimates and predictions of the abundance and yield of the species at regional and national levels in Finland and Sweden. In Finland, the model-based predictions are used in evaluating the impacts of cutting intensity on forest berries needed in forest-related decision making. In Sweden, seasonal inventory-based estimates are used to evaluate the annual national and regional berry yields, and in a forecasting system aimed at large public and berry enterprises. Based on the NFI sample plots measured between 2014 and 2018, the total annual yields are estimated to be 208 Mkg of bilberry and 246 Mkg of lingonberry on productive forest land (increment at least 1 m3 ha–1 year–1) in Finland, and 336 and 382 Mkg respectively in Sweden (average of NFI inventories in 2015–2019). The predicted development of berry yields is related to the intensity of cuttings in alternative forest management scenarios: lower removals favoured bilberry, and higher removals lingonberry. The model-based method describes the effects of stand development and management on berry yields, whereas the inventory-based method can calibrate seasonal estimates through field observations. In providing spatially and timely more accurate information concerning seasonal berry yields, an assessment of berry yields should involve the elements of both inventory-based and model-based approaches described in this study.

  • Miina, Natural Resources Institute Finland (Luke), Yliopistokatu 6 B, FI-80100 Joensuu, Finland ORCID https://orcid.org/0000-0002-8639-4383 E-mail: jari.miina@luke.fi (email)
  • Bohlin, Swedish University of Agricultural sciences (SLU), Department of Forest Resource Management, Skogsmarksgränd, S-901 83 Umeå, Sweden E-mail: inka.bohlin@slu.se
  • Lind, Swedish University of Agricultural sciences (SLU), Department of Forest Resource Management, Skogsmarksgränd, S-901 83 Umeå, Sweden E-mail: torgny.lind@slu.se
  • Dahlgren, Swedish University of Agricultural sciences (SLU), Department of Forest Resource Management, Skogsmarksgränd, S-901 83 Umeå, Sweden E-mail: jonas.dahlgren@slu.se
  • Härkönen, Natural Resources Institute Finland (Luke), Latokartanonkaari 9, FI-00790 Helsinki, Finland E-mail: kari.harkonen@luke.fi
  • Packalen, Natural Resources Institute Finland (Luke), Yliopistokatu 6 B, FI-80100 Joensuu, Finland; Ministry of Agriculture and Forestry of Finland, P.O. Box 30, FI-00023 Government, Finland E-mail: tuula.packalen@mmm.fi
  • Tolvanen, Natural Resources Institute Finland (Luke), Paavo Havaksentie 3, FI-90014 University of Oulu, Finland E-mail: anne.tolvanen@luke.fi
article id 10449, category Research article
Emanuel Strieder, Sonja Vospernik. (2021). Intra-annual diameter growth variation of six common European tree species in pure and mixed stands. Silva Fennica vol. 55 no. 4 article id 10449. https://doi.org/10.14214/sf.10449
Keywords: growing season; climate effects; dendrometer; logistic model; mixing effect; seasonal growth; social tree position
Highlights: 244 intra-annual growth patterns of six tree species on five sites in mixed and corresponding pure stands were analyzed; Humid sites showed a longer growing season than dry sites; Deciduous species showed an earlier growth culmination than conifer species; Mixture effects were both positive and negative and clearly differed between years, indicating that climate alters mixture effects.
Abstract | Full text in HTML | Full text in PDF | Author Info

Studies of intra-annual growth are particularly useful for understanding tree growth because of their high temporal resolution. This study was performed in Austria and included hourly band dendrometer data of 244 annual tree recordings from six tree species (Picea abies (L.) Karst., Pinus sylvestris L., Larix decidua Mill., Abies alba Mill., Fagus sylvatica L., Quercus spp. (Quercus petraea (Matt.) Liebl., Quercus robur L.) sampled on five sites with contrasting site conditions in pure and mixed stands and on trees of different social position. Measurements encompassed 1–7 years. Cumulative diameter increment was modelled by logistic mixed-effects models with random effects at the tree and year level. The results showed large differences in seasonal growth patterns between sites, with a clearly shorter growing season at the drier sites. Species specific response on dry sites could be linked to drought characteristics, whereas response on more humid sites was related to light requirements or successional status. The deciduous trees showed earlier growth culmination and shorter growing periods than the evergreen species. Individual tree growth of Quercus spp., P. abies, and F. sylvatica was positively affected by mixture whereas L. decidua, P. sylvestris and A. alba showed no or adverse mixture effects. Mixture effects differed between years and social position. Furthermore, increment culmination was earlier in mixed stands, but shifts were minor. Tree growth differed by social position with dominant trees showing the largest increment and the longest growth duration, with shifts in tree growth patterns due to social position being as large as those between different sites.

  • Strieder, Boku, University of Natural Resources and Life Sciences Vienna, Department of Forest- and Soil Sciences, Institute of Forest Growth, Peter-Jordan-Str. 82, A-1190 Vienna, Austria ORCID https://orcid.org/0000-0001-6398-8536 E-mail: emanuel.strieder@students.boku.ac.at
  • Vospernik, Boku, University of Natural Resources and Life Sciences Vienna, Department of Forest- and Soil Sciences, Institute of Forest Growth, Peter-Jordan-Str. 82, A-1190 Vienna, Austria ORCID http://orcid.org/0000-0002-4201-6444 E-mail: sonja.vospernik@boku.ac.at (email)
article id 10441, category Research article
Dipak Mahatara, Amul K. Acharya, Bishnu P. Dhakal, Dipesh K. Sharma, Sunita Ulak, Prashant Paudel. (2021). Maxent modelling for habitat suitability of vulnerable tree Dalbergia latifolia in Nepal. Silva Fennica vol. 55 no. 4 article id 10441. https://doi.org/10.14214/sf.10441
Keywords: rosewood; satisal; distribution mapping; environmental variables; Maxent modelling
Highlights: Dalbergia latifolia is a vulnerable species of Nepal with very few conservation priorities; Habitat suitability modelling for this species is essential to endorse different conservation interventions; 43 presence locations and different environmental variables were retained for model prediction in Maxent; Province 2 was found most suitable habitat for the growth of D. latifolia, with western most province as unsuitable.
Abstract | Full text in HTML | Full text in PDF | Author Info

Dalbergia latifolia Roxb., commonly known as rosewood, is one of the highly valuable tropical timber species of Nepal. The tree species was widely distributed in the past, however, over-exploitation of natural habitat, deforestation, forest conversion for agriculture, illegal logging and the invasion of alien species resulted in the classification of this species as vulnerable by the IUCN (International Union for Conservation of Nature) category. So, the prediction of habitat suitability and potential distribution of the species is required to develop restoration mechanisms and conservation interventions. In this study, we modelled the suitable habitat of D. latifolia over the entire possible range of Nepal using a Maxent model. We compiled 23 environmental variables (19 bioclimatic, 3 topographic and a vegetative layer), however, only 12 least correlated variables along with 43 spatially representative presence locations were retained for model prediction. We used a receiver operating characteristic (ROC) curve to assess the model’s performance and a Jackknife procedure to evaluate the relative importance of predictor variables. The model was statistically significant with an area under the curve (AUC) value of 0.969. The internal Jackknife test indicated that elevation was the most important variable for the model prediction with 71.3% contribution followed by mean temperature of driest quarter (9.8%). The most (>0.6) suitable habitat for the D. latifolia was 235 484 hectares with large sections of area in two provinces whereas, the western most provinces were not suitable for D. latifolia as per Maxent model. The information presented here can provide a framework for nature conservation planning, monitoring and habitat management of this rare and endangered species.

  • Mahatara, Forest Research and Training Centre, Government of Nepal, P.O. Box 3339, Babarmahal, Kathmandu 44600, Nepal E-mail: honeystar73@gmail.com (email)
  • Acharya, Forest Research and Training Centre, Government of Nepal, P.O. Box 3339, Babarmahal, Kathmandu 44600, Nepal E-mail: acharya.amulkumar@gmail.com
  • Dhakal, Forest Research and Training Centre, Government of Nepal, P.O. Box 3339, Babarmahal, Kathmandu 44600, Nepal E-mail: dhakalbp.shorea@gmail.com
  • Sharma, Forest Research and Training Centre, Government of Nepal, P.O. Box 3339, Babarmahal, Kathmandu 44600, Nepal E-mail: dipeshsharmadiyu2015@gmail.com
  • Ulak, Forest Research and Training Centre, Government of Nepal, P.O. Box 3339, Babarmahal, Kathmandu 44600, Nepal E-mail: sunitaulak@gmail.com
  • Paudel, Agriculture Forestry University, P.O. Box 13712 Rampur, Chitwan, Nepal E-mail: prashant.paudel88@gmail.com
article id 10494, category Research article
Hannu Hökkä, Ari Laurén, Leena Stenberg, Samuli Launiainen, Kersti Leppä, Mika Nieminen. (2021). Defining guidelines for ditch depth in drained Scots pine dominated peatland forests. Silva Fennica vol. 55 no. 3 article id 10494. https://doi.org/10.14214/sf.10494
Keywords: Pinus sylvestris; forest management; peatland; drainage; ditch network maintenance; process model; water table
Highlights: Process-based hydrological model was applied to drained peatland forests representing a wide range of conditions in Finland; Ditch depth keeping the median July–August water table below 0.35 m was defined; Ditch depth depended on climatic conditions, stand volume, peat properties, and ditch spacing; Shallower ditches than recommended in practice proved to be sufficient in most situations.
Abstract | Full text in HTML | Full text in PDF | Author Info

We used a process-based hydrological model SUSI to improve guidelines for ditch network maintenance (DNM) operations on drained peatland forests. SUSI takes daily weather data, ditch depth, strip width, peat properties, and forest stand characteristics as input and calculates daily water table depth (WTD) at different distances from ditch. The study focuses on Scots pine (Pinus sylvestris L.) dominated stands which are the most common subjects of DNM. Based on a literature survey, and consideration of the tradeoffs between forest growth and detrimental environmental impacts, long term median July–August WTD of 0.35 m was chosen as a target WTD. The results showed that ditch depths required to reach such WTD depends strongly on climatic locations, stand volume, ditch spacing, and peat thickness and type. In typical ditch cleaning areas in Finland with parallel ditches placed about 40 m apart and tree stand volumes exceeding 45 m3 ha–1, 0.3–0.8 m deep ditches were generally sufficient to lower WTD to the targeted depth of 0.35 m. These are significantly shallower ditch depths than generally recommended in operational forestry. The main collector ditch should be naturally somewhat deeper to permit water outflow. Our study brings a firmer basis on environmentally sound forestry on drained peatlands.

  • Hökkä, Natural Resources Institute Finland (Luke), Natural resources, Latokartanonkaari 9, P.O. Box 2, FI-00791 Helsinki, Finland E-mail: hannu.hokka@luke.fi (email)
  • Laurén, University of Eastern Finland, Faculty of Science and Forestry, School of Forest Sciences, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: ari.lauren@uef.fi
  • Stenberg, Natural Resources Institute Finland (Luke), Natural resources, Latokartanonkaari 9, P.O. Box 2, FI-00791 Helsinki, Finland E-mail: leena.stenberg@luke.fi
  • Launiainen, Natural Resources Institute Finland (Luke), Bioeconomy and environment, Latokartanonkaari 9, P.O. Box 2, FI-00791 Helsinki, Finland E-mail: samuli.launiainen@luke.fi
  • Leppä, Natural Resources Institute Finland (Luke), Bioeconomy and environment, Latokartanonkaari 9, P.O. Box 2, FI-00791 Helsinki, Finland E-mail: kersti.leppa@luke.fi
  • Nieminen, Natural Resources Institute Finland (Luke), Natural resources, Latokartanonkaari 9, P.O. Box 2, FI-00791 Helsinki, Finland E-mail: mika.nieminen@luke.fi
article id 10496, category Research article
Jouni Siipilehto, Harri Mäkinen, Kjell Andreassen, Mikko Peltoniemi. (2021). Models for integrating and identifying the effect of senescence on individual tree survival probability for Norway spruce. Silva Fennica vol. 55 no. 2 article id 10496. https://doi.org/10.14214/sf.10496
Keywords: forest dynamics; model comparison; between-tree competition; mortality model
Highlights: The effect of senescence was integrated into an individual tree survival model; The best model showed good fit for managed, unmanaged and old-growth stands; The probability for a large tree to survive decreased with increasing stand age; The best performed model included an interaction term between stem diameter and stand age and also stand age as a separate independent variable.
Abstract | Full text in HTML | Full text in PDF | Author Info

Ageing and competition reduce trees’ ability to capture resources, which predisposes them to death. In this study, the effect of senescence on the survival probability of Norway spruce (Picea abies (L.) Karst.) was analysed by fitting alternative survival probability models. Different model formulations were compared in the dataset, which comprised managed and unmanaged plots in long-term forest experiments in Finland and Norway, as well as old-growth stands in Finland. Stand total age ranged from 19 to 290 years. Two models were formulated without an age variable, such that the negative coefficient for the squared stem diameter described a decreasing survival probability for the largest trees. One of the models included stand age as a separate independent variable, and three models included an interaction term between stem diameter and stand age. According to the model including stand age and its interaction with stem diameter, the survival probability curves could intersect each other in stands with a similar structure but a different mean age. Models that did not include stand age underestimated the survival rate of the largest trees in the managed stands and overestimated their survival rate in the old-growth stands. Models that included stand age produced more plausible predictions, especially for the largest trees. The results supported the hypothesis that the stand age and senescence of trees decreases the survival probability of trees, and that the ageing effect improves survival probability models for Norway spruce.

