Shifting patterns of ecosystem service trade-offs and synergies: Evidence from the Yangtze River Economic Belt, China

Understanding the trade - offs and synergies among ecosystem services (ESs) is crucial for effective ecosystem management, yet most current research fails to capture the intricate, non - linear transitions, and sudden changes triggered when driving factors exceed critical thresholds. These relationships exhibit pronounced spatial heterogeneity due to the varying influence and interactions of biophysical assocaited with socio-economic drivers. This study investigates the spatiotemporal variations in three key ESs—water yield (WY), soil conservation (SC), and carbon sequestration (CS)—across the Yangtze River Economic Belt (YEB) from 2000 to 2020. Using Multiscale Geographically Weighted Regression and Piecewise Structural Equation Modeling, we analyzed the spatial distribution of ESs trade-offs/synergies and the threshold effects of driving factors. Results show clear spatial differentiation among the YEB's upstream, midstream, and downstream regions. WY peaks downstream, while SC and CS are higher upstream. The WY-CS relationship shifts from trade-offs in low-elevation urban areas to synergies in high-elevation regions. WY-SC shows trade-offs in provincial capitals and northwestern part of the YEB, with synergies elsewhere. SC-CS generally exhibits strong synergies, except in the northwest (e.g., Sichuan and Chongqing province). Precipitation is the primary driver of WY, with varied topographic effects across regions. SC is shaped by natural and socio-economic factors, while CS is strongly effected by vegetation cover and climate. Path analysis reveals region-specific impact pathways: with topography exerting a dominant influence upstream, and socio-economic disturbances (e.g., nighttime light) driving patterns in the midstream and downstream. Threshold effects are evident: higher human activity and lower precipitation increase WY-CS trade-offs; flatter areas need greater disturbance to shift WY-SC from synergy to trade-off; SC-CS synergy declines above 3000 m elevation. This study highlights how spatially heterogeneous driver interactions shape ES relationships, providing insights for region-specific ecological management and sustainable development.