Mechansims To Maintain Specise Diversity Of Deciduous Forest Of Baotianman In Temperate-Subtropical Ecological Transition Zone

Species coexistence mechanism has always been the core content of community ecology.Developed in recent years many species coexistence of hypothesis,one of the most strikings is the niche differentiation theory and the theory of community neutral.Studies of both role in community building is becoming a hot spot of international ecological field in recent years,but more relevant research focused on a single climate zone,such as tropical,subtropical,and temperate forest,the ecological transition zone between adjacent climatic zone of such studies are seldom reported.In this study,on the basis of the aforementioned investigation at Baotianman 1-ha plot in the warm temperate-subtropical transition zone,the spatial point pattern analysis,Torus conversion test,variance decomposition and model fitting methods were selected for research the community structure of deciduous broad-leaved forest in this area,and the role that maintain community species diversity of the niche differentiation hypothesis and communities neutral theory.Firstly we analyze the species composition and community structure of the five 1ha monitoring plots,results showed that:there were woody plants belonging to 162 species,79 genus and 40 families in 5 monitoring plots totally.Analysis of the floristic composition based on family shows that the tropical families are more than temperate families.However,at the genera and species level,the temperate elements are predominant,followed by the tropical elements.This shows a clear characteristic of transition zone.The analysis of size structure in the five lha monitoring plots shows that there are large number of saplings and the regenerative condition of whole community is well,but the size structure of main species show the inverted "J" type distribution,approximate normal distribution and bimodal distribution characteristics,advantages constructive species of Quercus variabilis and Quercus aliena var.acutiserrata are difficult to regenerate.The analysis under the Complete Spatial Randomness null model shows that the population pattern of major woody species includes effects of habitat heterogeneity are more likely to aggregate,habitat heterogeneity may be one of the factors affecting the distribution of species.To determine the existence of habitat heterogeneity effects,we focus on the species spatial distribution pattern of the mixed broadleaf-conifer forest,the results show that:the analysis of L(r)function,and the comparative analysis of complete spatial randomness model and heterogeneous Poisson process model show that environmental heterogeneity is one of the important factors in affecting spatial distribution of species;bivariate analysis of g(r)function shows that there are fierce competition between the two dominant species in plots(i.e.Quercus aliena var.acutiserrata and Pinus armandii),and lead to difficult to regenerate,but with the succession of community,the Quercus aliena var.acutiserrata populations will further expand its advantages,and Pinus armandi will disappear.In order to prove the existence of habitat heterogeneity extensiveness and manifestation,five 1-plots as whole,Torus conversion test were selected for research the correlation of species and habitat,the results show that:more than half of the species in the study area performances characteristics of habitat specialization,topography and aspect are the important factors that affect community structure and species distribution in this area,validated the inference of topography is more complex and more related species.In order to quantify the topography,stand density and spatial variables influence on species distribution,the principal coordinates of neighbor matrices(PCNM)is introduced as space variables,using the variance decomposition method for further study that the influence factors of species distribution,the results show that:community structure in different scales are widespread variability,spatial factor is one of the important factors affecting community structure;topography,spatial factors,stand density in five plots can partly explain the distribution pattern of species at Baotianlan,the proportion of their independence to explain range of 2.5%?11.89%,5.2%?15.1%and 5.1%?15.1%,the niche theory,neutral theory and negative density dependence mechanisms played a certain role on spatial distribution and community building of deciduous broad-leaved forest in this area.Finally,we compare the pre?(live and dead trees together)and post-mortality(live trees only)spatial patterms of Quercus aliena var.acutiserrata.And use the Random Labeling and Case-Control design to analysis the community of Quercus aliena var.acutiserrata.The results show that:the negative density dependence is one of the important factors affects the population spatial distribution pattern of Quercus aliena var.acutiserrata,and the strength of negative density dependence varies with the growth stage;the density dependent effects of interspecific is greater than intraspecific,there are intense interspecific competition between Pinus armandi and Quercus aliena var.acutiserrata.The results of this study indicate that niche differentiation processes(such as terrain,slope factor,stand density,intraspecific and interspecific negative density dependence),neutral process(such as propagation limits)are important mechanism for maintaining the diversity of species in Baotianman sample area,but the contribution of each factors were not big enough.So we need more and further study of other factors in maintaining species diversity in this region's that we can make a comprehensive understanding of the formation of species diversity and maintenance mechanism in this area.