Spatial-temporal Change of Landscape Structure in the Distribution Region of Tetraena mongolica

The distribution and the change of Tetraena mongolica,endemic to the western Ordos,are studied in the form of patch units based on the aerial image(1972),CCT of TM(1988) and the image of TM(1995)(Scale: 1:100000 ).The results are as follows:(1) the distribution of Tetraena mongolica is determined and distribution area is 2754 km²;(2) the distribution area and the average patch area of Tetraena mongolica are decreasing,from 1456 km² to 1268 km² in 1995.The average patch area of Tetraena mongolica is 1879 km²,and decreases to 1538 km² in 1995,decreasing 18.1%;and (3)the decreasing of distribution area of Tetraena mongolicais varied in different spatial-temporal scale,the annual rate of decreasing is 5 times higher in periods of 1988～1995 than in periods of 1972～1988,and the decreasing rate in the urban and industry area is higher than that in the grazing area.