Inventory and modelling for forests in transition from even-aged to uneven-aged management

In plantation forestry, as well as in forests managed according to the single tree selection system (Plenter forest), there are well established methods available to control sustainable management in terms of timber resources. If a shift from even-aged to uneven-aged management is intended, there is usually a lack of a clear, numerically defined aim. Then individual tree growth models help to (i) check if certain aims can be achieved at all and (ii) to define these aims more clearly and numerically, e.g. in terms of structural indices. Regular inventories, based on permanent sample plots, help to determine deviations from these aims. As a feedback of these results, management may be changed or aims may be adjusted. Two forest management districts in Austria were investigated. In one of them, continuous cover forestry was intended where, as soon as regeneration has reached a certain height, the upper layer was removed. In the other case, individual tree harvesting has been performed for 30 years, and a single tree selection system is intended. In both cases, permanent inventories based on angle-count sampling have been installed and re-measured at least once after 10 years. Using the individual tree simulator PrognAus it is shown, that the intended management strategy for the single tree selection system leads to an equilibrium of harvests and growth after about 80 years, accompanied by the intended high structural diversity of the stands, while species diversity and between-stand variation cannot be enhanced by much. In the natural regeneration system without single tree selection, species diversity, structural diversity and between-stand variation is enhanced, but during the 100 years simulated no equilibrium between harvests can be reached. Periods where there is a lack of large timber to be harvested occur regularly. From these examples it is concluded that inventories with permanent sample plots, together with individual tree growth simulators are appropriate tools to evaluate forest management changes.     

Spatial patterns in mixed coniferous even-aged,uneven-aged and conversion stands

Different methodological approaches from the field of spatial statistics, the index of cluster size (ICS) and quadrat methods such as the two-term and three-term local quadrat variance (TTLQV and 3TLQV) and the new local variance (NLV) were tested to find a simple spatial measure to classify mixed coniferous uneven-aged, even-aged and conversion stands in the central Black Forest area of Germany. Altogether six stands were analysed with regularly distributed sample plots of 0.25 ha (50×50 m), each subdivided into 25 quadrats of 10×10 m. In each of the quadrats, diameter at breast height (dbh) for trees of the overstory (dbh>7 cm) was assessed and classified into three diameter classes. Height measurements were used to develop specific stand height curves for each stand and to calculate the standing volume per tree and per quadrat. The even-aged stands showed a regular distribution of the standing volume, while the conversion and uneven-aged stands were more clustered. This was detected using ICS, which proved to be a simple but very efficient measure for stand structure. The ICS also showed a highly random distribution of small and medium trees and a regular distribution of large trees of the overstory in the uneven-aged stand. Large and medium trees of one even-aged stand were also regularly distributed while conversion stands showed a regular, random or slightly clustered distribution of these trees. The more uneven the ages in the stands were, the larger were the phases detected by the NLV. The findings of the ICS were generally supported by the TTLQV and 3TLQV. The more uneven the ages in a stand were, the less clustered were the trees of different sizes of the understory. Clustering also decreased with increasing height of understory trees. The patterns detected in the investigated stands were related to the effect of different management regimes. Implications for the management of conversions stands based on the findings of the study are given.     

Effects of even-aged and uneven-aged timber management on dung beetle community attributes in a Missouri Ozark forest

The goal of this study was to estimate the effects of even-aged, uneven-aged and no-harvest forest management on dung beetle community attributes at both landscape and local (either closed or open canopy within treatments) scales. We collected a total 2579 individuals of Scarabaeoidea with 72 baited pitfall traps in the Missouri Ozark Forest Ecosystem Project throughout the summer of 2003. Six species accounted for 81% of all individuals collected, with community composition changing over the summer. At the landscape scale, the effects of treatments on overall abundance and abundance of individual species varied geographically, with forest thinning reducing abundance compared to clear-cutting forest stands and no harvest but in only one of the three blocks. The effects were also dung beetle species-specific, as there were unique responses of abundances of individual beetle species to the treatments. Five species (Ateuchus histeroides, Deltochilum gibbosum, Onthophagus pennsylvanicus, O. taurus, and O. tuberculifrons) were affected by forest thinning. In contrast, at the local scale, canopy opening (through timber harvesting and natural tree falls) increased expected (rarefied) species richness. Ordination showed that community composition was uniquely different among the six harvest treatments by canopy openness combinations. Together these results demonstrate that timber extraction from a temperate forest ecosystem influenced community composition of dung beetles at the landscape level, but this impact varied with cutting treatment, geographically, and by dung beetle species.     

