Changes in vegetation diversity and structure in response to heavy grazing pressure in the northern Tianshan Mountains, China

Due to changes in Chinese land-use policy in the mid-1980s, increased livestock populations have imposed a significant impact on the diversity of Seriphidium borotalense communities. Four sites with different grazing pressures were chosen within a tenured area on the northern slopes of the Tianshan Mountains of Xinjiang Uygur Autonomous Region in western China to examine the response of plant communities to heavy grazing. Our field experiment demonstrated that heavy grazing not only altered the diversity of the palatable plants but also changed the morphological structure and distribution patterns of dominant S. Borotalense which responded by shortening stems, reducing foliage biomass, increasing the size of clumps and decreasing the number of reproductive branches. With increased grazing pressure, tender palatable genera such as Stipa and Kochia disappeared and then S. borotalense started to decline. However, the biomass of S. borotalense changed little in extremely degraded land near the tenured area. The extremely overgrazed land was difficult to rehabilitate because of serious deterioration of the habitat and the poor condition of S. borotalense populations, which is indicative of failure of the plant to reproduce.