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.

October 6, 2017

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.

More about trees

Primer: Ecosystem Services

Tree-Covered Neighborhoods Pop Out Healthier Babies

Kids Breathe Easier When Trees Eat Smog

Urban Trees Curb Shady Behavior

For more information:

Ecological Modeling, Volume 360, 24 September 2017, Pages 328–335
sciencedirect.com

 

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