Productivity and optimal management of the uneven-aged hardwood forests of Hyrcania

Hyrcania is a productive region near the southern coast of Caspian Sea. Her forests are mostly uneven-aged beach-dominated hardwood mixtures. There is increasing willingness to treat these forests without clear-felling, following the ideas of continuous cover management. However, lack of growth and yield models have delayed this endeavor, and no instructions for uneven-aged management have been issued so far. This study developed a set of models that enable the simulation of stand development in alternative management schedules. The models were used to optimize stand structure and the way in which various initial stands should be converted to the optimal uneven-aged structure. The model set consists of individual-tree diameter increment model, individual-tree height model, survival model, and a model for ingrowth. The models indicate that the sustainable yield of the forests ranges from 2.2 to 7 m³ ha^?1 a^?1 in uneven-aged management, depending on species composition. Better ingrowth would substantially enhance productivity. The optimal stand structure for maximum sustained yield has a wide descending diameter distribution, the largest trees of the post-cutting stand being 80–100 cm in dbh. If cuttings are conducted at 30- or 40-year intervals, they should remove 20–40 largest trees per hectare. Despite moderate growth rate, uneven-aged management produces high incomes, 850–1,000 UDS ha^?1a^?1, because the timber assortments that are obtained from the removed large trees have very high selling prices. Optimal conversion to uneven-aged structure showed that the steady-state stand structure depends on initial stand condition and discount rate when the length of the conversion period is fixed. Discount rates higher than 1 % lead to reduced wood production, heavy cuttings, and low basal areas of the steady-state forest.     

A transition matrix growth model for uneven-aged mixed-species forests in the Changbai Mountains,northeastern China

A transition matrix growth and an ingrowth model were developed and applied to an uneven-aged mixed-species forest in the Changbai Mountains, northeastern of China. Results indicate that the constant-parameter transition probabilities for all species in the mixed uneven-aged forest could be classified into three groups based on the mean upgrowth probabilities of each species. Constant-parameter transition probabilities of all species in each diameter class fluctuate within a narrow range except for diameter classes below 8 cm and greater than 60 cm. Variable-parameter transition probabilities were found to be a function of residual basal area for small diameter classes. For large trees, transition probabilities are not affected by the residual basal area. Based on this study, variable-parameter transition probabilities for large diameter trees can be replaced with constant-parameter transition probabilities. In addition, a new ingrowth model was developed and the new ingrowth model was shown to perform better than existing ingrowth model used in the region.     

Tree diameter, height and stocking in even-aged forests

? Empirical observations suggest that in pure even-aged forests, the mean diameter of forest trees (D, diameter at breast height, 1.3 m above ground) tends to remain a constant proportion of stand height (H, average height of the largest trees in a stand) divided by the logarithm of stand density (N, number of trees per hectare): D = β(H ? 1.3)/ ln(N).

? Thinning causes a relatively small and temporary change in the slope β, the magnitude and duration of which depends on the nature of the thinning.

? This relationship may provide a robust predictor of growth in situations where scarce data and resources preclude more sophisticated modelling approaches.

