article id 528, category Commentary
Challenges and opportunities of the optimality approach in plant ecology. Silva Fennica vol. 36 no. 3 article id 528. https://doi.org/10.14214/sf.528
A meeting was held in Hyytiälä, Finland 10–12 April 2000 to assess critically the current challenges and limitations of the optimality approach in plant ecophysiology and botany. This article summarises the general discussions and views of the participants on the use of optimisation models as tools in plant ecophysiological research. A general framework of the evolutionary optimisation problem is sketched with a review of applications, typically involved with balanced regulation between parallel processes. The usefulness and limitations of the approach are discussed in terms of published examples, with special reference to model testing. We conclude that, regardless of inevitable problems of model formulation, wider application of the optimality approach could provide a step forward in plant ecophysiology. A major role of evolutionary theory in this process is simply the formulation of testable hypotheses, the evaluation of which can lead to important advances in our ecophysiological understanding and predictive ability.
article id 547, category Commentary
Introduction. Disturbance dynamics in boreal forests: defining the ecological basis of restoration and management of biodiversity. Silva Fennica vol. 36 no. 1 article id 547. https://doi.org/10.14214/sf.547
Category: Research article
article id 526, category Research article
The opportunity costs of forest conservation in a local economy. Silva Fennica vol. 36 no. 4 article id 526. https://doi.org/10.14214/sf.526
Costs generated by nature conservation are repeatedly under discussion. Most often the costs of conservation are estimated as aggregate figures at the national or regional level or alternatively, for a forest owner. In this study they were examined at the local level, in the forestry dependent municipality of Ilomantsi in Eastern Finland. The estimations of lost net revenues (stumpage income less silvicultural costs), wages, entrepreneurial income and profits, employment and value added were based on alternative forest management plans calculated for conservation areas. The annual losses as regards employment during the first decade were estimated to be 5.7–20.4 jobs. Later, the employment effects were estimated to be 2.4–6.3 lost jobs. Although the value added lost during the first decade was estimated to be at maximum only 3.4% of the present total value added of the municipality, the share of the value added of forestry was estimated to be higher than the mere protected forest land share would indicate. The use of conservation areas for forestry would create a moderate increase of employment in forestry, i.e. 3.8–14%, during the first decade, but it would later stabilise at a much lower level. Employment impacts at the municipal level were estimated as very small (at maximum 0.9%), but on the other hand, for some villages even single jobs may matter. The main reasons for the minor impacts were the high mechanisation rate of logging and the major flow of stumpage income outside the locality.
article id 525, category Research article
Value of complete information on red heartwood formation in beech (Fagus sylvatica). Silva Fennica vol. 36 no. 4 article id 525. https://doi.org/10.14214/sf.525
Beech (Fagus sylvatica L.) is the most important deciduous tree species in Germany. The wood of beech shows normally a bright colour (white beech) as long as no coloured heartwood has been formed. The facultative heartwood formation is induced when oxygen enters central parts of older trees, where dead or at least less vital parenchyma exist. The coloured heartwood is usually called ‘red heartwood’. Beech without red heartwood can preferably be found in younger trees which show a high water content even in central parts of the stem. The presence of red heartwood is regarded as a severe reduction of timber quality. Numerous studies have investigated opportunities to derive information on the presence and characteristics of red heartwood of standing beech trees. But until now it has not been tested whether such information could be helpful to improve the economics of beech-silviculture. This paper investigates whether complete information on the heartwood of standing beech could be useful to control the proportion of discoloured timber harvested during one rotation. It is also examined, which kind of information on the heartwood could be used to improve the economic results. To verify this, simulations based on simple algorithms were conducted. The general assumption was made that all information on the heartwood would be available. The results show that information which is restricted on the mere existence of red heartwood is neither suited to significantly reduce the amount of coloured timber nor is it possible to improve economic results based on this information. Only based on information on the recent formation of red heartwood of beech, which is actually still white the amount of discoloured timber can be reduced significantly. Consequently the discounted cash flows can only be substantially improved based on information on an expected formation of recent red heartwood.
article id 524, category Research article
Thinning response and thinning bias in a young Scots pine stand. Silva Fennica vol. 36 no. 4 article id 524. https://doi.org/10.14214/sf.524
The study analyses the annual post-thinning response and thinning bias of a young Scots pine stand as a function of tree size, competition faced by the tree, and competition that is removed around the tree in the thinning treatment. The thinning response of a tree was defined as the change of tree growth due to a thinning treatment. The thinning bias was defined as the difference between the true growth and model prediction. A distance-dependent (spatial) and a distance-independent (non-spatial) growth model were used in the calculations. The empirical data were measured from a thinning experiment consisting of ten plots, each 40 x 30 m in size, which were thinned to different stand densities. The ten-year post-thinning growth of every remaining tree was measured. The results indicated that the highest thinning response is among medium-sized and co-dominant trees. The thinning response is quite small, and even negative for some trees, for two years after thinning but it becomes clearly positive from the third year onwards. The spatial model underestimated the growth of small trees (which usually face high competition) while the non-spatial model overestimated the growth of trees that are small or face much competition. The spatial model used in this study overemphasized the effect of competition while the non-spatial model underestimated this effect. Both growth models overestimated the growth of trees in heavily thinned places, but this bias disappeared in two years. The negative bias was more pronounced with a spatial growth model because the tendency of the non-spatial model to underestimate the growth of trees facing little competition partly compensated for the negative bias.
article id 523, category Research article
Effect of early thinning on the diameter growth distribution along the stem of Scots pine. Silva Fennica vol. 36 no. 4 article id 523. https://doi.org/10.14214/sf.523
The absolute and relative effects of the first thinning on the diameter growth distribution along the stems were studied in 98 Scots pines (Pinus sylvestris L.) at heights of 1.3, 4, 6 and 8 m. The data cover one 3-year pre-thinning period and four 3-year post-thinning periods in plots with densities varying from 575 to 3400 stems ha–1. A shift in the point of maximum diameter growth down the bole was found during the first 3 years after thinning, with a shift back up the stem later. The thinning response over the whole 12-year post-thinning period was strongest the nearer the stem base and the heavier the thinning. The largest trees had the highest diameter growth after thinning in absolute terms, and the growth was greater the heavier the thinning. The absolute thinning response over the 12-year post-thinning period was highest in the medium tree size and in the largest trees, especially on the heavily thinned and lightly thinned plots. Whereas in the moderately thinned stand the smaller and larger trees responded more than did those of medium size on average. In relative sense, however, the small trees on heavily or moderately thinned plots responded more rapidly and more strongly than the medium-sized or large trees over the whole stem. The small trees on the lightly thinned plots responded only slightly to thinning. The results suggest that it is possible to affect the uniformity of wood properties (such as ring width) both within and between trees by thinning.
article id 522, category Research article
Anticipating the variance of predicted stand volume and timber assortments with respect to stand characteristics and field measurements. Silva Fennica vol. 36 no. 4 article id 522. https://doi.org/10.14214/sf.522
Several models and/or several variable combinations could be used to predict the diameter distribution of a stand. Typically, a fixed model and a fixed variable combination is used in all conditions. The calibration procedure, however, makes it possible to choose the measurement combination from among many possibilities, although the model used is fixed. In this study, the usefulness of utilizing additional stand characteristics for calibrating the predicted diameter distribution is examined. Nine measurement strategies were tested in predicting the total stand volume, sawlog volume and pulpwood volume. The observed errors of these variables under each strategy were modeled as a function of basal area, basal area median diameter and number of stems. The models were estimated in three steps. First, an Ordinary Least Squares (OLS) model was fitted to the observed errors. Then, a variance function was estimated using the OLS residuals. Finally, a weighted Seemingly Unrelated Regression (SUR) analysis was used to model the observed errors, using the estimated variance functions as weights. The estimated models can be used to anticipate the precision and accuracy of predicted volume characteristics for each stand with different variable combinations and, consequently, to choose the best measurement combination in different stands.
