Multivariate analysis of plant communities and environmental factors in Ngari, Tibet

Ngari is the driest, coldest, and highest region on the Tibetan Plateau. During the 1976 Interdisciplinary Scientific Expedition of the Chinese Academy of Sciences to the Qinghai-Xizang (Tibetan) Plateau there was a rare opportunity to study this area. Sampling of 163 sites was done, recording abundances of 241 vascular plant species, along with basic environmental information. The purpose of this study were (1) to analyze these data statistically despite their complexity and limitations, and (2) to produce a quantitative description of the vegetation of Ngari and of its relationship to environmental factors. The principal analysis of these data involved two steps: first the vegetation matrix was summarized in two vectors of ordination scores produced by detrended correspondence analysis (DCA), and then these scores were related to environmental and geographical parameters by multiple regression analysis. This analysis successfully handled the extreme diversity of plant communities, from low montane warm desert to high mountain periglacial communities, and from intrazonal saline meadow and bog to zonal montane desert and steppe. The plant community pattern in Ngari is largely determined by thermal and moisture gradients, as determined by geographical position and soil conditions.