Quantitative Classification and Ordination of Stipa purpureaSteppe Community in Qinghai Plateau

Stipapurpurea steppe is the largest area and most important community type of alpine steppe ecosystems in Qinghai-Xizang Plateau.Currently,the number of studies on the S.purpureasteppe classification and ordination is still lacking.In this study,the typical S.purpureasteppe in Qinghai Plateau was selected as subject.Multivariate statistics methods including TWINSPAN(Two-way Indicator Species Analysis)and CCA(Canonical Correspondence Analysis)were used to classify the S.purpureasteppe on the basis of investigating a large number of vegetation communities in this region.The results showed that:(1) The species composition of S.purpureasteppe in the study area is relatively simple.The dominant families of seed plants were Gramineae and Compositae,and the dominant areal types of genera were North temperate type.(2)The 90transects of S.purpureasteppe in Qinghai Plateau could be merged into 8main ecological associations:Ass.Stipapurpurea+Poa indattenuata,Ass.Stipapurpurea+Kobresia humilis,Ass. Stipapurpurea+Astragalus polycladus,Ass.Stipapurpurea+Kobresia pygmaea,Ass.Stipapurpurea +Potentilla bifurca,Ass.Stipapurpurea+Saussurea arenaria,Ass.Stipapurpurea+Leontopodium humilumand Ass.Stipapurpurea+Kengyilia thoroldia.(3)The major environmental factors influenced the distribution of S.purpureasteppe ecological associations in Qinghai Plateau firstly were space factors(altitude,longitude and latitude)and heat factor(temperature),then water factors(precipitation,wetness).(4) For internal ecological association division of S.purpureasteppe community,CCA could complement and correct the TWINSPAN results,make the classification more realistic ecological significance,and reflect more clearly relationship between the associations and environmental gradients.