A 20% increase in the canopy of urban forests would double their benefits in megacities

Katie Hill - Editor-in-Chief, My Green Pod

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Published: 27 January 2018

This Article was Written by: Katie Hill - My Green Pod

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Planting 20% more trees in our megacities would double the benefits of urban forests, like pollution reduction, carbon sequestration and energy reduction, according to a study in Ecological Modelling.

The authors of the study, which was carried out at Parthenope University of Naples in Italy, say city planners, residents and other stakeholders should start looking within cities for natural resources and conserve the Nature in our urban areas by planting more trees. Their work has been selected by an international scientific committee to be given the Atlas award.

What is an urban forest?

Nearly 10% of the world’s population live in megacities – cities 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.

An urban forest contains the single tree in someone’s back yard, the row of trees along a street or a wooded area in a public park; joining these areas with additional trees extends the size of the urban forest.

‘By cultivating the trees within the city, residents and visitors get direct benefits. 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.’

Lead author, professor of the Department of Environmental Resources Engineering at the State University of New York ESF campus

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% of the area of each of the world’s megacities is urban forest today.

But the new study reveals that a further 20% could be transformed into forest – something that would change residents’ lives for the better.

Urban forests worth $500m per year

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 10 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 $500 million 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.

Sustainable cities

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% 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. You can visit the free resource itreetools.org 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.’

Lead author, professor of the Department of Environmental Resources Engineering at the State University of New York ESF campus

Click here for tips from Suzi Martineau, organiser of The Tree Conference, on how to plant trees.

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