Research on the Upper Boundary Change of Alpine Meadow and Its Relationship with Climate Change During the Past 23 Years in Xiangride,in Northeast Tibetan Plateau
We adopted the unsupervised classification and visual interpretation to extract upper boundary of alpine meadow in Xiangride by using remote sensing images of 1990,1999 and 2013 to summarize the change characteristics and analyze its relationship with climate change.The results showed that:(1)the temperature had a significant increasing trend and the precipitation remained unchanged from 1990 to 1999;the temperature remained unchanged and the precipitation increased significantly from 1999 to 2013.(2)the upper boundary change of alpine meadow was controlled by both temperature and precipitation,the alpine meadow expanded in higher region in the past 23 years,the area increased fast from 1990 to 1999 which was controlled by temperature change,the area increased slowly from 1999 to 2013 which was controlled by precipitation change.(3)the upper boundary of alpine meadow increased in all slope aspects,alpine meadow increased mainly in north and west from 1990 to 1999 which was controlled by temperature,and it increased in southern slope aspect from 1999 to 2013 which was controlled by precipitation.(4)according to the distribution of slope gradient changes,the expansion of the upper boundary of the alpine meadow in 1990 to 1999 mainly occurred in steepness of 15°~25°,and the expansion in 19992013 mainly occurred in gradients of 20°~35°.