基于斑块评价的三峡库区腹地坡耕地优化调控方法与案例研究

Abstract

The center of the Three Gorges Reservoir area is an ecologically sensitive, economically poorest, and environmentally fragile region,and hence become a research hotspot for many researchers. There is a large amount of cultivated slope land( part of them being abandoned by local farmer) in the region and it is very difficult and sometimes impossible to return the lands with gradient 25° to forests. So,it is necessary to explore the optimization control theory and methods for the slop land with different characteristics in this region. Cultivated slope land optimization should consider the demands of local people' s production and living,and it is also a selection process of the combined efforts of natural resources,geographical accessibility and socio-economic conditions. This paper suggested that the control and optimization scheme should not only combine the spatial distribution pattern and the ecological functions of cultivated slope land,but also consider the current distribution and future trends of sloping farmland. In addition,this paper promoted six principles about how to control and optimize thecultivated slope land,plus the evaluation methods integrating the spatial patternsuitability to quantitatively assess farmers demand pressures. By applying the principles and evaluation,this paper chose Caotangxi watershed,a typical watershed in thecenter of the Three Gorges reservoir area,as a case study. According to the characteristics of the watershed three indices were selected to evaluate the suitability of the system,namely,the accessibility,the ecological functions and the feasibility of changing slope land into terrace. The accessibility means the distance from the settlements roads to the land; the ecological function means the land degradation( the soil erosion) and the distance from water and the large forest patches( that is the distance away from the rivers and ecological sensitive area);while the feasibility from slope land to terrace means the size of the farmland patches,aspect and the slope gradient At the same time,the pressure index of cultivated land and supplementary capability of orchards to farmer's demand were selected as evaluation indexes of the quantity regulation system. Accordingly,the cultivated slope land of the Caotangxi watershed were divided into four types,namely,the optimization utilization type,the key consolidation type,the type of gradually returning( farmland to forest) and the type of preferentially returning,which accounted for 30. 5%,32. 9%,29. 7% and30. 5% respectively. Finally,at the premise of reducing steep inappropriate cultivated land and soil erosion,this paper suggested four returning scenarios without increasing the pressure of cultivated land,based on the distribution of abandoned land of local farmers. The rational and validity were verified according to the indices for these scenarios. The result of this study provides a theoretical basis for the current cultivated slope land optimization as well as a certain guidance to the cultivated slope land regulation in the Three Gorges Reservoir area.