Effects of local biotic neighbors and habitat heterogeneity on tree and shrub seedling survival in an old-growth temperate forest

Seedling dynamics play a crucial role in determining species distributions and coexistence. Exploring causes of variation in seedling dynamics can therefore provide key insights into the factors affecting these phenomena. We examined the relative importance of biotic neighborhood processes and habitat heterogeneity using survival data for 5,827 seedlings in 39 tree and shrub species over 2?years from an old-growth temperate forest in northeastern China. We found significant negative density-dependence effects on survival of tree seedlings, and limited effects of habitat heterogeneity (edaphic and topographic variables) on survival of shrub seedlings. The importance of negative density dependence on young tree seedling survival was replaced by habitat in tree seedlings ??4?years old. As expected, negative density dependence was more apparent in gravity-dispersed species compared to wind-dispersed and animal-dispersed species. Moreover, we found that a community compensatory trend existed for trees. Therefore, although negative density dependence was not as pervasive as in other forest communities, it is an important mechanism for the maintenance of community diversity in this temperate forest. We conclude that both negative density dependence and habitat heterogeneity drive seedling survival, but their relative importance varies with seedling age classes and species traits.     

长白山阔叶红松林乔木幼苗组成及多度格局的影响因素

以长白山原始阔叶红松林样地为平台,以样方中胸径小于1 cm的乔木幼苗为研究对象,基于2018年两次的幼苗调查数据,利用广义线性混合模型分析影响群落乔木幼苗多度的生物邻体和生境因素。结果表明:该样地所有幼苗样方共调查到10064株乔木幼苗,累计17个物种,分属9科9属,水曲柳幼苗多度极高,在乔木树种幼苗中占优势地位;在群落水平,幼苗多度与异种大树效应、草本密度和林冠开阔度呈显著正相关,与草本盖度和土壤含水量呈显著负相关;在物种水平,水曲柳和紫椴幼苗多度的影响因素与群落水平筛选后的结果一致,红松幼苗多度与异种大树效应呈正相关,与同种大树效应及林冠开阔度呈负相关。该研究证实了生物邻体和生境因素共同影响幼苗多度格局,并且生物邻体和生境因素的相对重要性随幼苗物种种类不同而变化。     

The effect of conspecific density,herbivory, and bamboo on seedling dynamics of a dominant oak in a Neotropical highland forest

Conspecific negative density dependence (CNDD) is one of the main mechanisms influencing diversity maintenance in tropical forests. Tropical highland forests, in contrast to most lowland forests, are commonly dominated by a few tree species, and testing the importance of density dependence effects on seedling establishment of dominant trees may provide insights on the mechanisms regulating population dynamics and forest composition of tropical highlands. We tested the effect of CNDD regulation on seedling survival and recruitment of Quercus costaricensis, a monodominant oak in the Talamanca highland forests of Costa Rica. We used Ripley's K and generalized linear mixed models to test the effects of conspecific density, distance to the nearest adult, density of Chusquea bamboo shoots, and herbivory on the annual survival probability of 3579 seedlings between 2014 and 2017. We did not find a significant effect of CNDD on seedling survival. However, bamboo density and herbivory both significantly decreased oak seedling survival. All seedlings had signs of herbivory and predator satiation may explain the lack of density dependent regulation in seedlings of this species. We argue that the lack of intraspecific density regulation at the seedling stage may contribute to explain the dominance of Q. costaricensis in the highland forests of Costa Rica. Local seedling dynamics of this endemic oak are instead regulated by herbivory and the density of Chusquea. Abstract in Spanish is available with online material.     

Effects of biotic neighbors and habitat heterogeneity on tree seedling survival in a secondary mixed conifer and broad-leaved forest in Changbai Mountain

Aims Our study aimed to understand the effects and the relative importance of biotic neighborhood and habitat heterogeneity for tree seedling survival in a secondary mixed conifer and broad-leaved forest in Changbai Mountain, north-eastern China.
Methods The generalized mixed linear model was used to examine the relative effects of biotic neighborhood and habitat heterogeneity on seedling survival over two years.
Important findings Our results showed that both biotic neighborhood and habitat heterogeneity had significant effects on the seedling survival at community level. The local environment suitable for the adult growth was also suitable for seedling survival. The soil moisture and soil available nitrogen exhibited significant positive effects on seedling survival. On the other hand, seedling density had significant negative effects on seedling survival due to the individual competition. Particularly, we found significant negative density-dependent effects on seedling survival which was caused by conspecific adult and seedling neighbors. As expected, with the increasing of seedling survival age, the habitat heterogeneity became more important on seedling survival. These results suggest that both local biotic neighborhood and habitat heterogeneity drive seedling survival in this temperate forest, and their relative importance varies with different seedling age classes and species traits.     

