Browsing Silva Fennica by Issue Date

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  • Hökkä, Hannu; Alenius, Virpi; Penttilä, Timo (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    Models for individual-tree basal area growth were constructed for Scots pine (Pinus sylvestris L.), pubescent birch (Betula pubescens Ehrh.) and Norway spruce (Picea abies (L.) Karst.) growing in drained peatland stands. The data consisted of two separate sets of permanent sample plots forming a large sample of drained peatland stands in Finland. The dependent variable in all models was the 5-year basal area growth of a tree. The independent tree-level variables were tree dbh, tree basal area, and the sum of the basal area of trees larger than the target tree. Independent stand-level variables were stand basal area, the diameter of the tree of median basal area, and temperature sum. Categorical variables describing the site quality, as well as the condition and age of drainage, were used. Differences in tree growth were used as criteria in reclassifying the a priori site types into new yield classes by tree species. All models were constructed as mixed linear models with a random stand effect. The models were tested against the modelling data and against independent data sets.
  • Thornley, John H. M. (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    A shoot:root carbon:nitrogen allocation model, based on the two processes of transport and chemical conversion, is described and explored. The view is proposed that all allocation models, whether built for the purposes of theoretical investigation or practical application, should start with this irreducible framework. In the present implementation, the processes operate according to: for substrate sources, dependence on shoot and root sizes, with possible product inhibition; for transport, movement down a substrate concentration gradient; for substrate sinks or utilization, linear bisubstrate kinetics. The dynamic and equilibrium properties of the model are explored. Failure of this approach to allocation will indicate to the modeller that additional mechanisms to control the processes are needed, and the mode of failure will indicate the type of mechanisms required. Additional mechanisms are discussed which may involve hormones or teleonomic (goal-seeking) controls, and may be added to the irreducible framework. However, these additions should not replace the irreducible framework of transport and chemical conversion, because they do not in reality. Modifications to the basic model to reflect some possibilities such as ontogenesis with the transition from exponential growth towards a steady state or with the scaling of within-plant transport resistances, the influence of hormones, and active transport, are described.
  • Deleuze, Christine; Houllier, François (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    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 Münch theory. We propose a simpler gradient process to describe the carbon distribution in the phloem of conifers. This model is a re-formulation 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.
  • Nykänen, Marja-Leena; Peltola, Heli; Quine, Christopher; Kellomäki, Seppo; Broadgate, Marianne (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    Within the European Community snow damage affects an estimated 4 million m3 of timber every year, causing significant economic losses to forest owners. In Northern Europe, for example, the occurrence of snow damage has increased over the last few decades mainly due to the increase in total growing stock. The most common form of damage is stem breakage, but trees can also be bent or uprooted. Trees suffering snow damage are also more prone to consequential damage through insect or fungal attacks. Snow accumulation on trees is strongly dependent upon weather and climatological conditions. Temperature influences the moisture content of snow and therefore the degree to which it can accumulate on branches. Wind can cause snow to be shed, but can also lead to large accumulations of wet snow, rime or freezing rain. Wet snow is most likely in late autumn or early spring. Geographic location and topography influence the occurrence of damaging forms of snow, and coastal locations and moderate to high elevations experience large accumulations. Slope plays a less important role and the evidence on the role of aspect is contradictory. The occurrence of damaging events can vary from every winter to once every 10 years or so depending upon regional climatology. In the future, assuming global warming in northern latitudes, the risk of snow damage could increase, because the relative occurrence of snowfall near temperatures of zero could increase. The severity of snow damage is related to tree characteristics. Stem taper and crown characteristics are the most important factors controlling the stability of trees. Slightly tapering stems, asymmetric crowns, and rigid horizontal branching are all associated with high risk. However, the evidence on species differences is less clear due to the interaction with location. Management of forests can alter risk through choice of regeneration, tending, thinning and rotation. However, quantification and comparison of the absolute effect of these measures is not yet possible. An integrated risk model is required to allow the various locational and silvicultural factors to be assessed. Plans are presented to construct such a model, and gaps in knowledge are highlighted.