  • Siipilehto, Natural Resources Institute Finland (Luke), Natural resources, Latokartanonkaari 9, P.O. Box 2, FI-00790 Helsinki, Finland E-mail: jouni.siipilehto@luke.fi (email)
  • Mäkinen, Natural Resources Institute Finland (Luke), Production systems, Latokartanonkaari 9, P.O. Box 2, FI-00790 Helsinki, Finland ORCID https://orcid.org/0000-0002-1820-6264 E-mail: harri.makinen@luke.fi
  • Andreassen, Norwegian Institute of Bioeconomy Research (NIBIO), NO-1431 Ås, Norway E-mail: kjellandreassen@gmail.com
  • Peltoniemi, Natural Resources Institute Finland (Luke), Bioeconomy and environment, Latokartanonkaari 9, P.O. Box 2, FI-00790 Helsinki, Finland ORCID https://orcid.org/0000-0003-2028-6969 E-mail: mikko.peltoniemi@luke.fi
article id 10415, category Research article
Lele Lu, Sophan Chhin, Jianguo Zhang, Xiongqing Zhang. (2021). Modelling tree height-diameter allometry of Chinese fir in relation to stand and climate variables through Bayesian model averaging approach. Silva Fennica vol. 55 no. 2 article id 10415. https://doi.org/10.14214/sf.10415
Keywords: Cunninghamia lanceolata; Bayesian model averaging; height-diameter allometry; stand and climate variables; stepwise regression
Highlights: Bayesian model averaging (BMA) and stepwise regression (SR) were compared for modelling tree height-diameter allometry; The model acquired by SR was equal to the model with the third highest posterior probability of the BMA models; BMA produced estimates of the model parameters with slightly narrower ranges around the estimate of the population parameter; Temperature was the dominant climate variable shaping the allometry.
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Tree height-diameter allometry reflects the response of specific species to above and belowground resource allocation patterns. However, traditional methods (e.g. stepwise regression (SR)) may ignore model uncertainty during the variable selection process. In this study, 450 trees of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) grown at five spacings were used. We explored the height-diameter allometry in relation to stand and climate variables through Bayesian model averaging (BMA) and identifying the contributions of these variables to the allometry, as well as comparing with the SR method. Results showed the SR model was equal to the model with the third highest posterior probability of the BMA models. Although parameter estimates from the SR method were similar to BMA, BMA produced estimates with slightly narrower 95% intervals. Heights increased with increasing planting density, dominant height, and mean annual temperature, but decreased with increasing stand basal area and summer mean maximum temperature. The results indicated that temperature was the dominant climate variable shaping the height-diameter allometry for Chinese fir plantations. While the SR model included the mean coldest month temperature and winter mean minimum temperature, these variables were excluded in BMA, which indicated that redundant variables can be removed through BMA.

  • Lu, Key Laboratory of Tree Breeding and Cultivation of the National Forestry and Grassland Administration, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, P. R. China; Collaborative Innovation Center of Sustainable Forestry in Southern China, Nanjing Forestry University, Nanjing, 210037, P. R. China E-mail: 18556439861@163.com
  • Chhin, Division of Forestry and Natural Resources, West Virginia University, 322 Percival Hall, 1145 Evansdale Dr, Morgantown, West Virginia, 26506, USA E-mail: steve.chhin@mail.wvu.edu
  • Zhang, Key Laboratory of Tree Breeding and Cultivation of the National Forestry and Grassland Administration, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, P. R. China E-mail: xqzhang85@caf.ac.cn
  • Zhang, Key Laboratory of Tree Breeding and Cultivation of the National Forestry and Grassland Administration, Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, P. R. China; Collaborative Innovation Center of Sustainable Forestry in Southern China, Nanjing Forestry University, Nanjing, 210037, P. R. China E-mail: xqzhang85@yahoo.com (email)
article id 10351, category Research article
Karol Bronisz, Michał Zasada. (2020). Taper models for black locust in west Poland. Silva Fennica vol. 54 no. 5 article id 10351. https://doi.org/10.14214/sf.10351
Keywords: taper; Robinia pseudoacacia; mixed-effects models; section diameter over and under bark; volume prediction
Highlights: Seven taper models with different numbers of estimated parameters were analysed; Section diameter and volume was modelled using fixed and mixed-effects modelling approaches; The variable-form taper model with eight estimated parameters fitted the data the best; The lowest error for volume prediction was achieved for the fixed-effects taper model.
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The diameter at any point on a stem and tree volume are some of the most important types of information used in forest management planning. One of the methods to predict the diameter at any point on a stem is to develop taper models. Black locust (Robinia pseudoacacia L.) occurs in almost all forests in Poland, with the largest concentration in the western part of the country. Using empirical data obtained from 13 black locust stands (48 felled trees), seven taper models with different numbers of estimated parameters were analysed for section diameters both over and under bark using fixed and mixed-effects modelling approaches. Assuming a lack of additional measurements, the best fitted taper models were used for the prediction of over bark volume using both methods. The predicted volume was compared with the results from different volume equations available for black locust. The variable-form taper model with eight estimated parameters fitted the data the best. The lowest root mean square error for volume prediction was achieved for the elaborated fixed-effects taper model (0.0476), followed by the mixed-effects taper model (0.0489). At the same time, the difference between the volume relative errors achieved based on the taper models does not differ significantly from the results obtained using the volume equations already available for black locust (two of the three analysed).

  • Bronisz, Institute of Forest Sciences, Warsaw University of Life Sciences-SGGW, Nowoursynowska 159, PL 02-776 Warsaw, Poland E-mail: karol.bronisz@wl.sggw.pl (email)
  • Zasada, Institute of Forest Sciences, Warsaw University of Life Sciences-SGGW, Nowoursynowska 159, PL 02-776 Warsaw, Poland ORCID https://orcid.org/0000-0002-4881-296X E-mail: Michal.Zasada@wl.sggw.pl
article id 10309, category Research article
Petteri Seppänen, Antti Mäkinen. (2020). Comprehensive yield model for plantation teak in Panama. Silva Fennica vol. 54 no. 5 article id 10309. https://doi.org/10.14214/sf.10309
Keywords: simulation; teak; decision support system; Tectona grandis; Panama; taper curve; volume equation; yield model
Highlights: Tree level teak stem volume models, taper model and three sets of stand level yield models were developed using large empirical datasets; Tree volume models were satisfactorily validated against independent measurement data and other published models; Tree height as input parameter improved the stem volume model marginally; Stand level yield models produced comparable harvest volumes with models published in the literature; Stand level timber product outputs were found like actual harvests with an exception that the models marginally underestimate the share of logs in very large diameter classes.
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The purpose of this study was to prepare a comprehensive, computerized teak (Tectona grandis L.f) plantation yield model system that can be used to describe the forest dynamics, predict growth and yield and support forest planning and decision-making. Extensive individual tree and permanent sample plot data were used to develop tree-level volume models, taper curve models and stand-level yield models for teak plantations in Panama. Tree volume models were satisfactorily validated against independent measurement data and other published models. Tree height as input parameter improved the stem volume model marginally. Stand level yield models produced comparable harvest volumes with models published in the literature. Stand level volume product outputs were found like actual harvests with an exception that the models marginally underestimate the share of logs in very large diameter classes. The kind of comprehensive model developed in this study and implemented in an easy to use software package provides a very powerful decision support tool. Optimal forest management regimes can be found by simulating different planting densities, thinning regimes and final harvest ages. Forest practitioners can apply growth and yield models in the appropriate stand level inventory data and perform long term harvest scheduling at property level or even at an entire timberland portfolio level. Harvest schedules can be optimized using the applicable financial parameters (silviculture costs, harvesting costs, wood prices and discount rates) and constraints (market size and operational capacity).

  • Seppänen, Verdas Oy, Kihlinkuja 7, FI-50600 Mikkeli, Finland E-mail: petteri@verdas.fi (email)
  • Mäkinen,  Simosol Oy. Hämeenkatu 10, FI-11100 Riihimäki, Finland E-mail: antti.makinen@simosol.fi
article id 10272, category Research article
Ana de Lera Garrido, Terje Gobakken, Hans Ole Ørka, Erik Næsset, Ole M. Bollandsås. (2020). Reuse of field data in ALS-assisted forest inventory. Silva Fennica vol. 54 no. 5 article id 10272. https://doi.org/10.14214/sf.10272
Keywords: airborne laser scanning; data reuse; temporal model transferability
Highlights: Six biophysical forest attributes were estimated for small stands without using up-to-date field data; The approaches included reused model relationships and forecasted field data; The accuracy of height estimates was comparable with the accuracy of an ordinary forest inventory with up-to-date field- and ALS data; Both approaches tended to produce estimates systematically different from the ground reference.
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Forest inventories assisted by wall-to-wall airborne laser scanning (ALS), have become common practice in many countries. One major cost component in these inventories is the measurement of field sample plots used for constructing models relating biophysical forest attributes to metrics derived from ALS data. In areas where ALS-assisted forest inventories are planned, and in which the previous inventories were performed with the same method, reusing previously acquired field data can potentially reduce costs, either by (1) temporally transferring previously constructed models or (2) projecting field reference data using growth models that can serve as field reference data for model construction with up-to-date ALS data. In this study, we analyzed these two approaches of reusing field data acquired 15 years prior to the current ALS acquisition to estimate six up-to-date forest attributes (dominant tree height, mean tree height, stem number, stand basal area, volume, and aboveground biomass). Both approaches were evaluated within small stands with sizes of approximately 0.37 ha, assessing differences between estimates and ground reference values. The estimates were also compared to results from an up-to-date forest inventory relying on concurrent field- and ALS data. The results showed that even though the reuse of historical information has some potential and could be beneficial for forest inventories, systematic errors may appear prominent and need to be overcome to use it operationally. Our study showed systematic trends towards the overestimation of lower-range ground references and underestimation of the upper-range ground references.

  • de Lera Garrido, Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, NO-1432 Ås, Norway E-mail: ana.maria.lera.garrido@nmbu.no (email)
  • Gobakken, Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, NO-1432 Ås, Norway E-mail: terje.gobakken@nmbu.no
  • Ørka, Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, NO-1432 Ås, Norway E-mail: hans-ole.orka@nmbu.no
  • Næsset, Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, NO-1432 Ås, Norway E-mail: erik.naesset@nmbu.no
  • Bollandsås, Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, NO-1432 Ås, Norway E-mail: ole.martin.bollandsas@nmbu.no
article id 10392, category Research article
Paula Jylhä, Pasi Rikkonen, Katri Hamunen. (2020). Size matters – an analysis of business models and the financial performance of Finnish wood-harvesting companies. Silva Fennica vol. 54 no. 4 article id 10392. https://doi.org/10.14214/sf.10392
Keywords: profitability; business model; business model canvas; entrepreneur; success factor; wood-harvesting enterprise
Highlights: Economic success was related to company’s size, Small companies with a turnover of less than 600 000 € a–1 are struggling with profitability; Large enterprises continue to grow and innovate new business concepts; The competitive edge of large companies was reflected in large production capacity, efficient operations, versatile supply of services, and power in negotiations.
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The size of Finnish wood harvesting enterprises has grown, and entrepreneurs have become responsible for various additional tasks, resulting in networking with other harvesting enterprises of various sizes and suppliers of supporting services, but the profitability of the wood harvesting sector has remained low. In the present study, the financial performance of 83 wood harvesting companies in Eastern and Northern Finland was evaluated, based on public final account data from a five-year period between 2013 and 2017. The factors underlying economic success were identified based on 19 semi-structured entrepreneur interviews. The Business Model Canvas framework was applied in the analyses. In particular, the smallest companies (with an annual turnover of less than 600 000 €) struggled with profitability. They showed increasing indebtedness, suffered from poor power in negotiations, had typically short-term contracts, and faced difficulties in retaining skilled operators. Most of the small companies were subcontractors of larger wood-harvesting companies. The better economic success of larger companies was likely based on their capacity to provide wood harvesting services in large volumes and supply versatile services, power in negotiations, and more cost-effective operations. The future development of wood harvesting seems to be polarised: larger enterprises are likely to continue growing, while the size of smaller enterprises has stabilised. Enhancing business management skills and practices is required in enterprises of all size groups.

  • Jylhä, Natural Resources Institute Finland (Luke), Production systems, Teknologiakatu 7, FI-67100 Kokkola, Finland E-mail: paula.jylha@luke.fi (email)
  • Rikkonen, Natural Resources Institute Finland (Luke), Bioeconomy and environment, Lönnrotinkatu 7, FI-50100 Mikkeli, Finland E-mail: pasi.rikkonen@luke.fi
  • Hamunen, Natural Resources Institute Finland (Luke), Bioeconomy and environment, Yliopistokatu 6B, FI-80100 Joensuu, Finland E-mail: katri.hamunen@luke.fi
article id 10370, category Research article
Juha Lappi, Timo Pukkala. (2020). Analyzing ingrowth using zero-inflated negative binomial models. Silva Fennica vol. 54 no. 4 article id 10370. https://doi.org/10.14214/sf.10370
Keywords: regeneration; continuous cover forestry; count data; generalized linear model; overdispersion; right-censoring
Highlights: Models were developed to describe ingrowth in national forest inventory data; The data were more dispersed than Poisson data and included many zeros; Fixed-effects models had larger zero-inflation probability and overdispersion parameter than mixed-effect models; Mixed-effects models had larger likelihood than fixed-effects models but provided biased predictions; Prediction of right-censored ingrowth may be useful owing to large overdispersion.
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Ingrowth is an important element of stand dynamics in several silvicultural systems, especially in continuous cover forestry. Earlier predictive models for ingrowth in Finnish forests are few and not based on up-to-date statistical methods. Ingrowth is here defined as the number of trees over 1.3 m entering a plot. This study developed new ingrowth models for Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies (L.) H. Karst.) and birch (Betula pendula Roth and B. pubescens Ehrh.) using data from the permanent sample plots of the Finnish national forest inventory. The data were over-dispersed compared to a Poisson process and had many zeros. Therefore, a zero-inflated negative binomial model was used. The total and species-specific stand basal areas, temperature sum and fertility class were used as predictors in the ingrowth models. Both fixed-effects and mixed-effects models were fitted. The mixed-effects model versions included random plot effects. The mixed-effects models had larger likelihoods but provided biased predictions. Also censored prediction was considered where only a certain maximum number of ingrowth trees were accepted for a plot. The models predicted most pine ingrowth in pine-dominated stands on sub-xeric and xeric sites where stand basal area was low. The predicted amount of spruce ingrowth was maximized when the basal area of spruce was 13 m2 ha–1. Increasing temperature sum increased spruce ingrowth. Predicted birch ingrowth decreased with increasing stand basal area and towards low fertility classes. An admixture of pine increased the predicted amount of spruce ingrowth.

