Occurrence Process Of Understory Water-eroded Area And Multi-angle Remote Sensing Of Vegetation Restoration Degree Monitoring

Water and soil loss is a focus of various ecological problems in China, and a root stock of ecological deterioration and poverty accumulation. The red soil area,covering2030000km2,21%of total land area in China, had once become a "red desert" in some regions for its widest and severest water and soil loss in southern China. With forest planting and conservation by forestry and soil and water conservation departments in recent decades, forest-coverage rate had increased obviously in many provinces, most of them exceeded50%, some were more than70%. Nevertheless, soil erosion occurred moderately or even intensely on forested areas, for the bareness of under-forest soil without close-cover of vegetation or residue. This under-forest soil erosion requires scientifically monitoring and calculating of water and soil conservation effects for vegetations on forested areas, through feasible vegetation indices indicating occurrence mechanism of under-forest soil erosion, and objectively evaluating of vegetation restoration degree on such water-eroded areas, so as to make a foundation for planning and management of water and soil conservation. On12experimental plots built in early2010in Hetian town, Changting county, Fujian province, this paper focuses on the analysis of the relationships between vegetation structure and its effects on water and soil conservation, with56measurements of vegetation, runoff, and soil erosion parameters, at3time scales, single rain fall, seasonal, and all-year. Three parameters of vegetation structures, leaf area index (LAI), vegetation fractional coverage (VFC), and live vegetation volumn (LVV,the production of LAI and VFC) were used to indicate spatial distribution density of vegetation, and the water and soil conservation effects of sparse Pinus massoniana and forest-grass combination were analyzed through comparing the runoff and soil erosion on the plots planted with sparse Pinus massoniana and forest-grass combination with those on the control plot; Through field measurement and remote-sensedly inversion of vegetation structures in different vegetation succession communities, grass, shrub, coniferous forest, coniferous-broad-leaf forest,and broad-leaf forest, local vegetation restoration degree (VRD) was evaluated based on "best" vegetation structures evaluated for water and soil conservation. The main conclusions are presented below:(1) Water and soil conservation effects of forest, grass, and the combination of forest-grass are different. Compared to the control plot, the seasonal and all-year surface runoff increased by5%-16%on the plots planted with pure Pinus massoniana, while decreased by1%～33%on the plots planted with pure grass(Paspalurn wettsteinii), and decreased by15%～54%on the plots planted with the vegetation combination of tree (Pinus massoniana) and grass (Paspalurn wettsteinii). The seasonal and all-year soil loss decreased by56%～70%on the plots planted with pure Pinus massoniana,and decreased by91%～99%on the plots planted with pure Pinus massoniana or with the vegetation combination of tree (Pinus massoniana) and grass (Paspalurn wettsteinii). Water and soil conservation effects of forest-grass are not those additions of pure forest and grass, and there are temporal changes in the water and soil conservation effects. Consequently, it is required to finely and quantitatively indicate different vegetation structures and their effects on. water and soil conservation,so as to systematically study the relationships between them.(2) The accuracies of results estimating water and soil conservation effects of forests and grasses are different for the models based on different vegetation indices and time scales. Vegetation fractional coverage (VFC) and live vegetation volumn (LVV) could be used to indicate the water and soil conservation effects of vegetation on forested area. Among various models calculating the water and soil conservation effects of forests and grasses, some seasonal models are better than all-year ones while others the reverse, or close to each other. Under single rainfall, however, it is difficult to establish models between vegetation structures and water and soil conservation effects.(3) The union of remote sensing techniques and researches on water and soil conservation effects of vegetation is a credible means to monitor and study vegetation restoration degree on eroded areas. The monitoring and evaluation of local to regional vegetation restoration degree, compared with the "best" vegetation structures for water and soil conservation,are supported by accurate inversion of vegetation structures by remote sensing, and studies on water and soil conservation effects of vegetation on eroded areas. Our study showed that, vegetation restoration degree of the study area are at the low level, and are only30%at both seasonal and all-year time scales. The area where live vegetation volumn (LVV) restoration degree<20%and>80%respectively covered more than60%and less than20%of the total area in Hetian town, Changting county, Fujian province.