| The study of community assembly has long been a central issue in ecology.In recent years,more and more ecologists have conducted relevant validation work around the mechanistic theories:niche theory and neutral theory,but there is no consistent conclusion in understanding the mechanisms of local community assembly.Niche theory highlights the effects of deterministic processes in shaping the community.On the contrary,neutral theory emphasizes the importance of stochastic processes.Advances in statistics and theory make it possible to explore community assembly mechanisms based on multiple methods.Since multiple processes,including environmental filtering and interspecific competition based on niche theory,and dispersal limitation based on neutral theory,may simultaneously affect community assembly,it is important to integrate the structure and dynamic pattern together to understand community assembly comprehensively and predict the response of the community to disturbance.In this paper,we analyzed the mechanisms of local community assembly based on the taxonomic,phylogenetic structure,and the dynamics of forest community using the data of 3 large plots in coniferous and broad-leaved mixed forest located in Jiaohe,Jilin Province.We also detected the influence of harvest disturbance on forest structure and dynamics based on the records of harvest disturbance.The main results of the study are as follows:1.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 the large forest observational field studies,the taxonomic structure of the community was analyzed at different sampling scales.Two random null models were 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.We further applied a phylogeny-based method to compare results with those of the taxonomic approach.As expected,the taxonomic ratios decline with increasing grain size.The quantitative relationship between genera/families and species,described by a linearized power function,showed a good fit.The taxonomic ratios of the observed communities had significantly lower values than those of the simulated random community under the test of two null models at almost all scales.The results suggest that the effect of abiotic filtering is greater than the effect of interspecific competition in shaping the local community at almost all scales.Local processes influence the taxonomic structure,but their combined effects vary with the spatial scale.The taxonomic approach provides similar insights as the phylogenetic approach,especially when we applied a more conservative null model.Analyzing taxonomic structure may be a useful tool for communities where well-resolved phylogenetic data are not available.2.Empirical analyses of forest dynamics is important for understanding various ecological processes underlying particular forest communities,among which tree mortality is considered a key process driven by many local factors.Our study shows that the mortality rates are highly variable among the different tree species and the influence of habitat preference on the mortality rate of a species across habitats was insignificant.Using generalized linear mixed-effects models(GLMMs),we further found that among the drivers of tree survival,tree size had the strongest effect across different species.There are significant negative relationships between the basal area of conspecific neighbors and tree survival at the community level and almost all guild levels.Regarding abiotic factors,elevation had a greater effect on tree survival than other topographic variables did.Abiotic factors affected shrub species more than tall canopy species in terms of survival rate.Our study suggests that tree size,density-dependent effect and niche partitioning contribute to the regulation of survival pattern of temperate forest communities,but the relative importance of these factors varies greatly among guilds and species.3.The relationship between biodiversity and productivity has stimulated an increasing body of research over the past decades,and this topic still occupies a central place in ecology.We present an analysis of the effects of local diversity on individual tree growth with a data set of 30827 growth records from a 30-ha temperate forest plot using spatially explicit individual-tree based methods.Considering effects of tree size,local topography and local competition,we find that the Shannon index has a strong positive correlation with tree growth.This result demonstrates that a tree grows faster when there is greater species diversity in its immediate neighborhood.We provide evidence of a complementarity effect(niche partitioning or facilitation)on individual tree growth.The study also reveals many confounding factors which influence the biodiversity-productivity relationship.Failure to account for such factors may lead to a distorted interpretation of the true diversity effects.At species level,the diversity effects on individual tree growth were relatively weak,explaining only a very small fraction of the variation in growth which emphasizes the need for careful analysis of the variation of particular species interactions.We conclude that the use of individual-tree based methods may lead to a better understanding of the biodiversity-productivity relationship and the mechanisms of community assembly in forest communities.4.The influence of selective harvest,which is an important method of forest management influencing the structure and dynamics of forest stands,does,however,not achieve consistent results.Accordingly,there is an urgent need to use more comprehensive data to study harvest disturbance and the change in forest stands after harvest.The results showed that the harvest intensity of the managed plot was 5.4%,as computed by the basal area.The harvest disturbance did not noticeably change the species composition and diameter at breast height(DBH)distribution.During the 5 years,the stand density was lower than that of 2010 in both plots.The mortality of the managed plot was lower,whereas the recruitment status was not better,than those of the control plot.The basal area increment per year of the managed plot was larger than that of the control plot,indicating that the thinning resulting from harvesting promoted the growth of trees.We entered the predictors representing harvest intensity into the model and found that the DBH was the most significant variable for the growth analysis,followed by the asymmetric competition factor.The predictor representing harvest showed a significant effect only for the growth model of Tilia amurensis.In general,low harvest intensity had little effect on the structure and dynamics of the community,whereas the radial growth of different species showed various responses to harvest disturbance. |
PDF Full Text Request