  • Lappi, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: juha.lappi.sjk@gmail.com (email)
  • Pukkala, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: timo.pukkala@uef.fi
article id 10196, category Research article
Karri Uotila, Jari Miina, Timo Saksa, Ron Store, Kauko Kärkkäinen, Mika Härkönen. (2020). Low cost prediction of time consumption for pre-commercial thinning in Finland. Silva Fennica vol. 54 no. 1 article id 10196. https://doi.org/10.14214/sf.10196
Keywords: forest vegetation management; early cleaning; release treatment; linear mixed model; topographic wetness index; work productivity
Highlights: Time consumption (TC) in pre-commercial thinning (PCT) can be predicted by variables describing site and stands conditions and previous silvicultural management; Applying variables available in forest resources data the field-assessment of worksite difficulty factors is not needed; The TC model could facilitate the predictions of the labour costs of PCT in forest information systems.
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The time consumption (TC) of pre-commercial thinning (PCT) varies greatly among sites, stands and forest workers. The TC in PCT is usually estimated by field-assessed work difficulty factors. In this study, a linear mixed model for the TC in PCT was prepared by utilizing forest resources data (FRD). The modelling data included 11 848 and validation data included 3035 worksites with TC information recorded by forest workers within the period of 2008–2018. The worksites represented a range of site and stand conditions across a broad geographical area in Finland. Site and stand characteristics and previous management logically explained the TC in PCT. The more fertile the site, the more working time was needed in PCT. On sites of medium fertility, TC in the initial PCT increased with stand age by 0.5 h ha–1 yr–1. Site wetness increased the TC. PCT in summer was more time consuming than in spring. Small areas were more time consuming to PCT per hectare than larger ones. The between-forest worker variation involved in the TC was as high as 35% of the variation unexplained by the TC model. The coefficient of determination in validation data was 19.3%, RMSE 4.75 h ha–1 and bias –1.6%. The TC model based on FRD was slightly less precise than the one based on field-assessed work difficulty factors (removal quantity and type and terrain difficulty): RMSE 4.9 h ha–1 vs. 4.1 h ha–1 (52% vs. 43%). The TC model could be connected to forest information systems where it would facilitate the predictions of the labour costs of PCT without field-assessing work difficulty factors.

  • Uotila, Natural Resources Institute Finland (Luke), Natural resources, Latokartanonkaari 9, FI-00790 Helsinki, Finland E-mail: karri.uotila@luke.fi (email)
  • Miina, Natural Resources Institute Finland (Luke), Natural resources, Yliopistokatu 6 B, FI-80100 Joensuu, Finland E-mail: jari.miina@luke.fi
  • Saksa, Natural Resources Institute Finland (Luke), Natural resources, Survontie 9, FI-40500 Jyväskylä, Finland E-mail: timo.saksa@luke.fi
  • Store, Natural Resources Institute Finland (Luke), Bioeconomy and environment, Teknologiakatu 7, FI-67100 Kokkola, Finland E-mail: ron.store@luke.fi
  • Kärkkäinen, E-mail: kauko.karkkainen@gmail.com
  • Härkönen, Tornator Oyj, Pielisentie 2–6, FI-81700 Lieksa, Finland E-mail: mika.harkonen@tornator.fi
article id 10217, category Research article
Xingji Jin, Timo Pukkala, Fengri Li, Lihu Dong. (2019). Developing growth models for tree plantations using inadequate data – a case for Korean pine in Northeast China. Silva Fennica vol. 53 no. 4 article id 10217. https://doi.org/10.14214/sf.10217
Keywords: Pinus koraiensis; optimization-based modeling; quantile regression; self-thinning
Highlights: The permanent sample plots of Chinese plantation trees have not been designed for producing data for growth modeling; We used various methods to deal with the inadequacies of sample plot data; Optimization was used to fit diameter increment and survival models using data with varying measurement intervals and tree identification errors; Quantile regression was used to model self-thinning limit.
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Korean pine (Pinus koraiensis Siebold & Zucc.) is economically the most important tree species in northeast China. Korean pine plantations are established and managed for the production of timber and seeds. Despite the importance of the species, few models have been developed for the comparison of alternative management schedules. Model development is affected by the fact that permanent sample plots and thinning experiments have not been designed and managed for modeling purposes. The permanent sample plots include few non-thinned plots, and weak trees are removed in thinning treatments, leading to low mortality rate. Moreover, the measurement interval is irregular. This study used optimization-based modeling approach in tree-level diameter increment and survival modeling to deal with the above problems. Models for self-thinning limit were developed to alleviate the problem of underestimated mortality arising from the features of the data. In addition, improved site index and individual-tree height models were developed. The model of Lundqvist and Korf was used as the site index model and the model proposed by Schumacher as the height model. Quantile regression was used to model the maximum stand basal area and maximum number of trees as a function of mean tree diameter and site index. Tree diameter, stand basal area, basal area in larger trees and site index were used as the predictors of diameter increment and tree survival. The models developed in this study constitute a model set that is suitable for simulation and optimization studies. The models produced simulation results that correspond to measured stand development.

  • Jin, Key Laboratory of Sustainable Forest Ecosystem Management - Ministry of Education, School of Forestry, Northeast Forestry University, Harbin 150040, Heilongjiang, People’s Republic of China ORCID http://orcid.org/0000-0003-2971-2709 E-mail: xingji_jin@163.com
  • Pukkala, Key Laboratory of Sustainable Forest Ecosystem Management - Ministry of Education, School of Forestry, Northeast Forestry University, Harbin 150040, Heilongjiang, People’s Republic of China; University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: timo.pukkala@uef.fi (email)
  • Li, Key Laboratory of Sustainable Forest Ecosystem Management - Ministry of Education, School of Forestry, Northeast Forestry University, Harbin 150040, Heilongjiang, People’s Republic of China ORCID http://orcid.org/0000-0002-4058-769X E-mail: fengrili@126.com
  • Dong, Key Laboratory of Sustainable Forest Ecosystem Management - Ministry of Education, School of Forestry, Northeast Forestry University, Harbin 150040, Heilongjiang, People’s Republic of China ORCID http://orcid.org/0000-0002-3985-9475 E-mail: ldonglihu2006@163.com
article id 10187, category Research article
Timo Pukkala, Kjersti Holt Hanssen, Kjell Andreassen. (2019). Stem taper and bark functions for Norway spruce in Norway. Silva Fennica vol. 53 no. 3 article id 10187. https://doi.org/10.14214/sf.10187
Keywords: forest management; Picea abies; Kozak model; variable-exponent taper function
Highlights: New variable-exponent stem taper and bark functions were developed for Norway spruce; Both fixed and mixed-effects models were developed; Site index and tree age had statistically significant but small effects on stem taper.
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Based on data from long-term experimental fields with Norway spruce (Picea abies (L.) H. Karst.), we developed new stem taper and bark functions for Norway. Data was collected from 477 trees in stands across Norway. Three candidate functions which have shown good performance in previous studies (Kozak 02, Kozak 97 and Bi) were fitted to the data as fixed-effects models. The function with the smallest Akaike Information Criterion (AIC) was then chosen for additional analyses, fitting 1) site index-dependent and 2) age-dependent versions of the model, and 3) fitting a mixed-effects model with tree-specific random parameters. Kozak 97 was found to be the function with the smallest AIC, but all three tested taper functions resulted in fairly similar predictions of stem taper. The site index-dependent function reduced AIC and residual standard error and showed that the effect of site index on stem taper is different in small and large trees. The predictions of the age-independent and age-dependent models were very close to each other. Adding tree-specific random parameters to the model clearly reduced AIC and residual variation. However, the results suggest that the mixed-effects model should be used only when it is possible to calibrate it for each tree, otherwise the fixed-effects Kozak 97 model should be used. A model for double bark thickness was also fitted as fixed-effects Kozak 97 model. The model behaved logically, predicting larger relative but smaller absolute bark thickness for small trees.

article id 9918, category Research article
Ari Nikula, Vesa Nivala, Juho Matala, Kari Heliövaara. (2019). Modelling the effect of habitat composition and roads on the occurrence and number of moose damage at multiple scales. Silva Fennica vol. 53 no. 1 article id 9918. https://doi.org/10.14214/sf.9918
Keywords: forestry; Alces alces; damage probability; forest damage; forest plantation; habitat selection; habitat modelling; zero-inflated negative binomial distribution
Highlights: The occurrence and number of moose damage were modelled with a zero-inflated count model; An admixture of mature forests within plantations increased the number of damage; Vicinity of inhabited areas and roads reduced damage; Plantations in landscapes with a large amount of pine-dominated thinning forests had less damage in Lapland; Damage risk assessment should include characteristics specific to each region.
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We modelled the effect of habitat composition and roads on the number and occurrence of moose (Alces alces L.) damage in Ostrobothnia and Lapland using a zero-inflated count model. Models were developed for 1 km2, 25 km2 and 100 km2 landscapes consisting of equilateral rectangular grid cells. Count models predict the number of damage, i.e. the number of plantations and zero models the probability of a landscape being without damage for a given habitat composition. The number of moose damage in neighboring grid cells was a significant predictor in all models. The proportion of mature forest was the most frequent significant variable, and an increasing admixture of mature forests among plantations increased the number and occurrence of damage. The amount of all types of plantations was the second most common significant variable predicting increasing damage along with increasing amount of plantations. An increase in thinning forests as an admixture also increased damage in 1 km2 landscapes in both areas, whereas an increase in pine-dominated thinning forests in Lapland reduced the number of damage in 25 km2 landscapes. An increasing amount of inhabited areas in Ostrobothnia and the length of connecting roads in Lapland reduced the number of damage in 1 and 25 km2 landscapes. Differences in model variables between areas suggest that models of moose damage risk should be adjusted according to characteristics that are specific to the study area.

  • Nikula, Natural Resources Institute Finland (Luke), Bioeconomy and Environment, Ounasjoentie 6, FI-96200 Rovaniemi, Finland E-mail: ari.nikula@luke.fi (email)
  • Nivala, Natural Resources Institute Finland (Luke), Bioeconomy and Environment, Ounasjoentie 6, FI-96200 Rovaniemi, Finland E-mail: vesa.nivala@luke.fi
  • Matala, Natural Resources Institute Finland (Luke), Natural resources, Yliopistokatu 6, FI-80100 Joensuu, Finland E-mail: juho.matala@luke.fi
  • Heliövaara, University of Helsinki, Department of Forest Sciences, P.O. Box 27, FI-00014 University of Helsinki, Finland E-mail: kari.heliovaara@helsinki.fi
article id 10055, category Research article
Jaakko Repola, Hannu Hökkä, Hannu Salminen. (2018). Models for diameter and height growth of Scots pine, Norway spruce and pubescent birch in drained peatland sites in Finland. Silva Fennica vol. 52 no. 5 article id 10055. https://doi.org/10.14214/sf.10055
Keywords: Pinus sylvestris; Picea abies; Betula pubescens; drained peatlands; forest drainage; mixed model; tree growth model
Highlights: Tree growth strongly correlated with site drainage status; Between-tree competition had a higher impact on tree diameter growth than on height growth; Growth predicted by the constructed models were calibrated using NFI11 data to ensure generally applicable growth predictions level in whole country.
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The aim of this study was to develop individual-tree diameter and height growth models for Scots pine, Norway spruce, and pubescent birch growing in drained peatlands in Finland. Trees growing in peatland sites have growth patterns that deviate from that of trees growing in mineral soil sites. Five-year growth was explained by tree diameter, different tree and stand level competition measures, management operations and site characteristics. The drainage status of the site was influencing growth directly or in interaction with other variables. Site quality had a direct impact but was also commonly related to current site drainage status (need for ditch maintenance). Recent thinning increased growth of all species and former PK fertilization increased growth of pine and birch. Temperature sum was a significant predictor in all models and altitude for spruce and birch. The data were a subsample of the 7th National Forest Inventory (NFI) sample plots representing northern and southern Finland and followed by repeated measurements for 15–20 yrs. Growth levels predicted by the models were calibrated using NFI11 data to remove bias originating from the sample of the modelling data. The mixed linear models technique was used in model estimation. The models will be incorporated into the MOTTI stand simulator to replace the current peatlands growth models.

