基于地形因子的三峡库区腹地耕地演变——以草堂溪流域为例

Evolution of cultivated land in center region of the Three Gorges Reservoir Area based on terrain factors:A case study of Caotangxi watershed

以1990、2000、2004和2007年4期遥感影像数据和1∶5万的DEM数据为数据源,利用ArcGIS 9.3空间分析功能和Fragstas 3.3景观格局分析功能对库区腹地耕地演变进行了研究。首先建立草堂溪流域耕地数据库以及高程、坡度和地形位指数图,然后将高程、坡度和地形位梯度分别与耕地数据进行图层运算,提取坡耕地的面积,探讨不同地形下耕地的分布特征。结果表明:耕地在各地形因素上的分布表现为15°～35°坡度带、500～1000 m高程级别、东南坡及南坡以及中高地形上。1990—2007年,研究区耕地在面积和空间格局上均发生很大的变化,随地形梯度的增大,4个时期耕地分布面积随地形位指数的增大表现为先升后降;聚集度减少特别显著的主要集中在第4(1.2～1.5)和5(1.5～2.0)两个地形梯度带,即中高地形位的耕地之间聚集程度降低,破碎程度加剧,生态环境好转。

Based on the remote sensing images in 1990, 2000, 2004, and 2007 and the 1∶50000 DEM, and by using software ArcGIS 9.3 and Fragstas 3.3, this paper studied the evolution of cultivated land in Caotangxi watershed, a center region of Three Gorges Reservoir Area. The database of the cultivated land in Caotangxi watershed was established, and the slope, elevation, and terrain niche index were produced. Then, the slope gradient, elevation gradient, and terrain niche gradient were calculated with the database of the cultivated land so as to discuss the distribution characteristics of the cultivated land at different terrain gradients according to the dimensionless distribution index. The results showed that the cultivated land in the watershed was mainly distributed in the slope gradient range of 15°-35°, elevation range of 500-1000 m, southeast and south slopes, and in middle and high terrain gradient. An obvious change in the area and spatial distribution of cultivated land took place in the study area in 1990-2007. With the increasing terrain gradient index, the distribution area of cultivated land increased first and decreased then. The remarkable reduction in the aggregation index of cultivated land was mainly in the fourth and fifth terrain niche gradients （1.2-1.5 and 1.5-2.0, respectively）, showing that the aggregation of cultivated land in middle and high terrain gradient decreased, the cultivated land was fragmented, and the ecological environment was becoming well.