Green Cities Healthy for People and Nature

Tuesday, February 23rd, 2016
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For many of us, the natural world is a healthy place of respite from the crowded and hurried urban world where we live. Traveling and recreation in nature give us a sort of “reboot” before returning to the city.

Indeed, we tend to feel healthiest in the natural environment. It’s not just humans that benefit from nature, though. The health of cities, nature, and people are tightly intertwined, and green cities are healthy for people and nature alike.

With the world rapidly becoming urbanised, more and more people are moving away from significant daily contact with nature and into cities where contact with the natural world is minimal. That’s cause for concern, as a multitude of studies indicate myriad beneficial health effects from increasing people’s access to trees and green spaces.

Living on a block with 10 more trees, for example, results in self-reported health benefits similar to being seven years younger, moving to a neighbourhood with a median income $10,000 higher, or getting a $10,000 pay raise. A team of researchers, led by psychologist Marc Berman of the University of Chicago, conducted a study in Toronto and published their findings in the journal Scientific Reports.

The researchers compared general health surveys, an inventory of trees on public land, and satellite imagery of the city, and found that people who live on blocks with more trees are less likely to report health conditions such as diabetes, heart disease, hypertension, and obesity.

Nature, in the form of natural vegetation and green infrastructure, makes cities healthier and more functional. The Green Infrastructure Research Group (GIRG) at the University of Melbourne defines green infrastructure as “The network of natural and designed vegetation within our cities and towns, in both public and private domains. It includes public parks, recreation areas, remnant vegetation, residential gardens and street trees, as well as innovative urban greening technologies such as green roofs, green walls and rain gardens.”

Green infrastructure, such as the the stormwater harvesting project in Sydney Park’s wetlands, can replace traditional grey infrastructure with functional elements that mitigate flooding, improve water quality, and provide healthy recreational spaces for people. This approach becomes even more important as cities become denser, with the potential for concrete and asphalt streets, along with impermeable roofs, to claim more surface area within the city, leading to even more runoff.

Green Roof

Green roof planted with native species at L’Historial de la Vendée, a museum in western France.

Trees also are highly functional in the urban environment, as they combat pollution and the urban heat island effect while producing oxygen. According to studies by the US Environmental Protection Agency and the US Forest Service, one large healthy tree can remove more than 300 pounds of carbon dioxide from the atmosphere every year, while an acre of forest can produce more than three tons of oxygen per year.

Trees provide cooling both through shade and evapotranspiration. A tree providing shade on the west side of a home can lower energy bills by about 12 per cent after 15 years of growth, and evapotranspiration can reduce peak summer temperatures by two to nine degrees Fahrenheit.

Urban areas with 100 per cent tree cover see substantial improvements in air quality, with reductions of up to 13 per cent in particulate matter, 14 per cent in sulfur dioxide, and 15 per cent in ozone. Another study measured 27 to 42 per cent reduced dust reaching the ground within stands of trees compared to open areas.

Australia’s federal government has recognized the benefits of the urban forest and is assembling a program to increase the urban canopy in Australia’s cities.

An added benefit of well-designed, healthy cities is their effect on natural areas at the urban fringe and on true wilderness areas. In order to reduce development pressure on undeveloped land, we need cities to be healthy and pleasant places to live. The pressure is going to intensify in coming decades, as Australia’s population is projected to reach about 40 million by 2050. If sprawl is to be minimized as those people look for homes and work, cities must be developed as compact urban and suburban communities, with appropriate density and efficient transportation, including transit and human-powered options.

Suburbs can be a part of the solution, too, but not with the past model of car-dependent living. Current sprawling suburbs can be retrofitted to be more urban, walkable, and sustainable, as has been demonstrated in the book Retrofitting Suburbia by Ellen Dunham-Jones and June Williamson.

Writer and New Urbanist Kaid Benfield, writing in The Huffington Post, has noted the importance of creating great cities.

“There is simply no way we can protect and maintain a beautiful, thriving, natural and rural landscape outside of cities if we continue to spread highways and suburban sprawl across the countryside,” he wrote. “Healthy, robust, beautiful cities where people want to live are critical to the protection of nature.”

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