  • Repola, Natural Resources Institute Finland (Luke), Natural resources, Eteläranta 55, FI-96300 Rovaniemi, Finland E-mail: jaakko.repola@luke.fi (email)
  • Hökkä, Natural Resources Institute Finland (Luke), Natural resources, Paavo Havaksen tie 3, FI-90014 University OF Oulu, Finland E-mail: hannu.hokka@luke.fi
  • Salminen, Natural Resources Institute Finland (Luke), Natural resources, Eteläranta 55, FI-96300 Rovaniemi, Finland E-mail: hannu.salminen@luke.fi
article id 9996, category Research article
Mulualem Tigabu, Mostafa Farhadi, Lars-Göran Stener, Per C. Odén. (2018). Visible + Near Infrared Spectroscopy as taxonomic tool for identifying birch species. Silva Fennica vol. 52 no. 4 article id 9996. https://doi.org/10.14214/sf.9996
Keywords: Betula; silver birch; downy birch; seeds; NIRS; OPLS; multivariate modelling
Highlights: Multivariate modelling of visible + near infrared (NIR) reflectance spectra of single seeds distinguished Betula pubescens and B. pendula with 100% and 99% accuracy, respectively; The results demonstrate the feasibility of NIR spectroscopy as taxonomic tool for classification of species that have morphological resemblance.
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The genus Betula L. is composed of several species, which are difficult to distinguish in the field on the basis of morphological traits. The aim of this study was to evaluate the taxonomic importance of using visible + near infrared (Vis + NIR) spectra of single seeds for differentiating Betula pendula Roth and Betula pubescens Ehrh. Seeds from several families (controlled crossings of known parent trees) of each species were used and Vis + NIR reflectance spectra were obtained from single seeds. Multivariate discriminant models were developed by Orthogonal Projections to Latent Structures – Discriminant Analysis (OPLS-DA). The OPLS-DA model fitted on Vis + NIR spectra recognized B. pubescens with 100% classification accuracy while the prediction accuracy of class membership for B. pendula was 99%. However, the discriminant models fitted on NIR spectra alone resulted in 100% classification accuracies for both species. Absorption bands accounted for distinguishing between birch species were attributed to differences in color and chemical composition, presumably polysaccharides, proteins and fatty acids, of the seeds. In conclusion, the results demonstrate the feasibility of NIR spectroscopy as taxonomic tool for classification of species that have morphological resemblance.

  • Tigabu, Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, Box 49, SE-230 52 Alnarp, Sweden E-mail: mulualem.tigabu@slu.se (email)
  • Farhadi, Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, Box 49, SE-230 52 Alnarp, Sweden E-mail: mostafa.farhadi@gmail.com
  • Stener, The Forestry Research Institute of Sweden, Ekebo 2250, SE-268 90 Svalöv, Sweden E-mail: lars-goran.stener@skogforsk.se
  • Odén, Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, Box 49, SE-230 52 Alnarp, Sweden E-mail: per.christer.oden@slu.se
article id 10006, category Research article
Matti Maltamo, Tomi Karjalainen, Jaakko Repola, Jari Vauhkonen. (2018). Incorporating tree- and stand-level information on crown base height into multivariate forest management inventories based on airborne laser scanning. Silva Fennica vol. 52 no. 3 article id 10006. https://doi.org/10.14214/sf.10006
Keywords: forest inventory; LIDAR; alpha shape; crown height; nearest neighbor; mixed-effects model
Highlights: The most accurate tree-level alternative is to include crown base height (CBH) to nearest neighbour imputation; Also mixed-effects models can be applied to predict CBH using tree attributes and airborne laser scanning (ALS) metrics; CBH prediction can be included with an accuracy of 1–1.5 m to forest management inventory applications.
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This study examines the alternatives to include crown base height (CBH) predictions in operational forest inventories based on airborne laser scanning (ALS) data. We studied 265 field sample plots in a strongly pine-dominated area in northeastern Finland. The CBH prediction alternatives used area-based metrics of sparse ALS data to produce this attribute by means of: 1) Tree-level imputation based on the k-nearest neighbor (k-nn) method and full field-measured tree lists including CBH observations as reference data; 2) Tree-level mixed-effects model (LME) prediction based on tree diameter (DBH) and height and ALS metrics as predictors of the models; 3) Plot-level prediction based on analyzing the computational geometry and topology of the ALS point clouds; and 4) Plot-level regression analysis using average CBH observations of the plots for model fitting. The results showed that all of the methods predicted CBH with an accuracy of 1–1.5 m. The plot-level regression model was the most accurate alternative, although alternatives producing tree-level information may be more interesting for inventories aiming at forest management planning. For this purpose, k-nn approach is promising and it only requires that field measurements of CBH is added to the tree lists used as reference data. Alternatively, the LME-approach produced good results especially in the case of dominant trees.

  • Maltamo, University of Eastern Finland, School of Forest Sciences, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: matti.maltamo@uef.fi (email)
  • Karjalainen, University of Eastern Finland, School of Forest Sciences, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: tomimkarjalainen@gmail.com
  • Repola, Natural Resources Institute of Finland (Luke), Natural resources, Eteläranta 55, FI-96300 Rovaniemi, Finland E-mail: jaakko.repola@luke.fi
  • Vauhkonen, Natural Resources Institute of Finland (Luke), Bioeconomy and environment, Yliopistokatu 6, 80100 Joensuu, Finland E-mail: jari.vauhkonen@luke.fi
article id 9983, category Research article
Mika Rekola, Jaakko Nippala, Päivi Tynjälä, Anne Virtanen. (2018). Modelling competences and anticipating the future competence needs in the forest sector. Silva Fennica vol. 52 no. 3 article id 9983. https://doi.org/10.14214/sf.9983
Keywords: forest sector; competence modelling; human resources; work life; future needs
Highlights: The most frequently used practices of modelling competences in Finnish forest sector organisations were superior-subordinate review discussions and quantitative surveys; Competence modelling was used for several human resources functions but surprisingly not for hiring and compensation; The experts interviewed underlined the need for generic competences in the future, especially they highlighted the importance of information processing and personal self-management skills.
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This explorative study examined practices of competence modelling in the forest sector organisations and how organisations anticipate changes in competence needs in the future. Semi-structured in-depth interviews (n=10) were conducted amongst forest sector experts in Finland and data was analysed by thematic analysis. The findings showed that the practices of modelling competences were diverse, most frequently used ones being superior-subordinate review discussions and quantitative competence surveys. In addition to these formal systems, informal modelling, especially on the team level and in smaller companies was also frequent. Organisations used competence modelling for several human resources functions, such as appraisal, motivation and promotion of employees. Surprisingly hiring and compensation functions were not mentioned. Perceptions related to competence modelling were generally speaking positive. The most important challenges were the lack of further actions and sometimes the extraordinary burden to the employees. When anticipating the future, the experts interviewed mentioned several commonly recognised trends, e.g., development of information technology, fragmentation of working life and structural changes in labour markets. All these require more generic competences related to information processing and personal self-management, especially respondents highlighted the importance of self-awareness skills. It is concluded that several useful practices for competence modelling already exist and that present study provides a basis for further quantitative further study.

  • Rekola, Department of Forest Sciences, University of Helsinki, P.O. Box 27, FI-00014 University of Helsinki, Finland E-mail: mika.rekola@helsinki.fi (email)
  • Nippala, Suomen Partiolaiset – Finlands Scouter ry, Töölönkatu 55, FI-00250 Helsinki, Finland E-mail: jaakko.nippala@partio.fi
  • Tynjälä, Finnish Institute for Educational Research, P.O. Box 35, FI-40014 University of Jyväskylä, Finland E-mail: paivi.a.tynjala@jyu.fi
  • Virtanen, Finnish Institute for Educational Research, P.O. Box 35, FI-40014 University of Jyväskylä, Finland E-mail: anne.virtanen@jyu.fi
article id 9933, category Research article
Timo Saksa, Jari Miina, Hilkka Haatainen, Kauko Kärkkäinen. (2018). Quality of spot mounding performed by continuously advancing mounders. Silva Fennica vol. 52 no. 2 article id 9933. https://doi.org/10.14214/sf.9933
Keywords: soil preparation; slash; logging residues; forest regeneration; mixed modelling
Highlights: The number and quality of mounds varied considerably according to the operating conditions;The main factors reducing the quality of spot mounding were steep terrain, a thick humus layer, fresh logging residues, stoniness and soil texture;With careful selection of timing and conditions for mounding, the quality obtained by continuously advancing mounders can be improved.
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Operating conditions affecting the quality of spot mounding by Bracke continuously advancing mounders were investigated on 66 regeneration areas (124 ha) in eastern Finland. The quality of mounds was classified as suitable (good or acceptable after additional compression) or unsuitable for planting. Models were constructed for the number of suitable planting spots obtained per hectare (good and acceptable mounds), the probability of successful mounding (≥1600 planting spots ha–1) and the probability of creating a suitable mound as a function of terrain, site and soil characteristics, as well as slash conditions (removed, fresh or dry logging residues). The average number of mounds created was 1892 ± 290 mounds ha–1, of which 1398 ± 325 mounds ha–1 (74%) were classified as suitable for planting. The quality of spot mounding was reduced by steep terrain, a thick humus layer and fresh logging residues. Stoniness and soil texture also affected the number of planting spots created. Mounding after logging residues had dried increased the number of planting spots by 191 spots ha–1 compared with mounding in the presence of fresh residues. Removing residues did not significantly increase the number of planting spots compared with mounding amongst dry residues. A thick humus layer, very stony soil, steep slopes and valley terrain decreased the number of planting spots by 150–450 spots ha–1. The number and quality of mounds varied considerably according to the operating conditions, but with careful selection of timing and sites the quality obtained by a continuously advancing mounder can be improved.

  • Saksa, Natural Resources Institute Finland (Luke), Juntintie 154, FI-77600 Suonenjoki, Finland E-mail: timo.saksa@luke.fi (email)
  • Miina, Natural Resources Institute Finland (Luke), Yliopistokatu 6, FI-80100 Joensuu, Finland E-mail: jari.miina@luke.fi
  • Haatainen, Faculty of Science and Forestry, School of Forest Sciences, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: hilkka.haatainen@storaenso.com
  • Kärkkäinen, Tornator Oyj, Muuntamontie 2, FI-80100 Joensuu, Finland E-mail: kauko.karkkainen@tornator.fi
article id 7721, category Research article
Sakari Tuominen, Andras Balazs, Eija Honkavaara, Ilkka Pölönen, Heikki Saari, Teemu Hakala, Niko Viljanen. (2017). Hyperspectral UAV-imagery and photogrammetric canopy height model in estimating forest stand variables. Silva Fennica vol. 51 no. 5 article id 7721. https://doi.org/10.14214/sf.7721
Keywords: forest inventory; digital photogrammetry; aerial imagery; hyperspectral imaging; radiometric calibration; UAVs; stereo-photogrammetric canopy modelling
Highlights: Hyperspectral imagery and photogrammetric 3D point cloud based on RGB imagery were acquired under weather conditions changing from cloudy to sunny; Calibration of hyperspectral imagery was required for compensating the effect of varying weather conditions; The combination of hyperspectral imagery and photogrammetric point cloud data resulted in accurate forest estimates, especially for volumes per tree species.
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Remote sensing using unmanned aerial vehicle (UAV) -borne sensors is currently a highly interesting approach for the estimation of forest characteristics. 3D remote sensing data from airborne laser scanning or digital stereo photogrammetry enable highly accurate estimation of forest variables related to the volume of growing stock and dimension of the trees, whereas recognition of tree species dominance and proportion of different tree species has been a major complication in remote sensing-based estimation of stand variables. In this study the use of UAV-borne hyperspectral imagery was examined in combination with a high-resolution photogrammetric canopy height model in estimating forest variables of 298 sample plots. Data were captured from eleven separate test sites under weather conditions varying from sunny to cloudy and partially cloudy. Both calibrated hyperspectral reflectance images and uncalibrated imagery were tested in combination with a canopy height model based on RGB camera imagery using the k-nearest neighbour estimation method. The results indicate that this data combination allows accurate estimation of stand volume, mean height and diameter: the best relative RMSE values for those variables were 22.7%, 7.4% and 14.7%, respectively. In estimating volume and dimension-related variables, the use of a calibrated image mosaic did not bring significant improvement in the results. In estimating the volumes of individual tree species, the use of calibrated hyperspectral imagery generally brought marked improvement in the estimation accuracy; the best relative RMSE values for the volumes for pine, spruce, larch and broadleaved trees were 34.5%, 57.2%, 45.7% and 42.0%, respectively.

