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Articles containing the keyword 'stand structure'

Category : Article

article id 5598, category Article

Timo Kuuluvainen, Kari Leinonen, Markku Nygren, Antti Penttinen. (1996). Statistical opportunities for comparing stand structural heterogeneity in managed and primeval forests: an example from boreal spruce forest in southern Finland. Silva Fennica vol. 30 no. 2–3 article id 5598. https://doi.org/10.14214/sf.a9243

Keywords: boreal forests; Norway spruce; biodiversity; Picea abies; stand structure; semivariance; spatial analysis; K-function; structural variation

Abstract | View details | Full text in PDF | Author Info

The horizontal and vertical stand structure of living trees was examined in a managed and in a primeval Norway spruce-dominated forest in Southern Finland. Tree size distributions (DBHs, tree height) were compared using frequency histograms. The vertical distribution of tree heights was illustrated as tree height plots and quantified as the tree height diversity (THD) using the Shannon-Weaver formula. The horizontal spatial pattern of trees was described with stem maps and quantified with Ripley's K-function. The spatial autocorrelation of tree sizes was examined with semivariogram analysis. In the managed forest the DBH and height distributions of trees were bimodal, indicating a two-layered vertical structure with a single dominant tree layer and abundant regeneration in the understory. The primeval forest had a much higher total number of trees which were rather evenly distributed in different diameter and tree height classes. The K-function summaries for trees taller than 15 m indicated that the primeval stand was close to complete random pattern. The managed stand was regular at small distances (up to 4 m). The semivariograms of tree sizes (DBH tree height) showed that the managed forest had a clear spatial dependence in tree sizes up to inter-tree distances of about 12 meters. In contrast, the primeval spruce forest had a variance peak at very short inter-tree distances (< 1 m) and only weak spatial autocorrelation at short inter-tree distances (1–5 m). Excluding the understory trees (h < 15 m) from the analysis drastically changed the spatial structure of the forest as revealed by semivariograms. ln general, the structure of the primeval forest was both horizontally and vertically more variable and heterogeneous compared to the managed forest. The applicability of the used methods in describing fine-scale forest structure i discussed.

Kuuluvainen, E-mail: tk@mm.unknown
Leinonen, E-mail: kl@mm.unknown
Nygren, E-mail: mn@mm.unknown
Penttinen, E-mail: ap@mm.unknown

article id 5562, category Article

Janne Uuttera, Matti Maltamo. (1995). Impact of regeneration method on stand structure prior to first thinning. Comparative study North Karelia, Finland vs. Republic of Karelia, Russian Federation. Silva Fennica vol. 29 no. 4 article id 5562. https://doi.org/10.14214/sf.a9213

Keywords: natural regeneration; stand structure; artificial regeneration; potential biodiversity; regeneration strategy

Abstract | View details | Full text in PDF | Author Info

Comparisons were made between artificially and naturally regenerated stands in the south-eastern part of North Karelia, Finland, and naturally regenerated stands in the western parts of the Republic of Karelia, Russian Federation. The effect of soil fertility and silvicultural operations on the stand structure was also investigated.

The results of the study show clearly that when forests are artificially regenerated the stand structure includes less variation when compared with the stands naturally regenerated. Differences between the regeneration methods are clearer the more fertile the forest site is. Within the regeneration method there is also a clear trend in stand structure, with the variation decreasing the poorer the site. The effect of silvicultural operations, i.e. the cleaning of the sapling stand, has disappeared by the time of first thinning, although it appears to have a permanent effect on the dynamics of the tree species within a stand.

The variation of the stand structure can be regarded as an essential factor for the potential biodiversity of the stand also at its young vegetation succession stage. This capacity for maintaining the forest biodiversity, developed at the young vegetation succession stage, becomes increasingly important in subsequent vegetation succession stages. Natural regeneration provides improved possibilities for the operations preserving forest biodiversity, as it generates more dense stands with a wider variation in stand structure, compared to artificial regeneration.

Uuttera, E-mail: ju@mm.unknown
Maltamo, E-mail: mm@mm.unknown

article id 5341, category Article

Hannu Hökkä, Jukka Laine. (1988). Suopuustojen rakenteen kehitys ojituksen jälkeen. Silva Fennica vol. 22 no. 1 article id 5341. https://doi.org/10.14214/sf.a15498

English title: Post-drainage development of structural characteristics in peatland forest stands.

Original keywords: metsikön rakenne; turvemaat; ojitetut suot; eri-ikäisrakenne; runkoluku; läpimittajakauma

English keywords: stand structure; drained peatlands; diameter distribution; forest drainage; uneven-aged structure

Abstract | View details | Full text in PDF | Author Info

The effect of drainage on structure of tree stands is analysed by comparing the average structural characteristics (e.g. diameter distribution) of stands in the data for different drainage age classes and selected site types. The material consists of ca. 4,400 relascope sample plots, which are part of a large drainage area inventory project. The uneven-aged structure of the virgin peatland forest is preserved for several decades after drainage. This is enhanced by the post-drainage increase of small-diameter trees, especially birch. The number of trees per hectare increased during a period of ca. 30 years and levelled off thereafter. The increase in the number of saw log stems is clearly related to the fertility of the site and its geographical location.

The PDF includes a summary in English.

Hökkä, E-mail: hh@mm.unknown
Laine, E-mail: jl@mm.unknown

Category : Article

article id 7196, category Article

Erik Lönnroth. (1925). Studies on internal structure and development of even aged natural normal pine stands: based on the data from southern part of Finland. Acta Forestalia Fennica vol. 30 no. 1 article id 7196. https://doi.org/10.14214/aff.7196

Keywords: Pinus; stand structure; pine; natural normal stand; even aged

Abstract | View details | Full text in PDF | Author Info

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.

The article discusses the earlier literature on the factors effecting forest stands and presents the data in detail. The results section is divided into paragraphs on number of stems of the stand, height, crown, breast height diameter, basal area and volume. The statistical numbers are calculated and presented.

Lönnroth, E-mail: el@mm.unknown

article id 7624, category Article

Pertti Hari, Seppo Kellomäki, Annikki Mäkelä, Pirkko Ilonen, Markku Kanninen, Eeva Korpilahti, Markku Nygren. (1982). Metsikön varhaiskehityksen dynamiikka. Acta Forestalia Fennica no. 177 article id 7624. https://doi.org/10.14214/aff.7624

English title: Dynamics of early development of tree stand.