article id 521, category Research article
Site index conversion equations for mixed trembling aspen and white spruce stands in northern British Columbia. Silva Fennica vol. 36 no. 4 article id 521. https://doi.org/10.14214/sf.521
White spruce and trembling aspen are two important commercial species in British Columbia. They often grow in association, particularly in the Boreal White and Black Spruce and Sub-Boreal Spruce biogeoclimatic zones. Site index conversion equations are useful for estimating the site index of one species from the site index of another species. This study fills a need for site index conversion equations for mixed spruce/aspen stands. Seventy 0.01 ha study plots were established in mixed spruce/aspen stands. One site tree of each species was selected from each plot. The height and breast height ages of the site trees were measured and the site index was estimated with these data. The correlation between the site index of spruce and aspen was 0.6. Geometric mean regression was used to estimate the parameters of a linear site index conversion equation. The analysis did not reveal any differences in the conversion equations across the three major biogeoclimatic units (BWBSmw1, BWBSmw2, and SBS) that were sampled. Therefore, only one conversion equation is required.
article id 520, category Research article
Foliage and branch biomass estimation of coniferous and deciduous tree species. Silva Fennica vol. 36 no. 4 article id 520. https://doi.org/10.14214/sf.520
Under changing environmental conditions, biomass development on the tree and the stand level may differ from today, regardless if the induced change is due to a shift in the general climate properties or to forest management. Under these conditions, tree biomass can not be derived from tables based on former investigations but has to be defined from particular biomass investigations, which generally calculate tree and stand biomass from sample branches using allometric relationships. Therefore, sample measurements on harvested trees are needed. In this paper, foliage and branch biomass estimation for 6 Norway spruces (Picea abies) and 6 beeches (Fagus sylvatica) harvested in a 56-year-old mixed stand in southern Germany is presented. Different allometric models are investigated to derive branch biomass from branch dimension for both species. The equations that are based on branch length, foliated branch fraction, and branch diameter are used for tree and stand level estimates. However, the variation within the 6 trees of each species was too large for a reliable calculation of stand biomass, especially in case of beech branch wood. Furthermore, the necessity of allometric relations and their applicability in individual-tree models is discussed, and the importance of suitable branch- and tree selection is underlined.
article id 519, category Research article
Sensitivity of Picea abies to butt rot in pure stands and in mixed stands with Pinus sylvestris in southern Sweden. Silva Fennica vol. 36 no. 4 article id 519. https://doi.org/10.14214/sf.519
Repeatedly sampled data from permanent experimental plots in southern Sweden were used to model butt rot development in Norway spruce growing in pure stands and in mixed stands with Scots pine. The data come from 29 sites with pure spruce, altogether 100 plots, and from 15 sites of mixed spruce and pine, altogether 22 plots. A logistic model provided the best fit to the data. The study material revealed that in mixed stands the proportion of spruce trees with butt rot is lower than in pure Norway spruce stands. The difference in the incidence of butt rot cannot be explained by silviculture or windthrow since both factors are accounted for in the study. The most significant effect on butt rot development in Norway spruce by an admixture of Scots pine, was found when the Scots pine admixture was 50%. In order to reduce the incidence of butt rot in Norway spruce, the study material indicate that there is little to be gained by increasing the Scots pine admixture to much more than 50%.
article id 518, category Research article
Timing of seed dispersal in Pinus sylvestris stands in central Sweden. Silva Fennica vol. 36 no. 4 article id 518. https://doi.org/10.14214/sf.518
The objective of the study presented here was to describe the variation in timing of seed dispersal from Scots pine (Pinus sylvestris L.) seed trees in central Sweden. Seeds were collected in traps at two sites, for three years at one, and four years at the other . The traps were emptied from March to August each year at 1–2 week intervals during the main period of seed dispersal. The annual seed fall varied between 200 000 and 1.6 million seeds per hectare. The seed fall started in mid to late April, shortly after the heat sum had started to accumulate. The most intensive seed fall took place in early to mid May. The peak period, when 50% of the total seed dispersal occurred, lasted for 18–28 days at the different sites and years. The variation in timing among years seemed to be mainly due to climatic factors – high temperatures promoted seed dispersal, for instance. The results may be useful for planning the time of scarification to optimise the natural regeneration of Scots pine. The data suggest that scarification in the spring, no later than mid-May, would generally create a good seed-bed for most of the current year’s seeds, whereas scarification in late May or June would bury a large proportion of this cohort.
article id 533, category Research article
A model for optimal mycorrhizal colonization along altitudinal gradients. Silva Fennica vol. 36 no. 3 article id 533. https://doi.org/10.14214/sf.533
Mycorrhizal associations are generally favourable for vascular plants in nutrient-poor conditions. Still, non-mycorrhizal plants are common in high arctic and alpine areas, which are often poor in nitrogen and phosphorus. The relative proportion of mycorrhizal plants has been found to decrease along with increasing altitude, suggesting that the advantage of the mycorrhizal symbiosis may change along an altitudinal gradient. This may be related to the environmental factors that possibly constrain the amount of photosynthesized carbon to be shared with mycorrhizal fungi. We propose a simple optimization model for root colonization by fungal symbionts and analyze the advantages of mycorrhizas in relation to the nutrient use efficiency of photosynthesis (PNUE), the kinetics of nutrient uptake and the soil nutrient levels. Our model suggests that mycorrhizas are not usually favoured at low PNUE values. At low nutrient levels, mycorrhizas may be advantageous if they have a lower threshold concentration of nutrient uptake (xmin) compared to non-mycorrhizal roots. If mycorrhizal roots have a higher maximum capacity of nutrient uptake (Vmax), mycorrhizas can be favourable for the host plant even at relatively low nutrient concentrations and at relatively low PNUE. Consequently, the possible patterns along altitudinal gradients essentially depend on PNUE. If the soil nutrient concentration is constant and PNUE decreases, the advantage of mycorrhizal symbiosis declines independently of the nutrient uptake kinetics. If PNUE remains constant and the soil nutrient concentration decreases along with increasing altitude, the emerging colonization pattern (either increasing, decreasing or intermediate) depends on the nutrient uptake kinetics. Additionally, if both PNUE and the soil nutrient concentration decrease, several patterns may emerge, depending on the nutrient uptake kinetics.
article id 532, category Research article
Leaf life span and the mobility of “non-mobile” mineral nutrients – the case of boron in conifers. Silva Fennica vol. 36 no. 3 article id 532. https://doi.org/10.14214/sf.532
Nutrient conservation is considered important for the adaptation of plants to infertile environments. The importance of leaf life spans in controlling mean residence time of nutrients in plants has usually been analyzed in relation to nutrients that can be retranslocated within the plant. Longer leaf life spans increase the mean residence time of all mineral nutrients, but for non-mobile nutrients long leaf life spans concurrently cause concentrations in tissues to increase with leaf age, and consequently may reduce non-mobile nutrient use efficiency. Here we analyze how the role of leaf life span is related to the mobility of nutrients within the plant. We use optimality concepts to derive testable hypotheses, and preliminarily test them for boron (B), a nutrient for which mobility varies among plant species. We review published and unpublished data and use a simple model to assess the quantitative importance of B retranslocation for the B budget of mature conifer forests and as a mechanism for avoiding toxicity.
article id 531, category Research article
The mathematics of linked optimisation for water and nitrogen use in a canopy. Silva Fennica vol. 36 no. 3 article id 531. https://doi.org/10.14214/sf.531
We develop, and discuss the implementation of, a mathematical framework for inferring optimal patterns of water and nitrogen use. Our analysis is limited to a time scale of one day and a spatial scale consisting of the green canopy of one plant, and we assume that this canopy has fixed quantities of nitrogen and water available for use in photosynthesis. The efficiencies of water and nitrogen use, and the interactions between the two, are strongly affected by physiological and physical properties that can be modeled in different ways. The thrust of this study is therefore to discuss these properties and how they affect the efficiencies of nitrogen and water use, and to demonstrate, qualitatively, the effects of different model assumptions on inferred optimal strategies. Preliminary simulations suggest that the linked optimisation of nitrogen and water use is particularly sensitive to the level of detail in canopy light penetration models (e.g., whether sunlit and shaded fractions are pooled or considered independently), and to assumptions regarding nitrogen and irradiance gradients within leaves (which determine how whole-leaf potential electron transport rate is calculated from leaf nitrogen content and incident irradiance).
