Effects of climate trends and drought events on urban tree growth in Santiago de Chile

Urban trees and the services they provide (e.g., evapotranspirational cooling, shading, recreation, carbon storage, air pollution filtering) can have major effects on the microclimate of a city, although the growth conditions are often inadequate to ensure tree vitality and growth, negatively affecting their beneficial effects. In a worldwide dendrochronological study on ten urban tree species in four climatic zones, the growth and impacts of common urban tree species were assessed. This paper focuses on the results for Robinia pseudoacacia L. in the Mediterranean climate city of Santiago de Chile, highlighting the faster growth of the studied black locust trees since 1960 than its growth in the years before 1960. Furthermore, black locust displayed the best growth when situated closer to the city center than the city periphery and when in the northern and western parts of Santiago de Chile. The species characteristics of black locust also revealed an immediate negative growth reaction to drought events, followed by a rapid recovery, which was similarly influenced by the direction from and distance to the city center of the growing site. The results underline the overall worldwide findings on urban tree growth that indicate that a city climate with an extended growing season and increased temperatures can lead to improved growth of urban trees in the Mediterranean climatic zone. However, with increased growth, more rapid ageing and tree death might follow, leading to increased costs for new plantings and tree management.