Original keywords: tiheys; mänty; metsikön rakenne; metsikön kehitys; valo-olosuhteet; yhteyttäminen

English keywords: Pinus sylvestris; stand structure; photosynthesis; Scots pine; density; stand development; light conditions

Abstract | View details | Full text in PDF | Author Info

The report concludes a series of studies on the early development of young Scots pine (Pinus sylvestris L.) stands. The basis assumption made in the study series was that the within-stand light regime is the main driving force for total tree growth and its allocation of photosynthates for crown, stem and root growth. An individual tree growing in a stand under a varying light regime which is controlled by the stand structure, is the basic unit used in the study. The photosynthesis of an individual tree is determined by the light regime. The stand is formed from individual trees.

The model is applied in simulation of the growth and development of tree stands. Several computer runs representing various densities, height distributions and tree species mixtures were carried out. Potential application areas, properties of the model and future needs of investigations are discussed.

The PDF includes a summary in English.

Hari, E-mail: ph@mm.unknown
Kellomäki, E-mail: sk@mm.unknown
Mäkelä, E-mail: am@mm.unknown
Ilonen, E-mail: pi@mm.unknown
Kanninen, E-mail: mk@mm.unknown
Korpilahti, E-mail: ek@mm.unknown
Nygren, E-mail: mn@mm.unknown

Category : Research article

article id 1666, category Research article

Mareike Wieczorek, Alexei Kolmogorov, Stefan Kruse, Inga Jacobsen, Ingmar Nitze, Anatoly N. Nikolaev, Ingo Heinrich, Luidmila A. Pestryakova, Ulrike Herzschuh. (2017). Disturbance-effects on treeline larch-stands in the lower Kolyma River area (NE Siberia). Silva Fennica vol. 51 no. 3 article id 1666. https://doi.org/10.14214/sf.1666

Keywords: stand structure; fire; treeline; Larix cajanderi; Siberia

Highlights: Disturbances are an important shaping factor of larch stands at lower Kolyma; Youngest larch stands have the highest population densities and highest growth rates; Saplings grow clustered, irrespective of the underlying disturbance regime; Mixed climate-disturbance signals make it difficult to infer future treeline processes.

Abstract | Full text in HTML | Full text in PDF | Author Info

Tree stands in the boreal treeline ecotone are, in addition to climate change, impacted by disturbances such as fire, water-related disturbances and logging. We aim to understand how these disturbances affect growth, age structure, and spatial patterns of larch stands in the north-eastern Siberian treeline ecotone (lower Kolyma River region), an insufficiently researched region. Stand structure of Larix cajanderi Mayr was studied at seven sites impacted by disturbances. Maximum tree age ranged from 44 to 300 years. Young to medium-aged stands had, independent of disturbance type, the highest stand densities with over 4000 larch trees per ha. These sites also had the highest growth rates for tree height and stem diameter. Overall lowest stand densities were found in a polygonal field at the northern end of the study area, with larches growing in distinct “tree islands”. At all sites, saplings are significantly clustered. Differences in fire severity led to contrasting stand structures with respect to tree, recruit, and overall stand densities. While a low severity fire resulted in low-density stands with high proportions of small and young larches, high severity fires resulted in high-density stands with high proportions of big trees. At water-disturbed sites, stand structure varied between waterlogged and drained sites and latitude. These mixed effects of climate and disturbance make it difficult to predict future stand characteristics and the treeline position.

Wieczorek, Periglacial Research Section, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, 14473 Potsdam, Germany; Institute of Earth and Environmental Science, University of Potsdam, 14476 Potsdam, Germany E-mail: mareike.wieczorek@awi.de
Kolmogorov, Institute of Natural Sciences, North-Eastern Federal University of Yakutsk, 677000 Yakutsk, Russia E-mail: kilatroooon@gmail.com
Kruse, Periglacial Research Section, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, 14473 Potsdam, Germany; Institute of Earth and Environmental Science, University of Potsdam, 14476 Potsdam, Germany E-mail: Stefan.Kruse@awi.de
Jacobsen, Periglacial Research Section, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, 14473 Potsdam, Germany; Institute of Earth and Environmental Science, University of Potsdam, 14476 Potsdam, Germany E-mail: Inga.Jacobsen@awi.de
Nitze, Periglacial Research Section, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, 14473 Potsdam, Germany; Institute of Geography, University of Potsdam, 14476 Potsdam, Germany E-mail: Ingmar.Nitze@awi.de
Nikolaev, Institute of Natural Sciences, North-Eastern Federal University of Yakutsk, 677000 Yakutsk, Russia; Melnikov Permafrost Institute of the Siberian Branch of RAS, 677000 Yakutsk, Russia E-mail: yktnan@rambler.ru
Heinrich, GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany E-mail: heinrich@gfz-potsdam.de
Pestryakova, Institute of Natural Sciences, North-Eastern Federal University of Yakutsk, 677000 Yakutsk, Russia E-mail: lapest@mail.ru
Herzschuh, Periglacial Research Section, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, 14473 Potsdam, Germany; Institute of Earth and Environmental Science, University of Potsdam, 14476 Potsdam, Germany E-mail: Ulrike.Herzschuh@awi.de

article id 906, category Research article

Eivind Meen, Anders Nielsen, Mikael Ohlson. (2012). Forest stand modelling as a tool to predict performance of the understory herb Cornus suecica. Silva Fennica vol. 46 no. 4 article id 906. https://doi.org/10.14214/sf.906

Keywords: canopy layer; field layer; stand structure dynamics; forest simulator; composite models; Akaike’s information criterion

Abstract | View details | Full text in PDF | Author Info

Forest simulation models have been widely used to predict future stand structure. Generally these models do not include the understory vegetation and its response on stand structure change or other environmental factors. Previous simulation studies have shown that stand structure related variables, e.g. basal area, can explain diversity of the forest floor vegetation in boreal forests. We hypothesise that such variables also can be used to explain the performance of understory species and we conceptualise how plant ecology and forest modelling can be combined to predict the performance of understory plants in Norwegian boreal forests. We predict the performance of an understory plant species (Cornus suecica) over time using simulated values of forest variables as input to models expressing the relationship between forest environment variables and plant performance variables (viz. plant height, plant dry weight, number of flowers, number of branches and number of leaves). We also present relationships between plant performance and explanatory variables commonly used in basic ecological research, variables that currently not are readily compatible with forest simulators (e.g. soil chemical variables).We found basal area of canopy trees being the most important explanatory variable explaining C. suecica performance. The performance variable dry weight was predicted by one single model whereas the other performance variables were best predicted by model averaging. Forest simulations for 150 years showed values of plant performance of C. suecica to be reduced during forest succession.

