Study On Tradeoffs And Synergies Of Ecosystem Services In Agro-pastoral Ecotone In Western Sichuan

Agro-pastoral ecotone,as the boundary intersection zone of adjacent ecosystem,belongs to the ecological transition region,including the transition between grassland and arable land,planting and animal husbandry,and the ecological system is a fragile region in China.The agricultural and pastoral ecotone in western Sichuan is located in the transition region from Sichuan Basin to Qinghai-Tibet Plateau.Its natural environment is complex,and the disturbance of human activities mainly in agriculture and animal husbandry is strong,and the harsh ecological environment.At the same time,it is also an essential ecological barrier from the upper trams of the Yangtze River.It has important ecosystem service functions such as water conservation and soil conservation.It is one of the National Key Ecological Function Zones defined in the National Main Function Zone Planning.Under the influence of climate change,overgrazing and other factors,the alpine grassland desertification and swamp grassland degradation in the agro-pastoral ecotone in western Sichuan have made the regional ecosystem more fragile,water conservation and biodiversity conservation threatened,and thus affected the development of agriculture and animal husbandry in recent decades.In this paper,Arc GIS,SPSS,Geo DA and other software were used to evaluate soil conservation,water conservation,carbon sequestration and habitat quality in the agro-pastoral ecotone in western Sichuan using In VEST model and RUSLE model,and the ecosystem services of different counties,elevations and land types were compared and analyzed.Based on the spatial distribution patterns of ecosystem services and their correlations,the spatial tradeoffs and synergies of each service were revealed.The tradeoff degree of farming-pastoral ecotone in western Sichuan was quantitatively analyzed by root mean square deviation method.The main conclusions include the following points:（1）From 2000 to 2020,the average amount of soil conservation in the agro-pastoral ecotone in western Sichuan was 2.11×10~9t,in the study area the amounts of soil conservation upfront rise and then fall.Water conservation services showed a trend of fluctuation and decline,and the annual average water yield was214.19mm.The annual average NPP was 159.56g C/（m~2·yr）,and there was a large interannual difference in NPP,with the highest NPP in 2015 and the lowest in 2010.The habitat quality index was the highest in 2010 and the lowest in 2005,with an average value of 0.794.（2）Statistical analysis of ecosystem services under different spatial units:At the county level,the soil conservation function of Wenchuan county,Jiulong County and Mianning County was better,while that of Shiqu County,Zoige County and Hongyuan county was weaker.Shiqu county,Seda County and Jiuzhaigou County with relatively poor hydrothermal conditions are the low value areas of water conservation,while Mianning County,Yanyuan County,Luding County and Wenchuan county are the high value areas of water conservation.Luding county,Batang County,Derong County are carbon sequestration low value area,Hongyuan County,Zoige county,Aba county is carbon sequestration high value area;Muli Tibetan Autonomous County,Wenchuan county and Yanyuan County had the best habitat quality,while Aba,Zoige,Batang county and Shiqu county had the worst habitat quality.In terms of altitude gradient,soil conservation services decreased with elevation.As a whole,water conservation services showed a v-shaped trend of weakening with the elevation.The carbon sequestration service fluctuated and decreased with the elevation,and increase first and then fall with the elevation.The habitat quality index upfront rises and then fall with the growth of elevation.In terms of land type,the average soil conservation amount from high to low was woodland>grassland>cultivated land>unused land>water area>construction land.The index of water yield and habitat quality in order from smallest to largest:unused land,construction land,water area,grassland and forestland.The contribution of forest land,arable land,grassland,water area,unused land and construction land to carbon sequestration services in the agro-pastoral ecotone in western Sichuan from high to low.（3）In the study area,water conservation,soil conservation,and habitat quality were synergistic between the southeast and the northwest,while the special distribution of the synergistic relationship between carbon sequestration was not obvious.The static and dynamic temporal correlations among ecosystem services showed consistent trends.Soil conservation-carbon sequestration and water conservation-carbon sequestration were tradeoffs,and soil conservation-water conservation,soil conservation-habitat quality,habitat quality-carbon sequestration and water conservation-habitat quality were synergies.The correlation between water conservation and soil conservation was the strongest（correlation coefficient was0.3952）,and that between soil conservation and carbon sequestration was the weakest（correlation coefficient was-0.059）.（4）In the agro-pastoral ecotone in western Sichuan,the natural conditions are stable and the mean value of tradeoff synergistic RMSD has little change over the years.There were significant differences between the high value（RMSD>0.4）and the low value（RMSD<0.15）of the six ecosystem service system combinations.The tradeoff intensity of carbon sequestration-habitat quality,soil conservation-habitat quality and water conservation-habitat quality were low,and the tradeoff intensity of carbon sequestration-water conservation,carbon sequestration-soil conservation and water conservation-soil conservation were high.