Articles containing the keyword 'theory'

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
• Nikinmaa, E-mail: en@mm.unknown
• Perttunen, E-mail: jp@mm.unknown

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

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
• Houllier, E-mail: fh@mm.unknown

One-hectare plot in a Scots pine (Pinus sylvestris L.) forest was systemically sampled for surface soil characteristics: humus layer thickness, soil carbon and nitrogen content, pH, electrical conductivity and respiration were determined from 106 samples. The effects of large trees on the plot were mapped and their joint influences at the locations of soil sampling were described as the influence potential, derived from the ecological field theory, and were calculated based on the locations and dimensions of trees.

The range of variation of soil characteristics was from three to sevenfold; no spatial autocorrelation was detected. The calculated influence potential of trees, as determined by their size and spatial distribution, was related to the spatial variation of top soil properties. Top soil properties were also related to thickness of the humus layer but they were poorly correlated with underlying mineral soil characteristics. Humus layer thickness, with the calculated influence potential of trees, may provide a means to predict top soil characteristics in specific microenvironments in the forest floor.

• Hokkanen, E-mail: th@mm.unknown
• Järvinen, E-mail: ej@mm.unknown
• Kuuluvainen, E-mail: tk@mm.unknown

This paper summarises the main topics and conclusions from the joint meeting of two IUFRO working parties, S2.04-02, Breeding theory and progeny testing, and S2.02-16, Seed orchards, held in Tuusula, Finland on September 10–15, 1991. It concludes the main topics that need more research in these disciplines and future trends in the research.

• Roulund, E-mail: hr@mm.unknown
• Skrøppa, E-mail: ts@mm.unknown

This issue of Silva Fennica includes the presentations given in a joint meeting of two IUFRO working parties, S2.04-02, Breeding theory and progeny testing, and S2.02-16, Seed orchards. The sessions were held in Tuusula, Finland on September 10–15, 1991.

• Koski, E-mail: –

Comparative analysis could offer a number of advantages in the science of forest policy. Comparisons make use of the compiled material from different countries, point to new origins and solutions of issues of forestry and allow to question the common presuppositions in the national forest policy in a critical way.

The basic requirement of fruitful comparative research is a common scientific framework. In the light of empirical-analytical theory it is more promising to compare only one factor across regions than the whole system. The forest administration could be such a suitable object of comparison in particular because it is to be found all over the world, and it has a formal and partly public organization with a number of similarities. The product of forest administration is policy. The significance of the bureaucratic behaviour in agenda setting, policy formulation, legitimating, and implementation with regard to an issue of forest policy is to be analysed.

The two significant fields of analysis, namely forest administrations and the issues of forest policy characterize the strategies of research. By making use of a collection of papers dealing with forest bureaucracy we can select countries for comparison according to the following criteria: socioeconomic context, space and time. The next step is to analyse comparatively the behaviour of the forest bureaucracy in treating a special forest issue. The explanations can be tested empirically in different countries. Perhaps the dying of the forest could be a suitable issue as an object of comparative analysis which again could enlarge our knowledge about the forest administration as a political factor.

• Krott, E-mail: mk@mm.unknown

This special volume of Acta Forestalia Fennica is published in memory of professor A.K. Cajander (1879-1943), who was one of the founders of the Finnish Society of Forest Science. It contains a short biography, a complete list of his literary works and one of the papers on forest types he has written.

This article contains professor A.K. Cajander’s paper on the theory of forest types in English. The article can be found in Finnish in separate PDF (article id 7695).

The idea of forest types was developed by professor Cajander first in 1904-1909, when he was working as a student in the Evo Forestry Institute. The first publication in 1909 was followed by intensive research and the findings of the investigations were published in 1929 in Acta Forestalia Fennica 29 (Metsätyyppiteoria, The theory of forest types).

When classifying forest growing sites, the purpose is to combine those having the same or approximately same yield capacity, and to separate into different classes those whose yield capacity is widely different. The article states that site quality classification is a necessity in organized forest management as it gives a basis for all forest calculations concerning with yield and profit. The principles of site classification and its meaning in forest management is discussed.

