黄土高原典型流域退耕还林土地利用变化及其合理性评价

黄土高原大规模退耕还林使得该区土地利用结构发生了深刻变化,区域生态环境得到了明显改善。研究由此引起的土地利用变化及其合理性,对于加快黄土高原植被恢复、控制黄河泥沙以及实现区域经济社会可持续发展等具有十分重要的理论意义和应用价值。该文应用遥感(remote sensing,RS)和地理信息系统(geographic information system,GIS)技术对黄土高原典型流域清水河流域2000-2014年土地利用变化特征进行了分析,并通过构建判别准则体系对土地利用变化的合理性进行了评价。结果表明,该流域实施退耕还林工程以来,土地利用结构发生了重大变化,主要土地利用类型耕地、园地、林地和草地的比例由2000年的1:0.06:2.05:3.95大幅度调整至2014年的1:3.22:12.03:5.51,其变化经历了3个阶段:2000-2005年以退耕还林及其配套措施为主,重点突出了工程的生态效益,土地利用变化合理度为78.60%,属于低度合理;2006-2009年在继续推进荒山造林和封禁的同时,大力开展基本农田与果园建设,兼顾了生态、经济与社会效益,土地利用变化合理度为91.71%,进入高度合理状态;2010-2014年进一步加大苹果产业发展力度,重点突出了经济效益,土地利用变化合理度为95.20%,延续了高度合理态势。建议新一轮退耕还林工程应注意严格控制新的退耕,保护经营好现有林地,适当控制园地规模。

Land use change driven by Sloping Land Conversion Program in typical watershed on Loess Plateau and its rationality evaluation

Abstract: To combat the severe soil erosion and improve the regional eco-environment, the Chinese central government initiated the Sloping Land Conversion Program (SLCP) in 1999. This program implemented on the Loess Plateau has resulted in dramatic land use change in the region. It is of significance to understand the land use change and its rationality for developing effective strategies in the next period of the program in the region. In this study, we explored the spatiotemporal characteristics of land use change over 2000-2014 in Qingshuihe Watershed(436 km2) located in the west Shanxi Province, a typical watershed on the Loess Plateau. Land use data for 2000, 2005, 2011 and 2014 were interpreted from TM/ETM+ images by using the supervised classification method. To improve the interpretation accuracy, the high-resolution images of Google Earth were used to revise the supervised classification results. The concept of rational degree was introduced for evaluating the rationality of land use change. The discriminant criterion for rationality was developed based on the integrated analysis of ordinances, regulations, and policy of SLCP as well as the studies about soil erosion and vegetation succession on the Loess Plateau. The results showed that the land use structure of the watershed had changed significantly. Land use ratio of farmland: orchard: forestland: grassland was evolved from 1:0.06:2.05:3.95 in 2000 to 1:3.22:12.03:5.51 in 2014. From 2000 to 2005, the percentage of farmland and grassland decreased to 9.19% and 52.76%, while the percentage of orchard and forestland increased to 1.82% and 35.64% respectively. Incented by the favorable subsidy of SLCP, farmland on gentle slope(<15°) was even converted to forestland and grassland, leading to the low rational level of land use change with the rational degree of only 78.60%. In order to improve the livelihood of the program participating farmers, the local government carried out the construction of basic farmland and orchard actively in 2005-2011. Some grassland was converted to high-quality basic farmland, but at the same time large amounts of sloping farmland and grassland were converted to orchard, leading to the decrease of farmland and grassland and increase of orchard. The percentage of farmland and grassland decreased to 7.62% and 43.19% respectively, while the percentage of orchard increased to 6.29% during this period. Moreover, forestland coverage increased from 35.64% to 41.69%. The overall rational degree of land use change increased to 91.71% that was a high rational level. With the further expansion of apple tree planting from 2011 to 2014, farmland and grassland were continuously converted to orchard. The percentage of orchard increased to 14.52%, while the percentage of farmland and grassland decreased to 4.51% and 24.89%, respectively. Forestland had been increasing constantly up to 54.30% of the total watershed. The overall rational degree of land use change was up to 95.20%.We suggest that the ultimate objectives of SLCP should be focused on achieving the balanced tradeoffs between grain production, economic trees and ecological forests and the integration in the policy instrument for implementing more effectively the program. More specifically, major efforts for next period of SLCP for this watershed should be implemented by improving the stability, structure and function of current ecological plantation forests established while maintaining a reasonable farmland scale and controlling the expansion of orchard.