     

Dynamics of seedling establishment and survival in uneven-aged boreal forests

The aim of this study was to describe the dynamics of seedling establishment and development in spruce-dominated uneven-aged boreal forests. The study was based on empirical data from 15 stands with permanent plots, which had been intensively monitored for 10 years in southern Finland. All trees (height > 1.3 m) were measured every fifth year. Regeneration was measured on 64 permanent sample plots (4 m²) in each stand. The establishment of first-year seedlings was analysed on a yearly basis. The survival and development of older Norway spruce (Picea abies (L.) H. Karst.) seedlings were analysed based on observations made every five years. The establishment of spruce seedlings was closely correlated with the abundance of seed crops. Seedling cohorts originating from abundant seed crops were clearly detectable in the development of seedling height distributions over time. It took about 15 years for spruce seedlings to reach a height level of 15-30 cm. Local basal area had hardly any effect on the emergence or survival of small spruce seedlings, while the number of higher spruce seedlings decreased with increasing local basal area.     

异龄林经营决策优化

从林分密度、树种组成、林分直径分布、转换决策 (包括择伐周期与转换期长度 )等方面对异龄林经营决策优化进行了研究。     

Modelling coarse woody debris dynamics in even-aged Scots pine forests

Coarse woody debris (CWD) has become an important component in the study of forest ecosystems, being a key factor in the nutrient cycle as well as a habitat for many species. CWD dynamics varies greatly from primeval to managed forests. To assess the CWD dynamics, a chronosequence trial was established in two Scots pine forests in the Central mountain range in Spain. Although, the shelterwood system has been applied in both forests, one has received more intensive silviculture, whereas in the other, regeneration has been much more gradual and the thinning regime has not been so intensive. In order to inventory CWD, five decay classes and four categories according to size and CWD type (stumps and fallen logs or branches) were defined. The volume of branches and logs (estimated from length and mean diameter) and the number of stumps by size class and decay class are used to characterise the CWD. The most notable differences between the two silvicultural systems can be appreciated in the graph as peaks for temporary distribution of larger logs and stumps when intensive silviculture is applied. The CWD observed in the forests studied is mainly produced by logging. The maximum volume of logs and branches above 5 cm in diameter is 43.25 m³/ha after regeneration felling in the first forest, whereas in the other, a maximum of 16.30 m³/ha is reached at 60 years, just after thinning. Large stumps (diameter equal or greater than 30 cm) make up an important part of CWD biomass in these forests just after the regeneration felling. A model was developed to predict the changes in CWD quantity and quality distribution over time as well as predicting the effect of different silviculture options on CWD dynamics. The model integrates two different processes: the CWD inputs (which may be continuous or instant), and the decay process, modelled through a Richards–Chapman function. The average lifetime of CWD obtained ranges from 30 years for stumps over 30 cm in diameter to 8 years for logs with a diameter less than 10 cm.     

Transformation of even-aged European beech (Fagus sylvatica L.) to uneven-aged management under changing growth conditions caused by climate change

Transformation from even-aged to uneven-aged forest management is currently taking place throughout Europe. Climate change is, however, expected to change growth conditions—possibly quite radically. Using a deterministic approach, it was the objective of this study to investigate the influence of such changes on optimal transformation strategies for an even-aged stand of European Beech in Denmark. For a range of growth change scenarios, represented by changes in site index, optimal harvest policies were determined using a matrix modelling approach and a differential evolution algorithm. Transition probabilities were updated continuously based on stand level variables and the transition matrix was thus dynamic. With optimal transformation policies, stand development followed similar pathways during the transformation phase irrespective of climate change scenario. Optimal transformation policies were thus robust, suggesting that a good policy would work well under different outcomes of climate change, i.e., acting under erroneous assumptions about change would not lead to major economic loss. For the chosen case stand, the net present value (NPV) of the transformation phase (first 100 years) contributed 80–90 % of the total expectation value at a 2 % discount rate. To assess the robustness of the optimisation procedure and understand the nature of the response surface, 100 replications per scenario were carried out. Variation between replications peaked during the later stages of the transformation phase indicating several pathways for transformation, which were characterised by almost identical levels of profitability.     