  • Früh, Thomas (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    The model HYDRA, which simulates water flow in the branched tree architecture, is characterized. Empirical studies of the last decades give strong evidence for a close structure-function linkage in the case of tree water flow. Like stomatal regulation, spatial patterns of leaf specific conductivity can be regarded as a strategy counteracting conductivity losses which may arise under drought. Branching-oriented water flow simulation may help to understand how damaging and compensating mechanisms interact within the hydraulic network of trees. Furthermore, a coupling of hydraulic to morphological modelling is a prerequisite if water flow shall be linked to other processes. Basic assumptions of the tree water flow model HYDRA are mass conservation, Darcy’s law and the spatial homogeneity of capacitance and axial conductivity. Soil water potential is given as a one-sided border condition. Water flow is driven by transpiration. For unbranched regions these principles are condensed to a nonlinear diffusion equation, which serves as a continuous reference for the discrete method tailored to the specific features of the hydraulic network. The mathematical derivation and model tests indicate that the realization of the basic assumptions is reproducible and sufficiently exact. Moreover, structure and function are coupled in a flexible and computationally efficient manner. Thus, HYDRA may serve as a tool for the comparative study of different tree architectures in terms of hydraulic function.
  • Peltonen, Mikko; Heliövaara, Kari; Väisänen, Rauno (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    Distribution and occurrence of bark beetles and other forest insects in relation to environmental variation were analysed by multivariate methods. Eight different forest edges were studied using 10 x10 m sample plots that formed 200 m linear transects perpendicular to the forest edge. Forest edge affected the distribution of insect species only in the edges between mature, non-managed spruce stands and clear cuts or young seedling stands, but not in the pine stands. The occurrence of the selected forest insects mainly depended on variables associated with the amount and quality of suitable woody material. The most significant environmental variables were forest site type, crown canopy coverage, tree species, number of stumps, number of dead spruce trunks and amount of logging waste at site. Quantitative classification of species and sample plots showed that some specialized species (Xylechinus pilosus, Cryphalus saltuarius, Polygraphus poligraphus and P. subopacus) adapted to mature spruce forests, tended to withdraw from the forest edge to interior stand sites. By contrast many generalized species (Pityogenes chalcographus, P. quadridens, Pissodes spp., Hylurgops palliatus, Tomicus piniperda, Dryocoetes spp. and Trypodendron lineatum) benefitted from cuttings and spread over stand borders into mature forest.
  • Sievänen, Risto; Nikinmaa, Eero; Perttunen, Jari (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    The effects of two alternative formulations of sapwood senescence on the behavior of model LIGNUM (with parameter values adjusted for Scots pine 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.
  • Uuttera, Janne; Hyppänen, Harri (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    This study examined the relationships between forest management planning units and patches formed by forest habitat components. The test area used was a part of Koli National Park in North Karelia, eastern Finland. Forest management planning units (i.e. forest compartments) were defined by using a traditional method of Finnish forestry which applies aerial photographs and compartmentwise field inventory. Patches of forest habitat components were divided according to subjective rules by using a chosen set of variables depicting the edaphic features and vegetation of a forest habitat. The spatial distribution of the habitat components was estimated with the kriging-interpolation based on systematically located sample plots. The comparisons of the two patch mosaics were made by using the standard tools of GIS. The results of the study show that forest compartment division does not correlate very strongly with the forest habitat pattern. On average, the mean patch size of the forest habitat components is greater and the number of these patches lower compared to forest compartment division. However, if the forest habitat component distribution had been considered, the number of the forest compartments would have at least doubled after intersection.
  • Harstela, Pertti (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    Many kinds of planning systems have been labelled decision support systems (DSS), but few meet the most important features of real DSSs in planning and control of wood procurement. It has been concluded that many reasons exist to develop DSSs for wood procurement. The purchasing of timber seems to be one of the most promising areas for DSS, because there is no formal structure for these operations and decisions deal with human behaviour. Relations between DSSs and different features of the new approaches in wood procurement are also discussed, and hypotheses for future studies suggested.
  • Mäkinen, Harri (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    Possibilities of distance-independent and -dependent competition indices to describe the competition stress of an individual tree was studied in southern Finland. Five half-sib open-pollinated families and one check lot of Scots pine (Pinus sylvestris L.) was used as study material in order to analyse competitive interactions of crown form and stand density variation. Almost all competition indices correlated strongly with radial increment. Thus distance-independent indices were adequate to describe competition in young row plantations, where distance effects between trees were implicitly eliminated. Correlations between indices and height increment were not significant. Along with the increase in competition, the width and length of the crown and the diameter increment of the stem of some narrow-crowned families decreased slowly compared to wide-crowned families.
