Optimization Of Spatial Allocation And Stand Structure Regulation Of Protection Forests In Different Scales

In order to mitigate soil erosion and provision of firewood for local farmers, vegetation recovery programs were implemented starting from 1970s. With forest cover of 22.7%, extensive protection forests were established by the end of 1990s. At present, these forests turned into middle age, but their water and soil conservation functions were quite poor due to pure coniferous forests, over-dense stand, low coverage of grasses or shrubs, weak natural regeneration and community stability.In consideration of current ecological issues and scientific problems in protection forest systems in Sichuan Basin, the study was focused on the optimization of spatial allocation and stand structure of protection forests in medium-sized watershed, small watershed and stand scale. The main results were found as following.1 Suitable forest cover and optimization of spatial allocation of forest categories in medium-sized watershedThe hydrological process of forest watersheds was simulated by applying of forest catchment hydrological model (FCHM) in Pingtonghe and Liujiahe watersheds. The result has indicated the surface runoff decreased due to the existence of forests in both two watersheds; the annual catchments runoff enhanced with the increase of forest cover in Pingtonghe watershed, but it decreased in Liujiahe watershed.12 indicators (stand structure, soil type, slope, etc.) were selected to evaluate the classes of water conservation capacity of forest subcompartments, and the weighted soil saturated water-holding capacity was applied to identify the suitable forest cover in Pingtonghe watershed. After optimization of spatial allocation of forest categories in the watershed, the total area of timber forest and economic forest increased; thus, the water resource in the watershed was made full use and the flooding peak could be reduced during rainy season.2 Optimal site-stand type match in small watershedThrough matter element analysis, the land suitability was evaluated in Guangsihe small watershed, the area weight of the main forest types was calculated by analytic hierarchy process (AHP) with integrating of ecological, economic and social benefit as well as stand stability. Combining the results from field survey, the optimal site-stand type match was implemented, and partial current forest types and forest subcompart-ments were regulated. After the optimal match in Guangsihe small watershed, the area of pure coniferous forest decreased, but the mixed forest between coniferous and broad-leafed species increased to 39.9%.3 Suitable stand types and stand structure in central Sichuan hilly areasThe study on hydrological effects of the four cypress stand types has indicated that oak-cypress mixed forest was the best one in terms of canopy interception, litter water-holding capacity, maximal soil water-holding capacity, as well as reduction of surface runoff and sediment yield. Through analysis of the relationship between canopy closure and biomass of shrubs and grasses, canopy closure and coverage of shrubs and grasses, cypress monoculture in the central Sichuan hilly areas, the stand type with canopy closure of 0.6-0.7, shrub coverage of 35-50% and grass coverage>45%, was much better than other types in terms of water and soil conservation. Study on 8 main vegetation communities in the areas has shown that the biodiversity in shrub and grass layers were higher than that of in arbor layer. The M. Godron stability index of the 8 communities was far from the stable coordinate point (20/80), all the communities were in unstable stage to some extent.4 Regulation techniques for optimization of stand structureThree techniques were studied to regulate stand structure of the cypress and pine monoculture. The results from open-and-beating up with broadleafed species has indicated that the survival rates of camphor and Taiwan alder grew well in cypress forest; oak performed well in pine forest. Three treatments was tested for thinning in middle-aged pine monoculture, the result has shown that medium intensity thinning was the better option for management of middle-aged pine monoculture. Four treatments were designed in transformation of cypress monocultur. The result has indicated that cutting band with 6 m and 8 m were most suitable in improvement of low-function cypress monoculture.