Species with greater seed mass are more tolerant of conspecific neighbours: a key driver of early survival and future abundances in a tropical forest

Multiple niche‐based processes including conspecific negative density dependence (CNDD) determine plant regeneration and community structure. We ask how interspecific and intraspecific density‐dependent interactions relate to plant life histories and associated functional traits. Using hierarchical models, we analysed how such interactions affected first‐year survival of seedling recruits of 175 species in a tropical forest, and how species abundances and functional traits are related to interspecific variation in density‐dependent effects. Conspecific seedling neighbour effects prevailed over the effects of larger conspecific and all heterospecific neighbours. Tolerance of seedling CNDD enhanced recruit survival and subsequent abundance, all of which were greater among larger seeded, slow‐growing and well‐defended species. Niche differentiation along the growth–survival trade‐off and tolerance of seedling CNDD strongly correlated with regeneration success, with manifest consequences for community structure. The ability of larger seeded species to better tolerate CNDD suggests a novel mechanism for CNDD to contribute to seed‐size variation and promote species coexistence through a tolerance–fecundity trade‐off.     

长白山次生针阔混交林乔木幼苗存活的影响因素分析

基于长白山次生针阔混交林样地, 以520个1 m × 1 m幼苗样方中胸径小于1 cm的乔木幼苗为研究对象, 选取2013年和2014年的幼苗调查数据, 运用广义线性混合模型(GLMM)分析了生物邻体和生境异质性对幼苗存活的影响, 探讨了次生针阔混交林幼苗存活影响因素及物种共存机制。结果表明: (1)适宜大树生长的局域生境同样也适宜幼苗的存活, 幼苗存活率与土壤含水量和有效氮等土壤养分显著正相关。(2)幼苗个体之间存在明显的竞争, 较多的幼苗邻体显著降低幼苗的存活率。同种大树邻体和同种幼苗邻体与幼苗存活显著负相关, 表明存在负密度制约效应。(3)随着幼苗年龄的增加, 生境异质性对幼苗存活的影响逐渐增大。该研究证实了密度制约效应和生境异质性对幼苗存活有着重要影响, 其相对重要性随着幼苗年龄级、功能群以及物种种类而变化。     

Density dependence across multiple life stages in a temperate old-growth forest of northeast China

Recent studies on species coexistence suggest that density dependence is an important mechanism regulating plant populations. However, there have been few studies of density dependence conducted for more than one life-history stage or that control for habitat heterogeneity, which may influence spatial patterns of survival and mask density dependence. We explored the prevalence of density dependence across multiple life stages, and the effects of controlling for habitat heterogeneity, in a temperate forest in northeast China. We used generalized linear mixed-effects models to test for density-dependent mortality of seedlings and spatial point pattern analysis to detect density dependence for sapling-to-juvenile transitions. Conspecific neighbors had a negative effect on survival of plants in both life stages. At the seedling stage, we found a negative effect of conspecific seedling neighbors on survival when analyzing all species combined. However, in species-level analyses, only 2 of 11 focal species were negatively impacted by conspecific neighbors, indicating wide variation among species in the strength of density dependence. Controlling for habitat heterogeneity did not alter our findings of density dependence at the seedling stage. For the sapling-to-juvenile transition stage, 11 of 15 focal species showed patterns of local scale (<10 m) conspecific thinning, consistent with negative density dependence. The results varied depending on whether we controlled for habitat heterogeneity, indicating that a failure to account for habitat heterogeneity can obscure patterns of density dependence. We conclude that density dependence may promote tree species coexistence by acting across multiple life-history stages in this temperate forest.     