article id 530, category Research article
Optimal stomatal control in relation to leaf area and nitrogen content. Silva Fennica vol. 36 no. 3 article id 530. https://doi.org/10.14214/sf.530
We introduce the simultaneous optimisation of water-use efficiency and nitrogen-use efficiency of canopy photosynthesis. As a vehicle for this idea we consider the optimal leaf area for a plant in which there is no self-shading among leaves. An emergent result is that canopy assimilation over a day is a scaled sum of daily water use and of photosynthetic nitrogen display. The respective scaling factors are the marginal carbon benefits of extra transpiration and extra such nitrogen, respectively. The simple approach successfully predicts that as available water increases, or evaporative demand decreases, the leaf area should increase, with a concomitant reduction in nitrogen per unit leaf area. The changes in stomatal conductance are therefore less than would occur if leaf area were not to change. As irradiance increases, the modelled leaf area decreases, and nitrogen/leaf area increases. As total available nitrogen increases, leaf area also increases. In all the examples examined, the sharing by leaf area and properties per unit leaf area means that predicted changes in either are less than if predicted in isolation. We suggest that were plant density to be included, it too would further share the response, further diminishing the changes required per unit leaf area.
article id 529, category Research article
Comparison of an optimal stomatal regulation model and a biochemical model in explaining CO2 exchange in field conditions. Silva Fennica vol. 36 no. 3 article id 529. https://doi.org/10.14214/sf.529
Gas exchange of Pinus sylvestris L. was studied in subarctic field conditions. Aspects on optimal control of the gas exchange were examined using approach by Hari et al. (Tree Phys. 2: 169–175, 1986). Biochemical model by Farquhar et al. (Planta 149: 78–90, 1980) was utilized to describe the photosynthetic production rate of needles. The model parameters were determined from field measurements. The results from the optimization approach and biochemical model were compared and their performance was found quite similar in terms of R2 calculated using measured exchange rates (0.89 for optimization model and 0.85 for biochemical model). Minor differences were found in relation to responses to intercellular carbon dioxide concentration and temperature.
article id 545, category Research article
Eight heuristic planning techniques applied to three increasingly difficult wildlife planning problems. Silva Fennica vol. 36 no. 2 article id 545. https://doi.org/10.14214/sf.545
As both spatial and temporal characteristics of desired future conditions are becoming important measures of forest plan success, forest plans and forest planning goals are becoming complex. Heuristic techniques are becoming popular for developing alternative forest plans that include spatial constraints. Eight types of heuristic planning techniques were applied to three increasingly difficult forest planning problems where the objective function sought to maximize the amount of land in certain types of wildlife habitat. The goal of this research was to understand the relative challenges and opportunities each technique presents when more complex difficult goals are desired. The eight heuristic techniques were random search, simulated annealing, great deluge, threshold accepting, tabu search with 1-opt moves, tabu search with 1-opt and 2-opt moves, genetic algorithm, and a hybrid tabu search / genetic algorithm search process. While our results should not be viewed as universal truths, we determined that for the problems we examined, there were three classes of techniques: very good (simulated annealing, threshold accepting, great deluge, tabu search with 1-opt and 2-opt moves, and tabu search / genetic algorithm), adequate (tabu search with 1-opt moves, genetic algorithm), and less than adequate (random search). The relative advantages in terms of solution time and complexity of programming code are discussed and should provide planners and researchers a guide to help match the appropriate technique to their planning problem. The hypothetical landscape model used to evaluate the techniques can also be used by others to further compare their techniques to the ones described here.
article id 544, category Research article
Updating stand level inventory data applying growth models and visual interpretation of aerial photographs. Silva Fennica vol. 36 no. 2 article id 544. https://doi.org/10.14214/sf.544
In this study two procedures for updating stand level inventory data were developed and tested. The development of the growing stock of 62 stands over 12 years was simulated in the MELA stand simulator with no prior information of rapid changes, such as clear-cuttings. The acceptability of the simulation was decided standwise with visual interpretation of aerial false-colour photographs. If the simulated data were not accepted, new stand attributes were assessed with photo interpretation in procedure 1. In procedure 2, on the other hand, it was possible to utilise old management proposals. In case a cutting or other operation had been proposed and it looked like the operation had been realised, the interpreters accepted the proposal. Otherwise the last implemented operation and implementation year were interpreted. In case no operation had been carried out during the updating period but the growth model updated data were not acceptable, the same stand characteristics were estimated as in procedure 1. Stands where a proposal had been accepted or an operation interpreted were later updated again in MELA so that the program simulated the operations. The Root Mean Squared Errors of stem volume were 62 and 57 m3 per ha (34 and 30%) with procedures 1 and 2. With procedure 2 the accuracy of updating was comparable with a stand level field inventory carried out in the study area. The productivity of the photo interpretation procedures was 57 and 84 ha per h, respectively, whereas the productivity of a field inventory has been 3.3–5 ha per h.
article id 543, category Research article
The development and validation of pre-harvest inventory methodologies for timber procurement in Ireland. Silva Fennica vol. 36 no. 2 article id 543. https://doi.org/10.14214/sf.543
This article describes the development and validation of a decision-support system for sawmill wood procurement, dealing specifically with the integration of the pre-harvest inventory procedures, site-specific dbh/height models and a generic taper equation, with a crosscutting simulator. The crosscutting simulation program faithfully mimics the process of cut-to-length harvesting and provides detailed information on the potential volume, logs count and diameter distributions for different log assortment specifications. Four data sets, consisting of a total of 4153 diameter and height measurements, were used in the validation process. The sites included two Sitka spruce clearfells, a Sitka spruce thinning and a Norway spruce clearfell. The evaluation process has shown that the developed decision-support system produced accurate results for a wide range of stand types, as long as sufficient large data sets were used, and that it provides the wood procurement manager of a sawmill with an efficient means of gaining a comprehensive insight into the yield potential of standing timber lots and, as such, represents a valuable aid to timber procurement and production planning.
article id 542, category Research article
Intra-tree models of juvenile wood in Norway spruce as an input to simulation software. Silva Fennica vol. 36 no. 2 article id 542. https://doi.org/10.14214/sf.542
Juvenile wood found in the first 5–25 growth rings of a conifer has a structure and properties that differ from mature wood. Juvenile wood is therefore said to influence processing and the end-use of sawn products. Consequently, models describing the juvenile wood content, within and between trees, could be useful in improving the utilisation and value of wood as an industrial raw material. The objective of the present study was to develop juvenile wood models, based on Norway spruce trees, which could be used within a model system for conversion simulation studies. Nineteen stands of Norway spruce (Picea abies [L.] Karst.) were selected throughout Sweden. Based on DBH, two small, two medium, and two large diameter timber trees were taken from each stand. DBH varied between 180–470 mm, tree height between 17–34 m, and total age between 51–152 years. Each selected tree was cross-cut into logs; discs were prepared from the large end of each log and from the top end of the top log. Image analysis was used to determine growth ring development on sampled discs. Using tree and growth variables, the juvenile core radius and the logarithmic value of juvenile wood percentage were modelled. The two models had an R2Adj of 0.71 and 0.88 respectively.
article id 541, category Research article
Effectiveness of delayed brush cutting and herbicide treatments for vegetation control in a seven-year-old jack pine plantation in northwestern Ontario, Canada. Silva Fennica vol. 36 no. 2 article id 541. https://doi.org/10.14214/sf.541
Efficacy of three conifer release treatments, i) single application of glyphosate (Vision™) herbicide, ii) multiple application of glyphosate herbicide, and iii) motor-manual brush cutting for controlling competing plants, particularly trembling aspen (Populus tremuloides), pin cherry (Prunus pensylvanica), green alder (Alnus viridis spp. crispa), and beaked hazel (Corylus cornuta spp. cornuta), was studied in a seven-year-old jack pine (Pinus banksiana) plantation in northwestern Ontario, Canada. The single and multiple glyphosate applications were equally effective in controlling trembling aspen and pin cherry, causing over 90% stem mortality. The brushsaw treatment caused an initial decrease followed by an increase in stem density of these two species. A high degree of stem thinning by natural mortality in the untreated control plots was observed in trembling aspen (23–46%) and pin cherry (41–69%) over four years. As with trembling aspen and pin cherry, stem density of green alder and beaked hazel initially decreased and then increased following the brushsaw treatment, mainly due to resprouting. Stem mortality in green alder and beaked hazel was 45% and 97%, respectively, two years after the operational glyphosate treatment. Competition index (CI) was low (mean CI = 52, ranging from 18 to 115) in all the plots including the untreated control. There was a significant increase in basal diameter of jack pine in the brushsaw and herbicide-treated plots compared to the control three years after the treatments. Jack pine seedlings in the brushsaw and glyphosate treated plots were taller compared to that of control but differences were not significant. Lower species richness and diversity were recorded in the herbicide-treated plots compared to the brushsaw and control plots in the third growing season following treatment.