Meen, Norwegian University of Life Sciences, Department of Ecology and Natural Resource Management, P.O. Box 5003, NO-1432 Ås, Norway E-mail: eivind.meen@umb.no
Nielsen, Norwegian University of Life Sciences, Department of Ecology and Natural Resource Management, P.O. Box 5003, NO-1432 Ås, Norway E-mail: an@nn.no
Ohlson, Norwegian University of Life Sciences, Department of Ecology and Natural Resource Management, P.O. Box 5003, NO-1432 Ås, Norway E-mail: mo@nn.no

article id 89, category Research article

Russell Grenfell, Tuomas Aakala, Timo Kuuluvainen. (2011). Microsite occupancy and the spatial structure of understorey regeneration in three late-successional Norway spruce forests in northern Europe. Silva Fennica vol. 45 no. 5 article id 89. https://doi.org/10.14214/sf.89

Keywords: boreal forest; disturbance; microsite; spatial correlation; stand structure; natural forest

Abstract | View details | Full text in PDF | Author Info

We compared microsite occupancy and three spatial structure of regeneration in three primeval late-successional Norway spruce dominated forests. One area lay in the middle boreal zone in Russia (Dvina-Pinega) where larger-scale disturbance from bark beetles and drought had occurred; the other areas lay in the northern boreal zone, one in Finland (Pallas-Ylläs) had encountered only small-scale disturbance, and one in Russia (Kazkim) had been influenced by fire. We mapped all spruce (Picea abies) and birch (Betula pendula and Betula pubescens) trees with diameter at breast height (DBH) ≥ 10 cm on 40 m 400 m plots, and those with DBH < 10 cm on 2 m or 4 m 400 m subplots. On the subplots we also recorded microsite occupancy and estimated microsite availability. At all study areas small seedlings (h < 0.3 m) of both spruce and birch were found largely on disturbance-related microsites. Birch saplings (h ≥ 1.3 m, DBH < 10 cm) disproportionately occupied deadwood-related microsites at Dvina-Pinega. In contrast, spruce saplings at all study areas, and birch saplings at Kazkim and Pallas-Ylläs, showed less, or no, preference. Our results thus confirm the importance of disturbance-related microsites for regeneration establishment, but not necessarily for long-term survival. No spatial segregation between the overstorey (DBH ≥ 10 cm) and saplings (h ≥ 1.3 m, DBH < 10 cm) or seedlings (h < 1.3 m) was found at Pallas-Ylläs or Kazkim, and only three instances of very weak segregation were found at Dvina-Pinega. This suggests that the regeneration gap concept may not be useful for describing the regeneration dynamics of primeval boreal forests.

Grenfell, University of Helsinki, Dept of Forest Sciences, Helsinki, Finland E-mail: russell.grenfell@helsinki.fi
Aakala, University of Helsinki, Dept of Forest Sciences, Helsinki, Finland E-mail: ta@nn.fi
Kuuluvainen, University of Helsinki, Dept of Forest Sciences, Helsinki, Finland E-mail: tk@nn.fi

article id 451, category Research article

Thomas P. Sullivan, Druscilla S. Sullivan, Pontus M. F. Lindgren, Douglas B. Ransome. (2010). Green-tree retention and life after the beetle: stand structure and small mammals 30 years after salvage harvesting. Silva Fennica vol. 44 no. 5 article id 451. https://doi.org/10.14214/sf.451

Keywords: biodiversity; stand structure; Pseudotsuga menziesii; ecological indicators; green-tree retention; small mammals; mountain pine beetle; Pinus contorta; salvage harvest

Abstract | View details | Full text in PDF | Author Info

We report on a retrospective investigation of the impacts of salvage harvesting of lodgepole pine (Pinus contorta var. latifolia Engelm. ex S. Wats.), killed by an outbreak of mountain pine beetle (Dendroctonus ponderosae Hopk.) in the 1970s, with variable retention of Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco). Our inference to biodiversity was coniferous stand structure and four mammal species: the southern red-backed vole (Myodes gapperi Vigors), common shrew (Sorex cinereus Kerr), red squirrel (Tamiasciurus hudsonicus Erxleben) and northern flying squirrel (Glaucomys sabrinus Shaw). We tested hypotheses that, at 30 years after salvage harvest of beetle-killed lodgepole pine trees, (1) abundance and diversity of stand structure, and (2) abundance of mammal species, will increase with higher levels of green-tree retention (GTR). Stand structure attributes and small mammals were sampled during 2005–2008 in young pine stands, with a range of GTR seed-trees (none, dispersed, and aggregated Douglas-fir), and uncut forest in south-central British Columbia, Canada. Diameters and heights of Douglas-fir and lodgepole pine and basal area of total conifers supported hypothesis (1). Mean abundance of the red-backed vole was consistently higher (2.3 to 6.4 times) in the uncut forest than other stands. Overall mean patterns of abundance for common shrews, red squirrels, and northern flying squirrels were similar among treatment stands. Mean abundance of the red-backed vole supported hypothesis (2), but numbers of the other three species did not. There is “life after the beetle” at 30 years after salvage harvesting, and this was enhanced by GTR.

Sullivan, Department of Forest Sciences, Faculty of Forestry, University of BC, 2424 Main Mall, Vancouver, BC, Canada V6T 1Z4 E-mail: tom.sullivan@ubc.ca
Sullivan, Department of Forest Sciences, Faculty of Forestry, University of BC, 2424 Main Mall, Vancouver, BC, Canada V6T 1Z4 E-mail: dss@nn.ca
Lindgren, Applied Mammal Research Institute, 11010 Mitchell Avenue, Summerland, BC, Canada V0H 1Z8 E-mail: pmfl@nn.ca
Ransome, Applied Mammal Research Institute, 11010 Mitchell Avenue, Summerland, BC, Canada V0H 1Z8 E-mail: dbr@nn.ca

article id 138, category Research article

Santiago Martín-Alcón, José Ramón González-Olabarría, Lluís Coll. (2010). Wind and snow damage in the Pyrenees pine forests: effect of stand attributes and location. Silva Fennica vol. 44 no. 3 article id 138. https://doi.org/10.14214/sf.138