  • Tuominen, Natural Resources Institute Finland (Luke), Economics and society, P.O. Box 2, FI-00791 Helsinki, Finland ORCID http://orcid.org/0000-0001-5429-3433 E-mail: sakari.tuominen@luke.fi (email)
  • Balazs, Natural Resources Institute Finland (Luke), Economics and society, P.O. Box 2, FI-00791 Helsinki, Finland E-mail: andras.balazs@luke.fi
  • Honkavaara, Finnish Geospatial Research Institute, National Land Survey of Finland, Geodeetinrinne 2, FI-02430 Masala, Finland E-mail: eija.honkavaara@nls.fi
  • Pölönen, University of Jyväskylä, Faculty of Information Technology, P.O. Box 35, FI-40014 Jyväskylä, Finland E-mail: ilkka.polonen@jyu.fi
  • Saari, VTT Microelectronics, P.O. Box 1000, FI-02044 VTT, Finland E-mail: heikki.saari@vtt.fi
  • Hakala, Finnish Geospatial Research Institute, National Land Survey of Finland, Geodeetinrinne 2, FI-02430 Masala, Finland E-mail: teemu.hakala@nls.fi
  • Viljanen, Finnish Geospatial Research Institute, National Land Survey of Finland, Geodeetinrinne 2, FI-02430 Masala, Finland E-mail: niko.viljanen@nls.fi
article id 1740, category Research article
Ram P. Sharma, Zdeněk Vacek, Stanislav Vacek. (2017). Modelling tree crown-to-bole diameter ratio for Norway spruce and European beech. Silva Fennica vol. 51 no. 5 article id 1740. https://doi.org/10.14214/sf.1740
Keywords: Picea abies; Fagus sylvatica; dominant height; exponential decay function; mixed effect model; spatially explicit competition index; species proportion; species mixture effect
Highlights: Modelled crown-to-bole diameter ratio (CDBDR) using tree and stand-level predictors, and sample plot random effects; Spatially explicit mixed-effects model described the largest part of CDBDR variation with no significant trend in the residuals; The CDBDR increased with increasing stand development stage and site quality, but decreased with decreasing proportion of the species of interest, and increasing competition.
Abstract | Full text in HTML | Full text in PDF | Author Info

Crown dimensions are correlated to growth of other parts of a tree and often used as predictors in growth models. The crown-to-bole diameter ratio (CDBDR), which is a ratio of maximum crown width to diameter at breast height (DBH), was modelled using data from permanent sample plots located on Norway spruce (Picea abies (L.) Karst.) and European beech (Fagus sylvatica L.) stands in different parts of the Czech Republic. Among various tree and stand-level measures evaluated, DBH, height to crown base (HCB), dominant height (HDOM), basal area of trees larger in diameter than a subject tree (BAL), basal area proportion of the species of interest (BAPOR), and Hegyi’s competition index (CI) were found to be significant predictors in the CDBDR model. Random effects were included using the mixed-effects modelling to describe sample plot-level variation. For each species, the mixed-effects model described a larger part of the variation of the CDBDR than nonlinear ordinary least squares model with no trend in the residuals. The spatially explicit mixed-effects model showed more attractive fit statistics [conditional R2 ≈ 0.73 (spruce), 0.78 (beech)] than its spatially inexplicit counterpart [conditional R2 ≈ 0.71 (spruce), 0.76 (beech)]. The model showed that CDBDR increased with increasing HDOM – a measure that combines the stand development stage and site quality – but decreased with increasing HCB and competition (increasing BAL and CI), and decreasing proportions of the species of interest (increasing BAPOR). For both species, the spatially explicit mixed-effects model should be a preferred choice for a precise prediction of the CDBDR. The CDBDR model will have various management implications such as determination of spacing, stand basal area, stocking, and planning of appropriate species mixture.

  • Sharma, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague, Kamýcká 129, 16521, Praha 6 – Suchdol, Czech Republic E-mail: sharmar@fld.czu.cz (email)
  • Vacek, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague, Kamýcká 129, 16521, Praha 6 – Suchdol, Czech Republic E-mail: vacekz@fld.czu.cz
  • Vacek, Faculty of Forestry and Wood Sciences, Czech University of Life Sciences Prague, Kamýcká 129, 16521, Praha 6 – Suchdol, Czech Republic E-mail: vacekstanislav@fld.czu.cz
article id 6977, category Research article
Anett Schibalski, Aleksi Lehtonen, Thomas Hickler, Boris Schröder. (2017). Identifying important topics for model refinement in a widely used process-based model informed by correlative model analyses in a boreal forest. Silva Fennica vol. 51 no. 4 article id 6977. https://doi.org/10.14214/sf.6977
Keywords: Finland; treeline; competition; LPJ-GUESS; statistical modelling; forest ecology
Highlights: Continental-scale model parameterization of widely used LPJ-GUESS experiences problems when applied on the regional level; Competition, disturbances and soil conditions are crucial for explaining treeline position in Finland, besides climatic limitation; Picea abies is overly dominant in LPJ-GUESS model, as key competitive mechanisms are not implemented in sufficient detail.
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Models attempting to predict treeline shifts in changing climates must include the relevant ecological processes in sufficient detail. A previous correlative model study has pointed to nutrients, competition, and temperature as the most important factors shaping the treelines of Pinus sylvestris L., Picea abies (L.) H. Karst. and Betula pubescens Ehrh. in Finnish Lapland. Here, we applied a widely used process-based dynamic vegetation model (LPJ-GUESS) to (i) test its capability to simulate observed spatial and temporal patterns of the main tree species in Finnish Lapland, and (ii) to explore the model representation of important processes in order to guide further model development. A European parameterization of LPJ-GUESS overestimated especially P. abies biomass and the species’ northern range limit. We identified implemented processes to adjust (competition, disturbance) and crucial processes in boreal forests to include (nutrient limitation, forest management) which account for the model’s failure to (edaphically) restrict P. abies in Finnish Lapland and the resulting species imbalance. Key competitive mechanisms are shade and drought tolerance, nutrient limitation, fire resistance, and susceptibility to disturbances (storm, herbivory) which we discussed with respect to boreal ecology and promising model developments to provide a starting point for future model development.

  • Schibalski, Institute of Geoecology, Technische Universität Braunschweig, Langer Kamp 19c, D-38106 Braunschweig, Germany E-mail: a.schibalski@tu-braunschweig.de (email)
  • Lehtonen, Natural Resources Institute Finland (Luke), Management and Production of Renewable Resources, P.O. Box 2, FI-00791 Helsinki, Finland E-mail: aleksi.lehtonen@luke.fi
  • Hickler, Biodiversity and Climate Research Centre (BiK-F), Senckenberganlage 25, D-60325 Frankfurt am Main, Germany; Department of Physical Geography, Goethe University, Altenhöferallee 1, D-60438 Frankfurt am Main, Germany E-mail: thomas.hickler@senckenberg.de
  • Schröder, Institute of Geoecology, Technische Universität Braunschweig, Langer Kamp 19c, D-38106 Braunschweig, Germany; Berlin-Brandenburg Institute of Advanced Biodiversity Research BBIB, Altensteinstr. 6, D-14195 Berlin, Germany E-mail: boris.schroeder@tu-bs.de
article id 5662, category Research article
Samuel Egbäck, Urban Nilsson, Kenneth Nyström, Karl-Anders Högberg, Nils Fahlvik. (2017). Modeling early height growth in trials of genetically improved Norway spruce and Scots pine in southern Sweden. Silva Fennica vol. 51 no. 3 article id 5662. https://doi.org/10.14214/sf.5662
Keywords: Pinus sylvestris; Picea abies; individual tree growth model; genetic component; genetic multiplier; unimproved material; improved material
Highlights: The developed height growth model based on unimproved material predicted the development relatively well for genetically improved Norway spruce; For genetically improved Scots pine, however, the model needed to be modified; By incorporating a genetic component into the Scots pine model, the prediction errors were reduced.
Abstract | Full text in HTML | Full text in PDF | Author Info

Genetically improved Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) are used extensively in operational Swedish forestry plantations to increase production. Depending on the genetic status of the plant material, the current estimated genetic gain in growth is in the range 10–20% for these species and this is expected to increase further in the near future. However, growth models derived solely from data relating to genetically improved material in Sweden are still lacking. In this study we investigated whether an individual tree growth model based on data from unimproved material could be used to predict the height increment in young trials of genetically improved Norway spruce and Scots pine. Data from 11 genetic experiments with large genetic variation, ranging from offspring of plus-trees selected in the late 1940s to highly improved clonal materials selected from well performing provenances were used. The data set included initial heights at the age of 7–15 years and 5-year increments for almost 2000 genetic entries and more than 20 000 trees. The evaluation indicated that the model based on unimproved trees predicted height development relatively well for genetically improved Norway spruce and there was no need to incorporate a genetic component. However, for Scots pine, the model needed to be modified. A genetic component was developed based on the genetic difference recorded within each trial, using mixed linear models and methods from quantitative genetics. By incorporating the genetic component, the prediction errors were significantly reduced for Scots pine. This study provides the first step to incorporate genetic gains into Swedish growth models and forest management planning systems.

  • Egbäck, Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, P.O. Box 49, 230 53 Alnarp, Sweden E-mail: samuel.egback@slu.se (email)
  • Nilsson, Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, P.O. Box 49, 230 53 Alnarp, Sweden E-mail: urban.nilsson@slu.se
  • Nyström, Swedish University of Agricultural Sciences, Department of Forest Resource Management, Skogsmarksgränd, 901 83 Umeå, Sweden E-mail: kenneth.nystrom@slu.se
  • Högberg, Skogforsk, Ekebo, 268 90 Svalöv, Sweden E-mail: karl-anders.hogberg@skogforsk.se
  • Fahlvik, Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, P.O. Box 49, 230 53 Alnarp, Sweden E-mail: nils.fahlvik@slu.se
article id 1693, category Research article
Olalla Díaz-Yáñez, Blas Mola-Yudego, José Ramón González-Olabarria. (2017). What variables make a forest stand vulnerable to browsing damage occurrence? Silva Fennica vol. 51 no. 2 article id 1693. https://doi.org/10.14214/sf.1693
Keywords: moose; forest damage; cervid; machine learning; risk modelling; ungulates
Highlights: Stands more vulnerable to browsing damage are young with lower densities and dominated by birch, pine or mixed species; Stand size could play a role on forest susceptibility to browsing occurrence.
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Ungulate browsing results in important damages on the forests, affecting their structure, composition and development. In the present paper, we examine the occurrence of browsing damage in Norwegian forests, using data provided by the National Forest Inventory along several consecutive measurements (entailing the period 1995–2014). A portfolio of variables describing the stand, site and silvicultural treatments are analyzed using classification trees to retrieve combinations related to browsing damage. Our results indicate that the most vulnerable forest stands are young with densities below 1400 trees ha–1 and dominated by birch, pine or mixed species. In addition, stand diversity and previous treatments (e.g. thinnings) increase the damage occurrence and other variables, like stand size, could play a role on forest susceptibility to browsing occurrence although the latter is based on weaker evidence. The methods and results of our study can be applied to implement management measures aiming at reducing the browsing damages of forests.

  • Díaz-Yáñez, School of Forest Sciences, University of Eastern Finland, PO Box 111, 80101 Joensuu, Finland ORCID http://orcid.org/0000-0003-3829-5759 E-mail: olalla.diaz@gmail.com (email)
  • Mola-Yudego, Norwegian Institute of Bioenergy Research, P.O. Box, 115, 1431 Ås, Norway; School of Forest Sciences, University of Eastern Finland, PO Box 111, 80101 Joensuu, Finland ORCID http://orcid.org/0000-0003-0286-0170 E-mail: blas.mola@uef.fi
  • González-Olabarria, Forest Sciences Centre of Catalonia (CTFC-CEMFOR), Ctra. de St. Llorenç de Morunys, km 2, 25280 Solsona, Spain ORCID http://orcid.org/0000-0002-5040-712X E-mail: jr.gonzalez@ctfc.es
article id 1599, category Research article
Andrew McEwan, Michal Brink, Raffaele Spinelli. (2017). Factors affecting the productivity and work quality of chain flail delimbing and debarking. Silva Fennica vol. 51 no. 2 article id 1599. https://doi.org/10.14214/sf.1599
Keywords: modeling; plantation; coppice; efficiency; pulpwood; processing
Highlights: Machine productivity averaged 59 m3 ub SMH–1, with a 19% incidence of delay time; Productivity increased 70% if tree volume increased from 0.1 to 0.4 m3 ub; Debarking quality was good for 58% of the trees, medium for 29% and poor for 13%; The more trees in a bunch and the higher BWBS, the lower debarking quality.
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Chain flail delimbing and debarking may improve value recovery from small tree harvests, without renouncing the benefits of multi-tree processing. The technology is mature and capable of excellent performance, which has been documented in many benchmark studies. This paper offers new insights into the relationship between the performance of chain flail delimbing and debarking and such factors as tree volume, load volume, tree form and bark-wood bond strength (BWBS). The study was conducted in Chile, during the commercial harvesting of a Eucalyptus globulus Labill. plantation. In an observational study, researchers collected production data from over 780 work cycles, and work quality data from over 1000 individual trees. The analysis of these data shows that productivity is affected primarily by load volume. Work quality is affected by BWBS and by the number of trees in a load. Work quality degrades with increasing BWBS and tree number, since more trees tend to shield each other. Tree form has no effect on either productivity or work quality. Regression and probability functions are provided, and can be used for predictive purposes when trying to optimize current operations or to prospect the introduction of chain flail technology to new work environments.

