The Assembly And Development Mechanisms Of Typical Natural Forest Community In Changbai Mountains

Forests are an important component of the terrestrial biosphere,providing a range of key ecosystem functions such as carbon sequestration,water and nutrient cycling.Changbai Mountains Nature Reserve has a complete original broad-leaved Korean pine forest ecosystem,and it has formed a secondary succession series from the pioneer to the top community with the surrounding Populus-Betula forests of different forest ages,providing a smooth development for the research work.Since the decades times,the resources of the original broad-leaved Korean pine forest in Changbai Mountain have been severely damaged,forming a large area of secondary forest community.The protection of primitive broad-leaved Korean pine forests and the restoration of degraded secondary forest communities are imminent.In recent years,as the loss of species has become more severe,the mechanism for exploring the impact of biodiversity on ecosystem function is particularly urgent.In this paper,three 5.2 ha monitoring plots(secondary poplar and birch mixed forest,PBF;secondary mixed conifer and broad-leaved forest,CBF;mixed Tilia and Korean pine forest,TKF)were established in the typical forest community of Changbai Mountains.The three plots constitute a typical succession sequence from the secondary forest to the top vegetation type.Based on the sample environmental survey data and multiple recensused data,this study focus on seedling regeneration and tree survival driving mechanism,community assembly and relationship between community structure and ecosystem function.The results explained the coexistence mechanism of community species,provided theoretical and factual basis,which has certain guiding significance for rational prediction of forest ecosystem function.The main findings are as follows:1.The study was conducted in secondary conifer and broadleaved mixed forest and secondary poplar and birch mixed forest in Changbai Mountain of China.We used generalized linear mixed models(GLMMS)to analyze how the seedling survival relates to neighborhoods and habitat variables.The continuous monitoring data was used to calculation in 2011-2014.The following results were obtained:Both the conspecific negative density dependence(CNDD)and habitat filtering were regulated seedling survival;seedling survival were strongly negatively impacted by the density of conspecific adult neighbors in habitats both in the two forests;However,conspecific seedling-seedling positive density dependence was found in our study.2.Empirical analyses of forest dynamics is important for understanding various ecological processes underlying particular forest communities.Tree mortality is considered a key process driven by many local factors.Using generalized linear mixed-effects models(GLMMs),we want to analysis the effects of DBH,biotic neighbor variables and abiotic environmental variables on tree survival in three 5.2 ha permanent plots at different successional stages.Our study shows that(1)the mortality rates are highly variable among the different tree species.(2)Among the drivers of tree survival,tree size had the strongest effect across different species.The full model with tree size,biological variables and abiotic environment variables fits well the survival of individual trees in a secondary poplar and birch mixed forest and a secondary conifer and broad-leaved mixed forest;models containing only the tree size can better fit the survival of trees in mixed Tilia and Korean pine forest.Our study suggests that density-dependent effect and niche partitioning contribute to the regulation of survival pattern of temperate forest communities.3.Specific community patterns include specific ecological processes,and specific ecological processes can in turn explain the drivers of the specific community patterns.It has become a consensus that environmental heterogeneity and biological dispersal limitation can affect species-area relationships and beta diversity in habitats.In our study,the soil elemental data of three different succession stages in poplar-birch,mixed conifer and broad-leaved,and broad-leaved Korean pine forest were analyzed by principal component analysis(PCA),and four principal components(PCs)were extracted to represent the spatial variation characteristics of different soil properties.The homogenous Poisson model(HomP)and the homogenous Thomas model(HomT)were used to simulate species distribution and study soil-species relationships.The results show that the spatial distribution of species in the plot is related to the diffusion of species and the heterogeneity of spatial distribution of soil resources.In a completely randomized situation,the distribution of more than 90%of the three plots showed a significant correlation with the main components of the soil environment.Among them,92.7%of the tree species in poplar-birch forest were significantly correlated with at least one PC in the soil.92.6%of the coniferous and broad-leaved forests tree species were significantly associated with at least one PC in the soil,and 90.9%of the species and at least one soil PC is significantly correlated in the broad-leaved Korean pine forest.After eliminating the restriction of species diffusion,it was found that the number of species in the three plots that were significantly correlated with the soil principal components decreased,but nearly half of the species showed a distribution that would have a preference for the soil environment.Among them,29.3%of the tree species in poplar-birch forest were significantly correlated with at least one PC in