长江上游退耕还林工程合理规模与模式

陡坡耕地的水土流失对生态环境和农业可持续发展构成双重压力。退耕还林是促进人与自然协调，推动农业可持续发展的有效途径，但应避免退耕还林工程规模的盲目扩大。退耕还林的规模应根据自然条件、生态功能定位并考虑粮食安全保障以确定。地广人稀的金沙江中上游、盆周山地是长江上游最重要的水源涵养、水土保持功能区，其退耕还林规模可适度扩大，但川中丘陵区、三峡库区人口稠密，退耕还林不应过分追求规模，退耕后的林草地不应突破土地面积的40％。而退耕还林工程的实施更应注重模式的选择，防止一刀切，川中丘陵区、三峡库区退耕还林宜采用“旱坡地粮经弹性结构种植”技术，建立坡地农林复合系统，逐步实施退耕还林。

De-farming and Afforestation in the Upper Reaches of Yangzte River:Extension and Model Issues

Soil and water losses of steep slope cropland are serious problems on both eco-environment and sustainable agricultural development. De-farming and afforestation on steep slope land is an effective approach to promote not only harmony of human beings and nature but also sustainable agriculture. However, blindfold extension scale-up should be avoided in de-farming and afforestation projects. Natural conditions, ecological service function and food safety should be taken into account on extension for de-farming and afforestation. Those mountainous area around Sichuan Basin and upper reaches of Jin Shajiang with scarce residence, are main ecological area with function of soil and water conservation so that extension scale might be enlarged. Whereas, extension scale should be limited to less than 40% of forest and grass land in hilly area of the central Sichuan Basin and around Three Gorge Reservoir because of high population density. In these areas, techniques of "Flexible Planting Structure with Food Crop and Economic Tree" should be adopted to build agro-forestry ecosystem in slope cropland and put de-farming and afforestation into practice step by step.