[Spatiotemporal differentiation of land cover change and grassland degradation pattern in Yangtze River headwaters area].

Based on field survey data, remote sensing images and statistical data, this paper analyzed the spatiotemporal differentiation of land use and grassland degradation patterns in Yangtze River headwaters area in 1987-2007, and discussed the main natural factors (elevation, position and slope) leading to the changes of this area's grassland ecological environment. In 1987-2007, the fragmentation of this area' s landscape patterns had an increasing trend, and natural environment and climate change were the main driving forces of land use pattern change. There existed significant differences in the areas of grassland degradation at different altitudes. Grassland degradation mainly occurred at altitudes 4800-5100 m. The grassland degradation area tended to increase with increasing elevation, and the proportions of the degradation area varied greatly over different slopes and aspects. The climate in the study area became warm and dry, and the spatial structure of regional land cover changed obviously. The distribution patterns of grassland degradation at different elevation, position and slope coincided with alpine environment and human disturbances, suggesting that alpine environment and climatic change were the decisive factors to the grassland ecosystem pattern in Yangtze River headwaters area.