Irrigation in Mediterranean urban areas: a good strategy to face the ongoing climate change impacts on urban cedar trees?

Abstract

Irrigated trees are known to develop large aboveground structures that can be detrimental during dry spells, and therefore irrigated trees are expected to perform worse than non-irrigated ones under climate change. In this study, we evaluated the climate-growth relationship of irrigated and non-irrigated trees of the species Cedrus atlantica (Endl.) Manetti ex Carrière (Atlas cedar) in an urban environment in central Spain. We first studied climate-growth relationships with and without irrigation to test the hypothesis that irrigated trees should be less sensitive to interannual climatic variability than non-irrigated ones. Secondly, we identified the four most intense droughts over the 21st century (2005, 2012, 2017, 2019) to test the hypothesis that growth resilience should be lower in irrigated than non-irrigated trees due to traits such as total height. Our results support the idea that irrigated trees are less responsive to climatic interannual variability and notably less resilient to drought stress, with these differences becoming more pronounced with age. These results suggest that irrigation may increase the risk in a scenario of more frequent and intense droughts in Mediterranean urban areas. Thus, widening urban green areas to meet the European Green Deal 2030 in Mediterranean cities should consider better-adapted tree species and ad hoc adaptation to water shortage rather than watering and strategies based on resource supplements.