INDIRECT GRADIENT ANALYSIS,QUANTITATIVE CLASSIFICATION AND ENVIRONMENTAL INTERPRETATION OF PLANT COMMUNITIES IN NGARI,XIZANG(TIBET)
西藏阿里植物群落的间接梯度分析、数量分类与环境解释

Basing on the multivariate analysis--ordination, quantitative classifi-cation, and environmental interpretation of 163 plant community samplescollected from Ngari, Xizang, the primary vegetation types, ecologicalgradients, and their quantitative relations with environmental factors ofNgari are given. The basic analysis contains the following three steps; 1)the two principal ecological gradients are brought to light by two vectorsof ordination scores produced by detranded correspondence analysis (DCA);2) the nonhierarchical and hierarchical classification systems of plant com-munities are produced from the 2-dimensional scatter polt of DCA ordina-tion and two-way indicator species analysis (TWINSPAN), respectively;3) environmental indexes (quantitative interpretation) of various vegetationtypes are given by the multivariate regression analysis which connects theordination scores with environmental and geographical parameters. it isshown by the analysis that the vegetation types of Ngari and their distri-bution are mainly determined by the thermal and moisture gradients. Theformer could be expressed quantitatively with the mathematic expressionof geographical parameters, the latter with the soil characteristics. Thetwo gradients contain quite different vegetation types, species, and habi-tates, ranging from low montane warm desert to alpine periglacial vegeta-tion, and from intrazonal bog and saline meadow to tonal plateau desertand steppe with their paricular position and ordination scores. That showsthat the quantitative analysing method used here for handling the ecolo-gical data of plant communities with great ecological diversity is highlyefficient.