黄土丘陵小流域土地利用的时空分布及其与地形因子的关系

Spatio-temporal distribution of land use in relation to topography in a gully catchment of the Loess Plateau,China

采用航片解读、实地调查、土地规划和基于GIS的统计分析相结合的方法,从土地利用面积和地形分布格局的变化分析入手,研究了黄土丘陵小流域土地利用的时空分布格局及其影响因子。研究结果表明,黄土丘陵区大南沟小流域的土地利用变化可以分成两个阶段,第一阶段从1975、1998年到25°退耕,林地/灌木地面积增加,荒草地、休闲地和耕地的面积减少,果园/经济林地的面积变化不明显;第二阶段即3种土地利用规划方案,包括25°、20°和15°退耕方案,林地/灌木地和荒草地的面积保持不变,耕地和休闲地逐渐被果园/经济林地所替代。汇总与相关分析表明,这5种土地利用类型的地形分布格局也发生相应的变化。研究指出,近20年来,大南沟小流域土地利用格局日趋优化,3种土地利用规划方案体现了土地持续利用的生态、经济和社会效益,具有很强的操作性。

The spatio-temporal distribution of land use and its relation to several terrain indices were studied in Da nangou Catchment (3.5km 2 )on the Loess Plateau,China.The previous land use map was interpreted from an aerial photo in1975(LU75)and the present land use map was compiled based on the field survey in1998(LU98).The future land-use maps were made based on three land-use scenarios in which cropland areas are restricted to slope gradients smaller than25(FA25),20(FA20)and15degree s(FA15).The25and20-degree limit scenario can be seen as short-term(before2005)and intermediate(2005～2010)scenarios,and the15-degree limit scenario can be seen as long-term scenario(after2010).A temporal sequence of land use dy-namics in the catchment consists of these five land-use maps.Two stages were recognized based on the comparison analysis on these five maps.In the first stage from LU75,LU98to FA25,the area of the wood/shrub land increases while those of the wasteland,fallow land and cropland decrease,and the orchard/cash-tree land remains the same.During the second stage consisting of the FA25,FA20and FA15,there is a gradual decrease in the cropland and fallow land and a gradual increase in the orchard/cash-tree land;the other land-use types remain the same.Conse- quently,it is found that the topographic distribution pattern of each land use type also displays the corresponding change based on the statistical analysis on the relationships between the land use type and several terrain indices.During the first stage,the wood/shrub land changes from eastwards or northward s to westwards or southwards,from the profile - concave - slope to the profile - convex - slope,from the plan-convex-slope to the concave - slope,increases in the slope gra di ent in the relative elevation.The wasteland also increases in the slope gradient,but shows opposite changes in the slope aspect,surface curvature and relative elevation as the wood/shrub land.The fallow land and cropland keep the same condition in the slope aspect,but show a stable de-creasing trend in the profile-convex-degree,plan-concave-degree,slope gradient and relative el-evation.The orchard/cash-tree land also remain s the same aspect,but shows opposite change in the surface curvature and the slope gradient,and displays a decreasing-then-increasing trend in the relative elevation.During the second stage,the wood/shrub land and the wasteland re main the same in topography.However,the cropland and the fallow land change from the eastwards or northwards to the westwards or southwards,and gradually decrease in the profile-convex-degree,plan-concave-degree,slope gradient and relative elevation.The orchard/cash tree land also de-creases in the slope gradient,while exhibits an opposite change in the other topographical in-dices as comparing to the cropland and the fallow land.In a word,it is indicated that the land use pattern of this catchment is getting more sound in the sustainable land use during the recent decades,and especially the three land-use scenarios have advantages in ecology,economy and society.