Wednesday, October 1, 2003

Urban forests, necessary by nature

Our nation’s cities cover nearly 100 million acres of what was previously forestland. About 25 percent of these acres remain wooded and many cities lie on forest edges. Fewer trees are being re-planted as urban sprawl consumes thousands of acres a day.

It is unfortunate because trees provide “ecological services” that improve city life. Forest vegetation and soils provide for good water quality, minimize flooding and reduce siltation of streams. Although forests cover only a third of the contiguous 48 states, two-thirds of the runoff flows from them.

City trees are important too. Unrestrained water rushes over concrete and other city surfaces, leaving little to soak into the ground. Trees slows the rain drops as they travel to the ground, and low-growing plants, roots and organic matter cause it to penetrate soils. There, it gets filtered and then enters aquifers. Extra ground water seeps continuously into surface water. In many cities, storm water and sewage systems are connected and inadequate. Heavy downpours and prolonged rains frequently result in floods and overwhelm the systems, discharging raw sewage. Trees minimize these problems. The American Forests organization found that tree loss in Atlanta between 1974 and 1996 increased runoff by 33 percent during heavy rains and estimated that the cost to build retention facilities to handle the additional water would exceed $1 billion. On the other hand, Atlanta’s existing trees save the city $86 million in annual storm water services.

Trees also improve air quality by absorbing gases, trapping particulates and lowering summer temperatures. Although emissions must be reduced, planting more trees would improve air quality. One large tree can remove between 5 and 12 pounds of pollutants annually from the air. The U.S. Forest Service estimates that greater Atlanta’s trees annually remove 19 million pounds of pollutants from the air including carbon monoxide, nitrogen dioxide, ozone, particulates and sulfur dioxide. The American Forests organization estimates that Atlanta’s lost trees would remove 11 million more pounds of air pollutants each year.

Cleaning the air saves money too. According to American Forests, trees annually save Atlanta $47 million in air pollution services, and the lost trees cost the city $28 million annually in pollution services. Trees are no substitute for technology, but should be more central to urban environmental management. U.S. cities on average could double their tree cover. The U.S. Forest Service estimates that space for perhaps 700 million trees exists in America’s cities.

Ultimately, tree-planting campaigns do more than make cities look good Ð they measurably and significantly contribute to the quality of city life. For more information on Urban Forestry, benefits of trees, urban tree care and more visit www.gfc.state.ga.us/Services/UCF/index.cfm.

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