| Shelter-forest system in the Three Gorges Reservoir Area is the important foundation for the ecological and environmental construction and sustainable development of the region and even the Upper Yangtze River. It has very important significance in water conservation, erosion prevention and giving play to the ecological barrier function of the Three Gorges Project. However, the forest resources in the Three Gorges Reservoir have weak ecological protective function because of uneven distribution, unreasonable proportion and simple stand structure and so on. Therefore, it is essential to study of suitable spatial distribution of shelter-forest system in the region by advanced theory, method and technology.Based on Land Suitability Evaluation Model which was modified by the uncertainties and grey system related degree, the suitability of vegetation restoration on cultivated farmland (more than 25°) and unused land that were obtained by interpreting the Landsat TM images in 2007 in the Three Gorges Reservoir Area, was studied by the selected environmental factors. Meanwhile, take the suitable land for vegetation restoration and current forestland as the research object. On this basis, in order to yield the optimal integrated benefits of the shelter-forests in the Three Gorges Reservoir Area, based on the classified forest site types and multiple objective gray situation decision model, the suitable shelter-forest types for different forest sites were located by the selected benefit index. The results showed that:(1) Based on unsupervised classification and expert system, the interpreted Landsat TM images in 2007 in the Three Gorges Reservoir Area was classified as 7 land utilization types and 4 shelter-forest types. The land utilization types included cultivated land(less than 25°), cultivated land (more than 25°), grassland, forestland, unused land, water area and town. The shelter-forest types included coniferous forest, broadleaf forest, mixed forest and shrub. The overall accuracy and kappa coefficient was 88% and 0.8513 respectively. Therefore, the results'precision was satisfied with the requirement of the research.(2) Through analyzing the characteristics of land utilization types in the Three Gorges Reservoir Area, could be seen that forestland and cultivated land occupied the biggest percentage in area which accounted respectively for 48.8% and 38.2% of the total land area. The area of cultivated land (more than 25°) and unused land were 271976hm2 and 17768 hm2 respectively, reflected that the phenomenon of cultivation on steep slope was seriously and land resources exploitation in the region had great potentiality. Furthermore, according to the special distribution of each land utilization types, the forestland distributed in the middle and high mountain area of eastern regions and presented a characteristic of east more west few. Cultivated land distributed in the low mountains and hills area of western regions which was opposite to the forestland. Unused land mostly distributed in deep hills and low mountains area except that small part in river valley, where the northtern Wuxi had the largest area distribution.(3) Through analyzing the characteristics of shelter-forest types in the Three Gorges Reservoir Area, could be seen that the percentage of shelter-forest types were unreasonable and their distribution was uneven at present. The coniferous forest and shrub were accounted for 73% of the total forest area in the region, and the broadleaf forest and mixed forest was only accounted respectively for 19.2% and 7.8%. Furthermore, according to the special distribution of each shelter-forest types, the coniferous forest and shrub distributed in most regions, the broadleaf forest distributed in the middle and high mountain area of less human disturbance, mixed forest centralized distributed in weatern Hubei area, but rarely in Chongqing. The spatial distribution of shelter-forest had significantly different between Chongqing and weatern Hubei area.(4) The suitability of vegetation restoration on cultivated land (more than 25°) and unused land was studied by the selected factors as elevation, slope grade, annual average precipitation, soil thickness and soil type. The results showed that, main influencing factors for Vegetation Restoration in the Three Gorges Reservoir Area were slope grade and soil thickness. The highly suitable zone, suitable zone and moderately suitable zone, which the total land area were up to 282361 hm2, accounted respectively for 23.1%, 48.6% and 25.8% of 289744 hm2 evaluated land in the Three Gorges Reservoir Area. The 270345hm2 cultivated land (more than 25°) and the 12016 hm2 unused land were classified as highly suitable zone, suitable zone or moderately suitable zone, which should be exploited by the project of Conversion of Cropland to Forest or Grassland as well as the projects of Afforestation and Planting Grass in Barren Hill or Alluvial Flat. The vegetation coverage would be increased by 4.9% if the suitable lands of vegetation restoration had been fully utilized as soon as possible. The original environment should be maintained for the not suitable zone of 7383hm2, while they distributed in the places of above 1500m altitude, less than 25cm soil thickness, more than 35°slope and inadequate precipitation.(5) Forest site in the Three Gorges Reservoir Area can be divided into 40 types based on the hierarchic grouping method of key environmental factors as elevation, slope grade and soil thickness. Based on multiple objective gray situation decision models, the suitable spatial distributions of coniferous forest, broadleaf forest, mixed forest and shrub were studied by the selected benefit index as water conservation amount, biomass and stand productivity. The results showed that, the suitable shelter-forest types for better forest site was broadleaf forest, the suitable shelter-forest types for general forest site were coniferous forest and mixed forest, and the suitable shelter-forest types for poor forest site was shrub.(6) After the optimization of spatial distribution of shelter-forest types in the Three Gorges Reservoir Area, the coniferous forest, broadleaf forest, mixed forest and shrub accounted for 31.8%,28.1%,36.2% and 3.9%, respectively. By contrast with pre and post optimization, the proportion of broadleaf forest and mixed forest increased by 10.7% and 29.1%, while the proportion of coniferous forest and shrub reduced by 5.8% and 24.9%. Furthermore, the amount of water conservation, biomass and stand productivity of the shelter-forests in the Three Gorges Reservoir Area would be increased by 469038×104 m3, 4880×104t and 294×104 t after the optimization, respectively.
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