Urban trees through a functional traits’ lens: Exploring the interplay between tree functional groups and social-ecological factors

Abstract

Urban trees’ functional traits influence their resilience to environmental changes and the delivery of ecosystem services. However, research on classifying urban trees into functional groups based on species traits - clusters of species with similar responses to environmental stressors and providing similar ecosystem services - and exploring the factors that shape their distribution is limited. This study classified a subset of urban trees in Lisbon, Portugal, into functional groups using 20 traits related to survival, establishment, tolerance, and ecosystem services delivery. We analyzed their distribution patterns across the city and modelled their abundance at the local scale, considering various social and ecological factors. These results were integrated with the municipality’s tree selection criteria. Our results revealed three functional groups - temperate, mediterranean, and tropical - each with the potential to deliver complementary ecosystem services. The distribution of the temperate functional group, the most abundant, was primarily associated with social factors, such as proximity to roads and public spaces. However, the temperate group had lower potential resilience to climate change due to its association with humid temperate climates, raising concerns in areas dominated by these species. In contrast, the mediterranean and tropical groups were influenced by both social and ecological factors, with trait data suggesting their potential to thrive under future climate conditions. These findings emphasize the need to enhance local functional diversity to increase ecological resilience and ensure a wider range of ecosystem services, especially in the context of climate adaptation. Overall, this analysis demonstrates the importance of social-ecological factors in shaping the functional composition of urban green spaces, offering insights into the roles of traits in sustainable species selection and urban tree management.