Keywords: models; stand structure; conifers; Pyrenees; snow damages; stability; wind damages

Abstract | View details | Full text in PDF | Author Info

Wind and snow-induced damage have been analyzed at stand level for three pine forests in the Central-Eastern Pyrenees (Pinus nigra Arn. salzmanii, Pinus sylvestris L. and Pinus uncinata Ram.). Stand-level models have been then developed for the most affected two species, Pinus sylvestris L. and Pinus uncinata Ram., to describe damage severity. The models were based on data from national forest inventory plots. They included variables related to the spatial location and structure of the stands, being validated using a sub-set of the database (25% of the plots randomly selected). Mountain pine forests (Pinus uncinata Ram.) were the most heavily affected by wind and snow disturbances. For both mountain and Scots pine species, topographic exposure and the severity of the local storm regime had an important effect on the degree of damage. Stand’s resistance to wind and snow was found to be dependent on the combined effect of basal area and mean slenderness of the dominant trees. For a given slenderness ratio, damage increased strongly in lower-density stands, particularly in stands with basal areas below 15 m²/ha. Stand structure was particularly important to define the resistance of Scots pine stands, which presented a higher vulnerability to wind and snow under higher degree of even-agedness. The models presented in this study provide empirically-based information that can be used to implement silvicultural practices to minimize the risk of those forests to suffer wind and snow-related damages.

Martín-Alcón, Forest Technology Center of Catalonia, Solsona, Lleida, Spain E-mail: santiago.martin@ctfc.es
González-Olabarría, Forest Technology Center of Catalonia, Solsona, Lleida, Spain E-mail: jrgo@nn.es
Coll, Forest Technology Center of Catalonia, Solsona, Lleida, Spain E-mail: lc@nn.es

article id 216, category Research article

Juha Siitonen, Jenni Hottola, Auli Immonen. (2009). Differences in stand characteristics between brook-side key habitats and managed forests in southern Finland. Silva Fennica vol. 43 no. 1 article id 216. https://doi.org/10.14214/sf.216

Keywords: dead wood; woodland key habitats; stand structure; CWD; WKH; Forest Act

Abstract | View details | Full text in PDF | Author Info

Preservation of small habitat patches termed as “woodland key habitats” or “especially important habitats” in the Finnish Forest Act has become an integral part of biodiversity-oriented forest management. Forest Act habitats belong to particular habitat types defined in the act, and they are supposed to have natural-like stand characteristics. However, very little is known about the actual stand structure in the designated habitats. Our aim was to compare stand characteristics between brook-side key habitats and comparable managed forests as controls. Seven study areas were selected from four regions across southern Finland. Within each study area ten key habitats and ten controls (140 stands) were randomly selected. Living and dead trees and cut stumps were measured in each stand within a 0.2 ha plot. The average degree of previous cutting was significantly lower whereas the volume of dead wood, volume of deciduous trees, and stand diversity were each significantly higher in key habitats than controls. The average volume of dead wood was 11.7 m³ ha^–1 in key habitats and 6.5 m³ ha^–1 in controls. However, there was considerable variation among individual stands, and a large part of key habitats could not be distinguished from randomly selected control stands with respect to stand characteristics. The preservation of natural brook channels with their immediate surroundings is undoubtedly important for maintaining aquatic and semiaquatic biodiversity. Nevertheless, when complementing the forest conservation network in the future, main emphasis in selecting potentially valuable stands should be placed on important structural features such as dead wood and old trees.

Siitonen, Finnish Forest Research Institute, Vantaa Research Unit, P.O. Box 18, FI-01301 Vantaa, Finland E-mail: juha.siitonen@metla.fi
Hottola, Finnish Forest Research Institute, Vantaa Research Unit, P.O. Box 18, FI-01301 Vantaa, Finland E-mail: jh@nn.fi
Immonen, Finnish Forest Research Institute, Vantaa Research Unit, P.O. Box 18, FI-01301 Vantaa, Finland E-mail: ai@nn.fi

article id 232, category Research article

Thomas Wutzler. (2008). Effect of the aggregation of multi-cohort mixed stands on modeling forest ecosystem carbon stocks. Silva Fennica vol. 42 no. 4 article id 232. https://doi.org/10.14214/sf.232

Keywords: stand structure; thinning; inventory; scale; model; stratification; bias; inventorystand structure

Abstract | View details | Full text in PDF | Author Info

Studies of the carbon sink of forest ecosystems often stratify the studied stands by the dominating species and thereby abstract from differences in the mixed-species, multi-cohort structure of many forests. This case study infers whether the aggregation of forestry data introduces a bias in the estimates of carbon stocks and their changes at the scale of individual stands and the scale of a forest district. The empirical TreeGrOSS-C model was applied to 1616 plots of a forest district in Central Germany to simulate carbon dynamics in biomass, woody debris, and soil. In a first approach each stand was explicitly simulated with all cohorts. In three other approaches the forest inventory data were aggregated in several ways, including a stratification of the stands to 110 classes according to the dominating species, age class, and site conditions. A small but significant bias was confirmed. At stand scale the initial ecosystem carbon stocks by the aggregated approach differed from that of the detailed approach by 2.3%, but at the district scale only by 0.05%. The differences in age between interspersed and dominant cohorts as well as differences in litter production were important for the differences in initial carbon stocks. The amounts of wood extracted by thinning operations were important for the differences in the projection of the carbon stocks over 100 years. Because of the smallness of bias, this case study collects evidence that the approaches, that represent stands or stratums by a single cohort, are valid at the scale of a forest district or larger.

