Spatial pattern of steppe degradation in Xilin River Basin of Inner Mongolia

Steppe degradation is a major problem facing environment and animal husbandry in Inner Mongolia,China today.Using Landsat TM images of1999,and combining with field inves-tigation,and based on the diagnosis model of degradation succession of typical steppe in Inner Mongolia,the vegetation map in1999in the Xilin River Basin was compiled.Supported by ARC/INFO,the spatial pattern of steppe degradation was studied.The areas of steppe having different degradation degree throughout the Xilin River Basin,the upper,middle and lower reaches and different landform types were calculated.The total area of grazing degraded steppe in the Xilin River Basin in1999was7689.3km 2 ,71.86%of the total area basin.Light grazing degraded steppe was3678.8km 2 ,47.84%of the total grazing degraded steppe,medium grazing degraded steppe was1933.6km 2 ,25.15%of the total grazing degraded steppe,and heavy grazing degrad-ed steppe was2077.2km 2 ,27.01%of the total grazing degraded steppe.Based on the calculation formula of steppe degradation index,this paper calculated respectively the value of steppe degra-dation index of the whole basin,the upper,middle and lower reaches,and lower mountain,hill,lava tableland and high plain.Steppe degradation index per unit area of the upper,middle and lower reaches is middle reachlower reachupper reach;steppe degradation in dex per unit area of landforms is high plain hill lava tablelandlower mountain.With grid point sam pling on steppe vegetation degradation map,the value of steppe degradation index of each grid was calcu-lated,and the distribution map of steppe degradation index was compiled.The result is that the spatial pattern of steppe vegetation degradation in Xilin River Basin is complicated.Steppe degradation spatial pattern at large scale in the Xilin River Basin is related to human grazing in-tensity in the upper,middle and lower reaches and different landforms ,in the middle and low er reaches,steppe in river terrace,plain and hill area degraded obviously.Second,there are quite a number of central areas where steppe degraded seriously in the Xilin River Basin,which are all related to over-grazing.