Density dependence and habitat preference shape seedling survival in a subtropical forest in central China

Aims Seedlings are vulnerable to many kinds of fatal abiotic and biotic agents, and examining the causes of seedling dynamics can help understand mechanisms of species coexistence. To disentangle the relative importance of neighborhood densities, habitat factors and phylogenetic relatedness on focal seedling survival, we monitored the survival of 5306 seedlings of 104 species>15 months. We address the following questions: (i) How do neighborhood densities, habitat variables and phylogenetic relatedness affect seedling survival? What is the relative importance of conspecific densities, habitat variables and phylogenetic relatedness to seedling survival? (ii) Does the importance of the neighborhood densities, habitat variables and phylogenetic relatedness vary among growth forms, leaf habits or dispersal modes? Specially, does the conspecific negative density dependence inhibit tree and deciduous seedlings more compared with shrub and evergreen species? Does density dependence affect the wind and animal-dispersed species equally?Methods We established 135 census stations to monitor seedling dynamics in a 25-ha subtropical forest plot in central China. Conspecific and heterospecific seedling density in the 1-m 2 seedling plot and adult basal area within a 20-m radius provided neighborhood density variables. Mean elevation, convexity and aspect of every 5- × 5-m grid with seedling plots were used to quantify habitat characteristics. We calculated the relative average phylodiversity between focal seedling and heterospecific neighbors to quantify the species relatedness in the neighborhood. Eight candidate generalized linear mixed models with binominal error distribution were used to compare the relative importance of these variables to seedling survival. Akaike's information criteria were used to identify the most parsimonious models.Important findings At the community level, both the neighborhood densities and phylogenetic relatedness were important to seedling survival. We found negative effects of increasing conspecific seedlings, which suggested the existence of species-specific density-dependent mortality. Phylodiversity of heterospecific neighbors was negatively related to survival of focal seedlings, indicating similar habitat preference shared among phylogenetically closely related species may drive seedling survival. The relative importance of neighborhood densities, habitat variables and phylogenetic relatedness varied among ecological guilds. Conspecific densities had significant negative effect for deciduous and wind-dispersed species, and marginally significant for tree seedlings>10cm tall and animal-dispersed species. Habitat variables had limited effects on seedling survival, and only elevation was related to the survival of evergreen species in the best-fit model. We conclude that both negative density-dependent mortality and habitat preference reflected by the phylogenetic relatedness shape the species coexistence at seedling stage in this forest.     

The contribution of understory light availability and biotic neighborhood to seedling survival in secondary versus old-growth temperate forest

Seedling survival plays an important role in the maintenance of species diversity and forest dynamics. Although substantial gains have been made in understanding the factors driving patterns of seedling survival in forests, few studies have considered the simultaneous contribution of understory light availability and the local biotic neighborhood to seedling survival in temperate forests at different successional stages. Here, we used generalized linear mixed models to assess the relative importance of understory light availability and biotic neighborhood variables on seedling survival in secondary and old-growth temperate forest in north eastern China at two levels (community and guild). At the community level, biotic neighborhood effects on seedling survival were more important than understory light availability in both forests. In both the old-growth and secondary forests, conspecific basal area had a negative effect on seedling survival, consistent with negative conspecific density dependence. At guild levels, the relative importance of light and biotic neighborhood on seedling survival showed considerable variation among guilds in both forests. Available understory light tended to have positive effects on seedling survival for shrub and light-demanding species in the old-growth forest, but negative effects on survival of shade-tolerant seedlings in the secondary forest. For tree species and shade-tolerant species, the best fit models included neighborhood variables, but that was not the case for shrubs, light-demanding, or mid shade-tolerant species. Overall, our results demonstrate that the relative importance of understory light availability and biotic factors on seedling survival vary with species life-history strategy and forest successional stage.     

Drivers of seedling survival in a temperate forest and their relative importance at three stages of succession

Negative density dependence (NDD) and niche partitioning have been perceived as important mechanisms for the maintenance of species diversity. However, little is known about their relative contributions to seedling survival. We examined the effects of biotic and abiotic neighborhoods and the variations of biotic neighborhoods among species using survival data for 7503 seedlings belonging to 22 woody species over a period of 2 years in three different forest types, a half‐mature forest (HF), a mature forest (MF), and an old‐growth forest (OGF), each of these representing a specific successional stage in a temperate forest ecosystem in northeastern China. We found a convincing evidence for the existence of NDD in temperate forest ecosystems. The biotic and abiotic variables affecting seedlings survival change with successional stage, seedling size, and age. The strength of NDD for the smaller (<20 cm in height) and younger seedlings (1–2 years) as well as all seedlings combined varies significantly among species. We found no evidence that a community compensatory trend (CCT) existed in our study area. The results of this study demonstrate that the relative importance of NDD and habitat niche partitioning in driving seedling survival varies with seedling size and age and that the biotic and abiotic factors affecting seedlings survival change with successional stage.     

