长江上游不同地形条件下的土地利用/覆盖变化

ON LAND USE/COVER CHANGES OF DIFFERENT TOPOGRAPHIC CONDITIONS IN THE UPPER YANGTZE RIVER BASIN

基于1∶10万的1980、2000和2005年的土地利用/覆盖数据和90 m分辨率的DEM数据,采用转移概率矩阵和地形-面积频度方法,分析了1980~2005年长江上游地区不同地形因子条件下的土地利用/覆盖变化。结果表明：1）1980~2000年,草地、林地和农业用地面积变化趋势与2000~2005年相反。后5 a,可能由于退耕的土地出现反弹现象增多,草地和林地面积出现缩减而农业用地面积增加。两个分析时段主要的土地利用/覆盖类型变化趋势类似,包括农业用地向林地和草地的转化,林地向农业用地的转化以及草地向裸地的转化。2）农业用地和城镇用地主要分布于低海拔区而林地、草地则主要分布于高海拔区。低海拔区主要是退耕还林和城市化过程。高海拔区主要是林地的退化消失和草地退化沙化过程。3）农业用地在坡度段10~25°所占面积比例最大。林地用地面积比例随坡度变陡呈现规则递增,城镇用地分布趋势与之相反。近年裸地趋向分布于缓坡区。坡度0~5°的区域主要是草地退化沙化过程;5~10°坡度段主要是退耕还林过程;大于10°的区域造林工程与森林退化并存。4）各种土地利用/覆盖类型对不同坡向的适宜性相差不大。各种坡向上土地利用/覆盖类型变化类似。

Based on land use/cover data（scale is 1∶100000） in the years of 1980,2000 and 2005 and digital elevation model（DEM） datum（cell size is 90 m）,the methods of percentage of land use/cover transformation matrix and the frequency-area distribution of land use/cover were used to analyze the land use/cover dynamic change from 1980 to 2005 in the Upper Yangtze River Basin under different topographic conditions.The results were as follows：（1） The change trends of grassland,forest and farmland area from 1980 to 2000 were different with that from 2000 to 2005.It might be the result of the increase of farmland area and the decrease of grassland and forest area.The main land use/cover changes in two periods were similar.These were the transformation of farmland to forest and grassland,forest to farmland and grassland to bare land.（2） Farmland and built-up areas were almost in low elevation,while forest and grassland were almost in high elevation.The main changes in low elevation were National Grain for Green Project and the urbanization.The main land use/cover change process that occurred in high elevation was the forest degradation and grassland desertification.（3） Farmland was distributed primarily in areas where the slope gradient is from 10° to 25°.Percentages of forest increased when the slope gets steeper,on the contrary,the distribution trend of built-up decreased when the slope get steeper.Bare land occupied flat lands in recent years.When the slope gradient was below 5°,grassland desertification occurred;when slope gradient was from 5° to 10°,the National Grain for Green Project occurred;when the slope gradient was above 10°,both forestation and forest degradation occurred.（4） There was little difference of suitability of different types of land use/cover in various slop direction.