article id 540, category Research article
Reliability of foliar analyses of Norway spruce stands in a Nordic gradient. Silva Fennica vol. 36 no. 2 article id 540. https://doi.org/10.14214/sf.540
Norway spruce stands at eleven sites in Finland, Norway and Sweden have been studied under various climates, atmospheric deposition of N and S and fertilisation regimes. Nitrogen was growth restricting at eight inland sites, while P was growth restricting at three coastal sites. Liming and N fertilisation caused serious B deficiency on some of the inland sites. It is likely that liming affects uptake of B, whereas N fertilisation causes a dilution due to increased growth. Application of S combined with N probably caused K deficiency at one of the sites. The reliability of foliar analyses as a method to diagnose nutrient status and the likely changes after nutrient input to spruce forests in the Nordic countries, are discussed. The CR- and the DOP-method are evaluated for diagnostic purposes. Both methods seem to give reliable conclusions even if the CR-method often produces more specific results. Interpretation based on both current and one year old foliage improved the diagnostic prognoses. The accuracy of diagnosis also relies on knowledge and ability of the interpreter. Based on the results it is reason to be cautious about recommendations of single element fertilisations, e.g. with N alone, because the demand of other elements beyond available pools frequently occurs. Forest trees in the boreal region are probably well adapted to N deficiency, which means that they can handle the physiological consequences rather well, while deficiencies of other elements usually are more detrimental to growth vigour and stress related diseases.
article id 539, category Research article
Procedure for managing large-scale progeny test data: a case study of Scots pine in Finland. Silva Fennica vol. 36 no. 2 article id 539. https://doi.org/10.14214/sf.539
Large progeny test networks are typical for conventional forest tree breeding programmes. The individual progeny tests differ with respect to age, composition and ability to screen the breeding values of the parent trees. Several approaches have been introduced to manage the unbalanced and diverse nature of the data generated by progeny tests. This report presents a procedure for ranking breeding material on the basis of ‘messy’ data. Plot means were used as input values and missing plots were estimated from least squares. The differences between test means and variances were standardised by the performance level method. The different precision of the tests was quantified through the reliability coefficient. In order to facilitate the selection of plus trees for different purposes, all the available test results were combined into a single variable that was used for ranking. Three different kinds of ranking variable were calculated and each of them proved to be more useful for the selection of plus trees than an arithmetic or weighted mean. One of them, WMEAN, relied on the reliability and number of the progeny tests, while the others, WCONF0.50 and WCONF0.10, relied on the standard error of the plus tree mean, thus emphasising the precision of the values obtained. The analyses were carried out with SAS® procedures, which require only moderate skills in statistics, programming and data processing technology. The procedure has functioned well throughout an eight-year development phase. Nearly three thousand Scots pine (Pinus sylvestris) plus trees have been ranked for various characters, and the results have been used for roguing the seed orchards, to establish new ones, and to select plus trees for breeding populations.
article id 538, category Research article
The incidence of Gremmeniella abietina in relation to topography in southern Finland. Silva Fennica vol. 36 no. 2 article id 538. https://doi.org/10.14214/sf.538
Field data of the 8th National Forest Inventory (NFI) from southern Finland and digital elevation models (DEMs) were used in this study. Damage due to Gremmeniella abietina increased slightly with an increase in absolute elevation in mineral soils. Severe damage increased almost linearly with an increase in elevation in mineral soil plots. The mean elevation in the tract area (the 7 km x 8 km area surrounding the plot) was more strongly correlated with the disease than the elevation of individual plots. The relative altitude of the plot was important: the disease was most severe in the plots situated lower than the mean elevation of the tract area, especially in the peatland plots. In this group, the damage increased linearly with an increase in absolute elevation. According to detailed DEMs in the most diseased areas, steepness of the slope was negatively correlated with the disease. The aspect of the slope had a weak influence. On mineral soils, the disease was most common in south-facing slopes. The microtopography was not as important for the disease occurrence as the relative elevation of the plot. The disease frequencies were very similarly related to the three most common types of surface features (channels, ridges and planar regions) within the 50-m scale. At the cell size of 100 metres, the disease was more common in channels than in ridges, except in mineral soil plots. Topographic variables only partly explained the regional patterns in the occurrence of this disease. The disease was frequent on upland areas, but, on the other hand, it was also common on lowland areas. The most diseased areas studied in detail differed very much from each other with respect to topography and the disease incidence.
article id 537, category Research article
Crown condition as an indicator of the incidence of root rot caused by Heterobasidion annosum in Scots pine stands. Silva Fennica vol. 36 no. 2 article id 537. https://doi.org/10.14214/sf.537
Trees in three Scots pine stands seriously infected by Heterobasidion annosum were classified according to their crown condition into four classes, from healthy to dead trees. After cutting the stands, the classification was compared with the symptoms of annosum root rot on stump surfaces (pitched area) and with the extension of decay in the roots of excavated stumps. When dead trees were included, the average crown condition on the survey plots correlated with disease incidence. Without dead trees the correlation was not significant. Slightly infected trees could not be distinguished from healthy trees on the basis of crown condition. It was concluded that only the proportion of dead and dying trees in a stand is a reliable indication of the disease incidence for making decisions about the future management.
article id 568, category Research article
Anthropogenic effects on understorey vegetation in Myrtillus type urban forests in southern Finland. Silva Fennica vol. 36 no. 1 article id 568. https://doi.org/10.14214/sf.568
The growth of urban population in Finland has resulted in increased fragmentation of urban forests and consequently increased recreational pressure on these forests. The effects of fragmentation and trampling on the ground and field layer vegetation were studied in mesic Myrtillus type Norway spruce-dominated urban forest stands of varying size in the greater Helsinki area. The number of residents living in the vicinity of the forest stands was an important factor affecting the understorey vegetation in urban forests. The cover of understorey vegetation in urban forests was remarkably lower than in rural areas, especially the ground layer cover, e.g. cover of Pleurozium schreberi, was significantly lower in urban forests than in the reference areas. Thus, the ground layer proved to be most susceptible to trampling. In the field layer, the cover of dwarf shrubs, especially of Vaccinium myrtillus, was lower in deteriorated than in undeteriorated urban forest stands.
article id 567, category Research article
Influence of forest composition on understory cover in boreal mixedwood forests of western Quebec. Silva Fennica vol. 36 no. 1 article id 567. https://doi.org/10.14214/sf.567
Forest overstory composition influences both light and nutrient availability in the mixed boreal forest. The influence of stand composition on understory cover and biomass was investigated on two soil types (clay and till deposits). Four forest composition types were considered in this study: aspen (Populus tremuloides Michx.), paper birch (Betula papyrifera Marsh.), jack pine (Pinus banksiana Lamb.) and a mixture of balsam-fir (Abies balsamea (L.) Mill.) and white spruce (Picea glauca (Moench) Voss). The cover of all understory species was recorded while the biomass of two important and ubiquitous species was measured: mountain maple (Acer spicatum Lam.) of the shrub layer and large-leaved aster (Aster macrophyllus L.) of the herb layer. Soil analyses were conducted to evaluate the influence of overstory composition on understory biomass through its influences on soil characteristics. Analyses of variance showed a significant effect of forest canopy type on mountain maple biomass, understory cover and shrub cover but not on herb cover and large-leaved aster biomass. Path analysis was performed to explore the relationships between canopy type, nutrient availability and understory biomass. Contrary to what was expected, the variation in plant biomass associated with forest composition was weakly related to soil nutrient availability and more strongly related to stand structural attributes.
