Unveiling the role of soil in urban vegetation greenness: City-scale evidence from field sampling across green spaces in Shanghai

Urban green spaces (UGSs) provide essential ecological functions in highly urbanized landscapes, yet city-scale associations between soil conditions and vegetation greenness remain insufficiently understood due to limited field-based evidence. This study investigated Shanghai, China, by integrating long-term Enhanced Vegetation Index (EVI) time-series data from 2000 to 2020 with field soil sampling from 183 UGS sites, covering 18 edaphic properties. Together with vegetation baseline, human activity, and climate covariates, we assessed the relative and spatially heterogeneous associations of soil conditions with vegetation greenness dynamics (VGD) and current vegetation greenness (VG). Shanghai's UGSs showed substantially stronger greening than the broader urban background, with a mean VGD of 0.074 decade⁻¹ compared with 0.017 decade⁻¹ citywide, and 87.98% of sampled sites exhibited positive greening trends. Park green spaces maintained higher VG and stronger VGD than roadside green spaces, while VGD and VG were significantly but only moderately associated, indicating that they represent distinct dimensions of UGS performance. Attribution analysis showed that vegetation baseline and soil properties were the dominant contributors to VGD, explaining 17% and 11% of the variance, respectively. For VG, soil emerged as the leading determinant, independently explaining 15% of spatial variation, with associations distributed across multiple edaphic dimensions rather than controlled by a single soil property. Spatial modeling further revealed scale-dependent soil associations: soil–VGD associations were strongest in intermediate and outer urban zones, whereas soil–VG associations were more outward-oriented and more frequently negative. These findings provide city-scale empirical evidence that soil conditions are associated with urban greenness patterns in spatially heterogeneous ways, highlighting the need for soil-sensitive UGS assessment and management across urban gradients.