Density dependence is not very prevalent in a heterogeneous subtropical forest

There is a growing body of evidence demonstrating that tree survival is influenced by negative density‐dependence, but it is still controversial how the effect may vary with life‐stage, and to what extent it plays a role in regulating tree survival in heterogeneous subtropical forests. In this study, we investigated density‐dependent effects on tree survival of six tree species in a 5‐ha subtropical forest in eastern China. The roughly 45 000 individuals in the forest were fully censused in 2003 and 2008. For each of these species, we used an inhomogeneous pair‐correlation function to quantify the change in spatial distribution for different size classes, and a case‐control design to study seedling–adult associations in 2003. Autologistic regression was used to determine the influence of neighborhood factors on individual survival from 2003 to 2008. We found that seedlings of five species were repulsed by distance to nearest conspecific adults in terms of their survival, consistent with predictions of the Janzen–Connell mechanism. By contrast, only the least shade‐tolerant Schima superba had a negative relationship with individual survival and conspecific distance‐weighted basal area. This suggests that the Janzen–Connell effect is only prevalent at the early seedling stage or seed‐to‐seedling phase. The strength of clustering significantly declined at sapling–pole and pole–adult transitions for Sycopsis sinensis and at seedling–sapling transition for Cleyera pachyphylla. Correlations between individual survival and conspecific abundance for these species were consistent with trends in the strength of clustering. These results suggest that density dependence plays a limited role in individual survival and species spatial structure beyond the early seedling stage (i.e. after true leaves growing) in this forest. In addition, this study indicates that including individuals from early life‐stages and factoring out potential confounding factors such as habitat preference are important in studies that seek evidence for density dependence in forest trees.     

The Relative Importance of Fungal Infection,Conspecific Density and Environmental Heterogeneity for Seedling Survival in a Dominant Tropical Tree

A gap remains in our understanding of how host‐specific fungal pathogens impact negative density dependence (NDD). Here, we investigated survival of Cinnamomum subavenium Miq. seedlings, the dominant canopy species in a seasonal tropical evergreen forest, Thailand. It is infected by a host‐specific fungus that is easily identifiable in the field. We quantified the effects of conspecific seedling and adult density on fungal infection and seedling survival over a wide range of environmental heterogeneity in elevation, understory vegetation and presence of forest gaps. Generalized linear mixed models (GLMMs) for seedling survival revealed that fungal infection significantly reduced survival and had the strongest effect on seedling survival as compared with conspecific density and environmental heterogeneity. Adult conspecific density was not, however, significantly correlated with the probability of infection, and conspecific seedling density was positively associated with increased infection only at high elevations. In contrast to infection, we found a significant positive correlation between conspecific seedling density and the probability of seedling survival. Consequently, our results demonstrate that fungal infection can have major impacts on seedling survival, but not in a manner consistent with local NDD effects on seedlings, as assumed in the Janzen–Connell hypothesis. Our study provides an example of how quantifying the interaction between environmental heterogeneity and a host‐specific plant‐pathogen can yield unexpected insights into the dynamics of seedling populations. The combined effects of host‐specific pathogens and environmental heterogeneity on survival of dominant seedling species may ultimately provide a chance for rarer species to recruit.     

长白山次生杨桦林种群空间点格局及密度制约效应

以长白山5.2 hm²次生杨桦林样地为研究对象,利用空间点格局分析的双相关函数g（r）以及随机标签零模型和案例-对照设计法,探讨了树木种群空间格局及其密度制约效应。研究结果表明：生境异质性对不同生活型以及不同树种的成熟个体在大尺度范围上具有强烈影响。剔除生境异质性带来的影响后,在14个常见树种中有12个树种在小尺度上呈显著的空间聚集分布格局;随着空间尺度的增加聚集性分布树种数量急剧下降,在18 m尺度上聚集率下降到0。全部14个常见树种均呈现出显著的密度制约效应,表明密度制约是调节温带森林树木种群空间结构的主要作用机制。此外,密度制约与物种多度呈负相关,与亚林层和灌木层树种的同种聚集强度呈正相关。并且随着空间尺度增大受密度制约影响的树种百分比逐渐减小,14个常见树种中有11个在0-1 m处达到最大的密度制约强度。     

Density‐dependent survival varies with species life‐history strategy in a tropical forest

Species coexistence in diverse communities likely results from multiple interacting factors. Mechanisms such as conspecific negative density dependence (CNDD) and varying life‐history strategies related to resource partitioning are known to influence plant fitness, and thereby community composition and diversity. However, we have little understanding of how these mechanisms interact and how they vary across life stages. Here, we document the interaction between CNDD and life‐history strategy, based on growth‐mortality trade‐offs, from seedling to adult tree for 47 species in a tropical forest. Species’ life‐history strategies remained consistent across stages: fast‐growing species had higher mortality than slow‐growing species at all stages. In contrast, mean CNDD was strongest at early life stages (i.e. seedling, sapling). Fast‐growing species tended to suffer greater CNDD than slow‐growing species at several, but not all life stages. Overall, our results demonstrate that coexistence mechanisms interact across multiple life stages to shape diverse tree communities.     

