Impacts of urbanization on ecosystem services in the Chengdu-Chongqing Urban Agglomeration: Changes and trade-offs

The urban-rural transitional areas in southwestern China are crucial in the creation of sustainable ecosystems, which have the characteristics of mountain-plain transitions. Herein, we developed a framework to assess the changes in multiple ecosystem services in the transition zone which is the product of urbanization. We explored the interactions between the ecosystem services from 2000 to 2015 in the Chengdu-Chongqing urban agglomeration (CCUA) in southwestern China and quantified their relationships across the entire study area in 2015. All of the interactions and relationships between five critical ecosystem services were analyzed to develop new strategies for optimizing land use. Our results reveal that the rural-urban fringe exhibited high proportions (17.2-91.1% of the region) of significant correlations in all 10 pairs of ecosystem services. In the rural area, high proportion (> 96%) with nonsignificant relationships made up 4 for the 10 pairs. However, there were fewer areas with significant correlations in the urban areas, and only one high proportion of positive synergy occurred (water yield vs. soil conservation, 81.2%). Moreover, in the urban area, almost all of the pairs of interactions were weaker than those in other areas. Many pairs of interactions were stronger in the urban-rural fringe than in other areas. In particular, the synergy correlation (R-2 = 0.81, P < 0.01) between habitat quality and carbon storage was stronger than any of the other pairs of interactions anywhere throughout the entire study area. The areas surrounding the core cities were prone to development priority. These findings provide an opportunity to perform explicit trade-offs between ecosystem services, to understand the coupling between the evolutionary process of socioeconomics and natural elements, and to assist in guiding regional sustainability with respect to ecosystem service use, crucial area identification, and urban development.