黄土丘陵区典型小流域土地利用变化研究——以陕西延安地区大南沟流域为例

利用航片解译和景生态学方法研究了陕北黄土丘陵区大南沟流域在20世纪70年代和90年代的土地利用结构的特点和变化，结果表：从1975年到1999年，梯田，坡耕地，稀疏林地，灌丛面积减少，所占百分比呈下降趋势，而有林地，果园，荒地所占百分比呈上升趋势，梯田，有林地，灌丛和茺地平均斑块面积在增大，而坡耕地，稀疏林地，果园的平均斑块面积在减小，果园和坡耕地分维数在变大，斑块形状趋于复杂化，而有林地，稀疏林地，灌丛，梯田和荒地的斑块分维数在变小，斑块形状趋势规则小，有林地，灌丛，果园，荒地的分离度在下降，稀疏林地，梯田和坡耕地的分离度在上升，说明有林地，罐丛，果园和荒地的地位在上升，而稀疏林地，梯田和坡耕地的地位在下降，全区单位面积的斑块数目的磁大，在一定程度上表明农田中地块之间的边界增多，其结果是导致一些土地资源和浪费和不利于土地管理，景观多样性指数和土地利用相对合理指数在增大，但变化较小，1997年与1975年相比，整体上土利用结构稍有好转，但这种土地利用结构远未达理想状态。

Study on Land Use Change in a Small Typical Catchment in Loess Hilly Area——A Case Study in Danangou Catchment, Yan’an, Shaanxi Province

Land use change to some extent results from the change of landpolicy and human environmental consciousness. It will lead to profound influence on regional environment, as well as a global change. Loess Plateau, as the most serious area of soil erosion in the world, receives a lot of attention from Chinese government and international society. The soil erosion is mainly attributed to population growth and irrational land use. In this paper, a case study on land use change from the 1970s to the 1990s was carried out in a small catchment in a loess hilly area of northern Loess Plateau through aerial photograph interpretation and using landscape approaches. The results indicate that some changes occurred from the 1970s to the 1990s. This is greatly due to the change of land policy during early the 1980s when a land reform, the household responsibility system was widely started in countryside in China. With the new land policy carried out in countryside, the manner and environmental consciousness of local farmers on land use has changed a lot, which results in land use modification and conversion.① Compared to 1975, areal percentage of terrace farmland, sloping farmland, sparse woodland, bushland in 1997 declines obviously,while the percentage of woodland, orchard and unused land increases. The increase of woodland, bushland and orchard, and the decrease of sloping farmland in steep slope sections are helpful for soil erosion control. ② Considering the mean patch area, it is becoming bigger for terrace farmland, woodland, bushland and unused land in 1997 than that in 1975, whereas it is smaller for sloping farmland and sparse woodland and orchard in 1997 than that in 1975. This reflects that with the implementation of household responsibility system in countryside, most agricultural activities are carried out in small group, that induce the patch size of the human-closely-related land use types becoming smaller (excluding terrace farmland), such as sloping farmland and orchard, and the patch size of the human-less related land use types becoming bigger, such as woodland, sparse woodland, bushland and orchard. ③ The fractal dimension of orchard and sloping farmland in 1997 is bigger than that in 1975, which implies the shape of patch of these land use types is getting complex, while the fractal dimension is becoming smaller for woodland, sparse woodland, bushland, terrace farmland and unused land in 1997. ④ Compared to 1975, the landscape isolation for woodland, bushland, orchard and unused land is decreasing and it is increasing for sparse woodland, terrace farmland and sloping farmland in 1997. ⑤ As a whole of the catchment, landscape diversity is becoming bigger and patch number unit area increases. This phenomenon indicates the land use is tending to diverse and landscape become fragmented from whole. ⑥ The relative land use rationality index in 1997 is a little bigger than that in 1975, but the difference is very small. It means the land use structure is improved, but it is much below the ideal situation for controlling soil erosion. The increase of relative land use rationality index is mainly due to land use change in steep slope area where the area of woodland, bush land, orchard and unused land increase a lot and the area of sloping farmland is reduced.