Ecological Monitoring And Evaluation Of Different Modes Returning Farmland To Forests In Guangxi

Grain for Green Project is a symbol engineering that implements natural ecosystem renovation in China, and it is also one of the top ten key forestry ecological projects in the world. It has built 1.063 million hm2 afforestation in Guangxi, since returning farmland to forest in 2001.Grain for Green Project increased 880 thousand hm2 forest, and enhanced the forest coverage by 3.7% directly in Guangxi. With the development of engineering construction, how to evaluate the ecological benefit effectively has become a pressing concern for government sections.This paper makes six reforested patterns Eucalyptus as the research object including urophyllaS, Zenia insignis Chun, Toonasinensis (A.Juss.) Roem and Castanea mollissima in Guangxi Pingguo, Donglan, and Xingbin,and evaluate vegetation restoration, changes of water conservation and water quality,improvement of soil fertility and ecological benefits in the forestation area by some theories such as forest ecology and so on,that can facilitate the project implementation,and provide the scientific basis and practical guiding significance for it.The results show that:(1) After implementing Grain for Green Project, undergrowth has recovered well and vegetation coverage has researched more than 80% in returned farmlands, there are marked difference between Margalef richness indexes,Simpson indexes and Shannon-Wiener diversity indexes of undergrowth under different modes returning farmland to forests, diversity indexes of shrub layer are bigger than those of the herb layer, species richness and diversity indexes of community are bigger than the control group which was not returned farmland.What’s more, biomass of shrub-grass layer is bigger than the control group too.(2) After implementing Grain for Green Project, soil structure of returned farmlands have certain improvement, soil bulk density is bigger than the control group, however,total porosity, capillary porosity,non-capillary porosity, the maximum water holding capacity and field capacity are smaller than those of the control group, because the control group is affected by cultivation. The contents of soil organic matter, Nitrogen, Phosphorus, Potassium, Hydrolyzed nitrogen,available Phosphorous and available Potassium are all more than those of the control group, which states that the Grain for Green Project can really improve soil fertility.(3) After implementing Grain for Green Project, soil and water loss of returned farmlands has been controlled, water storage and soil conservation function have improved, runoff and sediment of different modes returning farmland to forests are smaller than those of the control group.What’s more, the water quality of surface runoff has certain improvement too, Nitrogen, Phosphorus and heavy metal content are less than those of the control group.(4) Total ecological value has reached 1.1607715 billion yuan of different modes returning farmland to forests in Pingguo, Donglan, and Xingbin based on by using project alternative method,opportunity cost method and so on value theory, values of water resources protection,nitrogen fixation and oxygen release,biodiversity,environment cleaning, soil Conservation account for 40%、 33%、13%、10%、4% of the total ecological value respectively, ecological benefits reflect Mainly in the water resources protection, nitrogen fixation and oxygen release.