Dynamic changes of grazing pressure on grassland on south slope ofGuanshan Mountains over the last 30 years

The safe and health of grassland ecosystem is very important for the sustainable development of animal husbandry. Based on the animal population data in the area of south slope of Guanshan and the climate data regarding to sunshine duration, temperature and precipitation in Qingshui and Zhangjiachuan Weather Stations in 1978 to 2008, the model of grassland pressure index was established to analyze the dynamic variation of animal population, grassland potential production and pressure index. The result showed that the annual animal population increase was 1.76104 sheep units; potential grassland production changed little and ecological pressure index increase was 0.2 since 1978. It indicated that the ecological pressure index increased greatly in the last 5 years and the animal population was over the capacity of the grassland. The main way for sustainable animal husbandry development was to control the animal population and expand the grassland area.