Spatial Distribution of Grassland Degradation and Trend in Northern Tibet

Based on the remote sensing data derived from NOAA/AVHRR with a spatial resolution of 8 km of 1981-2000,SPOT/VGT with a spatial resolution of 1 km of 2001,and MODIS with a spatial resolution of 0.25 km of 2002-2004,as well as other related data of northern Tibet,spatial distribution of grassland degradation in northern Tibet was analyzed with the help of Geographical Information System.This study established a new method to calculate grassland degradation trend coefficient in the northern Tibet and analyzed the grassland degradation trend of this area.The result indicated that grassland degradation mainly occurred on flat(slope gradients 1) in the Northern Tibet and the grassland degradation index(GDI) was higher on the sunny slope than that on the shady slope;the trend of grassland degradation on flat was more significant than that on the slope.Grassland degradation mainly occurred on the elevations ranging from 4500m to 5250m where the largest grassland area is.In this area,grassland degradation is obvious and the trend of grassland degradation is considerable.