Contribution of Urban Trees to Ecosystem Services in Lisbon: A Comparative Study Between Gardens and Street Trees

Background: Lisbon’s urban trees are vital for providing environmental benefits, enhancing the city’s liveability and sustainabil- ity. As such, it is important to understand how different urban spaces, such as gardens and streets, affect the ecosystem services (ES) trees provide. Methods: In this study, we evaluate the composition, structure, and ES provision of trees in 3 gardens in Lisbon. Then, their indi- vidual tree size and ES supply were compared to street trees for the same species to assess the impact of management on ES. Additionally, four management scenarios were assessed for one garden, selected for its composition and susceptibility to change: Business as Usual (BAU); planned underground Metro Expansion Impact (MEI); Disease Outbreak (DO); and Removal of Monumental Trees (RMT). Results: Garden trees generally exhibited higher diameter and canopy dimensions than street trees for the same species, leading to enhanced ES pro- vision. The MEI scenario predicted significant reductions in canopy cover and ES due to tree removals and construction stress, highlighting the need for mitigation strategies. The DO scenario of a hypothetical fungal infection on Celtis australis L. predicted severe losses in tree health and ES, emphasizing the importance of disease management and resilient species selection. The RMT scenario revealed a substantial immediate reduction in ES following the removal of monumental trees, underscoring the importance of careful planning before such actions. Conclusion: The findings illustrate how an examination of data gathered on urban forests can facilitate an understanding of their dynamics and enable an evaluation of the impact of potential scenarios on the services they provide.