Multiscale Drivers and Thresholds of Urban Ecosystem Service Supply–Demand Relationships

Ecosystem services (ESs) link ecological capacity with human demand and play a critical role in sustainable urban planning. However, limited attention has been paid to how ES supply–demand (ESSD) relationships vary across spatial scales and respond to nonlinear changes in key drivers. To address this gap, we integrated 7 ESs into a composite ESSD ratio across 4 spatial resolutions in Guilin, a rapidly urbanizing karst city in southern China. A multimethod framework integrating random forest modeling, Sobol global sensitivity analysis, probability density analysis, and partial dependence analysis were applied to identify dominant drivers and detect nonlinear thresholds. The results reveal pronounced spatial mismatches between ES supply and demand, with deficit hotspots concentrated in densely urbanized areas and surplus zones mainly located in mountainous ecological regions. Across scales, urban development intensity was consistently the dominant driver of composite ESSD ratio, followed by biomass and population density. Sensitivity analysis indicates that urban development exerts the strongest structural influence, while vegetation productivity plays an increasingly important role in maintaining ESSD balance at coarser spatial scales. Nonlinear response analysis further reveals scale-modulated thresholds for key drivers. Overall, ESSD dynamics were jointly shaped by ecological capacity and anthropogenic pressures, with their relative influence varying across scales. These findings provide scientific and quantitative support for scale-sensitive zoning, green infrastructure prioritization, and hierarchical ecological planning aimed at balancing urban development with ecological sustainability in rapidly urbanizing cities.