article id 566, category Research article
Effects of clearcut edges on trees in the sub-boreal spruce zone of Northwest-Central British Columbia. Silva Fennica vol. 36 no. 1 article id 566. https://doi.org/10.14214/sf.566
Clearcut-forest boundaries were evaluated for their effects on mature and regenerating trees in the northern interior of British Columbia, Canada. Two hundred and eighteen rectangular plots measuring 200 m2 each were arrayed in transects across 12 cutblock edges created 9 to 21 years earlier, with the wall of standing timber facing either north or south. The density of canopy trees on the inner edge was found to be reduced by 19% (on north-facing edges) to 46% (on south-facing edges) from average densities found in forest interiors. This reduction was primarily due to windthrow after logging, which was elevated by 27% (over interior background levels) at north-facing edges, and by 216% at south-facing edges. Of the trees situated within 10 m of south-facing cutblock edges, 11% of the Pinus contorta, 18% of the Abies lasiocarpa, and 42% of the Picea engelmannii x glauca trees have apparently collapsed, primarily those having height-to-dbh ratios greater than 71:1. As a result, irradiance in the forest understory was elevated (over interior levels) at south-facing edges to distances of approximately 65 to 70 m into the forest. Increased irradiance from adjacent cutblocks enhanced the understory growth of Picea for approximately 60 m into the inner edge of forests, 75 m for Abies. Mature Pinus trees on south-facing edges showed an unexplained 48% decrease in radial growth compared to average growth rates in forest interiors, an effect that was detectable up to 45 m into the forest. Elevated densities of conifer seedlings were evident for up to approximately 70 m into clearcuts from north-facing forest edges. Seedling growth in clearcuts was largely unaffected by shade from stand edges. Though the extent of edge effects varies considerably with the statistical techniques used to detect them, it appears that opening effects on trees can extend between 40 and 120 m into this forest type, while canopy effects reach shorter distances into clearcuts.
article id 565, category Research article
Silvicultural disturbance severity and plant communities of the southern Canadian boreal forest. Silva Fennica vol. 36 no. 1 article id 565. https://doi.org/10.14214/sf.565
Boreal forest ecosystems are adapted to periodic disturbance, but there is widespread concern that conventional forest practises degrade plant communities. We examined vegetation diversity and composition after clearcut logging, mechanical and chemical site preparation in eight 5- to 12-yr old studies located in southern boreal forests of British Columbia and Quebec, Canada to find useful indicators for monitoring ecosystem integrity and to provide recommendations for the development and testing of new silvicultural approaches. Community-wide and species-specific responses were measured across gradients of disturbance severity and the results were explained in terms of the intermediate disturbance hypothesis and a simple regeneration model based on plant life history strategies. Species richness was 30 to 35% higher 5 to 8 years after clearcut logging than in old forest. Total and vascular species diversity generally peaked on moderately severe site treatments, while non-vascular diversity declined with increasing disturbance severity. On more-or-less mesic sites, there was little evidence of diversity loss within the range of conventional silvicultural disturbances; however, there were important changes in plant community composition. Removing soil organic layers caused a shift from residual and resprouting understory species to ruderal species regenerating from seeds and spores. Severe treatments dramatically increased non-native species invasion. Two important challenges for the proposed natural dynamics-based silviculture will be 1) to find ways of maintaining populations of sensitive non-vascular species and forest mycoheterotrophs, and 2) to create regeneration niches for disturbance-dependent indigenous plants without accelerating non-native species invasion.
article id 564, category Research article
The regeneration niche of white spruce following fire in the mixedwood boreal forest. Silva Fennica vol. 36 no. 1 article id 564. https://doi.org/10.14214/sf.564
Early establishment of white spruce (Picea glauca) in mixedwood boreal forest stands following fire was examined at several times-since-fire (1-, 2-, 4-, 6-, 14-years). Abiotic and biotic conditions in the stands were assessed at two scales, tree plot (5 m x 5 m) and microsite (1 m x 1 m), along with presence, density and height of white spruce seedlings. Germination and survival of seed sown 1- and 4-years post fire were quantified. Survival and growth of nursery-grown seedlings, and mycorrhizal colonization, survival and growth of sterile seedlings, planted 1-year post-fire were assessed. At the tree plot scale, presence of white spruce seedlings 1-year post-fire could be reliably predicted by organic layer depth and distance to and strength of seed source. In contrast, none of the biotic or abiotic factors measured was strongly correlated with occurrence or density of white spruce seedlings 6- and 14- years post-fire. At the microsite scale, seedling recruitment immediately post-fire was limited to a distinct subset of available microsites (greater % cover of downed wood and moss, lower % cover of litter and herbaceous vegetation). Likewise, seedling occurrence in older burns was associated with distinct microsite conditions; although this was more likely an effect of white spruce presence, rather than the cause. Less than 3% of seed sown 1 yr post-fire survived to become 1yr old germinants, survival was 41% over the next three years. Availability of suitable regeneration microsites declines rapidly with time-since-fire; less than 0.3% of seed sown 4 yrs post-fire survived one year. High rates of mycorrhizal colonization were found on white spruce seedlings planted 1-year post-fire, including early and late stage fungal species. Microsite characteristics were only weakly correlated with mycorrhizal fungal communities. We propose that immediate post-fire recruitment of white spruce is a key process in mixedwood boreal succession.
article id 563, category Research article
Spatial ecology of the three-toed woodpecker in managed forest landscapes. Silva Fennica vol. 36 no. 1 article id 563. https://doi.org/10.14214/sf.563
The effects of landscape structure and forestry on the abundance and dynamics of boreal forest bird species have been studied widely, but there are relatively few studies in which the spatial structure and quality of the landscape have been related to the spatial ecology of bird species. In this paper, we present methods to measure territory and landscape quality for the three-toed woodpecker (Picoides tridactylus) and similar territorial forest bird species based on data from the Finnish multi-source national forest inventory and metapopulation theory. The three-toed woodpecker was studied with territory mapping within an area of 340 square km in southern Finland in 1987–2000. Altogether 195 breeding territory sites were observed. The spatial occurrence of the territories was aggregated, and the highest densities were observed in spruce-dominated old-growth forest areas. Both territory and landscape quality had significant consequences for the occurrence of the three-toed woodpecker. The spatial patterning and permanence of breeding and non-breeding territories were influenced by a combination of spatial dynamics of the species and the quality of the landscape, the latter being much influenced by forestry. The landscape-level spatial occurrence of the three-toed woodpecker in the study area may represent source-sink dynamics. The results of this paper suggest the presence of threshold values at different spatial scales, which may determine the occurrence of the three-toed woodpecker and similar species in managed forest landscapes.
article id 562, category Research article
A method for generating stand structures using Gibbs marked point process. Silva Fennica vol. 36 no. 1 article id 562. https://doi.org/10.14214/sf.562
Stand growth modelling based on single tree responses to their surroundings requires a description of the spatial structure of a stand. While such detailed information is rarely available from field measurements, a method to create it from more general stand variables is needed. A marked Gibbs point potential theory combined with Markov chain Monte Carlo (MCMC) random process was used to create a spatial configuration for any given number of trees. The trees are considered as charges rejecting each other and building ‘potential energy’. As an analogue of the potential energy in physical systems, the potential of a stand is defined in terms of size-dependent tree-to-tree interactions that can be thought of as related to resource depletion and competition. The idea that bigger trees induce larger potentials brings 3-dimensional effects into the system. Any feasible spatial structure is a state of the system, and the related potential can be calculated. The probability that a certain state occurs is assumed to be a decreasing function of its potential. Because more regular structures have lower potentials, by adjusting the steepness of the probability distribution the spatial structure can be allowed to have a lot of randomness (naturally regenerated stands) or forced to be very regular (planted stands). The MCMC algorithm is a numerical method of finding stand configurations that correspond to the expected level of the potential, given the size distribution of trees and the shape of the probability density function. The method also allows us to take into account spatial variation in the terrain. Some spots can be defined to have lower basic potential than others (ditch, planting furrow, etc.) in order to create areas of higher than average stocking density. A preliminary test of the method was conducted on two measured stands. The results suggest that the method could provide an efficient and flexible means of mimicking variable stand structures.
article id 561, category Research article
Post-fire development of canopy structure and composition in black spruce forests of Abitibi, Québec: a landscape scale study. Silva Fennica vol. 36 no. 1 article id 561. https://doi.org/10.14214/sf.561
Fire reconstruction and forest inventory maps provided an opportunity to study changes in stand-level characteristics following fire using a data set comprised of all forest stands of fire origin in an area of over 10 000 km2. We assigned the date of the most recent fire occurrence to over 31 000 forest stands in an ecoforestry database. We categorized stands on different substrates into age classes to investigate differences in canopy composition, cover and height, and incidence of secondary disturbance. Stands with over 75% Picea mariana (Mill.) BSP dominated all age classes on organic sites. On other substrates, there was a change in canopy composition from deciduous stands and stands dominated by Pinus banksiana Lamb. to Picea mariana stands after about 100 yr. This transition was later for xeric sites. After a peak in canopy cover and height at about 100 yr, there was a decrease in the area occupied by stands with dense, tall canopies. Structural development was slower on less productive sites. There was little incidence of spruce budworm outbreaks. Partial disturbance by windthrow coincided with canopy break-up at 100 yr, but appeared to have little effect on overall canopy structure in later stages. Structural diversity was independent of compositional diversity; on organic sites, stands with similar composition had different canopy structure. Diversity of stands with different composition and structure was greatest in the first 150 yr following fire. Maintaining stands in different stages of structural development on the landscape would serve to maintain regional biodiversity.
