Community characteristics, distribution and environment interpretation of Cupressus gigantea along Yarlung Zangbo River in Tibet

It is important to understand the dynamics of plant community and its response to environmental change．Cupressus gigantea is a national-level protected plant distributed from Milin county to Lang county along the Yarlung Zangbo River．Two-way indicator species analysis (TWINSPAN) clustering and Canonical Correspondence Analysis (CCA) ordination were used to study plant community distribution and its relationship with environment．Plant communities in C. gigantea distribution area showed a simple structure and could be divided into C. gigantea community, C. gigantea-Artemisia sacrorum community and Pinus densata community．Canonical Correspondence Analysis showed that the first axis was significantly related to elevation and soil water content, soil bulk density and soil texture, mainly reflecting influence of moisture and thermal conditions, and soil properties．The second axis was related to latitude, slope aspect, soil phosphorus content, annual precipitation, soil total potassium and soil nitrogen-phosphorus ratio, mainly reflecting changes in soil nutrients, precipitation and light conditions．Two determining factors for community distribution were: difference in moisture and thermal conditions induced by changes in elevation and slope aspect, difference in soil physical and chemical properties．The main distribution altitudinal ranges of C. gigantea community, C. gigantea-Artemisia sacrorum community and Pinus densata community were 3000-3400, >3400-3500 and >3500-3600 m, respectively．These data are important to understand environmental characteristics of plant communities in the distribution area of C. gigantea, and will help to protect plant resources of C. gigantea more effectively．