Spatial structure of genetic variation within populations of forest trees

The spatial pattern and structure of genetic variation are important aspects of the population genetics of forest stands. Combined with limits to seed and pollen dispersal, spatial structure affects the level of inbreeding and the action of natural selection. The genetic constitution of stand regeneration, following different forestry practices, is also influenced by spatial structure. For example, natural regeneration with seed trees involves sampling seed trees from a stand that may be genetically nonhomogeneous. This paper reviews theoretical and empirical results on spatial patterns of genetic variation, produced under limited gene flow and selection, in terms of recently developed spatial statistics (e.g., spatial autocorrelation). Genetic correlations in samples from spatially structured populations are also described, as well as how spatial samples can be used to characterize the structure of genetic variation, and how inferences can be made about (spatially distributed) components of fitness and yield.     

Response of fungal and plant communities to management-induced overstorey changes in montane forests of the Western Carpathians

The effect of forest management on biodiversity is a crucial issue for sustainable forestry and nature conservation. However, the ways in which management affects macrofungal and plant communities and diversity of mountain temperate forests still remain poorly understood. We performed a random sampling stratified by stand age and stand type on the sites of temperate montane fir–beech forests. Diversity of macrofungi and the vascular plant understorey in beech- and spruce-dominated managed stands was investigated and compared to primeval forests located in the Po?ana Biosphere Reserve, Western Carpathians. Both the vascular plant and the macrofungal communities were altered by management, and the response of the macrofungal species (especially wood-inhabiting fungi) was more pronounced in terms of species composition change. Species turnover evaluation seems to be an important tool of forest natural status assessment, because alpha diversity did not change as much as species composition. Certain species of Carpathian primeval forests were confirmed as good indicators for natural forest change; others were proposed. Species pool and mean number of species per plot were the highest in unmanaged fir–beech forests, and species diversity significantly decreased in spruce plantations. The number of species decreased significantly due to the change of canopy tree species composition only in the macrofungal communities. As an outcome for forest management, we recommend keeping mixed forests involving all natural tree species and providing at least a minimal amount of dead wood necessary for wood-inhabiting organisms and leaving some area of unmanaged natural forests within complexes of managed stands.     

Spatial patterns and genetic structures within beech populations (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.) of forked and non-forked individuals

Analyses of distribution patterns and genetic structures of forest stands can address distinct family structures and provide insights into the association of genetic and phenotypic variation patterns. In this study, point pattern analysis and spatial autocorrelation were used to examine the spatial and genetic structures in two naturally generated beech stands, which differ in age, trunk morphology, and stand management. Significant tree clumping was observed at distances up to 20 m in the young forest stand, whereas dispersion at distances under 10 m was observed in the old stand. The spatial analysis based on Ripley’s k function of the two different groups of trees showed that the non-forked trees match in both stands the spatial pattern of all trees while the forked were randomly distributed. Additionally, according to the bivariate analysis, forked trees in both stands were randomly distributed as related to non-forked tree positions. Finally, Moran’s I values were not very high, though significant genetic autocorrelation was identified at distances up to 20 m in the young stand, suggesting the existence of distinct family structures. However, no significant genetic structuring was observed in the old stand. Our findings suggest that spatial genetic patterns are impacted by stand age, environmental factors and human activities. The spatial distribution of forked trees was not clearly associated to family structures. Random effects and also micro-environmental variation could be additional factors explaining forking of beech individuals.     

Impact of silviculture on dead wood and on the distribution and frequency of tree microhabitats in montane beech-fir forests of the Pyrenees

In forest ecosystems, the level of biodiversity is strongly linked to dead wood and tree microhabitats. To evaluate the influence of current forest management on the availability of dead wood and on the abundance and distribution of microhabitats, we studied the volume and diversity of dead wood objects and the distribution and frequency of cavities, dendrothelms, cracks, bark losses and sporophores of saproxylic fungi in montane beech-fir stands. We compared stands unmanaged for 50 or 100 years with continuously managed stands. A total of 1,204 live trees and 460 dead wood objects were observed. Total dead wood volume, snag volume and microhabitat diversity were lower in the managed stands, but the total number of microhabitats per ha was not significantly different between managed and unmanaged stands. Cavities were always the most frequent microhabitat and cracks the least frequent. Dendrothelm and bark loss were favored by management. Beech (Fagus sylvatica) carried many more microhabitats than silver fir (Abies alba), especially cavities, dendrothelms and bark losses. Fir very scarcely formed dendrothelms. Secondary tree species played an important role by providing cracks and bark losses. The proportion of microhabitat-bearing trees increased dramatically above circumference thresholds of 225 cm for beech and 215 cm for fir. Firs with a circumference of less than 135 cm did not carry microhabitats. In order to conserve microhabitat-providing trees and to increase the volume of dead wood in managed stands, we recommend conserving trees that finish their natural cycle over 10–20% of the surface area.     

