陕西省植被覆盖度变化特征及其成因

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

基于像元分解模型,利用2000—2009年MODIS NDVI数据(250m分辨率)定量分析了陕西省植被覆盖度的时空变化特征及其成因.结果表明:2000—2009年,陕西省植被覆盖度在波动中呈极显著增加趋势(P<0.001),变化率为35.0%,植被覆盖度由2000年的56.9%增至2009年的68.9%,其中,陕北地区植被覆盖度的增幅尤为显著,榆林市、延安市植被覆盖度分别增加了21.6%和22.0%.研究期间,陕西植被覆盖整体改善、局地退化,改善极显著(P<0.01)、显著(P<0.05)的面积比例分别为37.8和11.9%,变化趋势不明显的面积占46.1%,退化的面积仅占4.2%;植被覆盖度变化率>200%、100%～200%、10%～100%、-10%～10%和<-10%的面积分别占研究区总国土面积的12.2%、13.3%、38.8%、29.3%和6.4%.2000—2009年,陕西省植被覆盖结构转好,高覆盖植被所占的面积呈极显著上升趋势(P<0.001),增幅为10.0%;中覆盖植被所占的面积呈显著上升趋势(P<0.05),增幅为8.4%;低覆盖植被所占的面积呈极显著下降趋势(P<0.001),降幅为18.4%.陕西省植被覆盖度的增加是人类活动和自然因素共同作用的结果,封山育林、退耕还林等一系列生态建设工程的实施是陕北地区植被覆盖度增加的主要原因.

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.