Abstract: Ili River Valley is the main agricultural and animal husbandry base. Meanwhile, it is also one of the most serious soil erosion areas in Xinjiang, China. Vegetation is the most important component of terrestrial ecosystems and a key indicator for assessing the interaction between climate and the terrestrial ecosystems. The study of vegetation cover change is of great significance in preventing soil erosion and improving ecological environment. Based on the EOS/MODIS data from 2000 to 2015, the degree of vegetation coverage and its spatial change characteristics during 2000 to 2015 was analyzed. Trend analysis method was used to analyze vegetation cover change during 2000 to 2015. The Hurst index was used to predict the future change of vegetation cover. Coefficient of variation method was used to analyze the dispersion degree and fluctuation of vegetation spatial distribution. The results showed as follow: (1) Spatial distribution pattern of high vegetation coverage in Ili River Valley was distributed in the north, south, and east, while the region of low vegetation coverage is distributed in the west and middle. The ratio of vegetation area in poor, medium, and good condition accounted for 12.75%, 16.11%, and 71.14% of the total area, respectively. (2) Affected by natural factors such as temperature rise, precipitation decrease, and human factors such as overgrazing, the average NDVI in Ili River Valley fluctuated between 0.58 and 0.68, and the vegetation cover has a decreasing trend of fluctuation with the rate of 6.25 %·(10 a)- 1. (3) Generally speaking, there was a relatively low vegetation change trend in Ili River Valley. Regions with low fluctuation degree accounted for 73.16% , which were mainly distributed in the mountainous area of Ili River Valley. The vegetation types were mountain meadow, alpine meadow, and primitive forest. Regions with high fluctuation degree accounted for 26.84%, which were mainly distributed in the altitudes (0-1 500 m) of Tekes River, Künes River, Ili River, and the sunny slope of mountain body. (4) The vegetation coverage of Ili River Valley will decrease in future. The area of vegetation decreased accounting for 76.90% , which was mainly distributed in high altitude areas of Huocheng County, Yining County, Gongliu County, Xinyuan County, Tekes County, and Zhaosu County. The area of vegetation increased and accounted for 23.10%, which was mainly distributed in the low and gentle slopes of Qapqal County, Yining County, and Yining City. (5) The change trend of vegetation cover in Ili River Valley was more complex. The areas of continuous degradation and improvement of vegetation cover were obviously distributed in spatial distribution. The area of continuous degradation of vegetation accounted for 57.55%, which was mainly distributed in the higher altitude areas of the north Tianshan Mountains, the middle Tianshan Mountains, and the south Tianshan Mountains. The area of continuous improvement of vegetation accounted for 13.51% , which was mainly distributed in the newly reclaimed areas of the Ili River valley. Results of this study would provide a scientific support for better understanding the status of ecological environment and the vegetation change trend in Ili River Valley and also for formulating the corresponding ecological protection countermeasures in future.

Key words: Ili River Valley, spatiotemporal variation, vegetation cover, trend analysis