• Cajander, E-mail: ac@mm.unknown

This special volume of Acta Forestalia Fennica is published in memory of professor A.K. Cajander (1879-1943), who was one of the founders of the Finnish Society of Forest Science. It contains a short biography, a complete list of his literary works and one of the papers on forest types he has written.

This PDF includes his article on forest types in Finnish. The translation of the text in English can be found in a separate PDF (article id 7396).

The idea of forest types was developed by professor Cajander first in 1904-1909, when he was working as a student in the Evo Forestry Institute. The first publication in 1909 was followed by intensive research and the findings of the investigations were published in 1929 in Acta Forestalia Fennica 29 (Metsätyyppiteoria, The theory of forest types).

When classifying forest growing sites, the purpose is to combine those having the same or approximately same yield capacity, and to separate into different classes those whose yield capacity is widely different. The article states that site quality classification is a necessity in organized forest management as it gives a basis for all forest calculations concerning with yield and profit. The principles of site classification and its meaning in forest management is discussed.

• Cajander, E-mail: ac@mm.unknown

The article contains three parts and a summary. The first part presents the common foundations of forest economics and forest management.  The second part critically discusses the concept of sustainability and the third part takes critical view on the theories on profitability.

The author concludes by stating that the literature shows there are some old principles of forest management that always arise when the forest science progresses. The economics of forest management has been neglected in the sense that it should be acknowledged as self and not as mathematical problem as it has been handled in many theories of national economy, e.g. land rent theory. The science seems the turn back to previous findings as they are proved right again.  

The PDF contains a summary in German.

• Hagfors, E-mail: eh@mm.unknown

The article has two parts: the first are the common principles of forestry and forest economics and the second part presents different theories of forest economics. The aim of the study is to find out how the best possible economic result can be achieved from forest management and use of forest resources.

The first part presents the economic foundations of forestry; the division between following the concept of economic profitability in forestry and forest management; concepts of capital and operating result in forestry; and productivity and profitability. It discusses the idea of economy as a dynamic entity instead of static.

In the second part the different economic theories related to forestry and forest economics are presented. Theory on the highest interest on forest capital, theory of sustained yield management system, land rent theory, theory on forest profitability and dynamic economic theory are discussed.      

• Hagfors, E-mail: eh@mm.unknown

There are several competing theories about forestry: school on continuous forest management system, school on profitability of forestry and a dynamic view on economics. The article discusses the pros and cons of the different theories or viewpoints and wider the essence of forest as an economic asset.

To serve the needs of the practical forestry and the economics related to forests the forestry needs to seek for standardization in relation to growth potential of the forests and market orientation of the timber. A modern theory of forestry needs to base itself on both.  

The volume 34 of Acta Forestalia Fennica is a jubileum publication of professor Aimo Kaarlo Cajander.

• Hagfors, E-mail: eh@mm.unknown

The article presents the principle of working if a dendrometer and the mathematical theory behind it. Dendrometer is a new measuring instruments used to determine the height and diameter of a standing tree. The usability of the instruments is proofed to be very good thought there are some limitations to its use. 

• Lönnroth, E-mail: el@mm.unknown

The study presents a theory of utility models based on aspiration levels, as well as the application of this theory to the planning of timber flow economics. The first part of the study comprises a derivation of the utility-theoretic basis for the application of aspiration levels. Two basic models are dealt with; the additive and the multiplicative. Applied here solely for partial utility functions, aspiration and reservation levels are interpreted as defining piecewisely linear functions. The standpoint of the choices of the decision-makers is emphasized by the use of indifference curves. The second part of the study introduces a model for the management of timber flows. The model is based on the assumption that the decision-maker is willing to specify a shape of income flow which is different from that of the capital-theoretic optimum. The utility model comprises four aspiration-based compound utility functions.

The theory and the flow model are tested numerically by computations covering three forest holdings. The results show that the additive model is sensitive even to slight changes in relative importance and aspiration levels. This applies particularly to nearly linear production possibility boundaries of monetary variables. The multiplicative model, on the other hand, is stable because it generates strictly convex indifference curves. Due to a higher marginal rate of substitution, the multiplicative model implies a stronger dependence on forest management than the additive function. For income trajectory optimization, a method utilizing an income trajectory index is more efficient than one based on the use of aspiration levels per management period. Smooth trajectories can be attained by squaring the deviation of the feasible trajectories from the desired one.

