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

三峡库区腹地坡耕地大量存在,且25°的陡坡耕地实现全部退耕还林难度很大,同时还存在农户自发弃耕撂荒现象。有必要深入探讨库区腹地不同地域特征下坡耕地优化调控的理论与方法。在充分考虑坡耕地的分布现状和未来发展趋势的前提下,设定了坡耕地优化调控的6个原则,提出空间优化适宜性评价和农户对坡耕地资源的需求压力数量评价相结合的坡耕地综合优化调控方法。选取库区腹地典型流域草堂溪流域进行案例研究。根据草堂溪流域特点以及坡耕地分布特征,从坡耕地可达性、生态功能和坡改梯适宜性3方面选取相关指标作为格局适宜性调控体系,选取耕地压力指数和果园对农户需求的补充能力作为数量调控体系。综合优化将研究区坡耕地分为优化利用型、重点整治型、逐步退耕型和优先退耕型4种类型,结合研究区坡耕地特点在保持耕地压力不增加、减少陡坡不适宜耕地和土壤侵蚀的前提下设置了4种退耕情景。最后根据农户自发撂荒地的空间分布特征,验证了评价指标体系建立的合理性和正确性。

Optimizing theory and case studies of cultivated slope land in the center of three gorges reservoir area based on patch-scale land evaluation

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 pattern suitability 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% and 30.5% 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.