Study on the main forest community and species diversity of the natural forest types in upstream Heihe river,Shaanxi

【Objective】 Through the systematic investigation of plant communities and species diversity quantitative analysis in the study area,the study revealed the distribution of forest community types and species diversity characteristics,which provided theoretical basis to study plant community character and structure.【Method】 The forest community was classfied by two-way TWINSPAN,and the Shannon-Weiner index,Simpson,Pielou index and evenness index were applied to analyze the community diversity.【Result】 The 24 plots in the research area can be divided into 10 community types;the species diversity is distinctly different between the different layers of community structure,the species diversity of herb layer is bigger than tree layer and shrub layer;the order of the community diversity is Betula platyphylla+ Populus purdomiiPinus tabulaeformis+Quercus aliena var.acuteserrataPinus armandiCorylus chinensis+Populus cathayanaP.tabulaeformis+Populus davidianaUlmus bergmannianaAlangium chinenseQ.aliena var.acuteserrataP.davidianaP.tabulaeformis.There are 237 species,belonging to 65 families,150 genera,in 24 plots.【Conclusion】 Interference,environmental heterogeneity of undergrowth and biological characteristics of species may cause the difference of species diversity between plant communities and layers within each community.However,interference,environmental heterogeneity and biological characteristics are complex scientific problems,and they are integrated performance of many factors affection.