the soil.51.9%of the coniferous and broad-leaved forests tree species were significantly associated with at least one PC in the soil,and 45.5%of the species and at least one soil PC is significantly correlated in the broad-leaved Korean pine forest.4.Taxonomic structure could reflect the regulation of local processes,such as environmental filtering,interspecific competition and dispersal limitation by testing whether the co-occurring species are more closely related than would be expected by chance.Based on the species composition data collected in three large forest observational field studies,the taxonomic structure of the communities was analyzed at different sampling scales.Random null model was used and the "standardized effect size"(SES)of taxonomic ratios was calculated,to assess possible differences between the observed and simulated taxonomic structures,which may be caused by specific ecological processes.As expected,the taxonomic ratios decline with increasing grain size in all plots.The quantitative relationship between genera/families and species,described by a linearized power function,showed a good fit.In the mixed conifer and broad-leaved forest and Tilia-Korean pine forest,the taxonomic ratios of the observed communities had significantly lower values than those of the simulated random community under the test of tnull model at almost all scales.But that was not the case for the secondary poplar-birch forest,SES were larger than 0.The results suggest that the effect of abiotic filtering is greater than the effect of interspecific competition in shaping the local community for the mixed conifer and broad-leaved forest and Tilia-Korean pine forest.In the secondary poplar-birch forest,competition dominated the taxonmic structure of the community.Local processes influence the taxonomic structure,but their combined effects vary with the spatial scale.5.Thoroughly exploring the relationship between species and structural diversity with productivity is an important prerequisite for the improvement of both forest biodiversity and productivity,and is of great significance for forest scientific management.In this study,three typical forest communities in Changbai Mountains were selected as the research object to analyze the relationship between species and structural diversity with productivity in different succession stages.The early,middle and late stages of communities were represented by the secondary poplar-birch forest,coniferous-broadleaved mixed forest and broad-leaved Korean pine forest.Multiple regression models were built for the comparison of the correlations between different diversity indices and productivity,based on the regression results,the best index was determined to represent for species and structural diversity,and then the structural equation model was built to compare the relative importance of species and structural diversity on productivity.The results showed that:in the early succession stage,the relationship between species richness,DBH evenness and productivity was the most significant and the effects of these two diversity indices on productivity were similar but not strong.In the middle succession stage,the relationship between species richness,DBH evenness and productivity was the most significant,they both had positive effects on productivity,and the effect of species diversity on productivity was stronger than that of structural diversity.In the late stage of succession,there was no significant correlation between species diversity and structural diversity and productivity.6.The relationship between biodiversity and ecosystem functioning(BEF)has become a cornerstone of ecological research.Two alternative hypotheses,niche complementarity and mass-ratio mechanism,have been proposed to explain the effects of biodiversity on ecosystem functioning.Based on the niche complementarity hypothesis,the ecosystem functions are determined by niche partitioning and interspecific facilitation.However,based on the mass-ratio mechanism,the ecosystem functions are determined by the most dominant species,which are characterized by extraordinary traits and high productivity.Species diversity is the most commonly considered component of biological difference,however species diversity is silent on the function dissimilarity and evolutionarily relatedness of species.Compared with the species diversity,phylogenetic and function diversity contain more details.In this research,we tested the relative importance of species diversity,phylogenetic diversity and function diversity on ecosystem functioning,based on three permanent plots in Changbai Mountain,northeast China.We expect to obtain the basic relationships of biodiversity and ecosystem function and assist in achieving a better understanding of biodiversity conservation and forest management.Based on the results of this study,at the local scale,environmental filtering significantly affects the community assembly process of broad-leaved Korean pine forest in Changbai Mountains.Environmental factors including soil factors have an important impact on individual tree death and community structure.In the early stage of succession(PBF),competition is the main factor driving the assembly of the community.With succession proceeding,the importance of this effect gradually reduced.The negative density dependence had important effects on the the survival of individual trees and seedlings.This study found that biodiversity and ecosystem function were correlated at each succession stage,but phylogenetic diversity and structural diversity had the most significant impact on productivity at the intermediate succession stage.