  • Athanassiadis, Dimitris (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    The objectives of this study was to record residual stand damage during harvesting operations and evaluate the influence of factors such as distance of the tree from the strip road, machine parts, operational phase, on the occurrence of tree wounds. The machine was a farm tractor equipped with a crane mounted on the front axle and a single grip harvester head. The study was carried out in two stands located in Southeast Sweden. Stand 1 was a 30-year-old Norway spruce (Picea abies L.) plantation on an afforested pasture while stand 2 was a 90-year-old mixed stand of Norway spruce, Scots pine (Pinus sylvestris L.), birch (Betula pendula Roth) and aspen (Populus tremula L.). The mean damage percentage was 6.3% for the first stand and 6.5% for the second stand. Sixty-five percent of the wounds were less than 50 cm2, with 91% of the damage occurring on the stem and 9% of the damage on or below the root collar. Sixty-six percent of the wounds produced by the stem under processing or by the harvesting head while only 10% of the wounds were produced by the tractor wheel. Damaged trees were distributed evenly in the crane reach zone. Significant differences were found between rut depths after one, two, four and six passes of the tractor in stand 1.
  • Robinson, Andrew P.; Gregoire, Timothy G.; Valentine, Harry T. (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    Cut-off importance sampling (CIS) is introduced as a means of sampling individual trees for the purpose of estimating bole volume. The novel feature of this variant of importance sampling is the establishment on the bole of a cut-off height, HC, above which sampling is precluded. An estimator of bole volume between predetermined heights HL and HU > HC is proposed, and its design-based bias and mean square error are derived. In an application of CIS as the second stage of a two-stage sample to estimate aggregate bole volume, the gain in precision realized from CIS more than offset its bias when compared to the precision of importance sampling when HC = HU.
  • Godin, Christophe; Costes, Evelyne; Caraglio, Yves (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    In the last decades, architectural analysis has been used to understand and to model plant development. These studies have lead us to reconsider the problem of measuring plants while taking into account their topological structure at several scales of detail. A computational platform, called AMAPmod, was created to work on such plant representations. This paper outlines the general methodology used in AMAPmod to represent plant topological structures and to explore these special types of databases. Plant structures are first encoded in order to build corresponding formal representations. Then, a dedicated language, AML, enables the user to extract various types of information from the plant databases and provides appropriate analyzing tools.
  • 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.
  • Kauppi, Pekka E.; Posch, Maximilian; Hänninen, Pekka; Henttonen, Helena M; Ihalainen, Antti; Lappalainen, Eino; Starr, Michael; Tamminen, Pekka (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    The carbon reservoir of ecosystems was estimated based on field measurements for forests and peatlands on an area in Finland covering 263 000 km2 and extending about 900 km across the boreal zone from south to north. More than two thirds of the reservoir was in peat, and less than ten per cent in trees. Forest ecosystems growing on mineral soils covering 144 000 km2 contained 10–11 kg C m–2 on an average, including both vegetation (3.4 kg C m–2) and soil (uppermost 75 cm; 7.2 kg C m–2). Mire ecosystems covering 65 000 km2 contained an average of 72 kg C m–2 as peat. For the landscape consisting of peatlands, closed and open forests, and inland water, excluding arable and built-up land, a reservoir of 24.6 kg C m–2 was observed. This includes the peat, forest soil and tree biomass. This is an underestimate of the true total reservoir, because there are additional unknown reservoirs in deep soil, lake sediments, woody debris, and ground vegetation. Geographic distributions of the reservoirs were described, analysed and discussed. The highest reservoir, 35–40 kg C m–2, was observed in sub regions in central western and north western Finland. Many estimates given for the boreal carbon reservoirs have been higher than those of ours. Either the Finnish environment contains less carbon per unit area than the rest of the boreal zone, or the global boreal reservoir has earlier been overestimated. In order to reduce uncertainties of the global estimates, statistically representative measurements are needed especially on Russian and Canadian peatlands.
