定西关川河流域退耕还林还草对景观格局演变的影响

以甘肃定西关川河流域为研究对象，利用遥感影像和实地调查相结合的方法，获取退耕还林还草前后（1995年、2000年、2005年和2010年）的土地利用数据进行景观格局演变分析。结果表明：从1995-2010年，农地面积由56.86%减少到28.50%，而林地由9.01%增加到20.01%，草地由31.92%增加到48.30%；建筑用地持续增加，水域面积减少较快。流域景观破碎化程度略有上升，斑块形状指数有所降低。景观优势度指数、多样性指数、均匀性指数和连接度指数变化不大。1999年实施的退耕还林还草工程，是林草地面积增加的直接驱动因素。15 a间，有50.95%的农地转变为草地，有46.24%的林地和草地又转变为农地，说明流域人口和城市的扩张，林草地面积扩大的压力仍然很大。此外，关川河流域水域面积的快速减少，说明流域水资源环境呈恶化的趋势。

Effect of Grain-for-Green Project on Evolution of Landscape Pattern in the Guanchuan River Basin,Dingxi

Based on the field investigation and the remote sensing images in 1995, 2000, 2005 and 2010, the land use change and landscape pattern change after implementing the Grain for Green project in the Guanchuan River Basin in Dingxi, Gansu Province were studied using remote sensing analysis and geographical information system (GIS). The results showed that the main types of land use were the farmland, forestland and grassland, and their proportions were changed from 56.86%, 9.01% and 31.92% to 28.50%, 20.01% and 48.30%, respectively during the period of 1995-2010. However, the area of building land was continuously enlarged, and that of waters was sharply reduced. Fragmentation of landscapes was enhanced, and the patch shape index was decreased to some extent. The landscape pattern revealed that the change of the indexes of dominance, diversity, evenness and connectivity was not so significant. The implementation of the Grain for Green project from 1999 was an important factor of enlarging the areas of forestland and grassland on the Loess Plateau. About 50.95% farmland was changed to grassland, but 46.24% forestland and grassland were converted to farmland, which revealed that there was still a big pressure for enlarging the areas of forestland and grassland due to the continuous population growth and urban expansion in the drainage basin. Furthermore, the sharp reduction of area of waters in the drainage basin revealed that the environment of water resources became worse. It was difficult to explain the relationship between the implementation of the Grain for Green project and the reduction of area of waters. Our study would provide a scientific basis for investigating the relationship between the Grain for Green project and the hydrological process and for controlling soil erosion on the Loess Plateau.