| Zigui County which is located in the mountainous area of western Hubei Province on the banks of the Yangtze River, is also the first County of the Three Gorges Reservoir Area, and has the important ecological strategy status in china. In recent decades, it has caused seriously land degradation and soil erosion owing to unreasonable using of land and cultivating sloping fields, which has a critical influence on the safety of the local people's living and property and the dam's long-term stability. In order to effectively prevent soil form eroding and protect the safe operation of the Three Gorges Project on the Yangtze River, the Committee of the State Council listed Zigui County as the first batch of pilot projects for the program of converting farmland to forest in 2000. The program is an important measure to improve the deteriorating ecological environment in the western region, and is also the starting point and basic measure for the environment construction of the West development. From the polot project launched, the project has been successfully implemented for seven years in accordance with the principle of"highlight the key points, starting with the less difficult, setting an example and advancing with steady steps"and total completed the task of afforestation by 19 918.31 hectares. Now 14 towns,461 villages (farms) and 91 583 farmers had involved in the program in Zigui County. The country and the local government have invested lot of money,manpower and the physical resource, so it is the hot issue which all of society urgently pays attention to and awaits to be solved to confirm how program carries out and whether it has achieved the anticipated goal. Therefore, based on the analyze of the situation of the program of converting farmland to forest during 2000~2004 in Zigui County, we choose the program in 2000 as the research object and take slope farmland as the comparison to carry on the objective evaluation to the program of converting farmland to forest in Zigui County. The main results are as follows:1. Based on the type of forest ecology benefits, the paper defines the ecological benefits of the program of converting farmland to forestry as the following types: water-source conservation benefit, water and soil conservation benefit, fertilizing and ameliorating soil and carbon fixation and oxygen release benefit under the principle of the science, systematicness and target with the consideration of the background and the practical significance to carry out the project.2. Based on the existing models at home and abrod, the article establishes a set of ecology benefit measurement appraisal model for the program of converting farmland to forestry and makes a quantitative assessment on the project of Zigui County in 2000. The result indicates that the total quantity of the water-source conservation benefits of the project is 1 458 053.98 ton every year, which includs rainfall interception by 557 177.51 ton,increasing the surface water by 343 698.96 ton and the amount of water purification by 557 177.51 ton. The total quantity of reducing soil erosion is 65 846.76 ton,the quantity of preventing sedimentation is 15 232.53 ton, and the quantity of reducing the loss of soil organic matter and soil nitrogen,phosphorus and potassium is respectively 600.64 ton,30.25 ton,100.83 ton and 919.27 ton. Because the forest can produce the withering and falling which can produce lots of organic matters and nutrients throught its own corruption, the project increases the amount of soil organic matter and nutrients by 3 288.52 ton, including 3 156.63 tons of organic matter, 92.64 tons of the total nitrogen, 8.01 tons of the total phosphorus, and 92.64 tons of the total potassium; The forest absorbs 13 234.68 tons Carbon dioxide, and at the same time it releases 9 743.31 tons oxygen through the photosynthesis.3. Using the eco-efficiency evaluation method in Western economists based on the theory of Value Effect, the paper takes monetary analysis to the forest ecological benefits of the program of converting farmland to forest in 2000 in Zigui County. The total value of the project is 3.5536 million Yuan, and it's composed of four parts and the values of each ecological benefits are following (unit: yuan): water-source conservation benefits by 488 700 Yuan (in which storing water benefits value is 192 600 Yuan, increasing the surface effective water value is 115 600 Yuan, and purifying water value is 180 500 Yuan); water and soil conservation benefits by 1.066million Yuan (in which the value of soil fixation is 12 100 Yuan, the value of preventing the silt from silting up is 41 100 Yuan and the value of reducing the loss of the soil fertilizer is 1.0128 million Yuan); fertilizing and ameliorating soil 138 200 Yuan; carbon fixation and oxygen release benefits by 1.8607million Yuan(in which solid carbon value is 928 400 Yuan, releases the oxygen value is 932 300 Yuan)4. In the nine kinds of the ecology benefits of the program of converting farmland to forest in Zigui County, the quantity order of the benefits is fertilizer efficiency(28.05%)> releasing oxygen benefit(26.24%)> carbon fixation(26.13%)> storing water benefits(5.42%)> purifying water benefi(t5.08%)> increasing the surface effective water benefit(3.25%)> fertilizing and ameliorating soil benefi(t3.89%)> the benefit of preventing the siltation(1.16%)> fixation benefit(0.34%).5. Using the following methods, such as expert marking method,brainstorming and the method of meeting in and out, the paper establishes a set of evaluation index systems to assess the benefits of the program of the converting farmland to forest for the first time in Three Gorges Reservoir Region. The system is composed of three levels index: The first layer is the targeted level,that is comprehensive ecological benefits; the second layer is rule level, which composed of biological effects, fertilizing and ameliorating soil benefits and hydraulic ecological benefits; The third is the specific index layer, includeing vegetation coverage, species abundance, biomass, soil bulk density, soil porosity, organic matter content of soil, total nitrogen content of soil, total phosphorus content of soil, total potassium content of soil and the erosion modulus, and so on. 6. Using the method of fuzzy comprehensive evaluation, the paper evaluates the comprehensive ecological benefits to the program of converting farmland to forest in 2000 in Zigui County. The results show that the ecological benefits of all the types of withdrawing from farming to afforesting and grass planting, such as the ecologica1 forests,economic forests and ecological economic forest compound model,are higher than that of the agro-ecosystems', and the order is ecological economic forest compound model > ecologica1 forests > economic forests > slope cropland. According to classification standard for eco-efficiency assessment, the paper concludes the following results: The model of ecological and economic forest haveas the same integrated evaluation grade as the model of ecological forest, and the evaluation result is "good"; the economic forest's is third level, and the result is"medium"closing to "good"; But the slope cropland's is forth level and the result is "poor". The study proves it plays an important role in increasing vegetation coverage rate,maintaining biodiversity,improving soil physical and chemical properties and preventing soil from eroding to carry on the program of converting farmland to forest.7. According to study result of comprehensive evaluation benefits of the four different ecological restoration model, the benefit of ecological economic forest compound model is the best, worthily popularizing it in Three Gorges Reservoir Region.
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