Changes in Plant Species Diversity of Natural Coniferous Forests along the Altitudinal Gradient in the Youshui River,Qinling Mountains

This paper analyzed the clustering classification and plant species diversity of natural coniferous forests in the Youshui River basin.Based on the importance value matrix of sample plots,the communities of natural coniferous forests were divided into different formation types through two-way clustering method.Indices of species richness,diversity and β diversity were calculated and used to describe the variation patterns of plant diversity along the altitudinal gradient.The results showed that 14 plots of natural coniferous forests were categorized into six formations in the study area.With the increment of altitude,the species abundance,Shannon-Wiener index and Pielou evenness index increased firstly but declined subsequently.The order of species abundance and α diversity indices of the six natural coniferous forest formations was as follows: Tsuga chinensisPinus armandiiPinus tabulaeformisAbies fargesiiLarix chinensisAbies fargesii+ Betula albo-sinensis.β diversity,which is indicated by the Cody index,decreased gradually along with the altitudinal gradient.