Abstract:

Based on land use/cover data (scale is 1〖DK〗∶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 .

Key words: land use/cover change/ topographical factors/ DEM/ coversion matrix