| In the period of 2002 to 2007, Pingguo (involves 14 villages, towns or forest farms), a county in Guangxi Province, returned farmland to forest for 18,951.91 hm2; in the end of 2012, the grand total of benefit area reached 119,063.40 hm2. This paper analyzed through field investigation and laboratory tests on biomass, physical and chemical properties on soil, and forest canopy interception and so on about different forests which were returned from the farmlands in Pingguo County, to study the vegetation, soil, and hydrological effect. Moreover, the ecological benefit of returning farmland to forest project in Pingguo County was evaluated.According to the survey, in the 11 years of returning farmland to forest in Pingguo County, which is mostly Karst landforms, the vegetation layer formed a stable community structure, understory shrub and herb plants recovered effectively, the community succession is still in relative low-level stage; from the soil porosity, mechanical composition, bulk density, organic matter composition and other aspects, soil physical and chemical properties have been improved to some extent, but the effect is not that well. The soil porosity for the land of returning farmland to forest was lower than 40%, far less than the ideal index, soil mechanical composition does not have too much optimization, content of clay and fine silt is significantly lower than that of natural grassland, organic soil improvement effect is not obvious. From the forest canopy interception and soil infiltration rate aspects of different forest lands, returning farmland to forest formed preferable hydrological effect, and will improve with time. Since the implementation of returning farmland to forest in Pingguo County, the forest coverage rate increased from 32.1%t o 54.54%, with an increase of 22.44%. Then the soil erosion modulus decreased year by year, from 650 t/(km2.a), down to 510 t/(km2.a) after the project, effectively curb the occurrence of soil erosion. The higher grand total of Water conservation for forest is 633,488,700 m3. In the 11 years of returning farmland to forest, a total of 1,033,200 t of CO2 were fixed,754,300 t of O2 were created,7,2001 of SO2 were absorbed,82 t of dust were detained, which has a significant effect on purifying the environment.The paper through the screening of indicators, establish an evaluation model of ecological benefits. Based on this model, by using shadow engineering method, the market price method and other methods, the ecological benefits of the project of returning farmland to forest in Pingguo County are generated to evaluate, the results show that:the 11 years of the returning farmland to forest project in Pingguo County produced a initial total value of ecosystem which is 7,825,000,000 yuan; after the relative coefficient of willingness to pay 0.26 modified, the total value of the ecological benefit of returning farmland to forest project is 2,034,000,000 yuan. Among it, the value of water resource protection is 1,146,000,000 yuan, the value of soil conservation is 2,976,100 yuan, the value of carbon fixation and oxygen release is 650,000,000 yuan, the value of environmental purification is 1,844,400 yuan, the value of the microclimate improvement is 78,000,000 yuan, and the conservation of biological diversity in the value of 155,000,000 yuan. Studies show that after the implementation of the project of returning farmland to forest in Pingguo County, the local ecological environment has been improved obviously, has brought significant ecological benefits. |
PDF Full Text Request