Growth and climate sensitivity of native and non-native urban trees under varying soil conditions in Santiago, Chile

Urban forests are mainstreamed as a nature-based solution for climate mitigation and adaptation. However, the capacity of urban trees to provide the desired benefits is constrained by how they respond to site conditions. This study quantified the growth responses and climate sensitivity of five native and non-native urban tree species growing in green spaces of a Mediterranean climate city under periodic droughts. We used a dendrochronological approach, coupled with soil data at the individual tree level, seeking to gather data to inform the type and timing of tree management in Santiago, Chile. Differences in growth between native and non-native trees were not significant, suggesting that trees respond to urban conditions more than to their climate niche. However, we identified that native species require soils with good water-holding capacity, adequate for growing in semi-arid climates, while non-native trees benefit from well-drained soils. Climate sensitivity analysis was only feasible for the non-native trees, with most significant correlations related to precipitation at the start or mid of the growing season. Supplementing irrigation during the growing season of dry years could support higher productivity of urban trees. The resistance and recovery analysis showed varying responses to extreme events. Cedrus deodara had positive correlations with temperature, showing that the species copes better with increasing temperatures; however, it was more sensitive to dry years. Platanus acerifolia had overall lower resistance to hot years, but it was resilient to the 2003 event. The species less sensitive to extreme years was Liquidambar styraciflua, likely due to its lower productivity. Our results indicate that for maintaining growth rates through the years, soil management should focus on early years with particular attention to drainage and adequate soil texture for the species. Supplemental irrigation should be provided to larger trees during warmer years to maintain tree growth and, therefore, functioning.