Abstract: Species diversity of shrubs and herb under virgin forests of Abies georgei in Sejila Mountains of southeastern Tibet was measured quantitatively and analyzed by the investigating method of typical plot, three α diversity and two β diversity respectively.The results indicated that α and β diversities had the same law.With the increase of altitude,the species richness,evenness and diversity indices declined.The species distribution and number of shrubs and herb under forests had apparently changed.The similarity of community got more and more small.Abies georgei forests took on open distribution near the timberline,R.nivale and R.nyingchiesse were mainly dominant species of shrubs,and then C.fastigiata and R.yunnanensis were dominant species of herb.This distribution results in obvious characteristics of ecotone.The use of Motyka β diversity indices could much more reflect accurately the characteristics of mutual influence between the change of altitude gradients and species substituation.

Key words: land use type, soil carbon and nitrogen content, soil carbon and nitrogen storage, Loess Plateau.