Wutzler, Max Planck Institute for Biogeochemistry, Hans Knöll Str. 10, DE-07745, Jena, Germany E-mail: thomas.wutzler@bgc-jena.mpg.de

article id 241, category Research article

Hailemariam Temesgen, Tara M. Barrett, Greg Latta. (2008). Estimating cavity tree abundance using Nearest Neighbor Imputation methods for western Oregon and Washington forests. Silva Fennica vol. 42 no. 3 article id 241. https://doi.org/10.14214/sf.241

Keywords: stand structure; nearest neighbor imputation; snag size; snag frequency; forest landscape modeling

Abstract | View details | Full text in PDF | Author Info

Cavity trees contribute to diverse forest structure and wildlife habitat. For a given stand, the size and density of cavity trees indicate its diversity, complexity, and suitability for wildlife habitat. Size and density of cavity trees vary with stand age, density, and structure. Using Forest Inventory and Analysis (FIA) data collected in western Oregon and western Washington, we applied correlation analysis and graphical approaches to examine relationships between cavity tree abundance and stand characteristics. Cavity tree abundance was negatively correlated with site index and percent composition of conifers, but positively correlated with stand density, quadratic mean diameter, and percent composition of hardwoods. Using FIA data, we examined the performance of Most Similar Neighbor (MSN), k nearest neighbor, and weighted MSN imputation with three variable transformations (regular, square root, and logarithmic) and Classification and Regression Tree with MSN imputation to estimate cavity tree abundance from stand attributes. There was a large reduction in mean root mean square error from 20% to 50% reference sets, but very little reduction in using the 80% reference sets, corresponding to the decreases in mean distances. The MSN imputation using square root transformation provided better estimates of cavity tree abundance for western Oregon and western Washington forests. We found that cavity trees were only 0.25 percent of live trees and 13.8 percent of dead trees in the forests of western Oregon and western Washington, thus rarer and more difficult to predict than many other forest attributes. Potential applications of MSN imputation include selecting and modeling wildlife habitat to support forest planning efforts, regional inventories, and evaluation of different management scenarios.

Temesgen, Department of Forest Resources, Oregon State University, Corvallis, OR, USA E-mail: hailemariam.temesgen@oregonstate.edu
Barrett, Pacific Northwest Research Station, Anchorage, AK, USA E-mail: tmb@nn.us
Latta, Department of Forest Resources, Oregon State University, Corvallis, OR, USA E-mail: gl@nn.us

article id 282, category Research article

Annika Kangas, Lauri Mehtätalo, Matti Maltamo. (2007). Modelling percentile based basal area weighted diameter distribution. Silva Fennica vol. 41 no. 3 article id 282. https://doi.org/10.14214/sf.282

Keywords: stand structure; diameter distribution; prediction; interpolation

Abstract | View details | Full text in PDF | Author Info

In percentile method, percentiles of the diameter distribution are predicted with a system of models. The continuous empirical diameter distribution function is then obtained by interpolating between the predicted values of percentiles. In Finland, the distribution is typically modelled as a basal-area weighted distribution, which is transformed to a traditional density function for applications. In earlier studies it has been noted that when calculated from the basal-area weighted diameter distribution, the density function is decreasing in most stands, especially for Norway spruce. This behaviour is not supported by the data. In this paper, we investigate the reasons for the unsatisfactory performance and present possible solutions for the problem. Besides the predicted percentiles, the problems are due to implicit assumptions of diameter distribution in the system. The effect of these assumptions can be somewhat lessened with simple ad-hoc methods, like increasing new percentiles to the system. This approach does not, however, utilize all the available information in the estimation, namely the analytical relationships between basal area, stem number and diameter. Accounting for these, gives further possibilities for improving the results. The results show, however, that in order to achieve further improvements, it would be recommendable to make the implicit assumptions more realistic. Furthermore, height variation within stands seems to have an important contribution to the uncertainty of some forest characteristics, especially in the case of sawnwood volume.

Kangas, Department of Forest Resources Management, P.O.Box 27, FI-00014 University of Helsinki, Finland E-mail: ak@nn.fi
Mehtätalo, University of Joensuu, Faculty of Forestry, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: lm@nn.fi
Maltamo, University of Joensuu, Faculty of Forestry, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: mm@nn.fi

article id 295, category Research article

Pekka Kaitaniemi, Janne Riihimäki, Julia Koricheva, Harri Vehviläinen. (2007). Experimental evidence for associational resistance against the European pine sawfly in mixed tree stands. Silva Fennica vol. 41 no. 2 article id 295. https://doi.org/10.14214/sf.295

Keywords: stand structure; natural enemies; species diversity; tri-trophic interactions

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This study examined whether the saplings of Scots pine (Pinus sylvestris) exhibit associational resistance against the European pine sawfly Neodiprion sertifer (Hymenoptera, Diprionidae) when grown in a mixture with 50% silver birch (Betula pendula). The number of sawflies on pine trees in pure and mixed stands was manipulated at two experimental sites during two years. Survival of larvae and eggs was monitored, and the numbers of presumed sawfly predators were counted. A lower proportion of sawfly larvae and eggs survived on pines grown in the mixture with birch as compared with pure pine stands. Lower survival of sawfly larvae in the mixed stands was associated with the higher abundance of ants in these stands. The numbers of other sawfly predators (e.g. spiders and predatory heteropterans) differed between the study sites and were negatively associated with the presence of ants, which suggests possible interference between these groups. Although sawfly survival was lower on pines in the mixed stands, providing evidence of associational resistance, a related study shows the same trees had a higher number of ant-tended aphid colonies as compared with pines in the pure stands. Therefore, instead of considering resistance against individual herbivore species, it seems more practical to use associational resistance as a trait representing the resistance of larger systems, such as whole tree stands, against the total damage caused by herbivores in general.

Kaitaniemi, Hyytiälä Forestry Field Station, University of Helsinki, Hyytiäläntie 124, FI-35500 Korkeakoski, Finland E-mail: pk@nn.fi
Riihimäki, Section of Ecology, Department of Biology, University of Turku, FI-20014 Turku, Finland E-mail: jr@nn.fi
Koricheva, School of Biological Sciences, Royal Holloway, University of London, Egham, Surrey, TW20 0EX, UK E-mail: jk@nn.uk
Vehviläinen, Section of Ecology, Department of Biology, University of Turku, FI-20014 Turku, Finland E-mail: hv@nn.fi

article id 333, category Research article

Lauri Mehtätalo, Matti Maltamo, Annika Kangas. (2006). The use of quantile trees in the prediction of the diameter distribution of a stand. Silva Fennica vol. 40 no. 3 article id 333. https://doi.org/10.14214/sf.333

Keywords: stand structure; inventory; percentile; order statistics

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This study deals with the prediction of the basal area diameter distribution of a stand without using a complete sample of diameters from the target stand. Traditionally, this problem has been solved by either the parameter recovery method or the parameter prediction method. This study uses the parameter prediction method and the percentile based diameter distribution with a recent development that makes it possible to improve these predictions by using sample order statistics. A sample order statistic is a tree whose diameter and rank at the plot are known, and is referred to in this paper as a quantile tree. This study tested 13 different strategies for selection of the quantile trees from among the trees of horizontal point sample plots, and compared them with respect to RMSE and the bias of four criterion variables in a dataset of 512 stands. The sample minimum was found to be the most promising alternative with respect to RMSE, even though it introduced a rather large amount of bias in the criterion variables. Other good and less biased alternatives are the second and third smallest trees and the tree closest to the plot centre. The use of minimum is recommended for practical inventories because its rank is probably easiest to determine correctly in the field.

