Trends of grassland NPP and its response to human activity in Northern Tibet

According to remote sensing data climatic data and other related data in Northern Tibet from 1981 to 2004,using CASA(Carnegie-Ames-Stanford Approach)model estimated the NPP of alpine grassland in the Northern Tibet and analyzed the spatial pattern of changing tendency for the alpine grassland NPP and its response to human activity intensity based on GIS technique.We found that the change tendency of alpine grassland in most area of Northern Tibet was not obvious,which occupied approximately 88.61% of total grassland area;while that changing remarkable region only accounts for 11.39%,and among these 11.30% decreased significantly,while and 0.09% increased.In Northern Tibet,the alpine grassland NPP for high elevation region has a greater proportion(bigger than 26%) to fall down,that in the region of slope between 15-30° change bigger,and aspect has little influence on change tendency of the alpine grassland NPP.The negative effect of local residential area to the grassland NPP change tendency is smaller than that of road.From the synthesis affects that,the intensity of human activity in the region near to road and the residential area are strong and the influence on grassland NPP change tendency are bigger also.The grassland NPP remarkably increased region only distributed in first buffer outside where the human activity intensity is biggest particularly.