Rangelands are extremely important to society for the goods and services as well as for the ecological services they provide. They account for about one-half of all the lands in the world. In China，rangelands form the largest terrestrial ecosystem and one of the three most important food producers（Li，1997）. However，about 90% of the total usable rangelands in China has been degraded to various extents and become into one problem facing agricultural production，rural development and environmental i <<