Urban Tree Growth and Drought Responses Show Evidence of Climate Resilience.

Climate change has a negative impact on the vitality of forests, and drought and heatwaves are the most influential abiotic stressors that contribute to tree health decline and mortality. Urban trees are not only vulnerable to climate change, but they also face harsh environmental conditions, including the urban heat island effect, limited soil volume and water availability. Therefore, the long-term sustainability of urban forests relies on healthy and thriving trees and the identification of species that are resilient to climate change. Thus, it is fundamental to understand how urban trees respond to environmental conditions, including climate. This study investigates how urban trees respond to both long-term climatic conditions and episodic extreme climate events. We evaluated variation in urban tree growth across differing climates by reconstructing growth histories and developing drought response indices. We selected 10 tree species planted in seven cities distributed along temperature and precipitation gradients across the Australian continent. We determined spatial and temporal patterns of tree-ring growth in relation to extreme climate events. We found significant differences among cities, suggesting that local environmental conditions significantly influence tree growth. While some species showed fast annual growth in cool and wet cities, other species had similar growth across all cities or even faster growth in hot and dry cities. Urban trees generally responded positively to wetter conditions during the warmest month, which might be related to longer growing seasons and water availability. We found a positive effect of extreme hot conditions on growth, suggesting that urban trees might be well adapted to warm urban environments. Species climate-growth relationships can help guide species selection to maximize benefits delivered by urban forests and minimize environmental and socio-economic losses under current and future climates.