El Niño is officially under way and Australians are preparing for a hot spring and summer. Urban trees play a vital role in keeping cities cool, evaporating water to provide a natural form of air-conditioning, cooling air temperatures and reducing heat-related deaths by more than a third. But trees struggle with extreme heat. A study shows that simply planting trees isn’t enough; urban trees need continuing care.
Researchers investigated the impact of extreme heat on trees during Australia’s last major heatwave, in 2019 and 2020. They found species with large thin leaves, such as red maple, were particularly vulnerable to extreme heat, whereas trees with thicker leaves, such as ash and Chinese elm, were better able to regulate their temperature. The results, published in Global Change Biology, show that access to water is also crucial, with well-watered trees able to open their pores and evaporate water, preventing scorching of leaves.
As our climate heats, heatwaves are going to become more frequent, giving urban trees a tough time. Planting heat-resilient tree species is important, but we also need to consider new techniques to protect our urban trees, such as irrigation pits to capture and store stormwater, or rain gardens (gullies planted with vegetation that absorb and store flood runoff). Trees have never been more needed.
