Most urban trees are threatened by global warming by 2050

More than half of our urban trees are threatened by global warming which is heating up the planet. This is the main news from new research that shows that by 2050 more than three-quarters of urban tree species will be threatened by climate change

Urban trees are essential air conditioners: the shade they provide and the water they transpire can lower the temperature by several degrees.

This makes them important protections against increasingly deadly urban heat.

But, just like people, trees and urban forests are vulnerable to warmer temperatures.

A new study audiencefinished in Natural climate change is aimed at policy makers.

“This document is for governments to identify potentially vulnerable trees,” says lead author Dr Manuel Esperon-Rodriguez, a researcher at the Hawkesbury Institute for the Environment at Western Sydney University.

The international team of researchers used data from the Global Urban Tree Inventory to analyze 3,129 urban tree species from 164 cities in 78 different countries.

Tree Cemetery, Paris. Credit: Jonathan Lenoir

They compared the trees’ natural tolerance limits to expected temperature and precipitation conditions for each of the cities in 2050 and 2070.

They found that 56% of urban tree species already live in areas where the temperature range exceeds their natural preference.

Even more urban tree species – 65% – live under abnormal rainfall levels.

Assuming emissions continue to grow beyond 2050, peaking around 2060 (based on a commonly used scenario called CPR 6.0), the researchers found that 76% of urban tree species would be threatened by temperature and 70% would be stressed by changes in precipitation.

Cities near the equator are particularly vulnerable, as are Australian cities.

Urban trees in a harbor on a lawn in perth
Urban trees in Perth. Credit: Jaana Dielenberg

Perth can expect 83% of its urban tree species to be endangered by 2030 – and it has the most optimistic forecast. In Darwin, almost all species will be threatened.

“Common native tree species found in at least 10 Australian cities that are expected to experience climatic conditions beyond their natural tolerance limits by 2050, include manna gum, swamp gum, yellow box, narrow-leaved peppermint, blackwood and brushbox,” says senior author Associate Professor Rachael Gallagher, also at Western Sydney University.

“Many beloved non-native urban trees are also at risk – species like jacaranda, oaks, elms, poplars and silver birch.”

Read more: The importance of urban trees

Urban trees in front of a river and a palace in copenhagen, people sitting and eating in the foreground
Trees in Copenhagen. Credit: Rachel Gallagher

Fortunately, there are ways to plan for and address this risk.

“Trees can adapt and exhibit plasticity in traits that can allow them to tolerate harsh conditions,” says Esperon-Rodriguez.

“When we say they’re species at risk, we’re not saying they’re going to die. We’re just saying they could experience stressful conditions because of their tolerance,” says Esperon-Rodriguez.

According to Esperon-Rodriguez, vulnerable tree species can be protected through smarter watering and management, while local governments and city planners can identify which trees will be the most resilient when planted.

“It’s an option for managers and planners to say, ‘Okay, this is how we can start thinking about where we want to plant different species in the city’.”

Esperon-Rodriguez shines a light on the city of Sydney urban forestry strategy as an example of this.

“All of the major benefits provided by urban forests are primarily provided by large trees. So if we plant things that will fail today, then there will be problems in the future.

“But if we ensure that what we plant today will grow and survive for the next 20, 30, 40, 50 years, then we will be securing urban forests for future generations.”

Teresa H. Sadler