Land use change and its effect is one of the hotspots of global change research. It has always been more concerned about the cultivation of agricultural land use changes in food security, but the pastoral land use change on food security impact is significant deficiencies. It is different in the concept of food security in agricultural areas and pastoral areas. Besides agricultural areas of food security, pastoral land use change on food security study also deserves attention. In this paper, Dalag County, Qinghai Province in western China was taken as a case study area, and the township was taken as research unit. A model is built including the smallest per capita grassland area and grassland pressure index to calculate the food security of each township. There are similar trends of the food security in Dalag County and 10 townships which belong to Dalag from 1987 to 2007. With the animal husbandry production conditions showing deterioration, inadequate technical and material inputs, grassland degradation is getting more serious, the population increased and real per capita grassland area decreased, while the smallest per capita grassland area and the grassland pressure index keep increasing. The calculation of the pressure index of each township in 1997 and 2007 showed that there are four levels of food security (security area, alert area, shortage area and crisis area) in 1997. The security area and the alert area did not exist in 2007, replaced by crisis area and a wide range of food shortages area. The pressure index on grassland gradually reduced from Manzhang, Xiahongke, Deang, Wosai and Jimai which lie in the eastern part with lower altitude, better climate and more human activity to Shanghongke, Moba, Jiangshe, Sangrima and Tehetu which lie in the western part, indicating that unreasonable human activities are one of the main driving forces for grassland degradation and food supply shortage. It could relieve grassland pressure status by taking active measures to control the speed of smallest per capita grassland area and improving animal husbandry technology.
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