Changes in biodiversity indicators in managed and unmanaged forests in NE Spain

Major changes in Mediterranean forests have occurred in recent decades, mainly as a result of the abandonment of traditional activities and population decline in rural areas. In this study, we analyzed the short-term (11-year) evolution of forests in the region of Catalonia (NE Spain) and the role of management, by comparing seven biodiversity indicators estimated from 7,664 plots from the Second and Third Spanish National Forest Inventory. We evaluated the changes in unmanaged and managed stands with different silvicultural treatments, and considered the effect of stand density and land ownership on these dynamics. We found a general naturalization and maturation of forests and an increase in all of the biodiversity indicators investigated during the study period, with the increments being greater in unmanaged than in managed plots. Some types of silvicultural treatments, such as selection cutting or thinning, were shown to be compatible with an increase in the analyzed indicators, and thus were more adequate for a multifunctional management that considers forest production together with the maintenance or improvement of the diversity of forest communities. The increases in shrub species richness and in the number of large-diameter trees after silvicultural treatments were more prominent in dense stands. Private lands presented greater short-term increases than public forests in all biodiversity indicators, except for large-diameter trees. From these results, we concluded that the application of silvicultural treatments can be a key tool to shape and maintain diverse and healthy forest structures in the context of socioeconomic and environmental changes in the Mediterranean region, which may induce potentially excessive densification and homogenization of some forest stands and landscapes.     

The relationship between shelterwood cuts and crown thinnings and the abundance and distribution of birds in a southern New England forest

Forest regeneration methods such as shelterwood treatments have been shown to substantially increase the diversity of bird species, specifically of species that prefer early seral forests, now rare in the eastern United States. Stand improvement techniques such as thinnings have also been found to increase avian diversity under some conditions. A sustainably managed forest, however, must simultaneously apply regenerative harvesting with stand improvements, and the effect of such treatment combinations on bird community composition is not clear. We compared bird distribution and abundance on shelterwood cuts, crown thinnings, and unmanaged stands at the Yale Myers Forest, a large privately owned and actively managed forest in southern New England. Bird abundance and species diversity was highest in shelterwood cuts and lowest in unmanaged forest, with thinnings being intermediary. Different suites of species inhabited the three treatments, with 18 of 49 common species differing significantly in their abundances between treatments. Characteristics of the vegetation that were directly influenced by silvicultural intervention, including canopy openness, seedling regeneration and vertical structural diversity, appeared to be the dominant drivers of bird abundance. The abundances of some species or groups of species were correlated with the number of trees retained in the implementation of the forestry practices. In conjunction with the conservation of a variety of mature forest habitats, regenerative cuts and stand improvement techniques can be used together to sustain a diverse assemblage of bird species.     

Forest structure and C stocks in natural Fagus sylvatica forest in southern Europe: The effects of past management

Managed forests often differ substantially from undisturbed forests in terms of tree structure and diversity. By altering the forest structure, management may affect the C stored in biomass and soil. A survey of 58 natural stands located in the south-westernmost limit of European beech forests was carried out to assess how the C pools are affected by the changes in tree structural diversity resulting from past management. The mean tree density, basal area and the number of large trees found in unmanaged forests were similar to those corresponding to virgin beech forests in Central Europe, whereas large live trees were totally absent from partially cut stands. Analysis of the Evenness index and the Gini coefficient indicated high structural diversity in the three stand types. The results of the Kolmogorov–Smirnov test used to compare the diameter distributions of each group revealed significant differences between stand types in terms of distributions of total tree species and of Fagus sylvatica.

