陕西省退耕还林工程区植被覆盖度的变化分析

利用MODIS NDVI数据和像元二分模型计算的植被覆盖度，比较分析退耕还林工程区与周边区域、主要土地利用类型、不同坡度耕地植被覆盖度变化程度和趋势。结果表明：（1） 陕西省退耕还林区植被覆盖度从2000年到2011年呈现显著的增长趋势，增长速率高于周边区域；（2） 退耕还林区植被覆盖变化百分率≥10%的面积占79.8%，≤-10%所占面积不及1%；（3） 退耕还林区植被覆盖度显著增加的面积占其总面积的70.6%，显著减少的面积仅占0.1%，植被覆盖度显著增加的情况主要出现在未利用地、草地、林地和耕地，显著和极显著降低的发生在城乡、工矿、居民用地和极少部分耕地；（4） 坡耕地植被覆盖改善比例大，坡耕地植被覆盖改善对于耕地植被改善贡献较大。在陕西省气候呈现暖干化发展趋势背景下，退耕还林区植被覆盖度呈现显著增长趋势，增长速率高于周边区域，坡耕地、林地、草地均比其他类型有明显的增加，退耕还林政策实施区域取得了良好的植被恢复效果。

Variation of fractional vegetation coverage in returning cropland to woodland project zones in Shaanxi Province

MODIS NDVI data and dimidiate pixel model were used to analysis the variation degree and trend of FVC of main land use types and cultivated land with different slopes in both the project zones and the perimeter zones. The results showed: (1) The FVC in the project zones of returning cropland to woodland increased significant with a higher rate than that in the perimeter zones. (2) The ar ea with an increase rate of FVC being higher than 10% occupied for 79.8% of the project zones, while the area with a decrease gradient being higher than 10% occupied for less than 1%. (3) The area with a significant increased FVC occupied for 70.6% of the project zones, while the area with a significant decreased FVC only occupied for 0.1%. The FVC of unused land, grassland, forestland and most of cultivated land showed a significant increase trend, while that of construction land for industries, mines and residents in urban and rural regions, and a small part of cultivated land showed a significant or extremely significant decrease trend. (4) The FVC of sloping farmland was improved significantly, and it contributed with a high proportion to the vegetation improvement of whole farmland. Under the circumstance of warming and drying tendency, the FVC in the project zon es of returning cropland to woodland showed a significant increase trend, with a higher rate that in the perimeter zones. The FVC of sloping farmland, forestland and grassland increased more than that of other land use types. This could come to a conclusion that the policy of returning cropland to woodland produced a good effect of vegetation restoration.