Mehtätalo, Yale School of Forestry and Environmental Studies, 205 Prospect Street, New Haven, CT 06511, USA E-mail: lauri.mehtatalo@metla.fi
Maltamo, University of Joensuu, Faculty of Forestry, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: mm@nn.fi
Kangas, University of Helsinki, Department of Forest Resources Management, P.O.Box 27, FI-00014 University of Helsinki, Finland E-mail: ak@nn.fi

article id 351, category Research article

Jiaojun Zhu, Xiufen Li, Zugen Liu, Wei Cao, Yutaka Gonda, Takeshi Matsuzaki. (2006). Factors affecting the snow and wind induced damage of a montane secondary forest in northeastern China. Silva Fennica vol. 40 no. 1 article id 351. https://doi.org/10.14214/sf.351

Keywords: stem breakage; uprooting; stand structure; snow and wind damages; secondary forests; mixed forests

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In order to understand the processes of snow and wind induced damage in a natural montane, secondary forest in northeastern China, we examined the impacts of site conditions on the snow and wind damage; analyzed if the dominant tree species differed in their susceptibilities to the damage; and established the relationships between the characteristics of tree and stand and the damage. The results indicated that in regard to the topography factors, slope steepness and soil depth played a relatively important role for the damage. Damage ratios of all types combined were positively related with the composition of dominant tree species. The stand density was also important in determining resistance to the damage, i.e., the densely populated stand exhibited less overall damage ratios; however, the dominant tree species were commonly damaged easily by the snow and wind. Four damage modes found (uprooting, stem breakage, canopy damage and bending) were closely related to the stem taper (p < 0.05), and they could be ranked in following order: bending (92.0 ) > uprooting (85.3) > stem breakage (80.1) > canopy damage (65.0). In regard to differences in tree species’ susceptibilities to the damage, Betula costata exhibited the most uprooting, bending and overall damage ratios; while Quercus mongolica showed the highest breakage (both stem breakage and canopy damage) ratio, and Fraxinus mandshurica exhibited the least damage ratio (overall). The major six tree species could also be divided into two groups according to the overall damage ratios, i.e., more susceptible ones (B. costata, Ulmus laciniata and Q. mongolica), and less susceptible ones (F. mandshurica, Acer mono and Juglans mandshurica) to the snow and wind damage.

Zhu, Institute of Applied Ecology, Chinese Academy of Sciences, Wenhua Road 72, Shenyang 110016, China E-mail: zrms29@yahoo.com
Li, Institute of Applied Ecology, Chinese Academy of Sciences, Wenhua Road 72, Shenyang 110016, China; Graduate School of Chinese Academy of Sciences, Yuquan Road 19-A, Beijing, 100039, China E-mail: xfl@nn.cn
Liu, Institute of Applied Ecology, Chinese Academy of Sciences, Wenhua Road 72, Shenyang 110016, China; Graduate School of Chinese Academy of Sciences, Yuquan Road 19-A, Beijing, 100039, China E-mail: zgl@nn.cn
Cao, Institute of Applied Ecology, Chinese Academy of Sciences, Wenhua Road 72, Shenyang 110016, China E-mail: wc@nn.cn
Gonda, Faculty of Agriculture, Niigata University, Ikarashi 2-8050, Niigata, 950-2181, Japan E-mail: yg@nn.jp
Matsuzaki, Faculty of Agriculture, Niigata University, Ikarashi 2-8050, Niigata, 950-2181, Japan E-mail: tm@nn.jp

article id 479, category Research article

Ken Olaf Storaunet, Jørund Rolstad, Ivar Gjerde, Vegard S. Gundersen. (2005). Historical logging, productivity, and structural characteristics of boreal coniferous forests in Norway. Silva Fennica vol. 39 no. 3 article id 479. https://doi.org/10.14214/sf.479

Keywords: boreal forest; stand structure; decaying wood; forest history; naturalness; selective logging; dead trees

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Conservation of forest biodiversity has brought about an interest in evaluating the naturalness of forests, and to locate and protect semi-natural and old-growth forests in the Fennoscandian countries. However, it is not always clear how natural these forests really are, and how the past management history has affected their present structural composition. We studied the relationships between cut stumps from historical logging activity (50–100 years ago) and forest structural characteristics of today in a total of 385 0.25 ha plots in three boreal coniferous forests which are parts of National Nature Reserves in Norway. We also studied how forest productivity influenced these relationships. In plots with negligible logging impact we found the amount of living trees, dead wood, and size of the oldest trees mainly to increase with increasing productivity, whereas the age of the oldest trees decreased. The amount of deciduous trees was generally low irrespective of productivity. The intensity of logging did not consistently influence most of these forest structural variables, neither at low- nor at high-productive sites. The only consistent relationship in all study areas was a decreasing amount of dead wood with increasing logging intensity at high-productive sites. Also, the decay class distribution of dead wood was more right-skewed (indicating on-going accumulation of dead wood) the more logging had occurred at high-productive sites. Except from the effects on dead wood, previous logging does not show up as a major determinant of other stand structures of today.

Storaunet, Norwegian Forest Research Institute, Høgskolevegen 8, NO-1432 Ås, Norway E-mail: ken.storaunet@skogforsk.no
Rolstad, Norwegian Forest Research Institute, Høgskolevegen 8, NO-1432 Ås, Norway E-mail: jr@nn.no
Gjerde, Norwegian Forest Research Institute, Fanaflaten 4, NO-5244 Fana, Norway E-mail: ig@nn.no
Gundersen, Norwegian Forest Research Institute, Fanaflaten 4, NO-5244 Fana, Norway E-mail: vsg@nn.no

article id 377, category Research article

Saara Lilja, Timo Kuuluvainen. (2005). Structure of old Pinus sylvestris dominated forest stands along a geographic and human impact gradient in mid-boreal Fennoscandia. Silva Fennica vol. 39 no. 3 article id 377. https://doi.org/10.14214/sf.377

Keywords: disturbances; restoration; stand structure; managed forest; old growth forest