Intraspecific and phylogenetic density-dependent seedling recruitment in a subtropical evergreen forest

Recent evidence suggests that plant performance can be influenced by the phylogenetic diversity of neighboring plants. However, no study to date has examined the effect of such phylogenetic density dependence on the transition from seed to seedling. Using 6 years of data on seedling recruitment and seed rain of 13 species from 130 stations (one 0.5 m² seed trap and three adjacent 1 m² seedling plots) in a subtropical evergreen forest, we asked: (1) Does negative density dependence act across seed to seedling stages? (2) Is there evidence for phylogenetic density dependence during the seed to seedling transition? (3) Does the strength of density dependence vary among years? Generalized linear mixed-effects models were used to model seed to seedling transition as a function of conspecific seed and seedling densities, heterospecific seed and seedling densities, and mean phylogenetic distance of heterospecific seeds and seedling. Conspecific seed density had a significant negative effect on seedling transition rates for 12 of 13 focal species. In contrast, conspecific seedling density had a positive effect for 7 species, suggesting species-specific habitat preferences. Few species were significantly affected by the density or phylogenetic relatedness of heterospecific seeds and seedlings. Only conspecific seed density effects varied among years for most focal species. Overall, our results reveal that conspecific seed and seedling densities play a more important role than the density or relatedness of heterospecific seeds and seedlings during the seed to seedling stage, suggesting that species-specific seed predators, along with habitat preferences, may contribute to diversity maintenance in this forest.     

亚热带-温带过渡区秦岭落叶阔叶林幼苗存活机制

【目的】物种幼苗的存活与各种生物和非生物因素密切相关,研究关键因素对幼苗存活的影响有助于理解群落物种共存的主要作用机制。【方法】以秦岭落叶阔叶林25 hm²固定样地的木本植物幼苗为对象,对11 408棵幼苗的生存动态开展连续5年(2015—2019年)的监测,利用广义线性混合模型(GLMMs)在群落水平上对影响不同年龄阶段幼苗存活的主要生物与非生物因素进行分析。【结果】(1)从群落水平来看,对幼苗存活影响最大的是生物因素,幼苗存活率与同种幼苗邻体密度和同种大树邻体胸高断面积呈显著负相关,与异种幼苗邻体密度呈显著正相关,表明物种在幼苗时期受到强烈的负密度制约效应;(2)从苗龄水平上来看,除了生物因素,影响幼苗存活的主要因素还包括海拔等非生物因素,但非生物因素的影响随着苗龄增大而减小。【结论】影响幼苗存活因素是多样的,其中生物因素的影响更显著,促进秦岭大样地中幼苗共存的主要机制为负密度制约效应。     

Density dependence is prevalent in a heterogeneous subtropical forest

Although negative conspecific density dependence among neighbours is widely studied, the general prevalence of the effects is still poorly understood due to a lack of studies from zonal forests other than the tropics. In addition, the detection of density dependence may be confounded by the influence of habitat heterogeneity. Here we examined the spatial distributions of 47 common tree species (diameter at breast height≥1  cm) using the pair-correlation function g(r) in a fully mapped 24-ha subtropical forest in China. We first investigated whether habitat heterogeneity influenced tree distributions, and then examined the conspecific tree patterns and density dependence after removing the effects of habitat heterogeneity. We found that the forest plot exhibited strong large-scale heterogeneity in the distribution of both large adult trees of different growth forms and individual species. After the habitat heterogeneity was accounted for, 39 of the 47 species (83.0%) were found to exhibit density dependence predominantly at close distances among neighbors. Our findings highlight density dependence as a prevalent mechanism for regulating the population spatial structure of most tree species in the species-rich subtropical forest studied here. Furthermore, the occurrence of density dependence is closely associated with species abundance and the strength of conspecific aggregation at local scales. Abundant species with high strength of conspecific aggregation tend to show density dependence.     

