Spatial pattern and change gradient of alpine grassland in the Source Region of Yellow River

The Yellow River Source Region is China's important ecological barrier,and variation of alpine grassland ecosystem in this region with the climatic environment factors changing was worth to pay more attention.In this research,we used meteorological observation data and remote sensing normalized vegetation index(NDVI)to study the variation process of alpine grassland ecological system with the hydrothermal changing gradient in the source region of Yellow River The results showed that,during the past 12 years,the average of grassland NDVI was 0.557 8.The highest NDVI were in Jiuzhi and Gande County, followed by Dari and Maqin County.The lowest NDVI were in Maduo,Chengduo and Qumalai County. Alpine grassland NDVI was lower in north of Zhaling and Eling Lake than in other regions.During the last 12years,change rate of the grassland NDVI was 0.002 4·a-1,and the coefficient of variation is 0.076 7, which showed litter change of NDVI.Climatic environment factors of the source region of Yellow River changed with gradient from northwest to southeast and formed hydrothermal gradient,which led to the grassland gradient change of NDVI,NDVI change rate and NDVI coefficient of variation.With the annual average temperature rose,NDVI increased significantly,and NDVI change rate and variation coefficient decreased significantly.With the annual precipitation and moisture index rose,NDVI increased significantly,while NDVI change rate and variation coefficient decreased significantly.With the elevation rose,NDVI decreased significantly,while NDVI change rate and variation coefficient increased significantly.