The mean C stocks in the whole ecosystem – trees, litter layer and mineral soil – ranged from 220 to 770 Mg ha⁻¹ (average 380 Mg ha⁻¹). Tree biomass (above and belowground), which averaged 293 Mg C ha⁻¹, constituted the main C pool of the system (50–97%). The statistical test (Kolmogorov–Smirnov) revealed differences in the distribution of C pools in tree biomass between unmanaged and partially cut stands. As a consequence of the presence of large trees, in some unmanaged stands the C stock in tree biomass was as high as 500–600 Mg C ha⁻¹. In the partially cut stands, most of the C was mainly accumulated in trees smaller than 20 cm dbh, whereas in unmanaged stands the 30% of tree C pool was found in trees larger than 50 cm dbh. Furthermore, many unmanaged stands showed a larger C pool in the litter layer. The C content of mineral soils ranged from 40 to 260 Mg C ha⁻¹ and it was especially high in umbrisols. In conclusion, the implementation of protective measures in these fragile ecosystems may help to maintain the highly heterogeneous tree structure and enhance the role of both soils and trees as long-term C sinks.     

Storm legacies shaping post-windthrow forest regeneration: learnings from spatial indices in unmanaged Norway spruce stands

The anticipated increase in extreme disturbance events due to climate change is likely to expose Norway spruce (Picea abies (L.) Karst.) dominated forests in northern Europe to new conditions. Empirical data on the resilience of such natural (unmanaged) forests to disturbance and the long-term patterns of regeneration in its aftermath are currently scarce. We performed a quantitative assessment of natural forest stands in north–western Latvia to identify and characterise the patterns of stand structure 44 years after a stand-replacing disturbance and investigated the effects of legacies on regeneration. The spatial distribution of tree species and their dimensions were assessed in 71 circular sample plots (500 m² each) in natural forest areas, where Norway spruce dominated prior to the windthrow and salvage logging was not carried out. Spatial indices (species mingling index, size differentiation index, and aggregation index) were used to characterise stand structure and diversity. The different initial states (age and coverage of surviving trees) of stands affected eventual tree species dominance, size differentiation, degree of mingling and aggregation. Our results demonstrate a close relationship between disturbance legacies and spatial indices. The pre-storm understory and canopy survivors decreased species mingling, whereas survivors increased size differentiation. The size differentiation increased also with a higher degree of species mingling. Leaving differential post-storm legacies untouched promotes a higher structural and species diversity and therefore supports the management approach of preserving canopy survivors.

     

Plant β-diversity in human-altered forest ecosystems: the importance of the structural,spatial, and topographical characteristics of stands in patterning plant species assemblages

An understanding of spatial patterns of plant species diversity and the factors that drive those patterns is critical for the development of appropriate biodiversity management in forest ecosystems. We studied the spatial organization of plant species in human-modified and managed oak forests (primarily, Quercus faginea) in the Central Pre-Pyrenees, Spain. To test whether plant community assemblages varied non-randomly across the spatial scales, we used multiplicative diversity partitioning based on a nested hierarchical design of three increasingly coarser spatial scales (transect, stand, region). To quantify the importance of the structural, spatial, and topographical characteristics of stands in patterning plant species assemblages and identify the determinants of plant diversity patterns, we used canonical ordination. We observed a high contribution of β-diversity to total γ-diversity and found β-diversity to be higher and α-diversity to be lower than expected by random distributions of individuals at different spatial scales. Results, however, partly depended on the weighting of rare and abundant species. Variables expressing the historical management intensities of the stand such as mean stand age, the abundance of the dominant tree species (Q. faginea), age structure of the stand, and stand size were the main factors that explained the compositional variation in plant communities. The results indicate that (1) the structural, spatial, and topographical characteristics of the forest stands have the greatest effect on diversity patterns, (2) forests in landscapes that have different land use histories are environmentally heterogeneous and, therefore, can experience high levels of compositional differentiation, even at local scales (e.g., within the same stand). Maintaining habitat heterogeneity at multiple spatial scales should be considered in the development of management plans for enhancing plant diversity and related functions in human-altered forests.     

On the structural and species diversity effects of bark beetle disturbance in forests during initial and advanced early-seral stages at different scales

