Classification of vegetational diversity in managed boreal forests in eastern Finland

Diversity of vegetation in managed forests is studied. A classification based on forest stand structure, the abundances of vegetation species and variations in these abundances is developed and diversity indices are calculated for the classes to describe the diversity of the vegetation within the classes. The classes were formed using detrended correspondence analysis (DCA), global nonmetric multidimensional scaling (GNMDS) and TWINSPAN classification. Discriminant analysis was used to determine the environmental variables differentiating between the classes, and Duncan's multiple range test was used to examine the ability of the diversity measures to distinguish the classes. Beta diversity was estimated with Økland's method based on DCA ordination of the sample plots. The results point to fertility and the successional stage of the stand as the main factors affecting species diversity, in addition to which soil type, the number of tree species, crown cover, basal area and certain variables describing the management of the stand were relevant to the classification. The most distinct diversity indices were the reciprocal of Simpson, Pielou's J' and species richness, while the highest alpha diversity was found in young stands with a low crown cover on herb-rich or mesic forest sites. Beta diversity was quite high, its highest values of all for the whole data being recorded along the fertility gradient.     

广东中西部桉树人工林植物多样性与林龄和土壤因子的关系

以位于广东省中西部的高要市桉树人工林林下植被群落为研究对象,对不同龄级林分物种多样性进行比较分析,采用典范对应分析(CCA)方法进行排序并通过相关分析,对物种分布和多样性与土壤因子的关系进行了研究。结果表明,每龄级24块样地充足,从第9块样地开始不同龄级的物种数目出现一定程度的差异。桉树林分样地中共有136种植物,隶属54科107属,灌木层的种类最多,但以草本层物种为优势种。不同龄级林分之间物种多样性差异不显著,但1—2年生林分低于2—4年生和5—6年生两个龄级;3—4年生的Shannon指数、Simpson指数和丰富度最高。对植被物种的分布,土壤中有机质、全磷、全钾和容重的影响明显,pH值也有一定程度作用,而对物种多样性,pH值和全氮是最为稳定的影响因子。     

EVALUATING THE IMPACT OF INSECT COMMUNITY ON PINE CATERPILLAR DENSITY IN DIFFERENT STAND CONDITIONS

Abstract  Natural enemies play an important role in inhibiting population growth of pine caterpillar, but they are difficult to be used in systematic management models. This paper attempts to use some forest stand factors to substitute the effect of natural enemies, which could be used in management models. Through the studies from more than 200 stand plots with different stand conditions in Qu County, Changshan County, and Longyou County of Zhejiang Province, 16 predominant species groups from insect community were selected, and the canonical correlation coefficient between the diversity index, species number, individual number of predominant species and the stand factors was analyzed. The results indicated that the canopy density and ground vegetation were the key stand factors for characterizing the function of insect community. The forest area was divided into four types according to the variation of canopy and vegetation conditions by using cluster analysis. The regression models between the rate of variation of pine caterpillar density and the forest factors including canopy density and vegetation covers were developed in each type of forests. There were significant differences in diversity index, species number, individual number of insect community and population density of pine caterpillar among four types of forests, and correlation coefficients of the four regression models were rather high ( r =0. 924 — 0. 964). This means that the classification of the forest stands is reasonable and the stand factors can characterize the effect of natural enemies in practice.     

不同立地条件下昆虫群落对松毛虫密度影响的估计(英文)

天敌在松毛虫种群动态中起重要作用,但把天敌的作用加入系统管理模型中却很困难。本文试图用林分因子代替天敌的作用,因为林分条件可以方便地用于系统模型中。通过对浙江省衢县、常山县和龙游县不同立地条件的222块样地的调查数据的分析,从70多科的昆虫群落中选择了16个关键种（科）,并对林分因子和各样地关键种的种数、个体数、多样性之间的关系进行了典型相关分析。结果表明郁闭度和植被条件（灌木层盖度、灌木层高度、草木层盖度、草木层高度、总盖度）是刻划昆虫群落功能的关键林分因子。根据郁闭度的变化和植被条件用系统聚类方法可以把林区分为四种类型,这四种类型林地的昆虫多样性指数、种数、个体数量和松毛虫的密度都存在明显差异;在每种林地都建立了松毛虫密度的变化率与关键林分因子间的回归模型,所有的回归的相关系数都相当高（0．924－0．964）,因此可以认为对林地的分类是合理的,而且用林分因子评估天敌的影响在实践中是可行的。     

