* Any views expressed in this article are those of the author and not of Thomson Reuters Foundation.Trees in cities boost mental health, filter out air and noise pollution, cool cities and insulate homes from the cold
As you stroll along a leafy avenue in a busy town or city, you probably don’t have time to consider the benefit of those trees on either side of the road – or what urban life would be without them. Yet the canopy that trees offer, whether they are elms, palms or mandarins, does far more than simply provide welcome shade and soften the brittle lines of an urban landscape.
There is plenty of evidence that trees can actually improve mental health, reducing the stress and anxiety of urban life. One Toronto study found that having just 10 more trees in a city block improves health perception in ways comparable to an increase in annual personal income of $10,000, or being seven years younger. More people now live in cities than at any other time in history, but rapid urbanisation does not have to mean a grey and ugly sprawl.
In the traffic-clogged streets of many cities, trees play an invaluable role by filtering out harmful pollutants and mitigating the effects of climate change. They serve as highly efficient air filters, absorbing harmful carbon produced by vehicles and industry. One large tree can soak up 150 kg of carbon dioxide every year, as well as filtering airborne pollutants. In London alone, trees remove an extraordinary 2.4 million tonnes of air pollution each year.
Just pause a second to think how much more deafening cities would be without trees to absorb noise pollution, as they shield homes from nearby roads and industrial areas . Acting as buffers, trees and shrubs can reduce city noise levels significantly – for humans this can be as much as 50 percent.
It may also come as a surprise to learn that by shielding homes from cold winds, trees can also help halve the energy used for heating. And at the other end of the spectrum, trees serve as natural air conditioners, lowering temperatures by up to 8°C.
Beyond urban boundaries themselves – often hundreds of kilometres away – trees and forests in rural settings provide a range of services to cities, such as protecting watersheds and providing energy, construction materials and recreational opportunities for city dwellers.
All this makes sound economic sense, quite apart from improving the quality of life for the millions of people who live in cities. A cost-benefit study conducted by the New York City park department found that the benefits of its trees was $120 million a year, including protecting the city's water supply, and preventing flooding.
Well managed forests in and around cities provide habitats, food and protection for plants and animals, helping to maintain and increase biodiversity. In many cities, urban and peri-urban trees serve as a source of fuelwood, food and medicines. For example, the Jamun trees alongside roads in Delhi yield 500 tonnes of fruit each year for sale and consumption.
All too regrettably, trees are being actively torn down in some cities to make way for more roads and buildings. Yet when space is tight, trees don’t necessarily have to be grown at ground level. As cities grow and multiply, inventive ways of integrating trees into urban landscapes are being developed, such as the creation of a vertical forest, as in Milan, or planting trees on buildings, as in Singapore – though this should always be a last resort.
The theme of this year’s International Day of Forests is forests and sustainable cities, and here at the Food and Agriculture Organization of the United Nations we make a point of supporting member countries on urban forestry issues.
It is gratifying to report that around the world, a number of cities are going to great pains to nurture urban forests, and not all of these are from the wealthy North. In China, 170 cities have signed up for a greening programme that has dramatically increased tree cover. In Manila, miniature parks are being created on spaces such as wasteland, crossroads and along railway lines. In Seoul, South Korea, city planners actually removed an entire motorway from the city centre and replaced it with trees and plants.
Advanced planning is the key here, and the most successful urban landscapes are those that have factored trees in from an early stage, rather than tacked them on as an afterthought. After all, an average tree takes 10 to 20 years to develop and mature. Managing urban areas has become one of the most important development challenges of the 21st century, but trees and urban forests can make our cities greener, healthier and happier places to live. Let’s make sure that trees are included in the game plan.
Hiroto Mitsugi is assistant director-general, Forestry Department, at the Food and Agriculture Organization of the United Nations.