Following disturbances, early-seral stages of forests provide a variety of structures. Whether this variety is a short-term phenomenon or influences forest succession for several decades or even longer is not known. We tested the hypotheses that after spruce dieback caused by bark beetles, a high spatial heterogeneity of stand structures will persist within stands and among stands even in advanced early-seral stages and that species taxonomical and functional diversity measures will reflect this heterogeneity. We used a chronosequence of unmanaged forests in the Berchtesgaden National Park (Germany) consisting of mature undisturbed spruce stands (control), stands belonging to an initial early-seral stage (~3 years after disturbance) and stands in an advanced early-seral stage (~20 years after disturbance). We analysed diversity and heterogeneity of these forest stands including stand structure, species density, species composition and functional–phylogenetic diversity of vascular plants, wood-inhabiting fungi and saproxylic beetles within plots, among plots of the same successional stage and among stages. Stands of the advanced early-seral stage were characterized by a high spatial heterogeneity of structural attributes, such as crown cover, regeneration density and spatial distribution of trees. Among-plot taxonomic beta diversity was highest in the advanced early-seral stage for beetles, but lowest for fungi, while beta diversity of plants among plots remained unchanged during succession. The mosaic of successional stages initiated by bark beetles increased the gamma diversity of the study area, especially for fungi and beetles. Our findings support the hypothesis that structural heterogeneity continues for at least two decades at stand and landscape scales and that species turnover among successional stages is a major mechanism for gamma diversity in forests after bark beetle disturbance.     

Assemblages and species diversity of wood destroying termites in different land use systems in Western Ghat, India

Spatial distribution, abundance and assemblage of termites depend mainly on the local conditions and habitats in which they thrive. Striking differences are observed in the species richness, number of clades and functional diversity of termite assemblage between different habitats. This study aim was to examine effect of human interference in the diversity of wood destroying termite in forest areas as well as managed and unmanaged plantations in South India. Termites attacking trees and wooden logs were collected from forest areas, managed plantations and unmanaged plantations. The termites collected were identified and compared for species abundance, richness and species diversity. Results show that the species composition and species diversity of the wood destroying termites vary according to the conditions. The species diversity measures revealed that there is a significance variation among the forest fauna and plantations. The forest areas have the highest species composition compared to plantations. Species richness is high forest areas. Even though the abundance of termites are more in unmanaged plantations, there is no significant difference related to species diversity among the managed and unmanaged plantations.     

Stand specific occurrence of coarse woody debris in a managed boreal forest landscape in central Sweden

Forests long subjected to management for timber production contain only a fraction of the volumes of coarse woody debris (CWD) found in pristine forests. This is a threat to many organisms that depend on CWD. Forest management practices have been altered to achieve an increase in the amounts of CWD. Few studies have attempted to analyze the occurrence of CWD at the landscape level. We studied the occurrence of CWD in stands of different ages and management background in a boreal forest landscape in central Sweden. Volume of CWD in unmanaged stands (nature reserves and set-asides) was twice that in managed stands. The composition of CWD was influenced by stand age and management regime. Standing CWD was more common in unmanaged stands than in managed stands. Pine CWD was particularly prevalent in young forest stands (8–59 years of age). Bark-covered CWD was most common on deciduous and spruce wood and uncommon on pine. Bark area in young forest stands was almost 10 times lower than that in other managed stands. Using the age distribution of stands, we estimated the volume and bark area of CWD in the landscape. Recent clear-cuts harvested in accordance with new management guidelines contained more early decay CWD per ha than old managed stands. Young forests covered over half the landscape and had significantly lower volumes of spruce and deciduous CWD compared with other stands. The consequences of these results for biodiversity-oriented forest management are discussed.     

Tolerance of broadleaved tree and shrub seedlings to preemergence herbicides

Isoenzymes were used to study the genetic variation of 121 mature trees of Sorbus torminalis in a natural stand and a subset of 21 high yielding seed trees in the same stand used for a commercial harvest. Eight enzyme systems were studied. The genetic variation of the mature stand was higher than that of other stands reported in the literature. However, this level of genetic variation was not represented to the same extent by the seeds of the commercial harvest. Differences between the bud sample taken from the mature stand and the seed sample taken from the commercial subset were particularly obvious with respect to diversity measures and heterozygosities. The hypothetical gametic multilocus diversity (HGMD) of a bud sample of the mature Sorbus torminalis trees was more than 70% higher (94.1) than the value of the seed harvest sample (55.1). Deviations between the genetic structures of both samples were statistically significant. There is no indication that inbreeding is an essential component of the mating system of Sorbus torminalis. The potential causes for the lack of Sorbus torminalis seedlings and saplings originated from seeds and their consequences for regenerating this species are discussed. This research underscores that sampling a forest tree population for commercial harvest can result in a statistically significant reduction in the genetic diversity of the sampled group relative to the overall population.     