Legacy forest structure increases bird diversity and abundance in aging young forests

Many studies have demonstrated the importance of early‐successional forest habitat for breeding bird abundance, composition, and diversity. However, very few studies directly link measures of bird diversity, composition and abundance to measures of forest composition, and structure and their dynamic change over early succession. This study examines the relationships between breeding bird community composition and forest structure in regenerating broadleaf forests of southern New England, USA, separating the influences of ecological succession from retained stand structure. We conducted bird point counts and vegetation surveys across a chronosequence of forest stands that originated between 2 and 24 years previously in shelterwood timber harvests, a silvicultural method of regenerating oak‐mixed broadleaf forests. We distinguish between vegetation variables that relate to condition of forest regeneration and those that reflect legacy stand structure. Using principal components analyses, we confirmed the distinction between regeneration and legacy vegetation variables. We ran regression analysis to test for relationships between bird community variables, including nesting and foraging functional guild abundances, and vegetation variables. We confirmed these relationships with hierarchical partitioning. Our results demonstrate that regenerating and legacy vegetation correlate with bird community variables across stand phases and that the strength with which they drive bird community composition changes with forest succession. While measures of regeneration condition explain bird abundance and diversity variables during late initiation, legacy stand structure explains them during stem exclusion. Canopy cover, ground‐story diversity, and canopy structure diversity are the most powerful and consistent explanatory variables. Our results suggest that leaving varied legacy stand structure to promote habitat heterogeneity in shelterwood harvests contributes to greater bird community diversity. Interestingly, this is particularly important during the structurally depauperate phase of stem exclusion of young regenerating forests.     

The role of remnant trees in carbon sequestration,vegetation structure and tree diversity of early succession regrowing fallows in eastern Sierra Leone

Remnant tree presence affects forest recovery after slash‐and‐burn agriculture. However, little is known about its effect on above‐ground carbon stocks, especially in Africa. We focused our study on Sierra Leone, part of the Upper Guinean forests, an important centre of endemism threatened by encroachment and forest degradation. We studied 99 (20‐m‐radius) plots aged 2–10 years with and without remnant trees and compared their above‐ground carbon stocks, vegetation structure (stem density, basal area) and tree diversity. Above‐ground carbon stocks, stem density, basal area, species richness and tree diversity increased significantly with fallow age. Remnant tree presence affected significantly tree diversity, species dominance and above‐ground carbon stocks, but not vegetation structure (stem density, basal area). Number of remnant trees and number of species of remnant trees were also important explanatory variables. Although other factors should be considered in future studies, such as the size and dispersal modes of remnant trees, our results highlight that more strategic inclusion of remnant trees is likely to favour carbon stock and forest recovery in old fallows. To our knowledge, this is the first study on early succession regrowing fallows in West Africa.     

Stand structure, species diversity and regeneration of an endemic palm forest on the Seychelles

The ‘Vallée de Mai’ on the island of Praslin in the Seychelles group is a World Heritage Site because of its unique forest vegetation dominated by the palm Lodoicea maldivica. However, despite its great conservation importance, the stand structure, species diversity and regeneration of this forest have not previously been studied. Moreover, the conservation value of the reserve is currently threatened by invading alien plants and limited regeneration of some native species. The species composition of the forest was studied in six permanent plots (1985 and 1998) and along seven trail transects (1997). To explain potential variation in tree regeneration, the light climate within all plots was investigated using hemispherical photographs. The results reveal little change in forest structure, species diversity and regeneration in the permanent plots over the 13‐year period, but some regeneration of most woody species, presence of some alien species and a relatively high species turnover. We found no significant influence of local light climate upon forest structure, species diversity or regeneration. Although the stand characteristics seem to be relatively stable, the permanent plots and transects should be monitored in order to detect future changes in stand structure and to optimize the protection of this unique forest reserve.     

Effects of vegetation structure and landscape complexity on insect parasitism across an agricultural frontier in Argentina

