News Brief

To Save Cities, Save Trees

Urban forests do $500 million worth of heavy lifting each year for the world’s largest cities—and there’s plenty of room to plant more.

by P.J. Melton

Urban trees offer more than just shade. A new study looks at their considerable economic value to megacities.
Photo: Fons Heijnsbroek. License: Public domain.

Dr. Seuss’s Lorax spoke for the trees, but you don’t have to be a fantastical creature out of a children’s book to do that anymore. A new study published in Ecological Modeling suggests that urban forests play a vital economic role in very large cities, and they could be doing even more.

According to the researchers, urban trees are known to:

Remove air pollution
Manage stormwater runoff
Reduce heating and cooling costs in buildings
Sequester carbon

The scientists put a dollar amount on of each of these natural functions that benefit humans, also known as ecosystem services. Their goal? Provide a baseline that can be used strategically to increase conservation efforts in megacities worldwide, including London, Los Angeles, Cairo, Tokyo, and others. (A megacity has a population of more than ten million.)

Unlike in smaller cities, estimating tree cover in megacities is quite difficult and expensive when using on-the-ground surveys, according to the paper, so the scientists had to develop a way to do it using computer modeling. The models account for the costs of managing trees.

The total annual value of tree cover in each megacity averaged more than $500 million. Air pollution reduction was the most prominent benefit. Overall, researchers found that urban trees provide nearly $1 million in these services per square kilometer per year. Urban forests also provide $20,000/km² of stormwater processing, $820/km² in reduced heating and cooling expenses, and $17,000/km² in carbon sequestration services.

Perhaps the best news of all: according to modeled projections, the average megacity has space to increase its urban tree cover by 85%, which would increase all these benefits by a similar amount.