Green Street Smarts
Urban trees aid the environment and help people stay healthy.
Plants love the doting that comes with regular watering and maybe some occasional sweet talk from their caretakers, but they are paying people back in spades—at least the largest of the bunch are. Trees provide all sorts of crucial health and environmental benefits, research shows, from pacifying aggressive behavior and providing glare-reducing shade to staving off flooding and acting as noise buffers and leafy filters for soot and dust.
To reap those gains, environmentalists are proposing planting more trees in urban areas. They bemoan the loss of foliage to development and sprawl, as well as to plant disease and pests, as a source of human ills such as obesity and skin cancer.
“We’re losing pedestrian opportunities, we’re losing places outside where children can go out and play, we’re losing our connectivity to nature,” says Ed Macie, regional urban forester with the US Forest Service in Atlanta. “We’re exposing ourselves to more sun and increasing air pollution,” making us more prone to illness.
Sight for Sore Eyes
Among physical benefits, trees can be easy on the eyes—in every sense. “The sun has been implicated in cancers of the eye, of the eyelid. It’s been implicated in macular degeneration. It can also cause cataracts and pterygium,” a fleshy growth that invades the cornea, said Dr. Paul Finger, director of the New York Eye Cancer Center. Particularly vulnerable to direct sun exposure are people with blue eyes since darker pigment in the iris acts as a sunblock, Finger says. Certain medicines, including anti-hypertensive chlorothiazides, the antibiotic tetracycline and phenothiazines for seizures, increase the toxicity of the sun’s UV rays, as do sulfonamides, psoralens and allopurinol, adds Finger, who recommends sunglasses as a principal buffer from the sun.
Besides luring people outdoors for physical exercise, trees have psychological benefits. Those were evident in a five-year study of police reports and firsthand accounts at Chicago’s Robert Taylor Homes public housing development. Residents in areas with more trees were friendlier with their neighbors and less likely to engage in violence than residents surrounded by asphalt and pavement, said Frances Kuo, a co-author of the study and director of the Landscape and Human Health Laboratory at the University of Illinois at Urbana-Champaign.
Further, three separate studies that Kuo conducted found that trees had a positive impact on children with ADHD. “Children seem to have milder symptoms after spending time doing something in a green setting, and that could be anything from a tree-lined street or a shady backyard to soccer fields,” Kuo says. “The bottom line is it looks like nature is actually good for kids. We have evidence from kids with ADHD and kids without it.”
Also lending credibility to the idea that nature, and foliage in particular, boosts health is research showing that stress—and sometimes pain—levels are lower in hospital patients who enjoy views of trees and gardens. Hospital staff and visitors were also calmed by the green views, according to the research by Roger Ulrich, director of the Center for Health Systems & Design at Texas A&M University’s College of Architecture. Ulrich also conducted research showing that people were less stressed when driving along tree-lined streets.
“All of this research, and in combination, suggests that nature and trees in our cities are really necessary elements for our health and well-being,” says Kathleen Wolf, a research social scientist with the University of Washington’s College of Forest Resources. “Green is very good.”
Saving Cash, and the Environment
It turns out that money does grow on trees after all, in more ways than one. First, Wolf’s studies on trees and business neighborhoods show that consumers, no matter their age, gender or socio-economic status, were likely to spend about 11% more at retailers in landscaped districts. They also rated customer service at these stores 15% higher. What’s more, researchers say that environmental gains for communities are greater when trees are larger. Taxpayers and homeowners reap nearly $60 a year in payback, for instance, from a large 40-year-old tree, says the Center for Urban Forest Research, part of the US Department of Agriculture.
The Alliance for Community Trees (ACT, www.actrees.org), a College Park, Maryland, advocacy group, breaks down some of the annual savings. Because tree canopies and root systems filter water supplies, one tree can save $3.50 in storm water runoff, flooding and erosion costs, says ACT. By removing pollutants such as ammonia and sulfur dioxides, a tree can save $5 in air pollution cleanup costs. And by cooling the air with shade and evaporated water, a single tree, the group says, can save $10 in energy costs.
Environmentalists plug trees’ effectiveness as global warming fighters because the plants convert carbon dioxide into oxygen, although Duke University research qualifies this position. A group of North Carolina pine trees with 10 years of extra exposure to carbon dioxide grew more tissue to absorb the CO2, the Duke research found, but only pines receiving ample water and nutrients were able to help offset the effects of global warming. Fickle weather can sometimes hold those nutrients back.
The Forest Service’s Macie, for one, is nevertheless encouraged that more laws are being enacted to protect trees and that more municipal governments and grassroots groups are planting them. New York City, for example, plans to plant 220,000 trees along streets over the next decade and will prune trees more frequently to reduce tree disease, said Adrian Benepe, New York’s parks commissioner. “It also reduces liability because it keeps limbs from falling,” Benepe adds.
Says Macie, “Human beings are organic beings and have a very long genetic history on this planet that connects them very closely to natural systems. Through industrialization and moving away from an agrarian lifestyle we’ve become disconnected. We need to bring nature back to where we live.”