Insect parasitism patterns are influenced by vegetation structure and landscape complexity. Our objective was to examine the effects of vegetation structure and landscape complexity on parasitism based on direct measurements of structure and diversity indices as well as on metrics based on remote sensing using Quickbird images. We collected 2266 lepidopteran larvae and pupae, including different families and habits, to estimate parasitism, and recorded vegetation characteristics in five 100-m² transects and 18 1 ha-plots in the dry Chaco, Northwest Argentina. We calculated landscape metrics and semivariograms in the plots from the image. The plots represented four “complexity groups”: agricultural, riparian/hedgerow, bare ground, and forest plots. Mean parasitism in the study sites was 10.7% (min: 0%, max: 23%). Parasitism was highest in agricultural plots, lowest in forest plots, and intermediate in riparian/hedgerow and bare ground plots. The landscape model explained parasitism more than the vegetation model. The landscape final model included Normalized Difference Vegetation Index (NDVI) Range, a measure of landscape heterogeneity, and Mean Shape Index, a measure of patch shape irregularity, and their interaction. The vegetation model included basal area and the Coefficient of Variation of tree density among transects, a measure of tree spatial distribution within a plot. Our results agree with previous studies that found higher parasitism in agricultural vs. non-agricultural environments in the subtropics, while riparian/hedgerow plots were important for conserving parasitism, as reported for temperate environments. We showed that under-explored tools such as the semivariogram and satellite band combinations were useful for the assessment of parasitism and that studying vegetation and landscape complexity simultaneously can help us examine mechanisms in detail. The identified variables related to high parasitism should be used for image classifications with a functional approach.     

The influence of soil on vegetation structure and plant diversity in different tropical savannic and forest habitats

Aims Soil plays an important role in the formation and heterogeneity of habitats and thus can cause changes in vegetation structure and plant diversity. The differentiation between Cerrado/savanna and forest is well known, but the relationship between soil and habitats from savannic or forest formations still needs to be better understood, particularly in tropical ecotonal areas. We studied the association between attributes of plant communities, namely structure and diversity, and physicochemical characteristics of soils in the Caatinga domain at the transition to Cerrado in Brazil.Methods Chemical and physical analyses of soils were performed in samples of 38 plots from savannic formations and 30 plots from forest formations. Vegetation was characterized floristically and structurally in all plots, five habitats being assessed in each plant formation. Soil features and vegetation parameters were highly distinct among the different habitats.Important findings In general, forest habitats were more nutrient rich than savannic formation. Furthermore, soil variables showed effects both on vegetation structure and on its species diversity, more pronouncedly in the savannic formations. Habitats were structurally distinct, and diversity differed between savannic and forest communities; however, a higher differentiation occurred when the savannic formation habitats were compared among them. Although plant diversity did not differ among forest formation habitats, soil attributes showed a close relationship with edaphic factors and can contribute for similar vegetation. The soil–vegetation relationship in highly diverse ecotonal landscapes is important from the conservation biology point of view and aid in the execution of proactive plans for the maintenance of biodiversity. Thus, we noticed that diversity and soil behaves distinctly between savannic and forest communities.     

The impact of forest transformation on stand structure and ground vegetation in the southern Black Forest, Germany

The goal of this study was to investigate the effects of 'ecologically orientated' forest transformation on forest floor vegetation. Forest transformation, as defined by the BMBF southern Black Forest project group, is the process which converts even-aged spruce forest into structured continuous-cover forest, consisting principally of spruce (Picea abies), fir (Abies alba) and beech (Fagus sylvatica). In order to analyse the transformation process, four transformation stages were defined as part of a 'conceptual forest development model' (pure even-aged, species enrichment, structuring and continuous cover forest stage). Four forest districts representative of the southern Black Forest were selected for the study. The analysis included the separate classification of structures, sites, and ground vegetation. In a second step, the relationships between the three complexes were analysed. The influence of forest structure on ground vegetation was investigated by examining the relationships between so-called substructure types and ground vegetation types. The substructure types associated with the pure spruce stand, species enrichment and continuous cover forest stages exhibited a ground vegetation resembling that of the Luzulo-Fagetum and Luzulo-Abietetum, whereas the structuring stages exhibited a ground vegetation of the Galio-Fagetum type. Transformation of pure, even-aged spruce forest into mixed, uneven-aged continuous cover forest is considered an important silvicultural tool to combine the demands of sustainable timber production and nature conservation. Transformation brings about greater diversity in stand structure and tree species composition. The frequencies of acidophytic mosses and vascular plants in spruce forest decrease during the transformation process. The species requiring moderate base supply increase over the transitional stages. The continuous cover forest, the final stage of transformation, increasingly contains ground species of both, i.e., species normally associated with both conifer and deciduous forest.     

Avian species richness in relation to intensive forest management practices in early seral tree plantations

Background

Managers of landscapes dedicated to forest commodity production require information about how practices influence biological diversity. Individual species and communities may be threatened if management practices truncate or simplify forest age classes that are essential for reproduction and survival. For instance, the degradation and loss of complex diverse forest in young age classes have been associated with declines in forest-associated Neotropical migrant bird populations in the Pacific Northwest, USA. These declines may be exacerbated by intensive forest management practices that reduce hardwood and broadleaf shrub cover in order to promote growth of economically valuable tree species in plantations.

