| As a continuous and complicated ecological project, converting farmland into forest and grassland will locally influence the social and economic development as well as improving the ecological environment conditions, which inversely has great importance with the project's sustainable development. Now the problems that need to be urgently resolved, which meanwhile are the theoretical foundations of the conversion ecosystem's harmonious and sustainable development, mainly include researching the local livelihood and the social and economic development conditions with scientific methods, evaluating the ecological and economic effects of this project and most importantly, the coupling conditions of the two effects.Choosing Ansai County as the research location, the paper started with the descriptively analysis of the ecological and economic influence of local conversion project, and then quantitatively evaluated the ecological and economic effects based on the energy value theory, at last, by establishing the coupling degree model, the paper quantitatively evaluated the ecosystem's coupling conditions under different conversion patterns. The main results of this research could be concluded as follows:(1) Ecological effects of converting farmland into forest and grassland projectIn this paper the ecological benefit of the project was represented by the increase of ecosystem service value from the conversion of farmland into forest and grassland. According to the theories and methods of ecological economy and ecosystem service value and based on the actual situation of research location, six indexes, including soil conservation, water storage, nutrition circulation, assimilation of CO2 and O2 release, air purification and biodiversity protection, were adopted to measure the spatiotemporal changes of ecosystem service function and value combined with a series of scientific methods, also the service value of different vegetation type were evaluated. The results indicated that the total ecosystem service value of Ansai County increased by 27.95 percent, from 18.837 billion yuan in 1998 to 24.103 billion yuan in 2005; the service value of water storage was the highest, nearly accounted for 75 percent of total ecosystem service value, then followed by the soil conservation(11.43 percent), nutrition circulation(6.83 percent), assimilation of CO2 and O2 release(3.94 percent), the service value of biodiversity protection and air purification were much lower, only 0.54 and 0.18 percent of total ecosystem value; of all the vegetation types, shrub forest had the highest service value, then the grassland, arbor forest and economic forest; as to the per unit area service value, the sequence were arbor forest, shrub forest, grassland, economic forest, cropland. As a conclusion, converting farmland into forest and grassland has great significance in environment protection, mainly by controlling the water and soil erosion.(2) Social and economic effects of converting farmland into forest and grassland projectAccording to the geographic and social situations, the research location was divided into three regions and a total number of 290 peasant households were chosen randomly and investigated on food security, economic income, rural labor transfer, agricultural industrial structure adjustment and consumption structure. The analysis of the investigation indicated that although the cultivated area and the total grain yield both decreased because of the conversion, the grain yield per hectare increased steadily, and the single cultivated structure of crops was changed, too; peasants'income increased a lot and the income source was widened; A large number of surplus labor was generated and most of them were under the condition of concealed unemployment; the consumption structure was changed mainly on the decrease of food expenditure and the increase of medical, education and communication expenditure, and as for the energy consumption, the crop straw, used to be the dominant rural energy, was gradually replaced by coal, natural gas and biogas, which indicated that the energy structure of peasant household was much more reasonable and abundant.(3) Ecological and economic effects of converting farmland into forest and grassland projectBased on the theory and method of energy value established by H.T.Odum, a famous American ecologist, the research quantitatively evaluated the conversion project's ecological and economic effects in Ansai County through analyzing the dynamic change of ecosystem energy value. The results showed that both the total input and output energy value deceased first and then increased, of which the decrease of organic energy input and primary environmental resource input reflected the project's positive effect of controlling surface soil loss; the energy value of planting and animal husbandry industry used to be dominant in the total energy value output structure, but after the conversion, the energy value output of forestry industry increased rapidly; as the energy value indexes were mentioned, both the energy value investment ratio and environment loading ratio increased first and then decreased and increased again, pure energy value output ratio and energy value sustainability index first decreased and then increased, and the system stability was always increasing. The decreasing environment pressure, increasing ecosystem sustainability and stability and harmonious system function showed that the conversion project's ecological and economic purpose could be basically fulfilled.(4) Ecosystem coupling research of converting farmland into forest and grassland projectBy establishing the coupling degree model, the conversion ecosystem's coupling conditions under different conversion patterns were quantitatively evaluated and the sensitivity of the evaluation results was analyzed from two aspects, weight and index variable. The results indicated that although the ecosystem's coupling condition was gradually improved, the coupling situation in Ansai County was still not so good, basically in the stage of recession and over development.The coupling evaluation of six different conversion patterns and the control pattern showed a different result according to the comprehensive index of ecological environment and economic development, and pattern A was the best in both two indexes. Each pattern was higher than the control pattern in ecological environment index, but as for economic development, pattern A, pattern B and pattern C were higher than the control pattern while pattern D, pattern E and pattern F was lower than that. The coupling degree of all the six conversion patterns was better than that of the control pattern and pattern A was the best.The innovation points of this research:(1) The research combined the social and economic development factors with ecological effect of converting farmland into forest and grassland project, quantitatively and qualitatively analyzed the structure, function, characteristic, coupling degree and driving force of conversion ecosystem and evaluated the sustainability of the conversion project, which used to be a blank field, also the research enriched the theory system of ecosystem coupling and has great importance in theoretical innovation.(2) Few research using energy value theory and method to evaluated ecological and economic effects of converting farmland into forest and grassland project, which could clearly reveal the relationship between ecological environment and economic development and provide much more reliable and practical evaluation results, so this paper has great theoretical guiding significance in scientifically evaluating the ecological environment conditions, reasonably utilizing natural resources and establishing guideline for social and economic development in the conversion regions.(3) The paper introduced the conception and theory of conversion ecosystem coupling for the first time, quantitatively evaluated the conversion ecosystem's coupling conditions in county level and conversion pattern level by establishing the coupling degree model and the sensitivity analysis from weight and index variable greatly improved the reliability and prediction capability of the evaluation results.
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