How to quantify forest management intensity in Central European forests

Existing approaches for the assessment of forest management intensity lack a widely accepted, purely quantitative measure for ranking a set of forest stands along a gradient of management intensity. We have developed a silvicultural management intensity indicator (SMI) which combines three main characteristics of a given stand: tree species, stand age and aboveground, living and dead wooden biomass. Data on these three factors are used as input to represent the risk of stand loss, which is a function of tree species and stand age, and stand density, which is a function of the silvicultural regime, stand age and tree species. Consequently, the indicator consists of a risk component (SMI_r) and a density component (SMI_d). We used SMI to rank traditional management of the main Central European tree species: Norway spruce (Picea abies [Karst.] L.), European beech (Fagus sylvatica L.), Scots pine (Pinus sylvestris L.), and oak (Quercus robur L. and Quercus petraea L.). By analysing SMI over their whole rotation period, we found the following ranking of management intensity: oak<beech<pine?spruce. Additionally, we quantified the SMI of actual research plots of the German Biodiversity exploratories, which represent unmanaged and managed forest stands including conifer forests cultivated outside their natural range. SMI not only successfully separate managed from unmanaged forests, but also reflected the variability of forest management and stand properties across the entire sample and within the different management groups. We suggest using SMI to quantify silvicultual management intensity of stands differing in species composition, age, silvicultural system (even-aged vs. uneven-aged), thinning grade and stages of stand conversion from one stand type into another. Using SMI may facilitate the assessment of the impact of forest management intensity on biodiversity in temperate forests.     

Genetic variation of Fraxinus angustifolia natural populations in Greece based on nuclear and chloroplast microsatellite markers

Assessment of genetic variation within and among populations is an essential parameter for the effective conservation of forest genetic resources. In this work, the genetic diversity within and among natural populations of the forest tree species Fraxinus angustifolia Vahl in Greece was studied using selected nuclear and chloroplast microsatellite DNA loci. Eight natural populations of F. angustifolia were identified in different locations of the mainland of Greece, and a total of 230 individuals were studied. High polymorphism was observed within populations, while the genetic differentiation among populations was moderate. Intra-population diversity was correlated with geographical coordinates, but no isolation by distance was observed. Of the three haplotypes identified, only one was dominant. Putative ancestral haplotypes were found at small spatial scales suggesting that population expansions could have originated in the region. This study located in sympatry haplotypes that in other parts of Europe are in allopatry, reinforcing the notion of population expansions from the south of Balkans including Greece. Suggestions for conservation and management of F. angustifolia are also reported.     

Stand development of Norway spruce dominated subalpine forests of the Swiss Alps

In densely populated regions, forests can help protect communities and infrastructures from natural hazards such as avalanches and rockfall. To promote the protective function, substantial efforts are made to actively manage forest stands. In 2009 alone the Swiss government invested more than 60 million sfr for the maintenance of protection forests. However, to date there has been no comprehensive evaluation of how the structural development of actively managed stands differs from that of passively managed stands in the Alps. Over the past century the structure of Norway-spruce dominated subalpine forests of the Swiss Alps has been changing and it is not clear how these changes affect the potential protective function of these forests, as well as other forest functions such as wildlife habitat. Furthermore, it is not clear how stand dynamics and structural changes differ between stands that are actively managed and those that are passively managed, and thus to what degree active efforts of forest management are contributing to stands that actually have a greater protective function than passively managed forests.In this study, we analyzed the dynamics of subalpine forests using time series of forest inventory data and examined the influence of active vs. passive management, exposition, distance to treeline, elevation and slope steepness on stand structure and dynamics. We analyzed data from 395 plots in dense, subalpine, spruce-dominated forests in the Swiss Alps. Data were collected during three distinct periods (1983-1985, 1993-1995 and 2004-2006) as part of the Swiss National Forest Inventory (NFI). Using regression trees and multivariate statistics, we investigated which factors have the most important influence on tree growth and stand development.Overall, forest density increased significantly over the last 20 years and the predominance of dense forests increased at higher elevations. However, forest density has not increased in actively managed forests over the past 10 years. In passively managed stands, density was higher on south-facing slopes than on north-facing slopes. The volume and density of dead wood has increased over the last 20 years in both actively managed and passively managed forests. Active management over the last 20 years has maintained forest conditions that adequately maintain stands’ protection functions in the Swiss Alps. However, stand development, especially increasing density, in the passively managed stands of the Swiss Alps suggests that the majority of passively managed stands also provide adequate protective functions against rock and avalanche hazards without the high costs of active management.     