  • McEwan, Postgraduate Forest Programme, Faculty of Natural and Agricultural Sciences, University of Pretoria, Private Bag X20 Hatfield, Pretoria, 0028, South Africa E-mail: Andrew.McEwan@nmmu.ac.za
  • Brink, Postgraduate Forest Programme, Faculty of Natural and Agricultural Sciences, University of Pretoria, Private Bag X20 Hatfield, Pretoria, 0028, South Africa E-mail: michal@cmo.co.za
  • Spinelli, CNR IVALSA, Via Madonna del Piano 10, I-50019 Sesto Fiorentino (FI), Italy ORCID http://orcid.org/0000-0001-9545-1004 E-mail: spinelli@ivalsa.cnr.it (email)
article id 1680, category Research article
Liisa Kulmala, Indre Žliobaitė, Eero Nikinmaa, Pekka Nöjd, Pasi Kolari, Kourosh Kabiri Koupaei, Jaakko Hollmén, Harri Mäkinen. (2016). Environmental control of growth variation in a boreal Scots pine stand – a data-driven approach. Silva Fennica vol. 50 no. 5 article id 1680. https://doi.org/10.14214/sf.1680
Keywords: height growth; diameter growth; Gross primary production; turgor pressure; predictive modelling; Least Angle Regression
Highlights: High water potential and carbon gain during bud forming favoured height growth; High water potential during the elongation period favoured height growth; A spring with high carbon gain favoured diameter growth; The obtained regression models had generally low generalization performance.
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Despite the numerous studies on year-to-year variation of tree growth, the physiological mechanisms controlling annual variation in growth are still not understood in detail. We studied the applicability of data-driven approach i.e. different regression models in analysing high-dimensional data set including continuous and comprehensive measurements over meteorology, ecosystem-scale water and carbon fluxes and the annual variation in the growth of app. 50-year-old Scots pine stand in southern Finland. Even though our dataset covered only 16 years, it is the most extensive collection of interactions between a Scots pine ecosystem and atmosphere. The analysis revealed that height growth was favoured by high water potential of the tree and carbon gain during the bud forming period and high water potential during the elongation period. Diameter growth seemed to be favoured by a winter with high precipitation and deep snow cover and a spring with high carbon gain. The obtained models had low generalization performance and they would require more evaluation and iterative validation to achieve credibility perhaps as a mixture of data-driven and first principle modeling approaches.

  • Kulmala, University of Helsinki, Department of Forest Sciences, P.O. Box 27, FI-00014 University of Helsinki, Finland E-mail: liisa.kulmala@helsinki.fi (email)
  • Žliobaitė, Aalto University, Department of Computer Science and Helsinki Institute for Information Technology, P.O. Box 11000, FI-00076 Aalto, Finland; University of Helsinki, Department of Geosciences and Geography, P.O. Box 64, FI-00014 University of Helsinki, Finland E-mail: zliobaite@gmail.com
  • Nikinmaa, University of Helsinki, Department of Forest Sciences, P.O. Box 27, FI-00014 University of Helsinki, Finland E-mail: eero.nikinmaa@helsinki.fi
  • Nöjd, Natural Resources Institute Finland (Luke), Bio-based business and industry, Tietotie 2, FI-02150 Espoo, Finland E-mail: pekka.nojd@luke.fi
  • Kolari, University of Helsinki, Department of Forest Sciences, P.O. Box 27, FI-00014 University of Helsinki, Finland; University of Helsinki, Department of Physics, P.O. Box 64, FI-00014 University of Helsinki, Finland E-mail: pasi.kolari@helsinki.fi
  • Kabiri Koupaei, University of Helsinki, Department of Forest Sciences, P.O. Box 27, FI-00014 University of Helsinki, Finland E-mail: kourosh.kabiri@helsinki.fi
  • Hollmén, Aalto University, Department of Computer Science and Helsinki Institute for Information Technology, P.O. Box 11000, FI-00076 Aalto, Finland; University of Helsinki, Department of Geosciences and Geography, P.O. Box 64, FI-00014 University of Helsinki, Finland E-mail: jaakko.hollmen@aalto.fi
  • Mäkinen, Natural Resources Institute Finland (Luke), Bio-based business and industry, Tietotie 2, FI-02150 Espoo, Finland E-mail: harri.makinen@luke.fi
article id 1687, category Research article
Hannu Hökkä, Jori Uusitalo, Harri Lindeman, Jari Ala-Ilomäki. (2016). Performance of weather parameters in predicting growing season water table depth variations on drained forested peatlands – a case study from southern Finland. Silva Fennica vol. 50 no. 4 article id 1687. https://doi.org/10.14214/sf.1687
Keywords: peatland; precipitation; bearing capacity; evapotranspiration; mixed linear model; water table depth
Highlights: Four-week precipitation and evapotranspiration explain much of drained peatland water table depth variation during a growing season.
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The amount of water in peat soil is one factor affecting its bearing capacity, which is a crucial aspect in planning peatland timber harvesting operations. We studied the influence of weather variables on the variation of drained peatland growing season water conditions, here the ground water table depth (WTD). WTD was manually monitored four times in 2014 and three times in 2015 in 10–30 sample plots located in four drained peatland forests in south-western Finland. For each peatland, precipitation and evapotranspiration were calculated from the records of the nearest Finnish Meteorological Institute field stations covering periods from one day to four weeks preceding the WTD monitoring date. A mixed linear model was constructed to investigate the impact of the weather parameters on WTD. Precipitation of the previous four–week period was the most important explanatory variable. The four-week evapotranspiration amount was interacting with the Julian day showing a greater effect in late summer. Other variables influencing WTD were stand volume within the three-metre radius sample plot and distance from nearest ditch. Our results show the potential of weather parameters, specifically that of the previous four-week precipitation and evapotranspiration, for predicting drained peatland water table depth variation and subsequently, the possibility to develop a more general empirical model to assist planning of harvesting operations on drained peatlands.

  • Hökkä, Natural Resources Institute Finland (Luke), Management and Production of Renewable Resources, Paavo Havaksen tie 3, FI-90014 Oulun yliopisto, Finland E-mail: hannu.hokka@luke.fi (email)
  • Uusitalo, Natural Resources Institute Finland (Luke), Green Technology, Kaironiementie 15, FI-39700 Parkano, Finland E-mail: jori.uusitalo@luke.fi
  • Lindeman, Natural Resources Institute Finland (Luke), Green Technology, Kaironiementie 15, FI-39700 Parkano, Finland E-mail: harri.lindeman@luke.fi
  • Ala-Ilomäki, Natural Resources Institute Finland (Luke), Green Technology, Jokiniemenkuja 1, FI-01370 Vantaa, Finland E-mail: jari.ala-ilomaki@luke.fi
article id 1567, category Research article
Eetu Kotivuori, Lauri Korhonen, Petteri Packalen. (2016). Nationwide airborne laser scanning based models for volume, biomass and dominant height in Finland. Silva Fennica vol. 50 no. 4 article id 1567. https://doi.org/10.14214/sf.1567
Keywords: forest inventory; LIDAR; regression analysis; remote sensing; calibration; area-based approach; mixed-effect models
Highlights: Pooled data from nine inventory projects in Finland were used to create nationwide laser-based regression models for dominant height, volume and biomass; Volume and biomass models provided regionally different means than real means, but for dominant height the mean difference was small; The accuracy of general volume predictions was nevertheless comparable to relascope-based field inventory by compartments.
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The aim of this study was to examine how well stem volume, above-ground biomass and dominant height can be predicted using nationwide airborne laser scanning (ALS) based regression models. The study material consisted of nine practical ALS inventory projects taken from different parts of Finland. We used field sample plots and airborne laser scanning data to create nationwide and regional models for each response variable. The final models had one or two ALS predictors, which were chosen based on the root mean square error (RMSE), and cross-validated. Finally, we tested how much predictions would improve if the nationwide models were calibrated with a small number of regional sample plots. Although forest structures differ among different parts of Finland, the nationwide volume and biomass models performed quite well (leave-inventory-area-out RMSE 22.3% to 33.8%, mean difference [MD] –13.8% to 18.7%) compared with regional models (leave-plot-out RMSE 20.2% to 26.8%). However, the nationwide dominant height model (RMSE 5.4% to 7.7%, MD –2.0% to 2.8%, with the exception of the Tornio region – RMSE 11.4%, MD –9.1%) performed nearly as well as the regional models (RMSE 5.2% to 6.7%). The results show that the nationwide volume and biomass models provided different means than real means at regional level, because forest structure and ALS device have a considerable effect on the predictions. Large MDs appeared especially in northern Finland. Local calibration decreased the MD and RMSE of volume and biomass models. However, the nationwide dominant height model did not benefit much from calibration.

  • Kotivuori, University of Eastern Finland, School of Forest Sciences, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: eetu.kotivuori@uef.fi (email)
  • Korhonen, University of Eastern Finland, School of Forest Sciences, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: lauri.korhonen@uef.fi
  • Packalen, University of Eastern Finland, School of Forest Sciences, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: petteri.packalen@uef.fi
article id 1559, category Research article
Karol Bronisz, Mike Strub, Chris Cieszewski, Szymon Bijak, Agnieszka Bronisz, Robert Tomusiak, Rafał Wojtan, Michał Zasada. (2016). Empirical equations for estimating aboveground biomass of Betula pendula growing on former farmland in central Poland. Silva Fennica vol. 50 no. 4 article id 1559. https://doi.org/10.14214/sf.1559
Keywords: silver birch; simplified and expanded models; seemingly unrelated regression
Highlights: We developed equations for aboveground biomass components of young silver birch stands on post-agricultural lands in central Poland for single tree level; Simplified equations were based exclusively on diameter at ground level or breast height, while expanded ones were based on the appropriate diameter and tree height; For large trees, diameter at breast height is a more appropriate explanatory variable than diameter at ground level; Biomass estimations based on models from neighboring countries were consistent with our results.
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We determined empirical models for estimating total aboveground as well as stem, branches, and foliage dry biomass of young (age up to 16 years) silver birch (Betula pendula Roth.) growing on the post-agricultural lands. Two sets of allometric models for trees with a height below or above 1.3 m (small and large trees respectively) were developed. Simplified models were elaborated based exclusively on appropriate tree diameter (diameter at ground level for small trees, diameter at breast height for large trees), while expanded models also included tree height. Total aboveground biomass was estimated as the sum of biomass of all tree components. To assure additivity of the developed equations, the seemingly unrelated regression approach for the final model fitting was used. Expanded models in both tree groups were characterized by a better fit to the data (R2 for total aboveground biomass for small and large trees equaled 0.8768 and 0.9752, respectively). Diameter at breast height appeared to be a better predictor than diameter at ground level – simplified models had better fit for large trees (R2 for total aboveground biomass equals 0.9611) than for small ones (R2 = 0.7516). The developed equations provide biomass predictions consistent with available Latvian, Estonian, Finnish, Swedish, and Norwegian models for silver birch.

  • Bronisz, Laboratory of Dendrometry and Forest Productivity, Faculty of Forestry, Warsaw University of Life Sciences – SGGW, Nowoursynowska 159, 02-787 Warsaw, Poland E-mail: karol.bronisz@wl.sggw.pl (email)
  • Strub, Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA, 30605, USA E-mail: strub@mcfns.com
  • Cieszewski, Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA, 30605, USA E-mail: thebiomat@gmail.com
  • Bijak, Laboratory of Dendrometry and Forest Productivity, Faculty of Forestry, Warsaw University of Life Sciences – SGGW, Nowoursynowska 159, 02-787 Warsaw, Poland E-mail: szymon.bijak@wl.sggw.pl
  • Bronisz, Laboratory of Dendrometry and Forest Productivity, Faculty of Forestry, Warsaw University of Life Sciences – SGGW, Nowoursynowska 159, 02-787 Warsaw, Poland E-mail: agnieszka.bronisz@wl.sggw.pl
  • Tomusiak, Laboratory of Dendrometry and Forest Productivity, Faculty of Forestry, Warsaw University of Life Sciences – SGGW, Nowoursynowska 159, 02-787 Warsaw, Poland E-mail: robert.tomusiak@wl.sggw.pl
  • Wojtan, Laboratory of Dendrometry and Forest Productivity, Faculty of Forestry, Warsaw University of Life Sciences – SGGW, Nowoursynowska 159, 02-787 Warsaw, Poland E-mail: rafal.wojtan@wl.sggw.pl
  • Zasada, Laboratory of Dendrometry and Forest Productivity, Faculty of Forestry, Warsaw University of Life Sciences – SGGW, Nowoursynowska 159, 02-787 Warsaw, Poland E-mail: michal.zasada@wl.sggw.pl
article id 1546, category Research article
Jussi Manner, Lauri Palmroth, Tomas Nordfjell, Ola Lindroos. (2016). Load level forwarding work element analysis based on automatic follow-up data. Silva Fennica vol. 50 no. 3 article id 1546. https://doi.org/10.14214/sf.1546
Keywords: harvesting; cut-to-length logging; haulage; data gathering; automatic recording; classification algorithm; Hidden Markov Models
Highlights: Recent developments in on-board technology enables automatic collection of follow-up data on forwarder work; Time consumption per load was more strongly associated with Loading drive distance than with extraction distance, indicating that the relevance of extraction distance as a main indicator of forwarding productivity should be re-considered; Data, within variables, were positively skewed with a few exceptions with normal distributions.
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Recent developments in on-board technology have enabled automatic collection of follow-up data on forwarder work. The objective of this study was to exploit this possibility to obtain highly representative information on time consumption of specific work elements (including overlapping crane work and driving), with one load as unit of observation, for large forwarders in final felling operations. The data used were collected by the John Deere TimberLink system as nine operators forwarded 8868 loads, in total, at sites in mid-Sweden. Load-sizes were not available. For the average and median extraction distances (219 and 174 m, respectively), Loading, Unloading, Driving empty, Driving loaded and Other time effective work (PM) accounted for ca. 45, 19, 8.5, 7.5 and 14% of total forwarding time consumption, respectively. The average and median total time consumptions were 45.8 and 42.1 minutes/load, respectively. The developed models explained large proportions of the variation of time consumption for the work elements Driving empty and Driving loaded, but minor proportions for the work elements Loading and Unloading. Based on the means, the crane was used during 74.8% of Loading PM time, the driving speed was nonzero during 31.9% of the Loading PM time, and Simultaneous crane work and driving occurred during 6.7% of the Loading PM time. Time consumption per load was more strongly associated with Loading drive distance than with extraction distance, indicating that the relevance of extraction distance as a main indicator of forwarding productivity should be re-considered.

