Structural evolution of ecosystem service interaction networks across urban expansion gradients

Rapid urban expansion reshapes ecosystem services (ES) and their interactions, yet the structural responses of these interactions across urban expansion gradients remain insufficiently understood. Here, we investigate these dynamics in the Middle Reaches of the Yangtze River Urban Agglomeration (MRYRUA) in China through a combined framework of the urban expansion differentiation index (UEDI), integrated valuation of ecosystem services and trade-offs (InVEST), and network analysis. This framework enables a spatially explicit assessment of ES interaction changes at different urbanization stages. Our results indicate that ES interaction networks exhibit marked structural sensitivity to urban scale and expansion speed, as evidenced by 40% and 25% declines in network density and connectance. With rapid urbanization, ES networks shift toward a core–periphery structure, where carbon sequestration and water yield function as primary hubs. Redundancy analysis identifies UEDI as the dominant driver of ES network structural shift, accounting for 52.40% of the cumulative variance (p < 0.01). At the agglomeration level, the Poyang Lake Urban Agglomeration, characterized by slower expansion (UEDI: 0.90), maintains the most intricate ES network (density: 0.80; connectance: 0.78). Conversely, the Wuhan Urban Agglomeration, at a more advanced urban development stage (UEDI: 1.01), exhibits the lowest network connectance (0.55) and ES synergies. These findings highlight the destabilizing effects of advanced urbanization on ES interactions and provide insights for stage-specific urban planning and ecosystem management.