Trade-off And Synergy Of Ecosystem Services In Mengzi Karst Graben Basion

Mengzi Graben Basin is a typical karst graben basin in China.Its special geological structure results in poor ecosystem stability and decoupled spatial statue of water-soil resources.With increasing population,the region is facing greater environmental stress,and the regional ecosystem structure is facing greater interference,which changes ecosystem service ability to a certain extent.The regional ecosystem has gradually developed to healthy since the implementation of large-scale rocky desertification control in 2006.However,the future development model is not clear.Therefore,the study evaluated the regional NPP,water yield,soil retention and food supply and the relationship among them by using remote sensing and meteorological data from 2006 to2018.The study also used CLUE-S model to simulate the land use in 2030 by scenario setting.Then the future ecosystem services and relationships were evaluated.We concluded as follows:1.The land use in 2012 was taken as the referenced data in the basic period,and the land use in 2018 as the verification data.This study made use of CLUE-S modle to simulate land use in the MKGB.Kappa coefficient was 0.7821,which was grater than0.75 indicating that CLUE-S model was suitable for land use simulation in Mengzi Karst Graben Basin（MKGB）.2.According to the relevant contents of rocky desertification control project and development plan of the Honghe Prefecture,this study set land-use scenarios in 2030.The law of land use change in natural scenario will consistent with that in 2012-2018.In the mild ecological governance scenario,the cultivated land with slope>25°will transform into forest land,the cultivated land with slope of 15°～25°and slight rocky desertification will transform into orchard land,and the cultivated land with moderate and severe rocky desertification area will transform into forest land.In the moderate ecological governance scenario,the cultivated land with slope>20°will transform into forest land,the cultivated land with slope of 15°～20°and slight rocky desertification will transform into orchard land,and the cultivated land with moderate and severe rocky desertification area will transform into forest land.In the strong ecological governance scenario,the cultivated land with slope>15°will fully transform into forest land.3.The results of scenario simulation showed that the cultivated land and bare rock would constantly decrease,while the forest land,shrub,grassland,orchard land and construction land would constantly increase.In the natural scenario,the decrease area of cultivated land will be the least,154.5 km²,and the increase area of forest land will be the least,24.66 km².In the moderate ecological governance scenario,the increased area of orchard land will be the most,34.26 km².In the strong ecological governance scenario,the area of cultivated land will decrease the most,218.88 km²,the area of forest land will increase the most,152.74 km²,and the area of orchard will increase the least,28.54 km².4.Generally,the NPP,water yield,soil retention and food supply showed an increasing trend from 2006 to 2018.The average value of NPP in MKGB was 1023.3 g C m^-2 a^-1,with an average annual increasing rate of 9.57 g C m^-2 a^-1.The total water yield was 8.23×10⁸ m³ with annual average of 509.93 mm,showing decrease trend firstly and then increase trend.Soil retention in bared karst areas and covered karst areas were2.25×10⁴t/km²·a and 6.42×10⁴t/km²·a,respectively.The average food supply was31.1×10⁸ yuan,with a large increase rate from 2006 to 2012.The supply capacity of ecosystem services in different land use type is various.The regulation services level of forest land,shrub and grassland was high,while the supply services level was low.However,the regulation services level of cultivated land and construction land was low,while the supply services level was high.5.The paper determined the relationship among ecosystem services by calculating Person correlation coefficient.The trade-off relationships were as follows:NPP and water yield,NPP and food supply,water yield and soil retention,and soil retention and food supply.The synergy relationships were as follows:NPP and soil retention,and water yield and food supply.The trade-off relationship among ecosystem services has weakened from2006 to 2018,implying that the structure of ecosystem has become more reasonable.6.With the implementation of ecological governance measures,NPP and soil retention will show an increasing trend,but water yield will decrease continuously in2030.In the natural scenario,the increase amplitude of NPP,soil retention in covered karst areas and bared karst areas will be the least,which will be 3.56%,1.04%,and 0.5%,respectively.The decreasing amplitude of water yield will be the least,which will be1.92%.In the strong ecological control measures,the increase amplitude of the NPP,soil retention in covered karst areas and bared karst areas will be 7.75%,1.55%and 1.13%,respectively.The decreasing amplitude of water yield will be the most,which will be3.31%.The food supply will increase more in the natural scenario.The food supply will show slightly increase in the mild or moderate ecological governance scenario,but the food supply will decrease in the strong ecological governance scenario.Therefore,ecological management measures can promote NPP and soil retention but will limit the growth of water yield and food supply to a certain extent.7.Correlation analysis and Z–standardization value results showed that the synergy between NPP and soil retention,water yield and food supply would be the weakest in the natural scenario in the MKGB.The trade-off relationship between NPP and water yield,soil retention and water yield will be the most obvious in the mild ecological governance scenario.The trade-off relationship of food supply and NPP and food supply and soil retention will be significance in the stronge governance scenario.Generally,comparing with the other three scenarios,the degree of trade-off in the moderate ecological governance scenario will be acceptable,implying that it will be a reasonable ecological governance method.On the whole,the control of rocky desertification in the MKGB cannot blindly pursue the improvement of a certain ecosystem service capacity,but should pay attention to the overall coordination of the ecosystem so as to achieve the benefit maximization of ecological,economic and social in the future.Therefore,we should pay more attention to the ecological environment in rocky desertification area with slopes>20°,and speed up the pace of grain for green project.