Abstract:Minjiang river is an important branch of upper reach of the Yangtze River. The upper reach of Mingjiang river lies in the east margin of Qing-zang altiplano, a typical arid valley because of the special alpine canyon physiognomy, where the ecological security and the environment conservation is important for all of the Yangtze River valley. In this arid valley the mean annual precipitation is 493mm, the mean evaporation is 1332mm and the altitude 1300~2200m. The main plant communities are composed of xeroph...