Political legacies are associated with urban greening equity but not quantity

Urban green spaces are essential for climate adaptation and public health, yet their benefits are often unequally distributed across socioeconomic groups. Because urban greening is shaped by municipal governments — whose environmental and equity priorities differ along the left–right axis — political legacies could influence both the quantity of urban vegetation and how it is distributed across neighbourhoods. We tested these two possibilities across 380 mainland-Spanish municipalities and over 19,000 census tracts, combining 44 years of municipal electoral records (1979–2023) with 10-metre-resolution maps of aboveground woody biomass, tract-level income, and climate. At the municipal scale, population density and aridity dominated per-capita woody biomass, whereas historical political orientation showed no statistical association with aggregate greening. Within cities, however, wealthier tracts held more biomass per capita, and the stratification of vegetation abundance along income levels was associated with political legacy. Income–greening gradients tended to be weaker in historically left-leaning municipalities, consistent with a more equitable distribution of vegetation across socioeconomic strata. This relationship varied substantially across cities, but the population-average effect nonetheless predicts that a neighbourhood with income 60% above its city mean was associated with 17% more biomass per capita under consistently right-leaning governance, but only 9% under left-leaning governance. These results indicate that while biophysical constraints set a city’s overall greening capacity, political legacy is associated with which neighbourhoods, and thus which socioeconomic strata, concentrate vegetation within a city. The distinction carries a direct policy implication: raising total vegetation may be costly and slow under tight biophysical limits, whereas reducing income-based disparities offers a more attainable route to greening equity.