Spatiotemporal evolution of ecosystem services supply-demand and trade-off/synergy relationships in Chongqing of China based on urbanization zoning

Ecosystem services supply and demand can coordinate the socioeconomic and environmental systems for the regional ecological security. Their spatiotemporal dynamics can be used to identify the complex interactions among services under anthropogenic disturbance. In this study, six ecosystem services were assessed in Chongqing from 2005 to 2023. The InVEST model and Spearman correlation analysis were employed to quantify carbon sequestration, grain production, soil conservation, water yield, habitat quality, as well as recreation and leisure. Furthermore, a systematic analysis was also conducted on the spatiotemporal dynamics of their supply-demand relationships and trade-offs/synergies over urbanization zoning. The results indicate that: (1) Although Chongqing maintained a surplus of ecosystem services, the margin of the surplus consistently narrowed over the study period. The supply-demand ratio was slight but persistently declined. High supply-demand ratios for carbon sequestration, water yield, soil conservation, habitat quality, as well as recreation and leisure were concentrated in the northeastern and southeastern areas of Chongqing, whereas the low ratios were clustered in the key districts of the main metropolitan area. High values of grain production were distributed in the peripheral counties of the metropolitan region, with deficits in the urban, the northeastern, and southeastern parts of Chongqing. (2) Urbanization exhibited a monocentric-polycentric structure with the west-east gradient, which was characterized by urban expansion and concomitant rural contraction. There was an outstanding spatial gradient in the supply and demand of ecosystem services. Among them, the demand increased progressively from rural to urban areas, while the supply exhibited the inverse pattern. The rural areas were positioned as primary provisioning zones, while the urban as persistent deficit zones. Supply-demand ratios declined for most services; Urban expansion zones transitioned from a balance to a deficit, with the notable exceptions of soil conservation and water yield, indicating the increased surpluses. (3) Static relationships among ecosystem services in rural areas were dominated by strong, stable trade-offs or synergies. In urban-rural transition zones, the weak synergies prevailed and fluctuated significantly, whereas urban expansion zones exhibited a trade-off between synergy dominance. Only five service pairs exhibited consistent trade-off or synergy relationships with the minimal temporal variation in urban areas. Habitat quality was persistently synergistic with recreation and leisure over all urbanization zones. While water yield consistently traded off with recreation and leisure. Most dynamic relationships among services were not statistically significant in rural and urban areas. There was a pronounced differentiation in the urban-rural transition zones, whereas the trade-offs and synergies were in urban expansion zones; Soil conservation and water yield remained synergistic over the period. The strength of the synergy increased in urbanization intensity, whereas habitat quality and water yield remained persistently in trade-off. (4) Differentiated strategies were proposed to realize the divergent patterns of ecosystem services supply-demand and their interactions in the urbanization zones. In urban areas, ecological potential should prioritize enhancing the ecological network connectivity. Urban expansion and urban-rural transition zones are required for the enforcement of ecological redlines, particularly with context-specific natural restoration and topographic constraints. In rural areas, ecotourism and carbon sink markets can be coupled with the urban-rural ecological compensation. Ecological assets can also be translated into tangible values. Differentiation of urbanization zones in the mountainous metropolitan can be used to examine the spatial heterogeneity of ecosystem service dynamics along the urban-rural gradient. This finding can provide a robust scientific foundation to inform urban spatial and sustainable ecosystems in Chongqing.