Urban earthworm communities driven more by climate and elevation than urbanisation intensity

Abstract

Soil biodiversity, particularly earthworms, plays a crucial role in ecosystem functions and services but remains largely understudied in urban environments. In this context, we conducted a synthesis analysis of 41 studies from urban environments (726 records, 1995–2024) to (1) describe patterns of earthworm communities, (2) identify the main drivers shaping urban earthworm communities, focusing on the effects of climate, degree of urbanization, soil properties, and local land use, with the expectation that climate would be the strongest driver, and (3) assess the occurrence of exotic earthworm species. Urban earthworm communities showed considerable variation in their abundance, biomass and species richness. Within our dataset, exotic species were detected in North America, South America, and Asia, but no records from European and African cities, despite their known presence there. However, there was a strong geographical bias, with 75% of records from Europe. Our results reveal that at the global scale, elevation, and annual variation in temperature and potential evapotranspiration are the most important predictors shaping total earthworm abundance. For total earthworm biomass, variation in potential evapotranspiration is the key predictor. At the plot scale, we found both positive and negative correlations between earthworm community metrics, soil properties, and specific land uses, namely urban forests and grasslands. We recommend additional standardised sampling, broader geographical and temporal coverage, and the investigation of urban-specific direct and indirect stressors, as crucial steps for understanding urban soil biodiversity and promoting beneficial management practices. Overall, this analysis indicates that urbanisation intensity showed no consistent effects on earthworm communities once climate and soil variables were accounted for. Given the importance of climate impacts, mitigation of climate change effects would be valuable for the maintenance of earthworm communities.