  • Tokola, Timo; Heikkilä, Juho (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    The purpose of this study was to test the benefits of a forest site quality map, when applying satellite image based forest inventory. By combining field sample plot data from national forest inventories with satellite imagery and forest site quality data, it is possible to estimate forest stand characteristics with higher accuracy for smaller areas. The reliability of the estimates was evaluated using the data from a standwise survey for area sizes ranging from 0.06 ha to 300 ha. When the mean volume was estimated, a relative error of 14 per cent was obtained for areas of 50 ha; for areas of 30 ha the corresponding figure was below 20 per cent. The relative gain in interpretation accuracy, when including the forest site quality information, ranged between 1 and 6 per cent. The advantage increased according to the size of the target area. The forest site quality map had the effect of decreasing the relative error in Norway spruce volume estimations, but it did not contribute to Scots pine volume estimation procedure.
  • 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.
  • Maltamo, Matti (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    The purpose of this study was to compare the Weibull distributions estimated for the entire growing stock of a stand and separately for Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies Karst.) in describing the basal area diameter distributions in mixed stands. The material for this study was obtained by measuring 553 stands located in eastern Finland. The parameters of the Weibull distribution were estimated using the method of maximum likelihood. The models for these parameters were derived using regression analysis. Also, some parameter models from previous studies were compared with the measured distribution. The obtained distributions were compared using the diameter sums of the entire growing stock, diameter sums by tree species and of the sawtimber part of the growing stock. The results showed that far more accurate results were obtained when the distributions were formed using parameter models separately for the different tree species than when using parameter models for the entire growing stock. This was already true when considering the entire growing stock of the stand and especially when the results were examined by tree species. When the models for the entire growing stock were applied by tree species in relation to basal areas, the results obtained were overestimates for Norway spruce and underestimates for Scots pine. The models from earlier studies, where parameter models were estimated separately for tree species from the National Forest Inventory data, showed good fits also in regard to the data of this study.
  • Ruha, Tommi; Varmola, Martti (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    The effects of precommercial thinning on the quantity and external quality of young Scots pine stands were examined over two 10-year periods in an experiment comprising five stands growing on sub-dry sites in Finnish Lapland, northern Finland. The thinning treatments applied resulted in stand densities of 625, 1111, 1600, 2500 and 4444 stems ha–1 and a no-treatment, unthinned plot with a randomised block lay-out of two or tree replications in each stand. The dominant height of the stands varied between 4 and 8 m at the time of thinning. The trees reacted only slightly to the increase in growing space during the first ten years following precommercial thinning. During the second 10-year period, increased growing space was reflected more clearly in diameter and volume increment. These reactions were more evident in stands thinned at an early stage. The increment of the thinnest 100–200 trees ha–1 in each treatment was poor. The results showed that when the main principle in precommercial thinning is to achieve even spacing, the remaining smallest trees fail to react positively to the increase in growing space. In other words, the target of precommercial thinning should be to concentrate the increment on the tallest trees, even though they are located in groups. The external quality of the trees in stands where precommercial thinning was carried out at a later stage was high, and the diameter of the thickest branch along the butt log remained under 20 mm. Branch diameter was greater in stands thinned at an early stage. The effect of precommercial thinning on branch diameter when comparing the extreme treatments averaged 5 mm. When the aim of stand management is to combine high quality and good yield in naturally regenerated Scots pine stands in northern Finland, precommercial thinning should not be carried out before the dominant height of 7–8 m. The intensity of precommercial thinning depends on the yield targets of the first commercial thinning. A spacing of 2500 stems ha–1 satisfies the requirements of both high quality and adequate yield.
  • Amacher, Gregory S. (The Finnish Society of Forest Science and The Finnish Forest Research Institute, 1997)
    In this paper, different approaches and results concerning forest tax design are reviewed. In particular, comparisons are made between Scandinavian approaches, which rely on the two period model, and North American approaches, which largely rely on the Faustmann model. Existing work is critically evaluated according to several stylized facts that are common among forest taxation problems. These include the second best forest policy environment, joint production of public and private forest goods, the dynamic nature of forest capital, public and private ownership, competition between forest and nonforest sectors, and global policy constraints on taxation design. The gaps in addressing stylized facts are used to motivate new research directions. Problems and appropriate public finance literature are identified for investigating forest tax policy under government budget constraints, fiscal federalism, dynamic forest tax design, open economy forest tax policy, and econometric studies of reform. One conclusion reached from discussing future research is that two period and dynamic models will continue to prove useful in analyzing taxation design from the government’s perspective.