Methodology and Principal Findings

We used a Bayesian hierarchical model to evaluate relationships between avian species richness and vegetation variables that reflect stand management intensity (primarily via herbicide application) on 212 tree plantations in the Coast Range, Oregon, USA. Specifically, we estimated the influence of broadleaf hardwood vegetation cover, which is reduced through herbicide applications, on bird species richness and individual species occupancy. Our model accounted for imperfect detection. We used average predictive comparisons to quantify the degree of association between vegetation variables and species richness. Both conifer and hardwood cover were positively associated with total species richness, suggesting that these components of forest stand composition may be important predictors of alpha diversity. Estimates of species richness were 35–80% lower when imperfect detection was ignored (depending on covariate values), a result that has critical implications for previous efforts that have examined relationships between forest composition and species richness.

Conclusion and Significance

Our results revealed that individual and community responses were positively associated with both conifer and hardwood cover. In our system, patterns of bird community assembly appear to be associated with stand management strategies that retain or increase hardwood vegetation while simultaneously regenerating the conifer cover in commercial tree plantations.     

Patterns of density and structure of natural populations of Taxus baccata in the Hyrcanian forests of Iran

Iran's Hyrcanian forests cover a relatively narrow strip in the northeastern part of the country, and are among the most important and valuable ecosystems inscribed in United Nations Educational, Scientific and Cultural Organization (UNESCO) World Heritage List. European yew Taxus baccata L. is a Tertiary relict in the region and a long-lived dioecious tree with high ecological and economic importance in the Hyrcanian forests. To study the structure and analysing the survivorship of yew stands, we selected two forest reserves (Gazou and Afratakhteh) with European yew. In the two study areas, we established 165 0.1 ha circular sample plots (75 of the sample plots were in Gazou and 90 sample plots were in Afratakhteh) and measured three characteristics of each tree. The structure of the stands was quantified by means of 1) size distributions by diameter at breast height (DBH), 2) height classes, 3) and stand basal area. Comparison of the diameter distribution by DBH classes in two the forest reserves showed that there was no statistical difference between the two populations. The highest number of yew trees in the Afratakhteh and Gazou populations were in the 12–16 and 18–24 m height classes, respectively. In Gazou, abundance was greatest at 1000 m a.s.l. on mesic exposures and intermediate slopes (40–50%), whereas in Afratakhteh it was found at 1600–1620 m a.s.l. on east-facing areas with 55–65% slopes. Static life tables indicated that the first two age classes have particularily high mortality. Based on these results, we conclude that forest managers should support the regeneration of stands and increase survival rates by applying treatments such as thinning and selective removal of shrubs and saplings of other tree species.     

Effects of population density on forest structure and species richness and diversity of trees in Kampong Thom Province, Cambodia

This study examined differences in stand structure, tree species richness, and tree species diversity in relation to population density in Kampong Thom Province, Cambodia. Tree data were obtained from a 1997 forest inventory involving 60 clusters (540 plots) systematically distributed over 30% of the provincial forest area. Spatially referenced population data were obtained from the 1998 national population census. The average number of trees per cluster was 356/ha, the average basal area, 23 m²/ha, the average stand volume, 217 m³/ha, and the average aboveground biomass, 273 Mg/ha for all trees of DBH 10 cm and larger. The average species richness per cluster was 37 species, while average species diversity was measured as 0.916 using Simpson’s index and 2.98 by Shannon’s index. Significant negative correlations were generally found between population density surrounding clusters and tree density, basal area, stand volume, aboveground biomass, and species richness and diversity for three examined diameter classes (DBH of 10–30, ≥30, and ≥10 cm). As the distance from clusters for calculating population density increased, the correlation levels increased up to 5 or 7 km, depending on the variables and diameter class, and then stayed relatively constant for stand structure variables and decreased for species richness and diversity. The results indicate that evidence of disturbance was more pronounced at higher population density up to around 5 to 7 km. We suggest that introduction of greater controls on human disturbance should be a high priority for resource management and conservation in Kampong Thom Province and, presumably, Cambodia as a whole.     

Are cloud forest tree structure and environment related in the Venezuelan Andes?

