| At present,the construction of ecological civilization in China has made certain achievements,but resource constraints tend to tighten,and serious environmental pollution and the problem of ecosystem degradation still exist.As a direct and effective incentive,the ecological compensation system can provide economic or material compensation to the damaged ecological environment to protect and restore the ecosystem,providing important support for practicing the"two mountains"theory,realizing ecological priority and green development,and building an ecological civilization.How to determine reasonable ecological compensation thresholds and achieve the goal of preserving and adding value to the supply of ecosystem services is still an urgent problem to be solved in the study of ecological compensation mechanisms.Therefore,constructing an ecological compensation threshold discriminant model and clarifying the factors influencing the degree of change of ecological compensation threshold is of great theoretical significance and positive practical significance for promoting ecological protection and ecological restoration and establishing a long-term effective ecological compensation mechanism.This study takes the upper reaches of the Yangtze River(UYR)as the study area,constructs a water supply service supply and demand measurement model,analyzes the spatial and temporal characteristics of water supply and demand in the UYR sub-basin from 2005 to 2020,and identifies ecological compensation payment areas and compensated areas through the ecosystem service supply and demand ratio(ESDR);Based on the SWAT model and land use scenario setting to simulate the water conservation under different scenarios and determine the most suitable land use conversion scenario;The ecological compensation threshold discriminant model was constructed by coupling the minimum data method and scenario simulation,and the ecological compensation thresholds of different sub-basins were determined,as well as the corresponding proportion of fallowing and the increased water conservation.Finally,based on the optimal parameter geographic detector(OPGD),we analyze the influence level on the ecological compensation threshold and the influence of the interaction between the factors and propose the implementation path of ecological compensation in the UYR.The main findings are as follows:(1)The water supply in the UYR from 2005 to 2020 showed a trend of first decreasing and then increasing over time,and the overall spatial distribution pattern showed the distribution characteristics of low in the northwest and high in the southeast and showed a diffusion pattern of fragmentation and then patchiness over time.The total water supply is 3540.99×10~8m~3,3333.42×10~8m~3,4496.65×10~8m~3 and 5384.49×10~8m~3respectively.The total water consumption from 2005 to 2020 shows a trend of first falling,then rising,and then falling,showing a spatial pattern of high in the southeast and low in the northwest.The total water consumption is 1771.02×10~8m~3,1584.87×10~8m~3,1804.04×10~8m~3 and 1621.68×10~8m~3 respectively.The surplus area of water supply service from 2005 to 2020 is mainly located in the northwest,and the deficit area is mainly located in the Chengdu-Chongqing area.In 2020,the ecological compensation payment areas are sub-basins 56 and 66,and the remaining areas with an area of 96.53%are the compensated areas.(2)There is a significant difference in the water conservation capacity under different land use scenarios in the UYR:returning farmland to forest>returning farmland to grass>maintaining the status quo.The growth rate of the total water conservation in the returning farmland to grass scenario is 14%,and the returning farmland to forest scenario is 26.4%.Suitable areas for returning farmland to the forest are mainly distributed in eastern Sichuan,western Chongqing,and western Guizhou,with an area of38.44%;The suitable areas for returning farmland to grass are located in northern Sichuan,northern Guizhou,and northeastern Yunnan,with an area of 17.17%;The areas suitable for maintaining the status quo are located in western Sichuan Province,northern Yunnan Province and Tibet,with an area of 28.27%;The area unsuitable for land conversion is located in Qinghai Province,with an area of 12.65%.(3)As the compensation price per unit area increases,the proportion of farmers participating in the return of farmland to forests and grasses will increase,and the amount of water conservation resulting from the return of farmland to forests and grasses will also increase.The ecological compensation threshold discriminant curve first increases to the ecological compensation threshold point and then decreases to maximize the ecological compensation target benefit.For example,in sub-basin 30,when the compensation price of water conservation per unit area is 24.89 yuan/m~3,the ecological compensation threshold discriminant curve reaches the maximum at this time,and the proportion of returning farmland to forest is 90.61%that can be achieved under this threshold,and the area of returning farmland to forest reaches 690010.23 hm~2,and the new water conservation added by returning farmland to forest is 11.3×10~8m~3,and the total water conservation volume after the addition is 27.48×10~8m~3.The average value of the ecological compensation threshold for returning farmland to forests in the UYR is 46.48yuan/m~3,and the average value of the increased water conservation provided is22.02×10~8m~3.The average value of the ecological compensation threshold of returning farmland to grass is 107.87 yuan/m~3,and the average value of returning farmland to grass to provide increased water conservation is 3.72×10~8m~3.And the ecological compensation threshold for returning farmland to grass has increased by 2.3 times on average compared with that for returning farmland to forest.(4)The driver with the highest influence on ecological compensation threshold is grain yield,and the driver with the lowest influence is NDVI,and the influence on ecological compensation is significantly enhanced by the interaction of the influencing factors,and the government’s ecological governance capacity and economic conditions are in the dominant position on ecological compensation.Factor detector results q-values range from 0.022-0.4188;interaction detector results q-values range from 0.1327-0.5701.The highest effect of the interaction between grain yield and green cover of urban built-up areas on ecological compensation was found with a q value of 0.5701.The interaction of grain yield on other factors was significantly enhanced with q-values ranging from0.4439-0.5701.This study proposes an ecological compensation implementation path:improve diversification of compensation types,increase the total amount of compensation funds,and increase compensation methods;establish inter-provincial consultation and cooperation model for watershed ecological compensation;strengthen the publicity and education on ecological compensation policies. |
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