Genetic diversity in young and mature cohorts of cultivated and wild populations of Picea asperata Mast (Pinaceae), a spruce endemic in western China

Dragon spruce (Mast) is a conifer endemic to western China and a popular species for reforestation programs of this region. We used inter simple sequence repeats (ISSRs) molecular markers to conduct a population genetic study of nine geographically close stands from three types of dragon spruce forests: (1) intact, (2) plantation, and (3) natural regenerated following clearcut. Our main objective was to investigate the genetic structure of these populations and our expectation was that gene flow was an important evolutionary force among them. We were unable to sample a large number of individuals in each cohort. However, when young and mature cohorts from a particular stand were interpreted as a single unit, then sample size increased significantly. The highest levels of genetic diversity were found in mature cohorts of the intact forests, the lowest in young cohorts of these stands. Contrary to our expectations, low levels of gene flow existed between mature and young cohorts of different forest types; and most gene flow occurred between cohorts belonging to the same stand. There were major differences in the genetic structure of the three types of stands. Our results have conservation implications as the majority of wild populations of dragon spruce are small and fragmented. Low gene flow among populations will lead to high levels of genetic drift and a decline of genetic diversity within populations.     

经营强度对蜀南竹海楠竹保护的影响

竹林区竹类种质保育需要建立避免人为干扰的竹类自然生态系统,但现有的竹林粗放遍及各处的经营策略则直接威胁到竹类种质栖息地的保护。通过对蜀南竹海人工经营和未经营下楠竹林群落环境与种群结构的对比分析,认为保护区内楠竹林经营强度改变了植物群落结构,导致植物物种多样性的丧失,地表灌木、草本和凋落物的盖度降低,生物量减少;考虑天然楠竹林结构演替,楠竹的人工经营(纯林经营)是维持楠竹林生产力和楠竹林的必然途径。基于现代林业理论,提出了县域楠竹林适度经营与保护的空间分工性、集约化策略,以期获得保护区长期的生态经济社会效益与生态安全屏障的优化格局。     

基于GM(1,1)的天然次生林空间结构预测

【目的】系统地分析已有天然次生林林分空间结构数据,通过灰色模型预测天然次生林林分空间结构各指标未来的发展趋势,对天然林经营具有十分重要的意义。【方法】以湖南大围山自然保护区典型次生林为研究对象,依据结构化森林经营理论,选取了混交度、竞争指数、角尺度、空间密度指数、开阔比数、大小比数、林分综合均质性指数作为天然次生林林分空间结构合理性评价与预测的量化指标,构建了基于GM(1,1)的天然次生林林分空间结构灰色预测模型。模型将2008年林分空间结构各指标的平均值作为初始值,并在研究区设置了面积为20 m×20 m的5个研究样地(M1,M2,M3,M4,M5),利用保护区2008-2018年典型样地林分空间信息,预测了研究区调研样地2019年-2021年林分空间结构各指标未来的变化趋势。【结果】利用精度检验机制对该模型的精确度进行了有效性检验,检验结果表明,所有指标预测合格概率P合=71.43%,良好的概率P良好=22.86%,优的概率P优=5.71%,表明该预测模型符合精度检验要求。【结论】样地未来3 a各指标整体变化尺度不大,林分空间结构基本稳定。从各指标在2008-2018年时空上的变化规律来看,各样地林分平均竞争指数、平均大小比数及平均空间密度指数是影响林分均质性指数的关键指标。     

基于目标树经营的抚育采伐对云冷杉针阔混交林空间结构的影响

[目的]以长白山林区云冷杉针阔混交林为研究对象,分析目标树抚育采伐前后云冷杉针阔混交林空间结构参数的变化,探索目标树抚育采伐对森林空间结构的影响。[方法]基于6块面积1 hm~2的样地,首先遵循近自然森林经营的原理进行林木分类,选定目标树,伐除干扰树;再结合结构化森林经营的原理,计算并分析抚育采伐前后目标树空间结构参数和林分空间结构评价指数的变化。[结果]表明:经目标树抚育采伐后(1)目标树空间结构单元内的树种隔离程度得到进一步提高;林木透光条件有所改善;目标树的竞争压力得以减小;林木空间分布格局总体上得到优化。(2)林分空间结构评价指数进一步提高,林分空间结构水平稳中有升。[结论]通过采取合理的目标树抚育采伐措施能兼顾改善单木水平和林分水平的空间结构状况,在实现优化目标树空间结构的同时,保证林分整体空间结构的稳定。从目标树抚育采伐对林分整体空间结构的影响来看:所有样地的林分空间结构状况均得到进一步改善。