Analysis of vegetation changing trends and causes in Gannan since 2000

The normalized difference vegetation index (NDVI) can characterize the vegetation growth status. The temporal and spatial changes of Ganan vegetation and of its response to climatic factors and human activities are analyzed using EOS/MODIS NDVI data,precipitation, temperature and stock capacity data during 2000-2014.The results show that: 1) The overall stability of vegetation takes on an increasing trend in recent 15 years. The stability of forest is higher than that of grassland. The spatial variability of vegetation is mainly caused by the grassland. 2) The vegetation tends to be improved and accounting 70% of the studying area. The decreasing trend (P0.05) happens only in a local place occupying 21% of total studying area. The decreasing is mainly owing to grassland degradation which contributes to 75% of the total degraded area. The degraded regions are primarily distributed in Maqu, Luqu and Diebu County. 3) Temperature tends to increase mainly in degraded regions (Maqu, Luqu and Diebu). The stock capacities show an extremely significant increasing trend (P0.01) except Zhouqu County, which has a decreased trend (P0.05). The increasing stock capacity and overgrazing are the primary reasons caused the vegetation degradation, discrete, and nonuniform distribution.