Energy & Environment

'I Think That I Shall Never See...'

An active campaign to maintain urban forests and replenish tree canopies can repay a city in more ways than one.
by | August 2004

In the 1930s, Albuquerque Mayor Clyde Tingley knew that graceful trees make neighborhoods more pleasant and big-city life more bearable. So Tingley started giving away free Siberian elms, three to a household. He hoped to create a wooded oasis that would shelter the growing city from the relentless New Mexico sun. Now those stately elms are dying off, and municipal crews are cutting down 2,000 of them to keep windstorms from toppling them across parks and thoroughfares.

There's one bright side to the elms' demise: Albuquerque gets another crack at enriching the urban environment. Current Mayor Martin Chavez plans to replenish the city's tree canopy next year. Albuquerque officials are using satellite imagery and aerial photography to identify brown landscapes where trees aren't growing, and this fall will start working with volunteer groups to plant cottonwoods, Arizona ash, desert willows and other hardy and drought-resistant trees.

Like Albuquerque, other metropolitan regions have been losing trees at an alarming clip. Since 1972, the Washington, D.C., region has lost 30 percent of its densest tree stands, while 27 percent of the wooded areas in San Diego and surrounding communities have vanished in less than 20 years. As woodlands were replaced by asphalt streets and air- conditioned buildings, cooling vegetation gave way to hard-surfaced roads, parking lots and rooftops that soak up hot sunshine. Meteorologists have found that downtown Atlanta temperatures are typically 5 to 8 degrees higher than in the surrounding countryside, creating an urban "heat island" that fuels violent thunderstorms, raising the risk of flooding.

These days, public officials are employing sophisticated technology to further their commitment to the benefits that trees provide urban neighborhoods--in addition to cool summertime shade and colorful autumn foliage. In Chattanooga, for instance, municipal teams carrying global positioning system units have mapped trees growing on 200 downtown blocks, then combined the data through geographic information systems to plan for replanting, pruning and routine maintenance.

Studying satellite images from 40 urban areas, American Forests, a conservation organization, suggests that major American metropolitan regions need to plant more than 1.7 billion trees to restore dwindling urban forests and lower demands on electricity-producing power plants. Three tall trees in the yard can cut household air conditioning costs by one-fifth; by one estimate, Californians could save $3.6 billion on energy bills every year by shading homes and buildings.

Healthy forests and woodlands also turn out distinct and tangible environmental benefits. Vegetation sequesters carbon dioxide, helping curb global atmospheric warming. Trees remove pollutants from the air, including smog-forming ozone, particulates, carbon monoxide and sulfur dioxide. U.S. Forest Service researchers suggest that state and local air-quality agencies could figure out ways to take credit for preserving woodlands and maintaining trees along parks and roads as they implement strategies for complying with federal air-quality standards. Houston Green, a coalition of 15 public agencies and citizens' groups in Texas' largest city, persuaded state and local officials to write tree preservation steps into the city's smog- reduction plan.

Governments are also extending municipal water supplies by taking advantage of woodlands' ability to collect rainfall and filter out contaminants. Seattle has hired ecologists to restore the Douglas fir forest on the city-owned Cedar River watershed, which supplies 70 percent of the city's drinking water. In Garland, Texas, trees retain 19 million cubic feet of runoff when rainstorms hit, according to an American Forests calculation. That, in turn, saves the city $38 million it would have to spend on stormwater retention tanks. Similarly, planting more trees to cover 35 percent of San Antonio's land could reduce major storm runoff by 103 million cubic feet, saving $200 million in construction costs.

San Antonio is working with American Forests to integrate a "green data layer" into the city's geographic information system. Using satellite imagery that detects trees with 6-foot-wide crowns, local agencies can assess the city's tree canopy and determine the benefits each stand provides the city by storing storm runoff and cleansing pollutants from the air. Through similar methods, the urban forestry center at the University of California at Davis estimates that San Francisco's 100,000 street trees provide $7.5 million in annual benefits by enhancing property values and sparing local government substantial infrastructure costs.

Maybe public works engineers don't yet consider those calculations convincing. But it makes sense that restoring urban forests will pay off. It's time that city and county officials take this kind of "green infrastructure" into account in keeping communities livable.

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