Scientists find 65 per cent of tree species at risk

New research has found climate change is putting trees in urban spaces at risk across the globe with 65 per cent of tree species under threat. The study was developed by an international team of scientists, led by Western Sydney University, and funded through Hort Innovation’s Hort Frontiers Green Cities Fund.

The study has successfully identified species at risk and species that are likely to be climate resilient, allowing strategies to be developed that can help urban forests survive in future hostile climates.  

Study lead author Dr Manuel Esperon-Rodriguez from Western Sydney University’s Hawkesbury Institute for the Environment, said urban forests are essential to the liveability of cities, as they provide benefits to 4.2 billion people across the globe.

“Trees and shrubs absorb carbon dioxide and cool their surroundings by providing shade, and by pumping water up from their roots and releasing it through their leaves,” he said. “This cooling effect makes people more comfortable and reduces energy used for cooling.”

The research examined 3129 urban tree species in 164 cities across 78 countries to understand the impact predicted future temperatures and rainfalls will have on them by 2050 and 2070. The study found that by 2050 an average of 65 per cent of species in each city are at risk, including wattles, eucalyptus, pines, and oaks.

Senior author, from Western Sydney University’s Hawkesbury Institute for the Environment Associate Professor Rachael Gallagher said a high percentage of urban tree species in Australian cities are at risk of being exposed to damaging climate conditions by 2050. This figure varies from 83 per cent in Perth to 100 per cent in Darwin.

“Common native tree species found in at least 10 Australian cities and expected to experience climate conditions beyond their natural tolerance limits for high temperatures or lack of water by 2050.

This research has contributed to the future of climate-resilient urban forests, as it has identified how cities can be designed to improve the health of tree species. Dr Esperon-Rodriguez said in addition to selecting climate-resilient species, simple steps can be taken to ensure urban forests are maintained.

“Trees at risk from reduced rainfall can be helped through water-sensitive urban design, which allows rainfall to soak into the ground and reach root zones, instead of going down the drain,” she said.

“The urban heat island effect will exacerbate increased temperatures, but more tree and shrub cover in urban areas helps to reduce this effect, so leaving large trees and shrubs in place to perform these roles is really important.”

The study is being delivered through Hort Innovation’s Hort Frontiers Green Cities Fund.