Monitoring Environmental Effect of Ecological Restoration with Remote Sensing in the Three Gorges Reservoir Area

The Three Gorges Reservoir Area(TGRA) covers 21 counties and cities in central China's Hubei Province and Chongqing Municipality with a total area of 58 800km2.Though dominated by mountains,it is densely populated and has been intensively reclaimed and cultiv-ated.Due to long-term human activities including overuse and inappropriate development,soil erosion and forest degradation in TGRA have become serious ecological and environmental problems.To solve these problems,the Chinese government formulated a series of conservation policies including soil and conservation project in the middle and upper reaches of the Yangtze River,returning cultivated land to forest or pasture,and natural forest protection.In this study,the Letianxi Watershed,located at 1km downstream of the Three Gorges Dam lying between 30°51′～31°10′N and 110°8′～110°54′E,is taken as a case study to understand the impacts of ecological restoration measure on soil erosion,vegetation cover and land use change.Based on Landsat TM/ETM images in 1997 and 2002,the land use maps of the study area were compiled through methods of supervised classification and interactive modification,and land use type transition matrix and its three landscape indices(i.e.patch number,mean patch area and its standard deviation) were calculated by model and GIS.Relative land use suitability index(Lr),which is mainly used to reflect the suitability of land use structure,was calculated taking soil erosion into account. Vegetation coverage was estimated from soil-adjusted vegetation indices(SAVI) using a second-order polynomial equation.Dynamics of soil erosion were assessed with RUSLE using GIS,and data used for the RUSLE were either determined or taken from published literature pertai-ning to the Three Gorges Reservoir Area.As a result,this paper found that through 5 years ecological restoration measures,the vegetation coverage increased from 80.6% in 1997 to 83.23% in 2002.Furthermore,the quality of cover was improved,and the area of more densely covered type including forest and shrub increased 18.1% and 9.1%.The land use structure is more reasonable,and the rationality index of land use increased from 0.76 in 1997 to 0.81 in 2002.The intensive,moderate and slight eroded area reduced 4.61km2,26.43km2 and 11.49km2 respectively due to the improved land use structure.At the same time,the annual average soil loss rate was approximately 1 562.5t/km2 in 1997,whereas 870.7t/km2 was found in 2002.The ecolo-gical restoration measures taken from 1997-2002 in Letianxi Watershed have got good ecological and environmental effects.