Tree ring width and isotope ratios show that high temperatures exceed pollution effects on urban trees: evidence in Pinus pinea in Firenze and Pisa, Central Italy

Urban areas typically experience higher temperatures and reduced precipitation compared to periurban environments, conditions that may strongly influence tree performance. To assess these effects, we studied Pinus pinea in Firenze and Pisa, integrating dendroecological and stable isotope analyses. Ring-width index data did not reveal significant differences in radial growth between urban and periurban trees, suggesting that growth responses alone may underestimate urban stress. In contrast, isotopic analyses provided clearer evidence: δ¹³C and δ¹⁸O values indicated marked water stress in urban trees, particularly in Firenze, while δ¹⁵N and F¹⁴C suggested minimal incorporation of traffic-derived nitrogen or fossil CO₂, likely due to the protective role of urban parks. These findings highlight an apparent discrepancy, where tree growth suggests resilience, while physiological signals reveal stress linked to urban microclimates. This emphasizes the value of combining multiple indicators to capture tree responses in complex environments. Overall, our results suggest that urban climate exerts a stronger influence on P. pinea than localized traffic emissions, with implications for tree vitality and ecosystem services. Species selection for urban forestry should therefore account for microclimatic constraints to ensure long-term tree performance under ongoing urbanization and climate change.