Evaluation Of Ecological Effect Of Conversion Farmland To Forest In Qiaojia County Of Yunnan Province

This paper takes Qiaojia county as study area to evaluate ecological effect of conversion farmland to forest from the macro and micro scale. To get the land-use changes before and after the project of conversion cropland to forest, this study applys two remote sensing images. On the basis of sample investigation and laboratory analysis, the paper studys on the point that different patterns how to improve soil physical and chemical properties, intercept role and biomass and so on. Then set up scientific evaluation index system, and use multi-criteria decision grey relation projection method to get the comprehensive evaluation value of ecological effect of different patterns. And this paper finaly screenings the best pattern of the biggest ecological effect. The main results of this study were as follows:1) Changes of land-use type. After8years reforestation, the cultivated land, grassland area reduced. And forest land, water, industrial and mining land and residents area increased. The land utilization degree composite index in2001and2009respectively were226.81and227.32.2) Changes of soil physical and chemical properties. The soil properties have been improved obviously in8years reforestation.The mode5(Pinus armandii×Coriaria nepalensis×Arundinella setosa) has the least volume weight and PH value of soil,the biggest total porosity, field moisture, organic matter, total N, total P, total K of soil. And the mode6(Zanthoxylum bungeanum) has the biggest volume weight of soil. The mode4(Leucaena leucocephala×Dodonaea viscose) has the biggest soil reunion degrees, and the mode5can improve soil water stability obviously. The content of available N, available P and available K is bigger in the surface layer.3) The mode5(Pinus armandii×Coriaria nepalensis×Arundinella setosa) has the biggest content of biomass, litter, the rate and the maximum amount of interception of the living things. The mode2(Coriaria nepalensis) has minimum biomass and the biggest water capacity rate, and the mode1(Pinus armandii) has minimum litter.4) This paper use multi-criteria decision grey relation projection method to evaluate the ecological effects of different patterns in the study area. The comprehensive evaluation value of ecological effect of mode5(Pinus armandii X Coriaria nepalensis X Arundinella setosa) in different soil layer respectively are0.3210and0.3112, which are3.4and3.2times respectively of the farmland.The results show that the mode5is the best mode of the biggest ecological effect.