Plant Spec ies D iversity ofMa in Forest Commun ity Types inSan Jiangyuan Na tiona l Na ture Reserve

The characteristics of fourmain forest community types were analyzed by typ ical samp ling technology, αdiversity andβdiversitywere calculated with various calculation methods. The results showed that: (1) In fourmainforest communities of Picea crassifolia, Picea lik iangensis var. balfouriana, Picea purpurea and Sabina tibetica, α diversity which rep resented by Shannon-wiener index and Gleason richness index had the highest value in herb layers,the medium in shrub layers and the lowest in tree layers. (2) Among the 4 main forest communities, the ordinationorder ofα diversity in tree layers from high to low was that Picea crassifolia community > P. pu rpu rea community >S abina tibetica community > P. likiangensis var. balfou riana community. (3) There were no significant difference ofspecies diversity in shrub layers among Picea crassifolia comm unity, P. purpurea community and P. lik iangensis varbalfouriana community, which of them distributed in shade slopes, however, S abina tibetica community distributedin sunny slopes had the lowest species diversity in shrub layers because of grazing disturbance and natural conditionsof sunny slopes. (4) Species diversity in herb species of Sabina tibetica communitywas higher than other communities which distributed in shade slope. (5) Here, β diversity indicated that the similar degree of species compositionamong communities which was determined by ecological range and biological characteristics of dominant species.