Multi-city analysis of synergies and trade-offs between urban bird diversity and carbon storage to inform decision-making

Cities are particularly vulnerable to the impacts of biodiversity loss and climate change. Urban greenspaces are important ecosystems that can conserve biodiversity and help offset the carbon footprint of urban areas. However, despite large-scale tree planting and restoration initiatives in cities, it is not well known where trees or vegetation should be planted or restored to achieve multiple benefits. We considered urban greenspaces as nature-based solutions for urban climate mitigation and biodiversity conservation planning. Using bivariate mapping, we examined the spatial synergies and trade-offs between bird functional diversity and carbon storage in ten Canadian cities spanning a gradient of geography and population, and modelled the relationships between vegetation attributes and both bird diversity and amount of carbon. We found carbon and biodiversity are weakly positively correlated across the ten cities, however, this relationship varied in strength, direction and significance. Our maps highlight areas within our target cities where greenspaces could be managed, restored, or protected to maximize carbon storage and conserve biodiversity. Nationwide, our results also show that forest management strategies that promote increases in canopy cover and the proportion of needle-leaved species in urban greenspaces are potential win-win strategies for biodiversity and carbon. Our study shows NbS strategies are not always generalizable across regions. National policies should guide municipalities and cities using regional priorities and science advice, since a NbS promoting biodiversity in one region may, in fact, reduce it in another.