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Stand structural characteristics were examined in old Pinus sylvestris dominated sites in three regions along a broad geographic and human impact gradient in mid-boreal Fennoscandia. The study regions were: 1) Häme in south-western Finland, with a long history of forest utilization, 2) Kuhmo in north-eastern Finland, with a more recent history of intensive forest utilization, and 3) Vienansalo in Russian Karelia, still characterized by a large near-natural forest landscape. Within each region the sampled sites were divided into three human impact classes: 1) near-natural stands, 2) stands selectively logged in the past, and 3) managed stands treated with thinnings. The near-natural and selectively logged stands in Häme and Kuhmo had a significantly higher Picea proportion compared to stands in Vienansalo. In comparison, the proportions of deciduous tree volumes were higher in near-natural stands in Vienansalo compared to near-natural stands in Häme. The pooled tree diameter distributions, both in near-natural and selectively logged stands, were descending whereas managed stands had a bimodal diameter distribution. Structural diversity characteristics such as broken trunks were most common in near-natural stands and in stands selectively logged in the past. The results demonstrate the higher structural complexity of near-natural stands and stands selectively logged in the past compared to managed stands, and highlight that old near-natural stands and stands selectively logged in the past vary widely in their structures. This obviously reflects both their natural variability but also various combinations of pre-industrial land use and human impact on fire disturbance. These factors need to be acknowledged when using “natural” forest structures as a reference in developing strategies for forest management, restoration and nature conservation.

Lilja, University of Helsinki, Department of Forest Ecology, P.O. Box 27, FI-00014 University of Helsinki, Finland E-mail: saara.lilja@helsinki.fi
Kuuluvainen, University of Helsinki, Department of Forest Ecology, P.O. Box 27, FI-00014 University of Helsinki, Finland E-mail: tk@nn.fi

article id 410, category Research article

Jouni Siipilehto, Juha Siitonen. (2004). Degree of previous cutting in explaining the differences in diameter distributions between mature managed and natural Norway spruce forests. Silva Fennica vol. 38 no. 4 article id 410. https://doi.org/10.14214/sf.410

Keywords: Picea abies; stand structure; naturalness; Johnson’s SB distribution

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The degree of naturalness was assessed in 37 mature (stand age 80 198 yrs) Norway spruce dominated stands located in southern Finland by measuring the number (0 610 ha–1) and basal area (0 33 m2 ha–1) of cut stumps. The Johnson’s SB distribution was fitted for living spruce trees to describe the dbh-frequency and basal area-dbh distributions. Regression models were constructed for predicting the parameters of the SB distribution using traditional stand parameters (median diameter, basal area, stem number) and the cut stump variables (number, basal area). Stump variables improved the models and enabled to explain the differences in diameter distributions between stands with varying intensity of past cutting. Model for basal area-dbh distribution was more accurate than dbh-frequency model in terms of regression statistics, but less accurate in terms of generated stand variables. The number and basal area of cut stumps seem to be useful and simple measures of stand naturalness which have potential uses in stand modelling and biodiversity-oriented forestry planning.

Siipilehto, Finnish Forest Research Institute, Vantaa Research Centre, P.O. Box 18, FI-01301 Vantaa, Finland E-mail: jouni.siipilehto@metla.fi
Siitonen, Finnish Forest Research Institute, Vantaa Research Centre, P.O. Box 18, FI-01301 Vantaa, Finland E-mail: juha.siitonen@metla.fi

article id 408, category Research article

Sakari Sarkkola, Hannu Hökkä, Timo Penttilä. (2004). Natural development of stand structure in peatland Scots pine following drainage: results based on long-term monitoring of permanent sample plots. Silva Fennica vol. 38 no. 4 article id 408. https://doi.org/10.14214/sf.408

Keywords: Pinus sylvestris; peatland; tree mortality; stand structure; drainage; dbh distribution

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We studied the dynamics of stand structure on drained peatland sites in Scots pine dominated stands untreated with thinnings. The data consisted of consecutive stand measurements in 10 permanent sample plots where the monitoring periods varied from 29 to 66 years. We assumed that the stand’s structural development was driven by the natural processes of regeneration, growth, and mortality, all related to inter-tree competition within the stand. The DBH distributions of live and dead trees at different times of post-drainage stand development – smoothed by Weibull function – were analysed to characterise the change in stand structure. The initial uneven-sized structure of the natural, widely-spaced stands became more uneven during the first decades following drainage due to enhanced regeneration. Later, as stand density and mean tree size continuously increased, the DBH distributions approached bell-shaped distributions. Accordingly, the suppressed trees showed their highest mortality rate during the first decades, but the peak of the mortality distribution shifted to larger trees along stand succession. The change in structure was faster in southern Finland than in northern Finland. We assumed the changes in stand dynamics reflected increased inter-tree competition, initiated by enhanced site productivity and increased stand stocking resulting from the ditching operation.

Sarkkola, University of Helsinki, Department of Forest Ecology, P.O. Box 27, FI-00014 University of Helsinki, Finland E-mail: sakari.sarkkola@helsinki.fi
Hökkä, Finnish Forest Research Institute, Rovaniemi Research Station, P.O. Box 16, FI-96301 Rovaniemi, Finland E-mail: hh@nn.fi
Penttilä, Finnish Forest Research Institute, Vantaa Research Centre, P.O. Box 18, FI-01301 Vantaa, Finland E-mail: tp@nn.fi

article id 407, category Research article

Soili Kojola, Timo Penttilä, Raija Laiho. (2004). Impacts of different thinning regimes on the yield of uneven-structured Scots pine stands on drained peatland. Silva Fennica vol. 38 no. 4 article id 407. https://doi.org/10.14214/sf.407

Keywords: Pinus sylvestris; stand structure; silviculture; growth and yield; peatland forestry; intermediate cuttings

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Drained peatlands in northern Europe comprise more than 10 million ha of forestland and thus constitute a considerable production potential in forestry. Much of this area consists of stands dominated by Scots pine and close to maturity regarding commercial thinning. The trees within these stands typically vary in terms of age, size, and growth rate. The impacts of silvicultural cuttings on these uneven-structured stands are inadequately known. We simulated the impacts of a control regime with no thinnings, and three different thinning regimes, involving different thinning intensities, on the development of fifteen pine-dominated stands in Finland. The simulations started from the first thinnings and were continued until regeneration maturity. The predicted total yields ranged from 244 to 595 m3 ha–1, depending on site and thinning regime. The highest total yields were observed for the control regime in which 18–38% of the yield was, however, predicted to self-thin by the end of the simulation. Thus, the differences in the yields of merchantable wood were fairly small among the compared regimes. However, the regimes involving thinnings generally needed less time than the control regime to reach regeneration maturity. The mean annual increment of total stem volume was at its highest in the control regime. The highest mean annual increment of merchantable wood was obtained in the regime involving two moderate thinnings, but excluding the most low-productive sites where thinnings did not increase the yield of merchantable wood.