• Mykkänen, E-mail: rm@mm.unknown

The article is the first part of a wider project aiming to study the measurement practices of stand’s height-over-age based classifications and to develop new methods for actually measuring the side index.  

The first part of the article presents the concepts of site indexing and discusses it with a mathematical model. The second part of the article examines the structure of site indexing system regarding the reliability of the method. Third part presents the factors affecting the method development and the fourth part discusses the possible site index classes and their characteristics.   

The PDF contains a summary in Finnish. 

• Kangas, E-mail: yk@mm.unknown

• Karppinen, Department of Forest Sciences, P.O. Box 27, FI-00014 University of Helsinki, Finland E-mail: heimo.karppinen@helsinki.fi
• Korhonen, Kämnerintie 7e 41, FI-00750 Helsinki, Finland E-mail: mika.korhonen@gmx.com

• Hokajärvi, Oulu University of Applied Sciences, School of Renewable Natural Resources, Metsäkouluntie 4–6, FI-90650 Oulu, Finland E-mail: raili.hokajarvi@oamk.fi
• Hujala, Finnish Forest Research Institute, Joensuu Research Unit, P.O. Box 68, FI-80101 Joensuu, Finland E-mail: th@nn.fi
• Leskinen, University of Eastern Finland, Department of Geographical and Historical Studies, P.O. Box 111, FI-80101 Joensuu, Finland E-mail: lal@nn.fi
• Tikkanen, Oulu University of Applied Sciences, School of Renewable Natural Resources, Metsäkouluntie 4–6, FI-90650 Oulu, Finland E-mail: jt@nn.fi

• Hickey, University of British Columbia, Faculty of Forestry, Department of Forest Resources Management, 2045, 2424 Main Mall, UBC, Vancouver, Canada V6T 1Z4 E-mail: ghickey@interchange.ubc.ca
• Innes, University of British Columbia, Faculty of Forestry, Department of Forest Resources Management, 2045, 2424 Main Mall, UBC, Vancouver, Canada V6T 1Z4 E-mail: jli@nn.ca

• Samarasinghe, Lincoln University, P.O. Box 84, Canterbury, New Zealand E-mail: ss@nn.nz
• Kulasiri, Lincoln University, P.O. Box 84, Canterbury, New Zealand E-mail: kulasird@lincoln.ac.nz

• Buckley, Environmental Biology Group, Research School of Biological Sciences, The Australian National University, GPO Box 475, Canberra City, ACT 2601, Australia and Cooperative Research Centre for Greenhouse Accounting, RSBS, ANU E-mail: tom_buckley@alumni.jmu.edu
• Miller, Environmental Biology Group, Research School of Biological Sciences, The Australian National University, GPO Box 475, Canberra City, ACT 2601, Australia E-mail: jmm@nn.au
• Farquhar, Environmental Biology Group, Research School of Biological Sciences, The Australian National University, GPO Box 475, Canberra City, ACT 2601, Australia and Cooperative Research Centre for Greenhouse Accounting, RSBS, ANU E-mail: gdf@nn.au

• Farquhar, Cooperative Research Centre for Greenhouse Accounting and Environmental Biology Group, Research School of Biological Sciences, Australian National University, ACT 2601, Australia E-mail: farquhar@rsbs.anu.edu.au
• Buckley, Cooperative Research Centre for Greenhouse Accounting and Environmental Biology Group, Research School of Biological Sciences, Australian National University, ACT 2601, Australia E-mail: tnb@nn.au
• Miller, Research School of Biological Sciences, Australian National University, ACT 2601, Australia E-mail: jmm@nn.au

• Pakkala, Finnish Museum of Natural History, University of Helsinki, P.O. Box 17, FIN-00014 University of Helsinki, Finland E-mail: timo.pakkala@helsinki.fi
• Hanski, Department of Ecology and Systematics, University of Helsinki, P.O. Box 47, FIN-00014 University of Helsinki, Finland E-mail: ih@nn.fi
• Tomppo, Finnish Forest Research Institute, Unioninkatu 40 A, FIN-00170 Helsinki, Finland E-mail: et@nn.fi