Land Use Change And Landscape Pattern Evolution In The Typical Watershed Of The Hinterland Of The Three Gorges Reservoir Area

Since the Three Gorges Dam was built,it has experienced such stages as the construction period,the impoundment period and the post-Three Gorges era.The hinterland of the Three Gorges Reservoir Area is considered as an ecologically fragile zone and a habitat sensitive.Changes in land use or land cover are closely related to the construction of the Three Gorges water conservancy project and the resulting resettlement,urban relocation,and ecological support.This paper selects Tangxi River watershed which influenced deeply by human activities,Meixi River watershed with Karst-Non-Karst Combination and the Daning River watershed dominated by karsts as the typical watersheds,by using 3S technology to extract the watershed's DEM data and land use data,we systematically analyzed the land use change and landscape ecological security overall evolution laws of the Three Watersheds from 1986 to 2017.And based on these,we explored the evolutionary characteristics of land use changes and landscaping patterns and major land use types' landscape patterns of in different physiognomy buffers.(1)Characteristics of land use change in watershedsFrom 1986 to 2000,the Three Gorges project was in the construction period,and the land use was shown as the increase of waters,cultivated land and construction land.From 2000 to 2010,This stage was mainly in the Three Gorges Project water storage period.With the completion of the Three Gorges Emigration engineering,it entered the post Emigration period,meanwhile,it was affected by the policy of returning farmland to forest.Basin emergence the trend of conversion of farmland,shrub and grassland to woodland,water area and construction land;from 2010 to 2017,it fully entered the post Three Gorges era.In response to the construction of ecological civilization,the cultivated land with the dominant of production function was transformed into the economic fruit forest with the dominant of ecological and economic function.(2)Study on watershed landscape pattern and ecological security overall characteristicsAs for the landscape ecological safety index,the spatial distribution shows a trend of improvement,and the trend line shows a "U-shaped" change in the east-west direction and a fluctuation-increasing trend in the north-south direction.As far as landscape security is concerned,the safety level of landscape ecology has a strong positive correlation and has a better cluster status.Affected by elevation,slope and type of land use,the spatial evolution of the landscape ecological security index in the same watershed at different times and at the same time varies significantly.(3)Land use and landscape pattern evolution of different buffer zones in the watershedsThe overall comprehensive index of land use degree in the three watersheds and the comprehensive degree index of land use in each area show a fluctuant downward trend of “first reduction,then increase,and then decrease” with changes in the buffer distance.The Tangxi river watershed and Daning river watershed has the largest development degree at 30 km and 10 km,while the Meixi river watershed with time changes has difference characteristics.The landscape pattern index of the watershed has different characteristics along with the time change,in which the density of patch density PD increases first and then decreases,and the overall trend is increasing.The diversity index SHDI decreased continuously,and the reduction is obvious.The aggregation index AI decreases first and then increases,and the overall trend is increasing.The landscape shape index LSI increases first and then decreases,and the overall trend is decreasing.(4)Landscape pattern evolution of main land use types in river watershedsBecause of the existence of land use types,the landscape pattern index is different with the far and near of the buffer distance,in which the SHDI changes are the most complex and the AI is the next.Specifically,the total trend of landscape pattern evolution of different buffer zones under different cropland,woodland,shrub and grassland in three basins is consistent.That is,the landscape pattern index PD and LSI show an overall upward trend,and AI presents a downward trend.