Monitoring Vegetation Dynamic in Horqin Sandy Land from Spot Vegetation Time Series Imagery

The changes in the composition and distribution of vegetation represent one of the most main sources of systematic change on local, regional, or global scale. The temporal evolution of NDVI data strongly linked to changes in the state of the surface is regarded as an effective time window able to show the natural seasonal variations. This study investigated vegetation change between 1998 and 2006 in the Horqin region which is the east fringe of agro-pasture transitional zone in northern China. Time series of SPOTVEGETATION Normalized Difference Vegetation Index (NDVI) data are adopted to monitor the vegetation cover change during last 9 years. We found that the yearly maximum value composite mean NDVI over the study area increased slightly from 0.327 in 1998 to 0.338 in 2006, which indicated the increasing trend of vegetation activity. The annual average NDVI in whole area was stable and its inter-annual change rate between 1999 and 2006 were -1.603%. Vegetation activity improved area reached 6366.4 km, taking up 5.09% of the whole study area while the degraded regions occupied about 3.84% of Horqin region. The increasing amplitude is more considerable than the decreasing amplitude on the whole. In spring, monthly maximum NDVI showed obvious decrease while increasing tendency in summer and autumn was found. Original land desertification has been basically controlled during past nine years. Rational human economic activities and vegetation restoration measures played a positive role in vegetation increases. * Corresponding author.