Trees in Greenwich Park

Study reveals trees provide huge ecological benefits to megacities, urges rapid planting of ‘urban forests’

Image credit: Dreamstime

The ecological benefits of trees in megacities could be doubled if city planners utilised more of the available space to plant them according to researchers from Parthenope University of Naples in Italy.

Planting 20 per cent more trees in megacities would double the benefits of urban forests, such as pollution reduction, carbon sequestration and lower energy use, the study found.

It calls on city planners, residents and other stakeholders to start looking within cities for natural resources and conserve the nature in our urban areas by planting more trees.

Nearly 10 per cent of the world’s population currently live in megacities, which are defined as those with a population of at least 10 million people.

While those people often rely on nature outside of the city for their food and recreation, nature within the city in the form of urban forests can provide enormous benefits.

Many famous examples of urban forests in the megacities were studied, from Central Park in New York City to St James’ Park in London and Bosque de Chapultepec in Mexico City.

On average, about 20 per cent of the area of each of the world’s megacities is urban forest today. But the researchers found that a further 20 per cent could be transformed into forest - something that would change residents’ lives for the better it states.

“By cultivating the trees within the city, residents and visitors get direct benefits,” said Theodore Endreny lead author of the study.

“They’re getting an immediate cleansing of the air that’s around them. They’re getting that direct cooling from the tree, and even food and other products. There’s potential to increase the coverage of urban forests in our megacities, and that would make them more sustainable, better places to live.”

In the study, the team used a tool called i-Tree Canopy to estimate the current tree coverage in cities and the potential for more urban forest cover, and worked out the benefits that would bring.

They estimated the current tree cover in ten megacities in five continents, looked at the benefits of urban forests - including removing pollution from the air, saving energy and providing food - and approximated the current value of those benefits at over £350m per year.

Creating a model for each megacity, they estimated benefits such as reductions in air pollution, stormwater, building energy and carbon emissions, and assessed how those benefits changed as the tree cover was increased.

The model took into account the local megacity tree cover, human population, air pollution, climate, energy use, and purchasing power. The team was surprised to find that each city has the potential to host a further 20 per cent coverage of forest canopy.

However, city planners and authorities will need to change their perception of the natural resources available to cities before residents can enjoy the benefits of more trees: the less cities rely on nature outside the metropolitan area and the more they focus lands on conserving nature within the cities, the healthier and more sustainable those cities will be.

“Everyone can take action to increase the urban forest areas in our cities, not just city planners,” Endreny added. “You can visit the free resource to find out how much coverage there is in your city now, find out where you could plant more trees in your area and see how the benefits of the urban forest increase as more trees are planted.”

In November a study showed that trees that live in metropolitan areas typically grow faster than trees in rural areas due to the urban heat island effect. 

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