Cloud forest vegetation structure and composition were studied in the Venezuelan Andes at three sites in Mérida State. Although the sites are within 10 to 30 km of each other, climatic, geologic and topographic differences are remarkable. The main purpose of the study was to determine the relationship of specific environmental variables to forest vegetation characteristics, including basal area, tree height, density and diversity, and leaf area index (LAI). At 51 plots, all trees' diameter at breast height >10 cm were recorded and identified. Although the environment at the three sites is distinctive, the tree species composition of the most abundant species was very similar. None of the measured environment variables were significantly correlated with the measured vegetation structure variables, except LAI, which was correlated with slope orientation; LAI showed higher values at south‐facing plots. Tree height was relatively uniform, while basal area was highly variable and reached very high values. Stem densities were in the range reported elsewhere in cloud forests. Multivariate analysis using structure or composition data shows segregation of the plots by site. Principal component analyses by site indicate a minor impact of environmental factors on forest variables. At each site, a particular group of species are correlated with the ordination axes. We conclude that species pools and forest dynamics add to the complexity of the structure of the studied cloud forests.     

Understorey vegetation development in North Finnish Picea forests after disturbance: re‐analysis of Sirén's data

Abstract. Sirén (1955) studied understorey species composition, tree stand properties and humus‐layer thickness in 64 unlogged forest stands on topographically and pedologically comparable sites. The stands were of even age (6 – 300 yr), stocked with the first or second tree generation after wildfire. The view of Sirén and several authors after him, that the vegetation of old‐growth boreal Picea forests is homogeneous on a broad scale, was examined by applying, in parallel, the partial variants of two ordination methods (DCA and PCA) to Sirén's vegetation data. Two main vegetation gradients were found: a major gradient running from recently burnt plots with prominence of pioneer species to plots with stand age > 100 yr, a well stocked tree layer and a thick humus layer, dominance of feather‐mosses and ample occurrence of shade‐tolerant as well as light‐preferring vascular plant species, and a second gradient along which first‐ and second‐generation plots segregate. The more prominent element of Betula trees in first‐ than in second‐generation stands < 100 yr contributed to the latter. A minor third gradient related to humus‐layer thickness was recovered by partial DCA only. The main vegetation gradient reappeared in separate ordinations of data from 47 mature forest stands (> 100 yr), but without being correlated with forest age. Variation among mature‐forest stands in the importance of pioneer species is considered mainly to be brought about by fine‐scale disturbance processes such as tree uprooting. Increasing importance of factors operating on within‐stand scales [development of a varied gap structure and stronger gradients in tree influence (radiation at ground level), soil moisture, soil depth and nutrient availability] with time is also reflected in the second and third mature‐forest ordination axes. Possible implications of the results for conservation of biological diversity and monitoring of changes in boreal forests are discussed.     

Ectomycorrhizal and wood-decay macromycete communities along development stages of managed Pinus patula stands in Southwest Mexico

This study used fruit body surveys to evaluate the diversity and distribution of ectomycorrhizal and wood-decay macromycetes along developing stages of stands artificially reforested with Pinus patula in Southern Mexico. Three stand ages were selected: 1, 11, and 60 y old. Macromycetes were collected from June to October 2016 in 0.1 ha plots per stand age. A total of 106 taxa were recorded, 63 ectomycorrhizal and 43 wood-decay fungi. The highest diversity of ectomycorrhizal fungi was in 11-y stands, and 11- and 60-y stands had similar species composition. Wood-decay fungi showed a trend towards higher diversity in the 1- and 11-y stands, and species composition in these sites corresponded. Patterns of diversity and distribution were mainly determined by factors related to substratum availability and vegetation structure. Knowledge about the influence of artificially reforested stands on macrofungal communities is relevant to improve management plans and achieve a more sustainable use of forest timber and non-timber products.     

