Browsing by Title

Sort by: Order: Results:

Now showing items 1-20 of 251
  • Schabenberger, Oliver; Gregoire, Timothy G. (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1995)
    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 favor 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 ot these new approaches. This contribution introduces Estimating Function Theory as a principle with potential for unification and presents examples covering a variety of modeling issues to demonstrate its applicability.
  • Kangas, Jyrki; Pukkala, Timo (Suomen metsätieteellinen seura, 1992)
  • Toppinen, Anne; Laaksonen, Susanna; Hänninen, Riitta (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1996)
    This study investigates the relationship between Finnish sulphate pulp export prices and international pulp inventories using the Johansen cointegration method. Long-run equilibrium is found to exist between pulp price and NORSCAN inventory for the study period, 1980–94. Granger causality is found to exist from inventory to price but not vice versa. A simple short-run forecasting model for the Finnish pulp export price is formed. In preliminary analysis, the explanatory power of model is found to be acceptable but only under stable market conditions.
  • Hari, Pertti; Korpilahti, Eeva; Pohja, Toivo; Räsänen, Pentti K. (Suomen metsätieteellinen seura, 1990)
  • de Reffye, Philippe; Fourcaud, Thierry; Blaise, Frédéric; Barthélémy, Daniel; Houllier, François (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    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.
  • Tolvanen-Sikanen, Tiina; Sikanen, Lauri; Harstela, Pertti (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1995)
    The first aim of this study was to develop a simulation model describing the flow of different timber qualities to different firms. The second aim was to study preliminarily the factors which affect timber distributions. In addition, we tested the hypothesis that in a small sawmill firm the traditional way of organizing timber procurement does not direct effectively good quality logs to the special production. The game theoretic approaching and the principles of Monte-Carlo simulation were applied in developing of the simulation model. The most important factors of the model were tried to find for further studies with sensitive analyses. Empirical validation brought forth promising results in the area of one municipality. The buyer’s awareness of a marked stand, the seller’s willingness to sell a marked stand, the buyer’s ability to pay for wood and the proportion of first quality pine logs in a marked stand affected the distribution of pine logs. The results also supported the hypothesis that the traditional system, in which sawmills or their own forest department procure themselves all timber needed, is not the most effective way to direct enough good quality timber to the special production.
  • Hari, Pertti.; Kulmala, Markku.; Pohja, Toivo; Lahti, Tapani.; Siivola, Erkki.; Palva, Lauri; Aalto, Pasi; Hämeri, Kaarle; Vesala, Timo; Luoma, Sari.; Pulliainen, Erkki. (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1994)
    The Värriö environmental measurement station has been designed and constructed during 1991 and 1992. The measurement system consists of measurement units for gases (sulphur dioxide, ozone, carbon dioxide), particles, photosynthesis and irradiation. A meteorological station is also included. The preliminary measurement period was started on August, 1991. During the first year (1991–1992) some parts of the system were redeveloped and rebuilt. Full, continuous measurements started in August 1992. The system has been working quite reliably, with good accuracy. The preliminary results show that pollution episodes are observed when the wind direction is from Monchegorsk or Nikel, the main emission sources in Kola Peninsula.
  • Palander, Teijo (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    LP is an important method for allocation of wood inventory stock. It is, for instance, used alone in tactical planning systems, which currently are in wide use at the higher hierarchical level in the functionally decentralized planning of the Finnish forest industry. Unfortunately, LP as a solution method has not been capable of handling spatial data that seem to characterize planning systems in geographical decentralization. In the present study, a GIS was used to assimilate data from different wood procurement functions, to calculate transportation distances and cost figures, and to write the data in ASCII files, which were then used as input for the LP model. Using the experiments and methods of GIS on a planning system developed according to participatory planning, the results of this study suggest that the participatory method was faster than the conventional LP method, when solved using actual data. The participatory method was also capable of providing the same global optimum for a wood allocation problem. The implications of these results for improving operational and tactical planning of wood procurement in Finland are discussed.
