Assessing Urban Tree Responses to Climate and Pollution: Implications for Environmental Monitoring and Management

In the context of climate change, trees are increasingly used as tools to create healthier and more comfortable urban environments. However, the extent of their impact on urban settings is intricately tied to their physiological health, growth, and vitality. This study evaluates urban trees' physiological response to the urban climate's primary stressors, high temperatures, low precipitations, traffic emissions and environmental pollutants. We investigated tree growth and δ¹³C, δ¹⁸O, δ¹⁵N, radiocarbon (F¹⁴C) levels and heavy metals in tree rings by comparing periurban parks, urban parks, busy streets, and airport zones in two Italian cities, Firenze and Pisa with a focus on Pinus pinea.

Our preliminary findings indicate that climatic conditions did not directly affect tree growth in urban parks. However, high temperatures and reduced precipitations influenced tree physiology more than pollution. In detail, carbon (δ¹³C) and oxygen (δ¹⁸O) stable isotopes revealed sensitivity to high temperatures and drought in urban parks, whereas the indicators of pollution investigated in this study (δ¹⁵N and F¹⁴C) did not exhibit pronounced differences between urban and periurban parks.

The general hypothesis is that the other urban sites (busy streets and airport zones), characterized by environmental constraints such as water deficit and high temperatures, show a higher δ¹³C and a lower δ18O than the periurban area. Regarding the characterization of the ¹⁵N and ¹⁴C and environmental pollutant concentrations in the tree rings, we assume they are more evident in the urban neighbours than in periurban contexts.

These findings underscore the importance of selecting tree species adapted to urban conditions to maximise the ecosystem services provided by trees. In addition, it is essential to study the effects of the urban environment on plant growth and physiology, as the urban environment—characterized by higher temperatures and lower precipitations—represents a model of future climate conditions. This setting provides an opportunity to investigate tree responses to climate change, offering insights that may inform urban forestry and resilience strategies. Ultimately, our data demonstrate the utility of tree rings as an effective tool for assessing air and environmental quality in urban compared to periurban sites.