Objective A systematic understanding of how the urban-rural gradient and spatial scale modulate the trade-offs and synergies between recreation and habitat services provided by blue-green spaces remains largely absent. This knowledge gap severely constrains the precise planning and adaptive management of blue-green spaces in rapidly urbanizing metropolitan regions. To address this shortcoming, this study integrates the dual perspectives of the urban-rural gradient and spatial scale, aiming to systematically reveal the spatial heterogeneity and scale dependence of the trade-offs and synergies between recreation and habitat services in metropolitan blue-green spaces.

Methods The Wuhan Metropolitan Region was selected as the case study. A comprehensive analytical framework, termed the “gradient-scale” framework, was developed to examine the relationship between recreation and habitat services. Three complementary modelling approaches were employed: 1) the maximum entropy (MaxEnt) model to map recreation service potential based on environmental and socio-economic predictors; 2) the integrated valuation of ecosystem services and trade-offs (InVEST) model to quantify habitat services; and 3) the generalised additive model (GAM) to flexibly capture non-linear responses and interaction effects between the two services across gradients and scales. Multi-scale analyses were conducted using a series of spatial units (from 4 km² to 70 km²) to detect how the direction and magnitude of the recreation-habitat relationship change with increasing grain size.

Results First, along the urban-rural gradients, the distance thresholds at which habitat services either decline or rebound systematically lagged behind those of recreation services. Specifically, at the central-city level, the lag distance was 7.58 km; at the prefectural-city level, 7.74 km; and at the county-city level, 2.89 km, respectively, corresponding to relative lag rates of 11.59%, 21.48%, and 34.45%. Second, the spatial trade-off and synergy relationship between recreation and habitat services showed strong scale dependence. The 30–50 km² interval was identified as a relatively stable scale range at which the spatial relationship was captured most clearly, whereas 50−60 km² emerged as the critical scale at which the dominant spatial relationship shifted from spatial synergy to spatial trade-off. As analytical scale increased, local spatial heterogeneity was progressively smoothed, and the area proportion of “high-high” synergy zones was especially sensitive to scale enlargement. Third, the response thresholds of spatial trade-off and synergy types and their transitions to urban-rural gradients were jointly regulated by spatial scale and urban hierarchy. With increasing spatial scale, the gradient thresholds associated with type transitions and relationship reversals generally moved toward urban centers, indicating that the spatial trade-off and synergy relationship is less stable in areas closer to urban cores. Moreover, the modulating effect of spatial scale on gradient response patterns was more pronounced in lower-tier cities, particularly in prefectural-level and county-level city systems.

Conclusion By integrating the dual lenses of urban-rural gradients and spatial scales, this study provides a novel, empirically grounded understanding of how recreation and habitat services of blue-green spaces interact in a complex metropolitan setting. The proposed framework contributes to achieving a dynamic equilibrium between recreational use and ecological protection, thereby promoting regional sustainability in rapidly urbanizing metropolitan regions.