Spatiotemporal Changes Of Ecosystem Services In Chengdu-Chongqing Urban Agglomeration

To study the changing characteristics of ecosystem services in Chengdu-Chongqing urban agglomeration,and to explore the trade-offs/synergies among ecosystem services in different scales are of great importance for building ecological barriers in the upper reaches of the Yangtze river,the long-term development of Chengdu-Chongqing urban agglomeration and even the national ecological security.Based on GIS and InVEST model,this paper evaluated the spatial and temporal change characteristics of four ecosystem services in Chengdu-Chongqing urban agglomeration in 1997,2007 and 2017,including water yield(WY),net primary productivity of vegetation(NPP),soil conservation(SC)and habitat quality(HQ).Pearson index and moran index were used to analyze the trade-offs/synergies between ecosystem services at four scales/dimension(region,land use type,slope and city(district)),and the impact factors of ecosystem services were explored by regression analysis.Finally,the hot spots of ecosystem services in Chengdu-Chongqing urban agglomeration were identified and the clusters of ecosystem services were divided by SOFM neural network.The main conclusions of this paper are as follows:(1)The spatial and temporal change characteristics of four ecosystem services in Chengdu-Chongqing urban agglomeration were obtained.In 1997,2007 and 2017,the changes of water yield,soil conservation amount and habitat quality of ChengduChongqing urban agglomeration were low-high-low,while the changes of NPP were lowmedium-high.The spatial distribution of water yield in 1997 shows a semiring pattern,increasing from the central Sichuan mesa hill area to the surrounding area,and decreasing to the basin edge area.The spatial distribution pattern of water yield in 2007 and 2017 was similar: the northeast region was higher,and the central and southern regions was lower.In 1997,2007 and 2017,the spatial distribution of soil conservation amount and NPP showed a semiring distribution pattern,increasing from the mesa hilly area in central Sichuan to the edge of Sichuan basin.The spatial distribution pattern of habitat quality was similar: The high value areas were concentrated in the forest land of the northeast,southwest and south,while the low value areas were concentrated in the urban construction land and road construction areas.(2)The trade-offs/synergies among ecosystem services in the Chengdu-Chongqing urban agglomeration in 1997,2007 and 2017 were obtained under four scales/dimenson.In 1997,2007 and 2017,NPP-SC,NPP-HQ and SC-HQ were dominated by significant synergies at four scales,while WY-HQ was dominated by significant trade-offs.The relationship between WY-NPP and WY-SC varies greatly in different years and scales.The WY-NPP relationship showed a significant trade-offs at the regional scale in 1997,but no significant relationship in 2007 and 2017.There was no significant relationship between WY-SC at regional scale.WY-NPP and WY-SC in the forestland under the land use type showed significant trade-offs,and there was significant synergistic relationship between farmland and grassland.Under slope classification,WY-NPP was dominated by significant synergies,WY-SC by significant trade-offs.WY-NPP and WY-SC under the scale of city(district)mainly had significant trade-offs.Social-ecological factors had different effects and different contribution degree on the relationship between four ecosystem services and ecosystem services,in particular,construction land area,forest area and normalized vegetation index(EVI)factor contributed the most.With the change of research scale,the influence direction and contribution degree of social-ecological factors would also change.(3)There were multiple ecosystem service hotspots in Chengdu-Chongqing urban agglomeration,in 1997,2007 and 2017,type 0 and type 1 hot spots occupied the largest proportion of the area,and they were distributed in the cultivated land area in the middle of Chengdu-Chongqing urban agglomeration.Under the optimal clustering condition,Chengdu-Chongqing urban agglomeration can be divided into 6 ecosystem service clusters(named after A-F).Type A ecosystem service cluster(all the four types of ecosystem services were weak)occupied a large area and was mainly distributed in the central region of Chengdu-Chongqing urban agglomeration,which was dominated by cultivated land.Type D ecosystem service cluster(dominated by water yield service),there may be a trade-offs between water yield and other ecosystem services.In type E ecosystem service cluster,habitat quality service was the dominant type,but the other three ecosystems also had a high level of service.The whole was in a state of balanced development with high quality,but it occupied a small area.