article id 560, category Research article
An approach to predicting the potential forest composition and disturbance regime for a highly modified landscape: a pilot study of Strathdon in the Scottish Highlands. Silva Fennica vol. 36 no. 1 article id 560. https://doi.org/10.14214/sf.560
The existing native forests of Scotland are fragmented and highly modified and none are ‘natural’. There is considerable interest in expanding the area of this oceanic boreal forest and restoring forest habitat networks to benefit biodiversity. However, unlike regions with substantial remaining natural forest, it is difficult to provide reference values for forest composition and structure using methods related to historical variability. An alternative approach is to combine models that predict woodland type from knowledge of site conditions, and disturbance regime from knowledge of the disturbance agents (particularly abiotic agents). The applicability of this approach was examined as part of a public participatory planning exercise in a highly managed landscape in Eastern Scotland. Models of site suitability (Ecological Site Classification) and wind disturbance (ForestGALES) were combined to determine potential woodland composition and structure, and derive options for native woodland expansion. The land use of the upper Strathdon catchment is currently dominated by agriculture and planted forests of non-native species, and only small fragments of semi-natural woodland remain (< 0.5% of the land area). Model results indicated that a very substantial proportion of the land area could support woodland (> 90%) but of a restricted range of native woodland types, with Scots pine communities predominant. Structural types likely to be present included wind-induced krummholz (treeline) forest, forest with frequent stand replacement by wind, and also a large area where gap phase (or some other disturbance) would predominate. The merits of the approach are discussed, together with the difficulties of validation, and the implications for the management of existing forests.
article id 559, category Research article
Forest age distribution under mixed-severity fire regimes – a simulation-based analysis for middle boreal Fennoscandia. Silva Fennica vol. 36 no. 1 article id 559. https://doi.org/10.14214/sf.559
A simulation model was used to study the age structure of unmanaged forest landscapes under different fire regimes. Stand age was defined as the age of the oldest tree cohort in a stand. When most fires are not stand-replacing, the theoretical equilibrium stand age distribution is either bell-shaped or bimodal and dominated by old age-classes. Old-growth forests (oldest cohort > 150 y) dominate the landscape unless fires are both frequent and severe. Simulation results and analytical calculations show that if a regime of frequent fires (about every 50 y) maintains landscapes dominated by old-growth forests, then old-growth dominance persists when the number of fires is decreased, despite the associated increase in fire severity. Simulation results were applied to Pinus sylvestris-dominated landscapes of middle boreal Fennoscandia, which according to empirical results were dominated by old-growth forests when fires were frequent during the 19th century. Since the changes in the fire regime can be plausibly explained by changes in the number of human-caused ignitions, old-growth forests have evidently also dominated the landscapes earlier when fires were less frequent. The simulation model is used to produce plausible age distributions of middle boreal Fennoscandian forest landscapes under different historical fire regimes. In summary, the frequency of large-scale disturbance alone predicts forest landscape dynamics poorly, and the roles played by fire severity and residual stands need to be considered carefully. Maintaining and restoring old-growth structures is essential to regaining the natural variability of Fennoscandian forest landscapes.
article id 558, category Research article
Forest age distribution and traces of past fires in a natural boreal landscape dominated by Picea abies. Silva Fennica vol. 36 no. 1 article id 558. https://doi.org/10.14214/sf.558
Forest age distribution and occurrence of traces of past fires was studied in a natural Picea abies -dominated landscape in the Onega peninsula in north-west Russia. Forest age (maximum tree age) was determined and charcoal and fire scars were searched for in 43 randomly located study plots. In 70% of the study plots (30/43) trees older than 200 years existed. The largest 50-year age class consisted of plots with 251–300 year old forests. Traces of fires were found in all types of study plots, in forests on mineral soil as well as on peatlands. However, fire has been a rare disturbance factor, as traces of fires could not be found in 35% of the study plots (15/43). Estimated from the forest age class distribution, the fire rotation time for the whole area has been at least 300 years, but possibly considerably longer. This fire rotation time is much longer than fire history studies (largely based on examination of fire scars) commonly have reported for the average time between successive fires in Fennoscandia and Northwest Russia. The results suggest that the often stated generalisations about the importance and natural frequency of fire disturbance in boreal forests do not apply in landscapes dominated by Picea abies.
article id 557, category Research article
Spatial tree age structure and fire history in two old-growth forests in eastern Fennoscandia. Silva Fennica vol. 36 no. 1 article id 557. https://doi.org/10.14214/sf.557
Two near natural old-growth forests, one dominated by Picea abies and the other by Pinus sylvestris, were studied for their fire history, and spatial patterns of trees and tree ages. The spatial tree age structure and the disturbance history of the forests were examined by drawing age class maps based on mapped and aged trees and by dating fires based on fire scars, and by using spatial analyses at tree scale. The tree age structures of the Picea and Pinus dominated forests were different, mainly due to differences in fire history and sensitivity of the dominant tree species to fire. Fire histories and tree age structures of both sites have probably been affected by human in the ancient past. However, in the Picea dominated site, the fires had been severe, killing most of the trees, whereas in the Pinus dominated site the severity of fires had been more variable, leaving some Pinus and even Picea trees alive. In the Pinus dominated site, the tree age distribution was multimodal, consisting of two Pinus cohorts, which were established after fires and a later Picea regeneration. The Picea dominated site was composed of four patches of different disturbance history. In the oldest patch, the tree age distribution was unimodal, with no distinct cohorts, while a single cohort that regenerated after severe fire disturbances dominated the three other patches. In both sites the overall spatial patterns of living and dead trees were random and the proportion of spatially autocorrelated variance of tree age was low. This means that trees of different age grew more or less mixed in the forest without forming spatially distinct regeneration patches, even in the oldest patch of Picea dominated Liimatanvaara, well over 200 years after a fire. The results show that detail knowledge of disturbance history is essential for understanding the development of tree age structures and their spatial patterns.
article id 556, category Research article
Tree age distributions in old-growth forest sites in Vienansalo wilderness, eastern Fennoscandia. Silva Fennica vol. 36 no. 1 article id 556. https://doi.org/10.14214/sf.556
The age and size of trees was sampled and measured on eight sample plots (0.2 ha each) within a Pinus sylvestris -dominated boreal forest landscape in Vienansalo wilderness, Russian Karelia. The fire history of these plots was obtained from a previous dendrochronological study. All the studied sample plots showed a wide and uneven distribution of tree ages, but the shape of the age distributions of trees as well as tree species composition varied substantially. Trees over 250 years of age occurred in every studied plot, despite its small size. This suggests that old Pinus were common and rather evenly distributed in the landscape matrix. The oldest Pinus tree was 525 years of age. The correlations between tree age and size were often weak or even nil. In Pinus the correlation between age and diameter was stronger than that between age and height. In the dominant tree species Pinus and Picea, the largest trees were not the oldest trees. The tree age distributions together with the fire history data indicated that the past fires have not been stand replacing, as many of the older Pinus had survived even several fires. Tree age classes that had regenerated after the last fire were most abundant and dominated by Picea and/or deciduous trees, while the trees established before the last fire were almost exclusively Pinus. The results suggest that periodic occurrence of fire is important for the maintenance of the Pinus-dominated landscape. This is because fire kills most Picea and deciduous trees and at the same time enhances conditions for Pinus regeneration, facilitated by available seed from the continuous presence of old fire-tolerant Pinus trees.
