1983－2009年黄土高塬沟壑区耕地结构特征演变分析

为明确退耕还林前后黄土高塬沟壑区耕地数量和空间结构演变规律,以长武县为例,基于土地利用结构内涵,采用GIS技术和定量指标,对1983年、1993年和2009年黄土高塬沟壑区耕地数量和空间结构进行定量分析。结果表明:长武县3个时期的耕地数量分别为292.1、181.3和159.2km2,耕地减少主要位于0～2°,>15～25°和>25°坡度耕地,相对于1983年、1993年分别下降了29.6%、48.9%、60.1%和15.6%、15.7%、48.8%,耕地与其他地类的相互转化频繁。该区0～6°缓坡耕地主要转化为园地和居工地,>15°的陡坡耕地主要转化为林地和未利用地(荒草地)。结构分析表明耕地数量的坡度分布趋于合理,缓坡耕地空间结构上向均匀性、核心板块的团簇式发展,陡坡耕地主要以核心斑块的分散分布为主。耕地在过去30a是一个优化的过程,其结构演变有利于资源优化配置利用和农业集约化发展。1983-1993年期间的退耕为种植业效益驱动下农户自发性质的退耕或者弃荒,1993-2009年期间则是科学宏观退耕并对前期自发退耕地和弃荒地的整理利用。该文为区域土地利用管理和政策制订提供了借鉴和参考。

Evolution analysis of cultivated land structure characteristics on gully area of loess plateau in 1983-2009

To clear evolution law of quantitative and spatial structure for cultivated land in the gully area of the Loess Plateau before and after conversion of cropland to forest, taking Changwu county for example, the quantitative and spatial structure of the cultivated land in 1983, 1993, and 2009 in Changwu county were quantitatively analyzed using GIS technology and quantitative indexes based on the fully understanding of connotation of land use structure. The study results showed that the area of cultivated land in Changwu county in 1983, 1993, and 2009 was 292.1, 181.3, 159.2 km2, respectively. The reduction of cultivated land mainly occurred in the slope grades of 0-2°, >15-25° and >25°, respectively, with 29.6%, 48.9% and 60.1% from 1983 to 1993 and with 15.6%, 15.7% and 48.8% from 1993 to 2009. The transform between cultivated land and other land types was highly frequent. Cultivated land in gentle slope grades of 0-6° mainly converted to orchard land and residential, mining and traffic land, and cultivated land in steep slope grades of >15° mainly converted to forest land and unused land (waste grassland). The structural analysis showed that the quantitative distribution of the cultivated land in slopes tended to be reasonable, and the patches on gentle slope developed to a spatial structure of core-area-cluster and be uniform, and that on steep slope tended to be scattered distribution as core area. An optimized process was experienced in the last 30a in the study area, the structure evolution of cultivated land was helpful to optimize resources and its allocation, and develop agriculture intensification system. The abandonment of cultivated land in the former period from 1983 to 1993 primarily relied on the planting benefit comparison by farmers themselves, while the conversion of cultivated land to other land use types and the spatial distribution in the latter period from 1993 to 2009 occurred under much scientific planning. This paper provides a useful reference for management and policy formulation of regional land use.