Spatial distribution of regeneration in West-Carpathian uneven-aged silver fir forests

The objective of our study was to examine whether distribution of regeneration in uneven-aged fir (Abies alba Mill.) forests is related to the spatial pattern of trees. In 12 sample plots of size 0.45–1.00 ha (in total 8.65 ha, with stand basal areas ranging from 27.6 m² ha^–1 to 39.5 m² ha^–1), all live and dead trees above 5 cm in d_1.3 were mapped and their diameters measured. In eight plots, all live and dead fir saplings were mapped. In three plots, the number of live fir saplings and seedlings was registered on small systematically distributed circular plots. The values of an analytically developed index of stand influence were compared in patches occupied and unoccupied by live or dead fir regeneration. Contrary to preliminary assumptions, only in a few cases did saplings and trees 5–15 cm in d_1.3 appear more often in gaps and looser stand patches. Rather, in many plots, the opposite tendency was observed. The seedling density showed a weak but positive correlation with the index of influence. If the spatial pattern of regeneration reflects the spatially varying mortality of juvenile trees, then no evidence was found that stand competition was the most important factor inducing this mortality. On the contrary, on the basis of the results obtained, we can presume that the survival rate of juvenile firs was higher in patches with a relatively higher local basal area. Thus, it was hypothesised that, first, dispersion of regeneration in uneven-aged fir forests is controlled by easy-to-change edaphic factors such as humus form and acidity of the upper soil horizons, and second, that these soil features are linked with the spatial pattern of trees.     

Tree size distribution and abundance explain structural complexity differentially within stands of even-aged and uneven-aged structure types

Characterizations of physical structural complexity are an important surrogate for the potential of forested stands to provide desired ecosystem services such as biodiversity. Distinguishing between stands with different structural conditions is not only a necessary feature of useful structural metrics and indices, but how such measures vary among stands can reveal clues to the ecological processes driving structure. We used stand inventory metrics and indices of structural complexity to differentiate between even-aged and uneven-aged structure types using 10 stem-mapped coniferous stands of each type distributed across Switzerland. Within each structure type, we further explored relationships among stand inventory metrics and structural indices over a roughly 10-year period of management intervention. The even-aged and uneven-aged structure types were clearly differentiated using both stand inventory metrics and spatially explicit structural complexity indices. Overall, structural complexity within even-aged stands was strongly related to, and best predicted by, metrics including the distribution of basal area among canopy layers, while complexity in the uneven-aged stands was most strongly related to, and best predicted by, metrics including measures of abundance. Although predictive models could be developed for canopy position mixture, diameter differentiation, and small-scale structural complexity (but not spatial aggregation) using only stand inventory metrics, the prediction success after only a single management intervention was lower than expected. These results indicate that research to explore small-scale structural complexity requires detailed spatially explicit inventory data and that management to enhance structural complexity may require the manipulation of different attributes in stands of even-aged (diameter distribution) and uneven-aged (total abundance) structure types.     

Stand development after different thinnings in two uneven-aged Picea abies forests in Sweden

Two field experiments, located in Central and Northern Sweden, were used to study the influence of standing volume on volume increment and ingrowth in uneven-aged Norway spruce (Picea abies (L.) Karst.) stands subjected to different thinnings. Each experiment had a 3 × 2 factorial block design with two replications. Treatments were thinning grade, removing about 45, 65, and 85% of pre-thinning basal area, and thinning type, removing the larger or the smaller trees, respectively. Each site also had two untreated control plots. Plot size was 0.25 ha. Volume increment was 0.5–6.8 m³ ha⁻¹ year⁻¹ for the plots, and significantly positively (p < 0.01) correlated with standing volume. Within treatment pairs, plots thinned from Above had consistently higher volume increment than plots thinned from Below. Ingrowth ranged from 3 to 33 stems ha⁻¹ year⁻¹, with an average of 14 and 21 stems ha⁻¹ year⁻¹ at the northern and southern site, respectively. At the southern site ingrowth was significantly negatively (p < 0.01) correlated with standing volume, but not at the northern site. Mean annual mortality after thinning was 2 and 7 stems ha⁻¹ year⁻¹at the northern and southern site, respectively.     

东北林区天然林可持续经营

天然林可持续经营是现代世界林业发展的一个重要的研究课题。文章分析了东北林区可持续经营存在的问题,提出了天然林可持续经营技术。