article id 555, category Research article
Amount and diversity of coarse woody debris within a boreal forest landscape dominated by Pinus sylvestris in Vienansalo wilderness, eastern Fennoscandia. Silva Fennica vol. 36 no. 1 article id 555. https://doi.org/10.14214/sf.555
The amount, variability, quality and spatial pattern of coarse woody debris (CWD) on mineral soil sites was studied within a natural Pinus sylvestris L. dominated boreal forest landscape in Russian Viena Karelia. Data on the total CWD was collected on 27 sample plots (20 m x 100 m) and data on large CWD was surveyed along four transects (40 m wide and up to 1000 m long). The mean volume of CWD (standing and down combined) was 69.5 m3 ha–1, ranging from 22.2 m3 ha–1 to 158.7 m3 ha–1 from plot to plot. On average, 26.9 m3 ha–1 (39%) of CWD was standing dead wood and 42.7 m3 ha–1 (61%) down dead wood. The CWD displayed a wide range of variation in tree species, tree size, stage of decay, dead tree type and structural characteristics, creating a high diversity of CWD habitats for saproxylic organisms. Large CWD was almost continuously present throughout the landscape and its overall spatial distribution was close to random, although a weak autocorrelation pattern was found at distances less than about 50 m. On small spatial scales total CWD showed wide variation up to a sample area of about 0.1 ha, beyond which the variation stabilized. The fire history variables of the sample plots were not related to the amount of CWD. This and the spatial pattern of CWD suggest that the CWD dynamics in this landscape was not driven by fire, but by more or less random mortality of trees due to autogenic causes of death.
article id 554, category Research article
Tree mortality in a Pinus sylvestris dominated boreal forest landscape in Vienansalo wilderness, eastern Fennoscandia. Silva Fennica vol. 36 no. 1 article id 554. https://doi.org/10.14214/sf.554
Tree mortality and its causes and spatial pattern were examined along four transects (width 40 m, length 2550–3960 m), with a total length of 12 190 m and area of 48.8 ha, in a Pinus sylvestris L. dominated, boreal forest landscape. Tree mortality was determined within a time window of 3 years by identifying those trees (dbh ≥ 10 cm) along the transects that fitted into one of the three categories: 1) current mortality: trees that had died during the year of survey (1998), 2) recent mortality: trees that had died during the year (1997) before the survey year, and 3) predicted mortality: trees that were expected to die during the year (1999) following the survey year. Long-term tree mortality was studied on 10 plots (20 m x 100 m) by dating 87 dead trees using dendrochronological methods. The mean current mortality was 1.4 m3 ha–1 (3.7 trees ha–1). Both the recent and predicted mortalities were also 1.4 m3 ha–1. Mortality was, on the average, higher on peatlands than on mineral soils. The highest mortality was found within an area recently flooded by beavers. Over half of the examined trees (52%) were judged to die without any visible signs of an external abiotic cause. At the landscape scale, tree mortality was continuous although somewhat aggregated in space. Of the 66 dated standing dead Pinus trees, 23 (35%) had died during the 19th century and two during the 18th century, demonstrating that dead Pinus can remain standing for long periods of time before falling. Our results show that autogenic mortality of individual trees or small groups of trees was the predominant mode of disturbance in this Pinus dominated landscape.
Category: Review article
article id 535, category Review article
Adaptive significance of evergreen vs. deciduous leaves: solving the triple paradox. Silva Fennica vol. 36 no. 3 article id 535. https://doi.org/10.14214/sf.535
Patterns in the dominance of evergreen vs. deciduous plants have long interested ecologists, biogeographers, and global modellers. But previous models to account for these patterns have significant weaknesses. Bottom-up, mechanistic models – based on physiology, competition, and natural selection – have often been non-quantitative or restricted to a small range of habitats, and almost all have ignored belowground costs and whole-plant integration. Top-down, ecosystem-based models have succeeded in quantitatively reproducing several patterns, but rely partly on empirically derived constants and thresholds that lack a mechanistic explanation. It is generally recognized that seasonal drought can favor deciduous leaves, and that infertile soils can favor long-lived evergreen leaves. But no model has yet explained three great paradoxes, involving dominance by 1) evergreens in highly seasonal, boreal forests, 2) deciduous larch in many nutrient-poor peatlands, and 3) evergreen leaf-exchangers in nutrient-poor subtropical forests, even though they shed their leaves just as frequently as deciduous species. This paper outlines a generalized optimality model to account for these and other patterns in leaf longevity and phenology, based on maximizing whole-plant carbon gain or height growth, and building on recent advances in our understanding of the quantitative relationships of leaf photosynthesis, nitrogen content, and mass per unit area to leaf life-span. Only a whole-plant approach can explain evergreen dominance under realistic ecological conditions, or account for the boreal paradox, the larch paradox, the leaf-exchanger paradox, and expected shifts in shade tolerance associated with leaf phenology. Poor soils favor evergreens not merely by increasing the costs of nutrient acquisition, but also by depressing the maximum rate of photosynthesis and thus the seasonal contrast in photosynthetic return between leaves adapted to favorable vs. unfavorable conditions. The dominance of evergreens in western North America beyond the coastal zone of mild winters and winter rainfall appears related to the unusually long photosynthetic season for evergreen vs. deciduous plants there. Future models for optimal leaf phenology must incorporate differences between evergreen and deciduous plants in allocation to photosynthetic vs. non-photosynthetic tissue, rooting depth, stem allometry, xylem anatomy, and exposure to herbivores and leaching, and analyze how these differences interact with the photosynthetic rate, transpiration, and nutrient demands of leaves with different life-spans to affect rates of height growth in specific microsites.
article id 546, category Review article
GroupWare and group decision support systems for wood procurement organisation. A review. Silva Fennica vol. 36 no. 2 article id 546. https://doi.org/10.14214/sf.546
Many kinds of decision support systems (DSSs) have been suggested for use of wood procurement organisations, but few meet the real needs of team managers in group decision-making process. Therefore, it has been concluded that the important features of group decision support systems (GDSSs) should be developed for teamwork-based organisations. Electronic meeting systems (EMSs), Computer-aided Visualisations (CAVs) and heuristics as well as other numerical approaches as combined with optimisation seem to be some of the most promising elements of GroupWare, because decisions are made in distributed groups and they deal with human behaviour. Relations between GDSSs and spontaneous decision conferencing (SDC) for modern organisations are also discussed, and suggestions for future research of management approaches are also given.
article id 553, category Review article
Natural fire regime: a guide for sustainable management of the Canadian boreal forest. Silva Fennica vol. 36 no. 1 article id 553. https://doi.org/10.14214/sf.553
The combination of certain features of fire disturbance, notably fire frequency, size and severity, may be used to characterize the disturbance regime in any region of the boreal forest. As some consequences of fire resemble the effects of industrial forest harvesting, conventional forest management is often considered as a disturbance that has effects similar to those of natural disturbances. Although the analogy between forest management and fire disturbance in boreal ecosystems has some merit, it is important to recognise that it also has its limitations. Short fire cycles generally described for boreal ecosystems do not appear to be universal; rather, important spatial and temporal variations have been observed in Canada. These variations in the fire cycle have an important influence on forest composition and structure at the landscape and regional levels. Size and severity of fires also show a large range of variability. In regions where the natural matrix of the boreal forest remains relatively intact, maintenance of this natural variability should be targeted by forest managers concerned with biodiversity conservation. Current forest management tends to reduce this variability: for example, fully regulated, even-aged management will tend to truncate the natural forest age distribution and eliminate over-mature and old-growth forests from the landscape. We suggest that the development of strategic-level forest management planning approaches and silvicultural techniques designed to maintain a spectrum of forest compositions and structures at different scales in the landscape is one avenue to maintain this variability. Although we use the boreal forest of Quebec for our examples, it is possible to apply the approach to those portions of the boreal forest where the fire regime favours the development of even-aged stands in burns.
article id 552, category Review article
Natural variability of forests as a reference for restoring and managing biological diversity in boreal Fennoscandia. Silva Fennica vol. 36 no. 1 article id 552. https://doi.org/10.14214/sf.552
In Fennoscandia, use of the natural forest as a reference for restoration and management of forest biodiversity has been widely accepted. However, limited understanding of the structure and dynamics of the natural forest has hampered the applications of the natural variability approach. This is especially the case in areas, where the natural forests have almost totally vanished. This review was motivated by the idea that despite these difficulties the essential features of the natural forest can be reconstructed based on biological archives, historical documents, research done in adjacent natural areas, and modeling. First, a conceptual framework for analyzing the relationship between forest structure, dynamics and biodiversity is presented. Second, the current understanding of the structure and dynamics of natural forests at different spatiotemporal scales in boreal Fennoscandia is reviewed. Third, the implications of this knowledge, and gaps in knowledge, on research and on practical restoration and management methods aimed at forest biodiversity conservation are discussed. In conclusion, naturally dynamic forest landscapes are complex, multiscaled hierarchical systems. Current forest management methods create disturbance and successional dynamics that are strongly scale-limited when compared with the natural forest. To restore some of the essential characteristics of the natural forest’s multiscale heterogeneity, diversification of silvicultural and harvesting treatments, as guided by natural disturbance dynamics, is needed to produce more variation in disturbance severity, quality, extent, and repeatability.
