Study on the Vegetation Coverage Change and Its Impact Factors in Wulanmulun River Basin During the Recent 20 Years

The grade maps of vegetation coverage were extracted by selecting 3 sceneries of Landsat TM image of 1986,2002 and 2008 during Sep.in Wulanmulun River watershed,based on NDVI and the quantificational model of remote sensing,Through contrasting and analyzing the vegetation coverage of different grades in 3 phases,the results showed that the variable tendency of the vegetation coverage was obvious,despite deterioration in the limited areas,the overall situation was still getting better.The area of sand and low vegetation coverage significantly reduced(reduced by 45.21%),and the area of high vegetation coverage increased significantly(increased by 1.56 times).There would be two main reasons for vegetation improvement: one was climate factor such as precipitation,another was artificial factor such as returning farmland to forests grasslands and combating desertification.In particular,the most important impact factor should be precipitation.The results of correlation analysis showed that the correlation coefficient between the area of vegetation coverage and precipitation was very high in test area.In addition,the influence of coal mining on vegetation might be twofold.Overall,there are more beneficial effects than negative effects.