祁连山东部森林林分结构和环境因素对草本物种多样性的影响

林下草本物种多样性在维持西北干旱与半干旱地区的生态系统服务功能方面起着重要作用,探究其相关影响因素,可为祁连山东部地区的人工生态公益林的可持续经营提供理论基础。选取位于祁连山东部地区的针叶纯林、阔叶纯林、针叶混交林、针阔混交林(人工林)为研究对象,在相关性分析的基础上构建草本物种多样性的多因素参数预测模型和结构方程非参效应模型,探究多重因素(林分空间结构、林分非空间结构、环境因子)间的关系以及对林下草本物种多样性的影响程度。结果表明:(1)针阔混交林中林下草本的科、属、种数量最多。(2)平均胸径、平均树高、角尺度、混交度、大小比、坡度与草本物种多样性呈显著性相关(P<0.05)。(3)平均胸径是影响林下草本Simpson多样性指数的关键因子;坡度是影响林下草本Shannon-Wiener多样性指数的关键因子;角尺度、混交度是影响Pielou均匀性指数的关键因子;平均胸径、平均树高是影响物种丰富度的关键因子。(4)结构方程非参效应模型显示林分结构是影响草本物种多样性的关键因子(P<0.001),环境因子是影响草本物种多样性的重要因子(P<0.05)。因此,在后续森林植被恢复措施中,应当着重考虑林分的空间结构,形成随机分布的异龄复层混交林,以增加光合利用效率并遵循生态位互补理论,从而提高草本多样性。     

Woody plant diversity and structure of shade-grown-coffee plantations in northern Chiapas,Mexico

Shade-grown coffee is an agricultural system that contains some forest-like characteristics. However, structure and diversity are poorly known in shade coffee systems. In 61 coffee-growers' plots of Chiapas, Mexico, structural variables of shade vegetation and coffee yields were measured, recording species and their use. Coffee stands had five vegetation strata. Seventy seven woody species mostly used as wood were found (mean density 371.4 trees per hectare). Ninety percent were native species (40% of the local flora), the remaining were introduced species, mainly fruit trees/shrubs. Diametric distribution resembles that of a secondary forest. Principal Coordinates Analysis grouped plots in four classes by the presence of Inga, however the majority of plots are diverse. There was no difference in equitability among groups or coffee yields. Coffee yield was 835 g clean coffee per shrub, or ca. 1,668 kg ha-1. There is a significant role of shade-grown coffee as diversity refuge for woody plants and presumably associated fauna as well as an opportunity for shade-coffee growers to participate in the new biodiversity-friendly-coffee market.     

浙江西天目山主要森林类型的苔藓多样性比较

苔藓是森林的重要组分, 是森林保护区的重要保护对象, 在物种资源和生态系统功能维护中有重要作用。该研究以浙江西天目山国家自然保护区内7种主要森林类型(落叶矮林、落叶阔叶林、常绿-落叶阔叶混交林、常绿阔叶林、针阔混交林、针叶林和竹林)内的苔藓植物为对象, 调查了32个10 m × 10 m的样地, 记录地面生苔藓植物盖度和树附生苔藓植物多度, 采用重要值、相似性系数、多样性指数分析了森林类型间的苔藓植物多样性差异。共采集969份标本, 隶属41科84属142种, 其中苔类植物13科18属33种, 藓类植物28科66属109种, 优势科为灰藓科、青藓科和羽藓科。2种混交林(常绿-落叶阔叶混交林和针阔混交林)的物种丰富度和多样性指数均高于其余5种森林, 其中物种丰富度以针阔混交林最高, 苔藓植物多样性则以常绿-落叶阔叶混交林最高, 竹林两者均为最低。海拔等环境因子较为接近的植被类型的苔藓植物多样性相似性较高, 常绿阔叶林与针叶林相似性最高, 而落叶矮林和竹林相似性最小。     

基于结构方程模型的兴安落叶松天然林更新影响因素

以大兴安岭新林林业局翠岗林场49块兴安落叶松不同蓄积占比的固定样地调查数据为基础,分别从林分非空间结构、林分空间结构、林木多样性、土壤条件和立地条件5个方面37项观测指标,在相关性分析的基础上,构建林分尺度更新密度和更新多样性(包括树高和地径)的结构方程模型,并计算各路径的直接、间接和总影响系数,量化和提取影响大兴安岭地区兴安落叶松天然林更新密度和更新多样性的关键可控因素,为该地区森林的可持续经营提供理论基础和技术依据。结果表明: 对林分更新密度影响最大的潜变量依次为:林分非空间结构(-0.410)>林木多样性(0.380)>土壤条件(0.250)>立地条件(0.249)>林分空间结构(0.197);对林分更新多样性影响最大的潜变量依次为:土壤条件(0.778)>立地条件(0.748)>林分空间结构(0.684)>林分非空间结构(0.287)>林木多样性(0.105)。综合来看,影响更新密度和多样性的共性观测变量主要为:pH值、全钾、树种多样性、树高多样性、角尺度和单位蓄积。在后续经营中,可通过采伐或补植阔叶树种的方式来优化和调整林分的树种组成、多样性、土壤pH值和养分等特征,最终达到促进天然更新的目的。