  • Heiskanen, Juha; Laitinen, Jukka (Suomen metsätieteellinen seura, 1992)
  • Peltola, Heli; Kellomäki, Seppo (Suomen metsätieteellinen seura, 1993)
  • Fleming, R.A. (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1996)
    There is no doubt that tree survival, growth, and reproduction in North America’s boreal forest would be directly influenced by the projected changes in climate if they occur. The indirect effects of climate change may be of even greater importance, however, because of their potential for altering the intensity, frequency, and perhaps even the very nature of the disturbance regimes which drive boreal forest dynamics. Insect defoliator populations are one of the dominating disturbance factors in North America’s boreal forests and during outbreaks trees are often killed over vast forest areas. If the predicted shifts in climate occur, the damage patterns caused by insects may be considerably changed, particularly those of insects whose temporal and spatial distributions are singularly dependent on climatic factors. The ensuing uncertainties directly affect depletion forecasts, pest hazard rating procedures, and long-term planning for pest control requirements. Because the potential for wildfire often increases in stands after insect attack, uncertainties in future insect damage patterns also lead to uncertainties in fire regimes. In addition, because the rates of processes key to biogeochemical and nutrient recycling are influenced by insect damage, potential changes in damage patterns can indirectly affect ecosystem resilience and the sustainability of the multiple uses of the forest resource. In this paper, a mechanistic perspective is developed based on available information describing how defoliatoring forest insects might respond to climate warming. Because of its prevalence and long history of study, the spruce budworm, Choristoneura fumiferana Clem. (Lepidoptera: Tortricidae), is used for illustrative purposes in developing this perspective. The scenarios that follow outline the potential importance of threshold behavior, historical conditions, phenological relationships, infrequent but extreme weather, complex feedbacks, and natural selection. The urgency of such considerations is emphasized by reference to research suggesting that climate warming may already be influencing some insect lifecycles.
  • Kangas, Jyrki; Karsikko, Jari; Laasonen, Laura; Pukkala, Timo (Suomen metsätieteellinen seura, 1993)
  • Penner, Margaret; Penttilä, Timo; Hökkä, Hannu (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1995)
    The use of random parameter models in forestry has been proposed as one method of incorporating different levels of information into prediction equations. By explicitly considering the variance-covariance structure of observations and considering some model parameters as random rather than fixed, one can incorporate more complex error structures in analyzing data. Competition indices and variance component techniques were applied to 92 Scots pine (Pinus sylvestris L.)-dominated permanent sample plots on drained peatlands in northern Finland. By quantifying stand, plot, and tree level variation, it was possible to identify the level (stand, plot, or tree) at which the explanatory variables contributed to the model. The replication of plots within stands revealed little variation among plots within a single stand but significant variation occured at stand and tree levels. Positive and negative effects of inter-tree competition are identified by examining simple correlation statistics and the random parameter model.
  • Le Dizès, Séverine; Cruiziat, Pierre; Lacointe, André; Sinoquet, Hervé; Le Roux, Xavier; Balandier, Philippe; Jacquet, Patrick (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    An ecophysiological growth process model, called INCA, for simulating the growth and development of a young walnut tree (Juglans regia L.) during three or four years, is presented. This tool, currently under development, aims at integrating architectural and physiological knowledge of the processes involved, in order to give a more rational understanding of the pruning operation. The model describes a simple three-dimensional representation of tree crown, solar radiation interception, photosynthesis, respiration, growth and partitioning of assimilates to leaves, stems, branches and roots. It supports the hypothesis that the tree grows as a collection of semiautonomous, interacting organs that compete for resources, based on daily sink strengths and proximity to sources. The actual growth rate of organs is not predetermined by empirical data, but reflects the pattern of available resources. The major driving variables are solar radiation, temperature, topological, geometrical and physiological factors. Outputs are hourly and daily photosynthate production and respiration, daily dimensional growth, starch storage, biomass production and total number of different types of organ. The user can interact or override any or all of the input variables to examine the effects of such changes on photosynthate production and growth. Within INCA, the tree entities and the surrounding environment are structured in a frame-based representation whereas the processes are coded in a rule-based language. The simulation mechanism is primarily based on the rule chaining capabilities of an inference engine.
  • Mäkelä, Annikki; Vanninen, Petteri; Ikonen, Veli-Pekka (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    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 in Southern Finland, and example simulations are carried out to compare the development of quality characteristics in different stocking densities.
  • Häggman, Hely (Suomen metsätieteellinen seura, 1991)
  • Westman, Carl Johan (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1995)
    A simple, manually-operated and easily portable device for sampling volumetric soil cores to a depth of 100 cm with a minimum of soil disturbance is described. The device consists of a sample tube, a sampler and an extension tube. A dead blow nylon mallet is used to force the sampler into the soil and a small winch attached to an aluminium tube pulls the sampler from the soil. The total weight of the equipment (sampler, mallet and winch) is 18.5 kilograms and may be carried in the trunk of a small car. Sampling is easily done by one person in good physical condition but four-handed operation is recommended as more efficient. The sampling device has been in heavy use during the summers of 1993–95 when several hundred soil cores have been successfully extracted on various sites all over Finland.
  • Kellomäki, Seppo; Väisänen, Hannu; Hänninen, Heikki; Kolström, Taneli; Lauhanen, Risto; Mattila, Ulla; Pajari, Brita (Suomen metsätieteellinen seura, 1992)
  • Pukkala, Timo; Karsikko, Jari; Kolström, Taneli (Suomen metsätieteellinen seura, 1992)