吉林蛟河针阔混交林乔木幼苗组成及其密度格局影响因素

以吉林蛟河次生针阔混交林42 hm ²固定监测样地中209个幼苗监测站内的乔木幼苗为研究对象, 基于2016和2017年幼苗调查数据, 探究幼苗物种组成、数量动态等特征, 并运用广义线性混合效应模型分析了幼苗密度与生物邻体及其生境因素的相关性。结果表明: (1)该样地内所有幼苗监测站共调查到幼苗4 245株, 分属10科12属18种, 新生幼苗的数量在物种和调查年份间均有明显差异, 其中水曲柳(Fraxinus mandschurica)和紫椴(Tilia amurensis)幼苗表现出大量出生和死亡的动态特征。(2)群落水平上, 幼苗密度与局域同种成体胸高断面积之和、土壤全磷和有效钾等养分含量显著正相关, 适宜大树生长的生境同样适宜幼苗的生长。(3)水曲柳幼苗密度的影响因素与群落水平一致, 红松(Pinus koraiensis)存在明显的生境偏好, 在湿度较小、土壤全磷、有效氮和有效磷含量较低的生境中密度更高。相对于多年生幼苗, 同种成年邻体对当年生幼苗密度影响更加显著。该研究证实了扩散限制和生境过滤共同影响幼苗密度格局, 生物邻体和生境异质性的相对重要性随幼苗物种种类和年龄级变化。     

Drivers of composition and density pattern of tree seedlings in a secondary mixed conifer and broad-leaved forest,Jiaohe, Jilin,China

以吉林蛟河次生针阔混交林42 hm ²固定监测样地中209个幼苗监测站内的乔木幼苗为研究对象, 基于2016和2017年幼苗调查数据, 探究幼苗物种组成、数量动态等特征, 并运用广义线性混合效应模型分析了幼苗密度与生物邻体及其生境因素的相关性。结果表明: (1)该样地内所有幼苗监测站共调查到幼苗4 245株, 分属10科12属18种, 新生幼苗的数量在物种和调查年份间均有明显差异, 其中水曲柳(Fraxinus mandschurica)和紫椴(Tilia amurensis)幼苗表现出大量出生和死亡的动态特征。(2)群落水平上, 幼苗密度与局域同种成体胸高断面积之和、土壤全磷和有效钾等养分含量显著正相关, 适宜大树生长的生境同样适宜幼苗的生长。(3)水曲柳幼苗密度的影响因素与群落水平一致, 红松(Pinus koraiensis)存在明显的生境偏好, 在湿度较小、土壤全磷、有效氮和有效磷含量较低的生境中密度更高。相对于多年生幼苗, 同种成年邻体对当年生幼苗密度影响更加显著。该研究证实了扩散限制和生境过滤共同影响幼苗密度格局, 生物邻体和生境异质性的相对重要性随幼苗物种种类和年龄级变化。     

影响不同林型天然红松混交林林隙更新的土壤特征因子

采用野外调查、样品采集和统计分析等相结合的方法,对小兴安岭天然红松混交林3种不同林型(椴树红松混交林(TP)、枫桦红松混交林(BP)、云冷杉红松混交林(PAP))的林隙及其邻近郁闭林分的土壤特征因子和树木更新的相关性进行了研究,旨在阐明林隙土壤特征因子对树木更新的影响,从而为小兴安岭天然红松混交林植被更新、退化生态系统的恢复和可持续经营提供基础数据和实践参考。结果表明:郁闭林分土壤有机质、全氮质量分数显著高于3种不同林型的林隙。有效磷和速效钾含量在BP内与其他林型之间差异显著。3种林型林隙内p H值均略高于其郁闭林分,但与其差异均不显著。3种林型林隙内更新总密度、幼树更新密度与郁闭林分差异显著(P0.05),PAP林隙中更新总密度和幼树更新密度最高。BP林隙面积与更新密度相关不显著,乔木幼苗、幼树更新密度与有机质(r=-0.400,r=-0.475)、全氮均呈显著负相关(r=-0.519,r=-0.603)。TP林隙内全氮与乔木幼苗更新密度呈正相关(r=0.092),而与乔木幼树更新密度呈显著负相关(r=-0.585)。PAP林隙内全氮与乔木幼苗、幼树更新密度均呈负相关。郁闭林分幼苗更新密度分别与有机质、全氮、速效钾、p H值、脲酶和蛋白酶呈负相关。主成分分析表明,全氮是影响林隙和郁闭林分树木更新的关键因素。