陕北榆林市退耕还林前后土壤侵蚀及生态服务价值变化

利用RUSLE模型计算分析了陕北榆林市退耕还林前后土壤侵蚀状况与生态服务价值动态变化。结果表明:1）退耕还林前（2000年）榆林市平均土壤侵蚀模数和年侵蚀总量分别为3 002.75 t·km^-2·a^-1和1.41×10⁸t，退耕还林后（2010年）虽然林草地面积增加，土壤侵蚀强度等级向轻度和微度转变，水土流失状况显著改善，但由于2010年降雨侵蚀力比2000年增长了157.66%，人类经济社会活动对土壤侵蚀状况的影响依然存在，导致退耕还林后平均土壤侵蚀模数和年侵蚀总量分别增加了127.24%和128.37%。2）生态服务价值总量（13.23×10⁹元）较之前（56.31×10⁹元）增长了326%，其中，保持土壤和废物处理的价值增长幅度较大；生态服务功能得到显著提高，且林草地的贡献占比>50%。3）土壤侵蚀强度的低值区并非生态服务价值的高值区，不同坡度的生态服务价值组成并未发生显著变化，合理的土地利用是改善生态环境的关键。4）退耕还林后，榆林市整体呈现出土壤侵蚀强度降低、生态服务价值升高的趋势，表明退耕还林政策的实施取得了明显的水土保持生态效益。研究结果可为陕北榆林市及类似区域生态保护修复提供参考。

Changes of Soil Erosion and Ecological Service Value Before and After Implementing the Project of Returning Farmland to Forest in Yulin of Northern Shaanxi

In order to illustrate the variations of soil erosion and ecological service value before (2000) and after (2010) implementing the national project of returning farmland to forest in Yulin City of Northern Shaanxi,the RUSLE model was adopted to conduct relative calculations and analysis.The results showed that 1) in 2000,the average soil erosion modulus and total annual erosion amount in Yulin City were 3 002.75 t/(km²·a) and 1.41×10⁸ t,respectively,after implementing the project,the areas of forest and grassland increased,the soil erosion intensity turned to slight grade,the soil and water loss condition ameliorated significantly.On the other hand,the rainfall erosivity in 2010 increased by 157.66% compared with the year of 2000.At the same time,the impact of human activities on soil erosion still existed,and the average soil erosion modulus and total annual erosion amount increased by 127.24% and 128.37%,respectively.2) The total ecological service value in 2010 was 13.23×10⁹ yuan,increased by 326% compared with the figure in 2000 (56.31×10⁹ yuan),indicating that the ecological service function was significantly improved.The contribution of the forest and grassland to the improvement of the ecological service value was over 50%.3) Areas with lower erosion intensity were not exactly corresponded to the area with higher ecological service value.The composition of ecological service value at different slopes had not changed significantly.Reasonable land use should be the key to improve the ecological environment.4) Overall,the decreased soil erosion intensity and increased ecological service value in Yulin City indicated that the implementation of the project achieved significant ecological benefits to soil and water conservation.