  • Manner, The Forestry Research Institute of Sweden (Skogforsk), Uppsala Science Park, SE-751 83 Uppsala, Sweden E-mail: jussi.manner@skogforsk.se (email)
  • Palmroth, John Deere Forestry, P.O. Box 472, FI-33101 Tampere, Finland E-mail: PalmrothLauri@JohnDeere.com
  • Nordfjell, Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, SE-901 83 Umeå, Sweden E-mail: tomas.nordfjell@slu.se
  • Lindroos, Swedish University of Agricultural Sciences, Department of Forest Biomaterials and Technology, SE-901 83 Umeå, Sweden E-mail: ola.lindroos@slu.se
article id 1448, category Research article
Andrew McEwan, Natascia Magagnotti, Raffaele Spinelli. (2016). The effects of number of stems per stool on cutting productivity in coppiced Eucalyptus plantations. Silva Fennica vol. 50 no. 2 article id 1448. https://doi.org/10.14214/sf.1448
Keywords: modeling; logging; short rotation forestry; efficiency; operator effect
Highlights: Double- and single stem coppice stools were harvested mechanically; Stem size had the strongest impact on productivity; An experienced operator performed equally well with both stool treatments; Cost was ~10% higher with double stems for the less experienced operator; Operator experience may play a major role when cutting coppice stands.
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A time study was conducted to determine whether stem crowding had any impact on harvester productivity in Eucalyptus grandis stands. This represents an important element when trying to balance the advantages and disadvantages of coppice management in fast growing plantations designated for mechanized harvesting (i.e. machine felling, delimbing, debarking and cross-cutting). The study material consisted of 446 coppice stems, half of which grew as single stems per stool and half as double stems per stool as a result of different coppice reduction strategies. The dataset was balanced and randomized, with both subsets replicating exactly the same stem size distribution and the single and double stems alternating randomly. Harvester productivity ranged between 6 and 50 m3 under bark per productive machine hour, following the variation of tree diameter from 10 to 40 cm at breast height (1.37 m according to South African standards). Regression analysis indicated that both tree size and stem crowding (e.g. one or two stems per stool) had a significant effect on harvester productivity, which increased with stem size and decreased with stem crowding. However, operator experience may overcome the effect of stem crowding, which was not significant when the harvester was manned by a highly experienced operator. In any case, the effect of stem size was much greater than that of stem crowding, which resulted in a cost difference of less than 10%. However, this figure excludes the possible effects of stem crowding on volume recovery and stem development, which should be addressed in the future.

  • McEwan, Nelson Mandela Metropolitan University – George Campus, Saasveld, 6529, George, South Africa E-mail: Andrew.McEwan@nmmu.ac.za
  • Magagnotti, CNR IVALSA, Via Madonna del Piano 10, I-50019 Sesto Fiorentino (FI), Italy E-mail: magagnotti@ivalsa.cnr.it
  • Spinelli, CNR IVALSA, Via Madonna del Piano 10, I-50019 Sesto Fiorentino (FI), Italy E-mail: spinelli@ivalsa.cnr.it (email)
article id 1413, category Research article
Ilya Potapov, Marko Järvenpää, Markku Åkerblom, Pasi Raumonen, Mikko Kaasalainen. (2015). Data-based stochastic modeling of tree growth and structure formation. Silva Fennica vol. 50 no. 1 article id 1413. https://doi.org/10.14214/sf.1413
Keywords: terrestrial lidar; form diversity; morphological plasticity; stochastic functional-structural plant model; quantitative structure models; data fitting
Highlights: We propose a stochastic version of the tree growth model LIGNUM for producing tree structures consistent with detailed terrestrial laser scanning data, and we provide the proof-of-concept by using model-based simulations and real laser scanning data; Trees produced with the data-based model resemble the trees of the dataset, and are statistically similar but not copies of each other; the number of such synthetic trees is not limited.
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We introduce a general procedure to match a stochastic functional-structural tree model (here LIGNUM augmented with stochastic rules) with real tree structures depicted by quantitative structure models (QSMs) based on terrestrial laser scanning. The matching is done by iteratively finding the maximum correspondence between the measured tree structure and the stochastic choices of the algorithm. First, we analyze the match to synthetic data (generated by the model itself), where the target values of the parameters to be estimated are known in advance, and show that the algorithm converges properly. We then carry out the procedure on real data obtaining a realistic model. We thus conclude that the proposed stochastic structure model (SSM) approach is a viable solution for formulating realistic plant models based on data and accounting for the stochastic influences.

  • Potapov, Tampere University of Technology, Department of Mathematics, P.O. Box 553, FI-33101 Tampere, Finland E-mail: ilya.potapov@tut.fi (email)
  • Järvenpää, Tampere University of Technology, Department of Mathematics, P.O. Box 553, FI-33101 Tampere, Finland E-mail: marko.jarvenpaa@tut.fi
  • Åkerblom, Tampere University of Technology, Department of Mathematics, P.O. Box 553, FI-33101 Tampere, Finland E-mail: markku.akerblom@tut.fi
  • Raumonen, Tampere University of Technology, Department of Mathematics, P.O. Box 553, FI-33101 Tampere, Finland E-mail: pasi.raumonen@tut.fi
  • Kaasalainen, Tampere University of Technology, Department of Mathematics, P.O. Box 553, FI-33101 Tampere, Finland E-mail: mikko.kaasalainen@tut.fi
article id 1393, category Research article
Werner Poschenrieder, Andreas Rais, Jan-Willem G. van de Kuilen, Hans Pretzsch. (2015). Modelling sawn timber volume and strength development at the individual tree level – essential model features by the example of Douglas fir. Silva Fennica vol. 50 no. 1 article id 1393. https://doi.org/10.14214/sf.1393
Keywords: sawing; wood quality modelling; stem structure; grading; sensitivity test; R statistical environment
Highlights: An individual tree timber growth and quality model toolbox was designed; It realistically predicts an increase of bending strength with planting density; Prediction was shown to be based on consideration of essential intrinsic variables; Height‑diameter‑allometry depending on planting density was effective; Consideration of cambial age and knot area ratio was crucial.
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We designed a streamlined timber growth and quality model that aims at the effect of stand management on the efficiency of wood resource use. Applying the R based module toolbox to experimental plots of Douglas fir (Pseudotsuga menziesii [Mirb.] Franco) we analysed essential model features for reflecting the influence of planting density on board strength. The current version realistically predicted a significant increase of centre board bending strength at tree age 40 with initial stand density. Model performance gained clear advantage from a) parameterisation of height to diameter allometry as dependent on planting density b) consideration of cambial age and cross‑sectional knot area in board strength computation. Crown shape was less decisive. The model produced a significant effect of planting density even after a whole rotation period of 70 years as well as a realistic spectrum of board bending strength.

  • Poschenrieder, Technische Universität München, Chair of Forest Growth and Yield Science, Hans Carl von Carlowitz Platz 2, 85354 Freising, Germany ORCID http://orcid.org/0000-0002-9028-8583 E-mail: Werner.Poschenrieder@lrz.tum.de (email)
  • Rais, Technische Universität München, Chair of Forest Growth and Yield Science, Hans Carl von Carlowitz Platz 2, 85354 Freising, Germany; Technische Universität München, Holzforschung München, Winzererstrasse 45, 80797 Munich, Germany E-mail: Andreas.Rais@hfm.tum.de
  • van de Kuilen, Technische Universität München, Holzforschung München, Winzererstrasse 45, 80797 Munich, Germany E-mail: vandekuilen@hfm.tum.de
  • Pretzsch, Technische Universität München, Chair of Forest Growth and Yield Science, Hans Carl von Carlowitz Platz 2, 85354 Freising, Germany E-mail: Hans.Pretzsch@lrz.tum.de
article id 1395, category Research article
Joseph Buongiorno. (2015). Income and time dependence of forest product demand elasticities and implications for forecasting. Silva Fennica vol. 49 no. 5 article id 1395. https://doi.org/10.14214/sf.1395
Keywords: modeling; structural change; econometrics; markets
Highlights: Elasticities of demand with gross domestic product and prices were stable over time and income level for sawnwood and particleboard only; Other product elasticities differed with income and time, leading in conjunction with a sector model to higher projected world demand and prices than obtained by ignoring differences between countries and over time.
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In view of improving multi-country forest sector models, this study investigated to what extent the price and income elasticity of demand for forest products had changed in the past two decades, and how much they depended on the countries income level. For each of seven major product groups annual observations were divided between high-income (top 20% in gross domestic product per capita) and low-income, and between recent (2004–2013) and older (1992–2003) observations. The results indicated that for sawnwood and particleboard the data could be pooled across all countries and years. For the other commodity groups (veneer & plywood, fiberboard, newsprint, printing & writing paper, other paper & paperboard), there were statistically significant differences in gross domestic product or price elasticity between high and low-income levels or old and recent observations. Efficient elasticities were obtained by pooling the maximum number of observations while respecting the statistically significant differences. The resulting GDP elasticities were the same, or very close, across income levels for all products. The price elasticities differed by income level only for newsprint and for veneer and plywood. International forest sector projections to 2065 obtained with these elasticities compared with those based on pooling all data across time and income levels gave less than 3% difference for world consumption of sawnwood, particleboard, fiberboard, and newsprint, but 19% higher consumption for veneer and plywood, 31% for printing and writing paper, and 18% for other paper and paperboard. The world price was 1% to 11% higher for end products and 3% to 22% higher for raw materials and intermediate products.

  • Buongiorno, University of Wisconsin-Madison, Department of Forest and Wildlife Ecology, 1630 Linden Drive, Madison, WI 53706, USA E-mail: jbuongio@wisc.edu (email)
article id 1348, category Research article
Sakari Tuominen, Andras Balazs, Heikki Saari, Ilkka Pölönen, Janne Sarkeala, Risto Viitala. (2015). Unmanned aerial system imagery and photogrammetric canopy height data in area-based estimation of forest variables. Silva Fennica vol. 49 no. 5 article id 1348. https://doi.org/10.14214/sf.1348
Keywords: forest inventory; aerial imagery; unmanned aerial system; UAV; photogrammetric surface model; canopy height model
Highlights: Orthoimage mosaic and 3D canopy height model were derived from UAV-borne colour-infrared digital camera imagery and ALS-based terrain model; Features extracted from orthomosaic and canopy height data were used for estimating forest variables; The accuracy of forest estimates was similar to that of the combination of ALS and digital aerial imagery.
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In this paper we examine the feasibility of data from unmanned aerial vehicle (UAV)-borne aerial imagery in stand-level forest inventory. As airborne sensor platforms, UAVs offer advantages cost and flexibility over traditional manned aircraft in forest remote sensing applications in small areas, but they lack range and endurance in larger areas. On the other hand, advances in the processing of digital stereo photography make it possible to produce three-dimensional (3D) forest canopy data on the basis of images acquired using simple lightweight digital camera sensors. In this study, an aerial image orthomosaic and 3D photogrammetric canopy height data were derived from the images acquired by a UAV-borne camera sensor. Laser-based digital terrain model was applied for estimating ground elevation. Features extracted from orthoimages and 3D canopy height data were used to estimate forest variables of sample plots. K-nearest neighbor method was used in the estimation, and a genetic algorithm was applied for selecting an appropriate set of features for the estimation task. Among the selected features, 3D canopy features were given the greatest weight in the estimation supplemented by textural image features. Spectral aerial photograph features were given very low weight in the selected feature set. The accuracy of the forest estimates based on a combination of photogrammetric 3D data and orthoimagery from UAV-borne aerial imaging was at a similar level to those based on airborne laser scanning data and aerial imagery acquired using purpose-built aerial camera from the same study area.

  • Tuominen, Natural Resources Institute Finland (Luke), Economics and society, P.O. Box 18, FI-01301 Vantaa, Finland E-mail: sakari.tuominen@luke.fi (email)
  • Balazs, Natural Resources Institute Finland (Luke), Economics and society, P.O. Box 18, FI-01301 Vantaa, Finland E-mail: andras.balazs@luke.fi
  • Saari, VTT Technical Research Centre of Finland Ltd, P.O. Box 1000, FI-02044 VTT, Finland E-mail: Heikki.Saari@vtt.fi
  • Pölönen, University of Jyväskylä, Department of Mathematical Information Technology, P.O. Box 35, FI-40014 University of Jyväskylä, Finland E-mail: ilkka.polonen@jyu.fi
  • Sarkeala, Mosaicmill Oy, Kultarikontie 1, FI-01300 Vantaa, Finland E-mail: janne.sarkeala@mosaicmill.com
  • Viitala, Häme University of Applied Sciences (HAMK), P.O. Box 230, FI-13101 Hämeenlinna, Finland E-mail: Risto.Viitala@hamk.fi
article id 1347, category Research article
Paulo Borges, Even Bergseng, Tron Eid, Terje Gobakken. (2015). Impact of maximum opening area constraints on profitability and biomass availability in forestry – a large, real world case. Silva Fennica vol. 49 no. 5 article id 1347. https://doi.org/10.14214/sf.1347
Keywords: bioenergy; forest management planning; mixed integer programming; area restriction model; green-up
Highlights: We solved a large and real world near city forestry problem; The inclusion of maximum open area constraints caused 7.0% loss in NPV; Solution value at maximum deviated 0.01% from the true optimum value; The annual energy supply of 20–30 GWh estimated from harvest residues could provide a small, but stable supply of energy to the municipality.
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The nature areas surrounding the capital of Norway (Oslomarka), comprising 1 700 km2 of forest land, are the recreational home turf for a population of 1.2 mill. people. These areas are highly valuable, not only for recreational purposes and biodiversity, but also for commercial activities. To assess the impacts of the challenges that Oslo municipality forest face in their management, we developed four optimization problems with different levels of management constraints. The constraints consider control of harvest level, guarantee of minimum old-growth forest area and maximum open area after final harvest. For the latter, to date, no appropriate analyses quantifying the impact of such a constraint on economy and biomass production have been carried out in Norway. The problem solved is large due to both the number of stands and number of treatment schedules. However, the model applied demonstrated its relevance for solving large problems involving maximum opening areas. The inclusion of maximum open area constraints caused 7.0% loss in NPV compared to the business as usual case with controlled harvest volume and minimum old-growth area. The estimated supply of 20-30 GWh annual energy from harvest residues could provide a small, but stable supply of energy to the municipality.