Kojola, Finnish Forest Research Institute, Vantaa Research Centre, P.O. Box 18, FIN-01301 Vantaa, Finland E-mail: soili.kojola@metla.fi
Penttilä, Finnish Forest Research Institute, Vantaa Research Centre, P.O. Box 18, FIN-01301 Vantaa, Finland E-mail: tp@nn.fi
Laiho, University of Helsinki, Department of Forest Ecology, P.O. Box 27, FIN-00014 University of Helsinki, Finland E-mail: rl@nn.fi

article id 620, category Research article

Annika Kangas, Matti Maltamo. (2000). Performance of percentile based diameter distribution prediction and Weibull method in independent data sets. Silva Fennica vol. 34 no. 4 article id 620. https://doi.org/10.14214/sf.620

Keywords: stand structure; calibration estimation; Weibull function; diameter distribution prediction; distribution-free method; nearest neighbour method

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Diameter distribution is used in most forest management planning packages for predicting stand volume, timber volume and stand growth. The prediction of diameter distribution can be based on parametric distribution functions, distribution-free parametric prediction methods or purely non-parametric methods. In the first case, the distribution is obtained by predicting the parameters of some probability density function. In a distribution-free percentile method, the diameters at certain percentiles of the distribution are predicted with models. In non-parametric methods, the predicted distribution is a linear combination of similar measured stands. In this study, the percentile based diameter distribution is compared to the results obtained with the Weibull method in four independent data sets. In the case of Scots pine, the other methods are also compared to k-nearest neighbour method. The comparison was made with respect to the accuracy of predicted stand volume, saw timber volume and number of stems. The predicted percentile and Weibull distributions were calibrated using number of stems measured from the stand. The information of minimum and maximum diameters were also used, for re-scaling the percentile based distribution or for parameter recovery of Weibull parameters. The accuracy of the predicted stand characteristics were also compared for calibrated distributions. The most reliable results were obtained using the percentile method with the model set including number of stems as a predictor. Calibration improved the results in most cases. However, using the minimum and maximum diameters for parameter recovery proved to be inefficient.

Kangas, Finnish Forest Research Institute, Kannus Research Station, P.O. Box 44, FIN-69101 Kannus, Finland E-mail: annika.kangas@metla.fi
Maltamo, Finnish Forest Research Institute, Joensuu Research Station, P.O. Box 68, FIN-80101 Joensuu, Finland E-mail: mm@nn.fi

article id 619, category Research article

Annika Kangas, Matti Maltamo. (2000). Percentile based basal area diameter distribution models for Scots pine, Norway spruce and birch species. Silva Fennica vol. 34 no. 4 article id 619. https://doi.org/10.14214/sf.619

Keywords: stand structure; diameter distribution prediction; distribution-free method; rational spline

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Information about diameter distribution is used for predicting stand total volume, timber volume and stand growth for forest management planning. Often, the diameter distribution is obtained by predicting the parameters of some probability density function, using means and sums of tree characters as predictors. However, the results have not always been satisfactory: the predicted distributions practically always have a similar shape. Also, multimodal distributions cannot be obtained. However, diameter distribution can also be predicted using distribution-free methods. In the percentile method, the diameters at certain percentiles of the distribution are predicted with models. The empirical diameter distribution function is then obtained by interpolating between the predicted diameters. In this paper, models for diameters at 12 percentiles of stand basal area are presented for Scots pine, Norway spruce and birch species. Two sets of models are estimated: a set with and one without number of stems as a predictor. Including the number of stems as a predictor improved the volume and saw timber volume estimates for all species, but the improvements were especially high for number of stems estimates obtained from the predicted distribution. The use of number of stems as predictor in models is based on the possibility of including this characteristic to measured stand variables.

Kangas, Finnish Forest Research Institute, Kannus Research Station, P.O. Box 44, FIN-69101 Kannus, Finland E-mail: annika.kangas@metla.fi
Maltamo, Finnish Forest Research Institute, Joensuu Research Station, P.O. Box 68, FIN-80101 Joensuu, Finland E-mail: mm@nn.fi

Category : Review article

article id 548, category Review article

Kevin C. Ryan. (2002). Dynamic interactions between forest structure and fire behavior in boreal ecosystems. Silva Fennica vol. 36 no. 1 article id 548. https://doi.org/10.14214/sf.548

Keywords: boreal forest; disturbance dynamics; stand structure; fire behavior; fire severity

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This paper reviews and synthesizes literature on fire as a disturbance factor in boreal forests. Spatial and temporal variation in the biophysical environment, specifically, vegetative structure, terrain, and weather lead to variations in fire behavior. Changes in slope, aspect, elevation, and soil affect site energy and water budgets and the potential plant community. These terrain features also have a major influence on fire-caused disturbance through their role in determining moisture conditions and flammability of fuels on hourly, seasonal, and successional time-scales. On fine time scales (minutes to hours), changes in weather, specifically wind and relative humidity, significantly affect a fire’s intensity and aboveground effects. Normal seasonal changes in dryness and periodic drought influence fire intensity and severity principally by affecting the depth of burn and belowground effects. On decades-long time scales changes in vegetative structure affect the mass of fuel available for burning and therefore the potential energy that can be released during a fire. The severity of fire varies in time and space depending not only on the biophysical environment, but also on the location on the fire’s perimeter (head vs. flank vs. rear). Spatial and temporal variation in severity within a fire can have long-lasting impacts on the structure and species composition of post-fire communities and the potential for future disturbances. Characteristic temperature histories of ground, surface, and crown fires are used to illustrate variations in fire severity. A soil-heating model is used to illustrate the impact of varying depth of burn on the depth at which various fire effects occur in the soil profile. A conceptual model is presented for the effects of fire severity on fire-plant regeneration interactions. The conceptual model can be used by restoration ecologists to evaluate the differential effects of controlled or prescribed fires and wildfires and to plan and implement fire treatments to conserve biodiversity.

Ryan, USDA Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, P.O. Box 8089, Missoula, Montana 59807, USA E-mail: kryan@fs.fed.us

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