Trees provide $500 million in services per megacity every year

CC BY 2.0 Beatrice Murch/Flickr

From reducing air pollution and saving energy to mitigating climate change, researchers place a price tag on the work that urban trees perform.

Many of us city mice cherish our urban trees as if they were sacred beings. (Which of course, they are!) From behind windows they offer glimpses of life amid the manmade landscape and provide spots for city birds to nest and sing. We drink in their mind-body-soul benefits when walking in parks; we seek their shade in the summer heat. They offer a dose of nature for the nature-deprived, and for that, they are priceless.

It would be hard to place a value on the soul-soothing pleasure-giving worth of trees, but city trees do a whole lot more than just spark happiness. And now a study published in the online journal Ecological Modelling has come up with a bone fide dollar amount: $505,000,000 per year, thank you very much.

The figure was determined as per megacity (a city with over 10 million inhabitants), 10 of which were included in the research: Beijing, Buenos Aires, Cairo, Istanbul, London, Los Angeles, Mexico City, Moscow, Mumbai, and Tokyo. The cities span five continents and host nearly 10 percent of the world's 7.5 billion people.

The researchers estimated the benefits of tree cover for reducing air pollution, stormwater runoff, energy costs associated with heating and cooling buildings, and carbon emissions. The numbers look like this, according to the study:

The present median benefit value from urban trees in all 10 megacities can be estimated as $482 million/yr due to reductions in CO, NO2, SO2, PM10, and PM2.5, $11 million/yr due to avoided stormwater processing by wastewater facilities, $0.5 million/yr due to building energy heating and cooling savings, and $8 million/yr due to CO2 sequestration.

And if you're wondering: What would happen if we planted even more trees? The answer is, their services would increase accordingly.

"Megacities can increase these benefits on average by 85 percent," says the study's lead author, Dr. Theodore Endreny of the College of Environmental Science and Forestry in Syracuse, New York. "If trees were to be established throughout their potential cover area, they would serve to filter air and water pollutants and reduce building energy use, and improve human well-being while providing habitat and resources for other species in the urban area."

City planners need to take this into consideration. Developers need to reserve areas for green space. Property owners need to embrace trees on their property. People need to be more aware that urban trees are way more important than just eye candy for sidewalks.

As the study’s co-author Sergio Ulgiati puts it, "A deeper awareness of the economic value of free services provided by nature may increase our willingness to invest efforts and resources into natural capital conservation and correct exploitation, so that societal wealth, economic stability and well-being would also increase.”

So if you can't sell the idea of planting more trees with any of the other sensible pitches, go for the "free services" angle; who can say no to that? Though the trees don't care, they'll just continue saving us regardless.

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