黄土丘陵区生态退耕中的景观格局演变及其地形驱动

The Effects of Ecological Cropland-Conversion on Landscape Pattern Change and Its Topography Driving in Loess Hilly Region

黄土丘陵区大规模生态退耕对该区域土地利用、景观格局及其生态系统服务产生了重要影响。基于野外调查和GIS分析,以典型黄土丘陵小流域大南沟为例,分析了1975—2007年生态退耕前后土地利用结构变化、景观格局演变及其地形驱动。结果表明流域大规模退耕前有小面积弃耕现象,耕地和荒草地稍有减少,林地增加,斑块数量增加,景观格局趋于复杂,破碎化严重。2000年大规模退耕以后,耕地大量减少,退耕地和荒草地约占流域面积75%,林地增加,各景观类型形状趋于简单、分布趋于均匀和集中。随退耕年限增加,林地持续增加,存在小面积的复垦现象,流域景观结构趋于复杂,但整体格局趋于合理。相对海拔和坡度是生态退耕最重要的两个地形驱动因子,大规模退耕后,耕地和果园趋向于中低海拔和坡度较缓的区域分布,荒草地基本不变,退耕地和林地趋向于高海拔和较陡的区域分布。

Significant effects of large-scale ecological cropland-conversion on land use,landscape pattern and its ecosystem service have taken place in the loess hilly region.A typical small catchment in loess hilly region,Da′nangou Catchment,was chosen,and the filed investigation and GIS analysis were combined to analyze the land use structure change,landscape pattern change and its topography driving during the period from 1975 to 2007.The results showed that the spontaneous shift of farmland occurred before large-scale ecological cropland-conversion,during this period,area of cropland and waste-grassland reduced a little while forestland increased.The number of patches became more,the landscape pattern became more complex and fragmentation became more serious.In 2000,area of cropland reduced greatly,the proportion of natural waste-grassland and abandoned land was 75% of the area of the whole catchment,and forestland increased after the implementation of large-scale ecological cropland conversion.Shape of all landscape types became simple and the distribution became homogeneous and concentration.With the increase of ecological croplandconversion years,area of forestland increased continuously,but small area of cultivation occurred during this period.Meanwhile,landscape structure became more complex,but whole landscape pattern became more reasonable.Relative altitude and slope were the two most important topography impact factors on the ecological cropland conversion.After the implementation of large-scale ecological cropland conversion,the distribution of cropland and orchard tends to area with the lower altitude and gentle slope,and natural waste-grass-land had no significant changes,while the distribution of abandoned land and forestland tends to the area with higher altitude and steep slope.