Temporal and spatial changes of cropland and its ecological environment effects in Manas River watershed

The arid continental river watersheds of northwest China,have been damaged to different degrees in long term drought and water shortage,and especially formed a arid land use/land cover pattern.This research studied cropland changes and its ecological environment effects in a watershed of arid area-Manasi river watershed in last 30years since 1976a,by using GIS with remote images in 1976a,1989a,and 2005a.The results showed that the universal change of cropland changed mostly in the watershed.Area of cropland and residence land increased continually,from 3418.71km2 in1976 to 5907.62km2 in 2005.The significant spatial expansion in cropland led to rapid decrease of grassland and saline-alkali land.The decrease of cropland was mainly due to cropland abandoned,mandatory conversion of cropland to forestland and grassland,desertification and salinization,et al..The distribution of cropland inside of oasis was more centralized and the fragmentation became lower,but to the cropland near edge,its fragmentation increased.Some unreasonable rapid expansions of cropland had brought the land coverage changes exerting enormous influence on the eco-environmental,including land desertification,the vegetation destroy,the area of saline land and sand land was enlarged quickly,et al.,which made the eco-environmental more fragile in the region,will take bad effect to the local people.