article id 551, category Review article
Effects of fire on ectomycorrhizal fungi in Fennoscandian boreal forests. Silva Fennica vol. 36 no. 1 article id 551. https://doi.org/10.14214/sf.551
Fire, the primary natural disturbance factor in Fennoscandian boreal forests, is considered to have exerted major selection pressure on most boreal forest organisms. However, recent studies show that few ectomycorrhizal (EM) fungi appear to have evolved post-fire adaptations, no succession of EM fungi following fire is apparent after low intensity fires, and only two EM fungal taxa exclusively fruit at post-fire conditions. In this paper I review the present knowledge of effects of forest fire on EM fungal communities in Fennscandian boreal forests, put into perspective by a comparison from other parts of the world. Characteristically, these boreal forests consist of less than a handful of tree species, e.g. Scots pine and Norway spruce, while the below ground communities of EM fungi is impressively species rich with presently more than 700 known taxa. Commonly, forest fires in Fennoscandia have been of low intensity, with a considerable portion of the trees surviving and the organic humus layer partly escaping combustion. Hence, EM fungi appear to largely have evolved under conditions characterised by a more or less continuous presence of their hosts. In fact, the composition of EM fungi within a forest appear be more variable due to spatial variation than due to wildfire. However, in areas with high intensity burns and high tree mortality, most EM fungi may locally be killed. Thus, the legacy of EM fungi following wildfire depends on the survival of trees, which determine the potential for mycorrhizal growth, and the combustion and heating of the organic soil, which directly correlate to mortality of mycorrhizas. The questions if and to what degree fires may be of significance for yet unidentified spatiotemporal dynamics of EM fungal populations and communities are discussed. Recent experiments indicate a few EM fungi are favoured by high intensity burn conditions whereas others disappear. The consequences of wildfires in temperate conifer forests differ considerably from those in boreal forests. Wildfires in temperate conifer forests are typically high intensity stand-replacing fires that cause a total combustion of organic layers. Subsequently, pre-fire EM fungal communities are largely eradicated and a succession of post-fire EM fungi is initiated.
article id 550, category Review article
The role of moose as a disturbance factor in managed boreal forests. Silva Fennica vol. 36 no. 1 article id 550. https://doi.org/10.14214/sf.550
We review the interactions between moose (Alces alces) and native tree species in Fennoscandia. The Fennoscandian boreal forests have been intensively managed for wood production over decades. Moose population density is also relatively high in these northern forests. Forest management affects habitat characteristics and food resources from regeneration to final harvest, with the most significant effects occurring early in the stand development. The plant-animal interactions found in such a situation may be different from what has been observed in natural boreal forests with low densities of moose (e.g. in North America). The strong focus on Scots pine (Pinus sylvestris) in forest regeneration in conjunction with a homogenisation of the landscape structure by clear-cutting has favoured moose. Forest development is controlled by man from regeneration to final harvest, and in relation to human-induced disturbances the disturbance by moose is relatively small, but occurs on different spatial levels. At the landscape level, the most prominent effects of moose seem to be suppression and/or redistribution of preferred browse species. At the forest stand level moose primarily induce spatial heterogeneity by browsing patchily and exploiting existing gaps. At the tree level, moose damage trees and lower timber quality, but also create substrate types (e.g. dead and dying wood) valuable for many organisms. Co-management of moose and forest requires good monitoring programmes for both plants and animals, as well as extensive ecological knowledge on the relations between moose and their food plants on different spatial levels.
article id 549, category Review article
Natural disturbance dynamics in the boreal forests of European Russia: a review. Silva Fennica vol. 36 no. 1 article id 549. https://doi.org/10.14214/sf.549
In the European part of the Russian boreal zone the dynamics of pristine forests (taiga) has been studied by several generations of researchers. Many studies have examined the patterns and role of fire, windthrow, insect outbreaks and other natural disturbances. An attempt is made to provide a brief review of these studies. The reviewed studies show that lightning strikes were the only natural source of fires in taiga. The frequency of fires varied in various types of pristine landscape from 1–2 per century to 1–2 per millennium. Fires maintained a dynamic equilibrium between compositionally different forest communities or their certain ratio and areal occurrence. Fires favored the regeneration and recovery of pine forests and prevented the replacement of shade-intolerant species (e.g. pine) by shade-tolerant ones (e.g. spruce). Taiga forests generally displayed a mosaic pattern that varied from pioneer plant communities, growing in open burns, to climax communities that were extremely seldom affected by fire. The reviewed studies suggest that fires were a powerful ecological factor in pristine taiga, being largely responsible for the structure and spontaneous dynamics of forest communities. Windfalls were also common in pristine taiga landscapes and they regulated spontaneous dynamics in a gap-mosaic regime, which is most characteristic of spruce forests.
article id 548, category Review article
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
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.
Category: Research note
article id 534, category Research note
Adaptation of the timing of bud burst of Norway spruce to temperate and boreal climates. Silva Fennica vol. 36 no. 3 article id 534. https://doi.org/10.14214/sf.534
The adaptation of the annual cycle of development of boreal and temperate trees to climatic conditions has been seen as a result of stabilizing selection caused by two opposite driving forces of natural selection, i.e. the tolerance of unfavorable conditions during the frost exposed season (survival adaptation) and the effective use of growth resources during the growing season (capacity adaptation). In this study, two theories of the effects of climate on the adaptation of the timing of bud burst of trees were evaluated. This was done with computer simulations by applying a temperature sum model for predicting the timing of bud burst of different Norway spruce genotypes on the basis of air temperature data from various climatic conditions. High geographical variation in the temperature response of bud burst, typical for Norway spruce, was included in the theoretical analyses. The average timing of bud burst and the corresponding risk of occurrence of damaging frost during the susceptible period after bud burst were calculated for each genotype in each climate. Two contrasting theories of the stabilizing selection were evaluated, i.e. the overall adaptedness of each genotype was evaluated either 1) by assuming a fixed threshold for the risk of frost damage, or 2) by assuming a tradeoff between the risk of frost damage and the length of the growing season. The tradeoff assumption produced predictions of between provenance variation in bud burst which correspond more closely with empirical observations available in literature, compared to the fixed threshold assumption.
article id 569, category Research note
Occurrence of fires in the eastern Saariselkä area, north-west Russia. Silva Fennica vol. 36 no. 1 article id 569. https://doi.org/10.14214/sf.569
The occurrence of fires was studied in the eastern Saariselkä area, North-West Russia, by using satellite images and topographical maps. In total, more than 330 burned areas were pinpointed in the study area of 4770 km2. Old burns were concentrated in the eastern part of the study area, but young burns were more common in the west. Sites affected by fires in the more recent past were much smaller than those burnt over earlier. The abundance of burns along rivers and the border surveillance road provided evidence of human impact. The most significant changes in the landscape were found in the eastern part of the study area, where spruce forests had been replaced by birch woodlands.
Category: Discussion article
article id 527, category Discussion article
Socioecological landscape planning: an approach to multi-functional forest management. Silva Fennica vol. 36 no. 4 article id 527. https://doi.org/10.14214/sf.527
article id 536, category Discussion article
Fit, fitter, fittest; where does optimisation fit in? Silva Fennica vol. 36 no. 3 article id 536. https://doi.org/10.14214/sf.536
article id 573, category Discussion article
Boreal carabid beetles (Coleoptera, Carabidae) in managed spruce forests – a summary of Finnish case studies. Silva Fennica vol. 36 no. 1 article id 573. https://doi.org/10.14214/sf.573
article id 572, category Discussion article
Principles of ecological restoration of boreal forested ecosystems: Finland as an example. Silva Fennica vol. 36 no. 1 article id 572. https://doi.org/10.14214/sf.572
article id 571, category Discussion article
Using nature’s template to best advantage in the Canadian boreal forest. Silva Fennica vol. 36 no. 1 article id 571. https://doi.org/10.14214/sf.571
article id 570, category Discussion article
Scale, the dynamic stability of forest ecosystems, and the persistence of biodiversity. Silva Fennica vol. 36 no. 1 article id 570. https://doi.org/10.14214/sf.570