RS-based Study on Dynamics of the Vegetation Coverage in Recent 10 Years in Yanchi County

In order to understand the change of vegetation fraction in agro-pastoral transition area,based on TM/ETM+ images in 1999,2004 and 2010,this study deduced vegetation coverage by using the Normalized Difference Vegetation Index(NDVI) in Yanchi County.It was revealed that the average vegetation coverage in 1999,2004,2010 were 24.08%,26.96%,and 23.92%,respectively,the general trend was decreasing following an increase.The coverage vegetation coverage of these years was further classified.The results showed that the low proportion of vegetation coverage were 59.61%,50.75%,62.6% for 1999,2004,2010,respectively,showing decrease and then increase;the moderate proportion of vegetation coverage were 34.54%,34.58%,29.20%,showing decrease after an increase,and increasing trend was not obvious;the high proportion of vegetation coverage accounted for 5.85%,14.68%,8.2%,respectively,showing decrease after an increase.Major factors influencing local vegetation coverage in this area were human activity,policies and climate(precipitation).