Change characteristics and their causes of fractional vegetation coverage (FVC) in Shaanxi Province

Based on the sub-pixel analysis model,and by using 2000-2009 MODIS NDVI(250 m resolution),this paper quantitatively analyzed the spatiotemporal change characteristics and their causes of fractional vegetation coverage(FVC) in Shannxi Province.From 2000 to 2009,the FVC in the Province had a significant increasing trend,with the great magnitude of 35.0%.During that period,the vegetation coverage increased from 56.9% in 2000 to 68.9% in 2009 in the provincial scale,and the increment was much higher in northern Shannxi,being 21.6% in Yulin and 22.0% in Yan'an.Though the vegetation coverage had an overall increase,it was locally degraded in some areas.The areas with improved vegetation coverage at the significance levels of 0.01,and 0.05 were 37.8% and 11.9%,while those with non-improved and degraded vegetation coverage were 46.1% and 4.2%,respectively.The areas whose vegetation coverage had a change rate of 200%,200%-100%,100%-10%,10%-10%,and -10% occupied 12.2%,13.3%,38.8%,29.3%,and 6.4% of the total,respectively.During the study period,the structure of vegetation coverage in the Province also improved.The areas with high and normal vegetation density increased significantly by 10% and 8.4%,respectively,while the area with low vegetation density decreased significantly by 18.4%.The improvement of the FVC in Shaanxi Province was the interactive effect of natural factors and human activities,but the main cause was the implementation of a series of ecological construction projects such as closing hill for forestation and restoring farmland into forestland and grassland.