Urban Green Spaces as Biodiversity Refugia

Abstract

Urban green spaces -- parks, gardens, street trees, cemeteries, and watercourse margins within cities -- are increasingly recognised as potential refugia for biodiversity in rapidly urbanising landscapes, where they represent the primary remaining habitat for urban-adapted and periurban species that have persisted despite human disturbance. This study quantified biodiversity (plants, birds, bees, butterflies, and bats) across 42 urban green spaces in six European cities (Vienna, Madrid, Stockholm, Zurich, Tallinn, Berlin; 2019-2022; 2,840 species-site records) representing a gradient of green space type (urban forest > cemetery > botanical garden > city park > rooftop garden > road verge), management intensity, connectivity, and surrounding urban matrix permeability. Total species richness ranged from 284 species per site (largest, well-connected urban forests; 8 ha+) to 48 species (isolated rooftop gardens; 0.1 ha). Green space area (r = +0.84) and connectivity to the urban green network (r = +0.74) were the primary predictors of species richness, while management intensity was negatively correlated (r = -0.64). A hierarchical trait-based analysis confirmed that urban green spaces support a functionally distinct subset of the regional species pool -- urban-adapted species with high dispersal ability, broad habitat tolerance, and fast life history strategies -- rather than a random community subset. A Green Space Refugium Quality Index (GSRQI) integrating area, connectivity, management extensivity, and functional diversity predicted native species richness with r = +0.84 and classified green spaces as high, medium, or low refugium quality with AUC = 0.884. Design guidelines derived from GSRQI-high-performing green spaces identified five management practices associated with 2.84-fold higher species richness than conventional management.