  • Borges, Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, 1432 Aas, Norway E-mail: paulo.borges@nmbu.no (email)
  • Bergseng, Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, 1432 Aas, Norway E-mail: even.bergseng@nmbu.no
  • Eid, Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, 1432 Aas, Norway E-mail: tron.eid@nmbu.no
  • Gobakken, Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, 1432 Aas, Norway E-mail: terje.gobakken@nmbu.no
article id 1342, category Research article
Blas Mola-Yudego, Gianni Picchi, Dominik Röser, Raffaele Spinelli. (2015). Assessing chipper productivity and operator effects in forest biomass operations. Silva Fennica vol. 49 no. 5 article id 1342. https://doi.org/10.14214/sf.1342
Keywords: mixed models; efficiency; comminution; operator effect; raw material supply; wood chippers
Highlights: A model is constructed to assess the productivity in chipping of wood biomass at roadside; The data includes 172 trials and 67 operators in Italy; The operator effect was included in a mixed model approach; The R2 were 0.76 (fixed part) and 0.88 (incl. operator effects).
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The present research focuses on the productivity of energy wood chipping operations at several sites in Italy. The aim was to assess the productivity and specifically the effect attributed to the operator in the chipping of wood biomass. The research included 172 trials involving 67 operators across the country that were analysed using a mixed model approach, in order to assess productivity, and to isolate the operator effect from other potential variables. The model was constructed using different predictors aiming to explain the variability due to the machines and the raw-materials. The final model included the average piece weight of raw material chipped as well as the power of the machine. The coefficients of determination (R2) were 0.76 for the fixed part of the model, and 0.88 when the effects due to the operators were included. The operators’ performance compared to their peers was established, and it was compared to a subjective classification based on the operator’s previous experience. The results of this study can help to the planning and logistics of raw material supply for bioenergy, as well as to a more effective training of future forest operators.

  • Mola-Yudego, School of Forest Sciences, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland; NIBIO Norwegian Institute of Bioeconomy Research, P.O. Box 115, 1431 Ås, Norway ORCID http://orcid.org/0000-0003-0286-0170 E-mail: blas.mola@uef.fi (email)
  • Picchi, CNR IVALSA, Via Madonna del Piano 10, I-50019 Sesto Fiorentino, Italy E-mail: picchi@ivalsa.cnr.it
  • Röser, Forest Feedstocks Group, FPInnovations, Vancouver, British Columbia, Canada E-mail: dominik.roser@fpinnovations.ca
  • Spinelli, CNR IVALSA, Via Madonna del Piano 10, I-50019 Sesto Fiorentino, Italy E-mail: spinelli@ivalsa.cnr.it
article id 1337, category Research article
Leszek Bujoczek, Małgorzata Bujoczek, Jan Banaś, Stanisław Zięba. (2015). Spruce regeneration on woody microsites in a subalpine forest in the western Carpathians. Silva Fennica vol. 49 no. 3 article id 1337. https://doi.org/10.14214/sf.1337
Keywords: Picea abies; coarse woody debris; stumps; decomposition; regression model; fallen deadwood
Highlights: The occurrence probability of Picea abies seedlings on fallen deadwood was found to increase with diameter and decay stage of deadwood and with the volume of living trees, and to decrease with the density of living trees, sapling density, and land slope. It was also higher on stumps with greater diameter and in plots with higher sapling density, but decreased with increasing stump height.
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The density of Picea abies [L.] Karst. regeneration on different microsites, the quantity and quality of woody microsites, and seedling occurrence probability on stumps and fallen deadwood were studied in a subalpine forest that has been under protection for approximately 30–40 years (Gorce Mountains in the western Carpathians). Thirty percent of seedlings and 29% of saplings grew on stumps and fallen deadwood, while the remaining regeneration occurred on soil surface and mounds created by uprooted trees. The occurrence probability of Picea seedlings on fallen deadwood increased with deadwood diameter and decay stage and with the volume of living trees, and decreased with increased density of living trees, sapling density, and land slope. Furthermore, seedlings were more likely to grow on stumps with a greater diameter and in plots with higher sapling density, but less likely to grow on higher stumps. Stumps and fallen deadwood covered about 4% of the forest floor, but the material that is most important for promoting regeneration (strongly decomposed logs and those of a diameter exceeding 30 cm) took up only about 22 m2 ha-1. We have concluded that in a subalpine forest that has been protected for 30–40 years regeneration processes take place mostly on soil surface and stumps. The role of fallen deadwood increases over time as a greater number of suitable logs (in terms of size and decay stage) become available.

  • Bujoczek, University of Agriculture in Krakow, E-mail: lbujoczek@gmail.com (email)
  • Bujoczek, University of Agriculture in Krakow, E-mail: bujoczek.m@gmail.com
  • Banaś, University of Agriculture in Krakow, E-mail: rlbanas@cyf-kr.edu.pl
  • Zięba, University of Agriculture in Krakow, E-mail: rlzieba@cyf-kr.edu.pl
article id 1266, category Research article
Edwyn K. Midmore, Shelagh A. McCartan, Richard L. Jinks, Christine M. Cahalan. (2015). Using thermal time models to predict germination of five provenances of silver birch (Betula pendula Roth) in southern England. Silva Fennica vol. 49 no. 2 article id 1266. https://doi.org/10.14214/sf.1266
Keywords: climate change; seed source; assisted migration; thermal time model
Highlights: Using cumulative germination data, thermal time models were developed for Betula pendula; Models indicated varying degrees of dormancy and pre-chill requirements among provenances; Thermal time parameters were used with climatic data to predict germination times under mild and cold winters in southern England; Predictions suggest that pre-chilled French seeds would germinate about six weeks later than the fastest germinating provenance.
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Climate predictions indicate that growing conditions may become unfavourable for certain tree species in parts of Britain. Guidelines suggest some planting of seed sources from regions between 2° and 5° south of those currently used as part of a climate change adaptation strategy. However, there has been little research on the benefits and risks associated with the use of planting stock from more southerly seed sources. Seeds of five provenances of the ‘relatively’ dormant Betula pendula were germinated over a range of temperatures both with and without a pre-chill. Subsequently, a thermal time model was used to predict the impact of migrating these provenances to southern England. Results identified geographical differences in germination response; those from higher latitude were more sensitive to pre-chill.
  • Midmore, Forest Research Agency, Alice Holt, Surrey. Current: Dolwyddelan, Llandre, Ceredigion, Wales, SY24 5BZ E-mail: emidmore@gmail.com
  • McCartan, Forest Research, Alice Holt, Farnham, Surrey, GU10 4LH, UK E-mail: shelagh.mccartan@forestry.gsi.gov.uk (email)
  • Jinks, Forest Research, Alice Holt Lodge, Farnham, Surrey, GU10 4LH, UK E-mail: richard.jinks@forestry.gsi.gov.uk
  • Cahalan, Bangor University, School of Environment, Natural Resources and Geography, Bangor, Gwynedd, Wales, LL57 2UW E-mail: c.m.cahalan@bangor.ac.uk
article id 1192, category Research article
Hannu Hökkä, Hanna Mäkelä. (2015). Post-harvest height growth of Norway spruce seedlings in northern Finland peatland forest canopy gaps and comparison to partial and complete canopy removals and plantations. Silva Fennica vol. 48 no. 5 article id 1192. https://doi.org/10.14214/sf.1192
Keywords: Picea abies; height growth; peatlands; growth models; advance growth; canopy gap
Highlights: Norway spruce seedlings’ height growth recovered within four years after the cutting of canopy gaps; Growth was linearly related to tree height, being highest for tallest seedlings; Seedlings in the 20 m diameter gap and in the central and northern parts in the 15 m diameter gap showed the best growth; In gaps early height growth was 60% of that in peatland spruce plantations but 2–3 times higher than in uneven-aged cut forests.
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Recent studies have shown the establishment of Norway spruce (Picea abies (L.) Karst.) to be successful in small canopy gaps cut in drained spruce mire stands in northern Finland. The aim of this study was to quantify seedling height growth in gaps and compare it to that observed in other canopy cuttings and plantations. We sampled spruce crop seedlings (maximum density ca. 3000 ha–1) in the spring of 2013 in a field experiment in which canopy gaps of 10, 15 and 20 m in diameter had been cut in winter 2004. The total seedling height in 2013 and the length of annual shoots over the past five years (2012–2008) were recorded in the survey. Seedling height varied from 20 cm to 2.7 m, with an average of 65 cm. The average annual height growth was 7.1 cm. A mixed linear model analysis was carried out to investigate seedling height growth variation. Seedling height was linearly and positively related to growth. Height growth started to increase in the fifth growing season after cutting. Seedling height growth in the 20 m gap was slightly better than in the smaller ones. In the 15 m gap, both the centrally located seedlings and those located at the northern edge grew best. In the 20 m gap, southerly located seedlings grew more slowly than seedlings in all other locations. The average seedling height growth in this study was about 60% of that in peatland plantations, but comparable to that in mineral soil gaps, and 2–3 times higher than in uneven-age cut stands.
  • Hökkä, Finnish Forest Research Institute, Rovaniemi Unit, Eteläranta 55, FI-96300 Rovaniemi, Finland E-mail: hannu.hokka@metla.fi (email)
  • Mäkelä, Lapland University of Applied Sciences, Jokiväylä 11 C, FI-96300 Rovaniemi, Finland E-mail: hanna.makela@edu.ramk.fi
article id 1190, category Research article
Jaakko Repola, Kristina Ahnlund Ulvcrona. (2014). Modelling biomass of young and dense Scots pine (Pinus sylvestris L.) dominated mixed forests in northern Sweden. Silva Fennica vol. 48 no. 5 article id 1190. https://doi.org/10.14214/sf.1190
Keywords: boreal forests; pine; tree biomass; biomass models; unmanaged stands
Highlights: The biomass allocation to tree components is different in unmanaged and managed young stands; Higher foliage biomass and lower stem and branch biomass were detected in the unmanaged stands; Models for trees from young and dense stands provide better estimates of biomass in such stands than those based on data from managed stands.
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Biomass models for the biomass of above-ground tree components of Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies [L.] Karst.) and birch (Betula pendula Roth and Betula pubescens Ehrh.) in young dense Scots pine dominated forest stands in northern Sweden were constructed. Destructive above-ground biomass sampling was conducted in naturally generated young, dense, Scots pine dominated mixed stands. Three sampling campaigns were undertaken, the first in 1997 and 1998. The second was six years later (2003), and the last 13 years after the first (2010). In total, 280 trees (126 Scots pine, 68 Norway spruce and 86 birches) were sampled from six different stands in northern Sweden. The sampled trees’ diameter at breast height (dbh) was in the range 1–22 cm (Scots pine), 1–21 cm (Norway spruce) and 1–11 cm (birch). Biomass predictions were tested using our models and the widely used biomass models originally constructed for managed stands. The results showed that the biomass allocation to tree components is different in unmanaged and managed young stands; higher foliage biomass and lower stem and branch biomass were detected in the unmanaged stands. The overall conclusion is that the biomass models for managed stands did not produce satisfactory biomass estimates in unthinned, dense, young stands.
  • Repola, Finnish Forest Research Institute, Rovaniemi Research Unit, P.O. Box 16, FI-96301 Rovaniemi, Finland E-mail: jaakko.repola@metla.fi (email)
  • Ahnlund Ulvcrona, SLU, Forest Biomaterials and Technology, Skogsmarksgränd, SE-901 83 Umeå, Sweden E-mail: kristina.ulvcrona@slu.se
article id 1087, category Research article
Ilkka Korpela, Lauri Mehtätalo, Lauri Markelin, Anne Seppänen, Annika Kangas. (2014). Tree species identification in aerial image data using directional reflectance signatures. Silva Fennica vol. 48 no. 3 article id 1087. https://doi.org/10.14214/sf.1087
Keywords: forestry; reflectance calibration; BRDF; mixed-effects modeling; Monte-Carlo simulation
Highlights: Multispectral reflectance data showed a strong and spectrally correlated tree effect; There was no gain in species classification from using species-specific differences of directional reflectance in real data and only a marginal improvement in simulated data; The directional signatures extracted in multiple images are obscured by the intrinsic within-species variation, correlated observations and inherent reflectance calibration errors.
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Tree species identification using optical remote sensing is challenging. Modern digital photogrammetric cameras enable radiometrically quantitative remote sensing and the estimation of reflectance images, in which the observations depend largely on the reflectance properties of targets. Previous research has shown that there are species-specific differences in how the brightness observed changes when the viewing direction in an aerial image is altered. We investigated if accounting for such directional signatures enhances species classification, using atmospherically corrected, real and simulated multispectral Leica ADS40 line-camera data. Canopy in direct and diffuse illumination were differentiated and species-specific variance-covariance structures were analyzed in real reflectance data, using mixed-effects modeling. S