退耕还林还草工程对陕北地区生态系统服务价值时空演变的影响

基于陕北地区1990、2000、2015年土地利用数据，运用单位面积生态系统价值当量因子法、格网法、探索性空间数据法（ESDA），分析了退耕还林还草工程实施前后生态系统服务价值（ESV）的空间分布和演化规律，探讨了退耕还林还草工程对ESV的影响。结果表明：（1）陕北地区退耕还林还草工程实施效果显著，工程实施后共有297066.15 hm2耕地转化为林地和草地，林草覆盖率由57.33%增长至60.50%。（2）退耕还林还草工程使得陕北地区ESV得到了显著提升。25年间陕北地区ESV共增加了32.82亿元，ESV在工程实施后比工程实施前多增加了5.93亿元，增长主要源于退耕引起林地和草地面积的增加。（3）ESV空间分布上呈显著的“南高北低”分布格局，并表现出正向的集聚性和依存性，ESV热点区和冷点区集聚效果明显，热点区集聚与林地、草地的空间分布相吻合，冷点区集聚与未利用地、耕地和建设用地的空间分布相吻合。（4）受退耕还林还草工程影响，陕北地区中部中等等级和次高ESV分布区域逐渐增大、次热点区空间集聚性逐渐增强，北部次低等级和低等级ESV分布区域逐渐减少、冷点区空间集聚性逐渐减弱。整体而言，陕北地区土地利用类型转移和ESV的增减变化与推行退耕还林还草工程在时间上相呼应、在空间上相匹配，退耕还林还草工程实施使得陕北地区生态环境得到了有效改善，ESV得到了显著提升。

Impact of the Grain for Green Project on the temporal and spatial evolution of ecosystem service value in northern Shaanxi

Based on the land use data of northern Shaanxi in 1990, 2000, and 2015, the spatial distribution and evolution of ecosystem service value (ESV) before and after the implementation of the Grain for Green Project (GGP) were analyzed and the impacts of the GGP on the ESV were discussed, using the ecological service value equivalent factor method, grid method, and exploratory spatial data analysis (ESDA). The results indicate that: (1) The implementation of the GGP in northern Shaanxi has significant achievements. After the implementation of the project, a total of 297,066.15 hm2 of arable land was converted into forestland and grassland, and the coverage rate of forest and grass increased from 57.33% to 60.50%. (2) The GGP has significantly improved the ESV in northern Shaanxi. The ESV in northern Shaanxi increased by 3.282 billion yuan in the 25 years. The ESV increased by 591 million yuan after the implementation of the project, which was mainly contributed to the area increase of forestland and grassland by the GGP. (3) Spatial distribution of the ESV has a significant "High South and Low North" pattern and shows positive agglomeration and dependence. There were obvious clustering effects of the hotspot and cold-spot areas of the ESV. Hotspot clustering coincided with the spatial distribution of forestland and grassland whereas the cold-spot clustering coincided with the spatial distribution of unused land, arable land and construction land. (4) With the influence of the GGP, the distribution of the middle and second-high ESV areas gradually increased and the spatial agglomeration of sub-hotspot areas gradually strengthened in the central of northern Shaanxi, while in the north, the distribution of the second-lowest and low-level ESV areas gradually decreased and the spatial agglomeration of cold spots gradually weakened. From a whole perspective, the land transfer and the ESV changes in northern Shaanxi are consistent with the implementation of the GGP in time and in space. The implementation of the GGP has effectively improved the ecological environment in northern Shaanxi with significantly increased ESV.