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City improvement: Planting trees

By Ross Atkin / April 16, 2003

A tree may grow in brooklyn, but Gary Moll of American Forests, a conservation group, would like to see more of them there - and in Dallas, Des Moines, and Detroit as well.

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But the reality is that just the opposite is happening. Over the past 15 years, the number of trees in many US cities has declined by about 30 percent, while the space covered by concrete and other solid surfaces has risen by 20 percent, says Mr. Moll.

He estimates that to redress the imbalance, metropolitan areas need 634 million more trees.

That's a lot of new trees, especially in a time of belt-tightening municipal budgets. But in some cities, such as Atlanta and Detroit, volunteer groups are stepping in to help - planting and caring for trees on public land, and educating the public about why they matter.

Trees are natural pollution-control devices. They absorb carbon dioxide (a byproduct of burning fossil fuels) and return oxygen to the air. Their leaves, branches, and and trunks help slow the runoff of storm water.

They also provide sound buffering, shade, and measurably cooler temperatures on hot summer days, and breeding and roosting places for local and migratory birds, whose habitat has been disappearing.

The savings that result from these environmental benefits can really add up. Research has shown that substantial increases in the number of city trees can reduce storm-water and pollution-control expenditures by millions of dollars.

Unfortunately, there's more involved than simply planting more trees. Cities also have to keep them alive - and that can sometimes be a problem.

In some cases, as with elms, disease has been a factor. Generally, though, much of the problem stems from lax maintenance, outright neglect, and stressful growing conditions.

Think big

One solution, practiced by The Greening of Detroit, is to avoid tiny saplings and instead plant good-sized trees. Most of the 35,000 trees planted by the nonprofit group over the past 13 years have been about 12 feet tall.

A tree this size, says Rebecca Salminen Witt , executive director of the organization, makes a more immediate impact and stands a better chance of survival.

Landscape architect Henry Arnold of Princeton, N.J., likes to think of trees as beautiful, economical public utilities. Often, however, they are shortchanged in planning underground infrastructure, and as a result, wind up crowded for space. "Trees are not looked upon with the same seriousness as other utilities," he says.

This is beginning to change as word spreads that tree size and longevity count more than quantity. "The benefit of an urban tree is proportional to its crown size or volume," Mr. Arnold explains. "One tree that lasts 50 years is worth more than 20 trees that last only 10 years."

Consequently, attention is shifting toward doing a better job of improving growing conditions. To thrive, city trees need better soil and more of it than they commonly receive, plus good drainage and aeration.

When trees are planted too hastily, without proper attention to soil and selection, they may never mature or produce the desired benefits. In fact, many live only seven to 10 years.

"A lot of community groups like to push tree planting because it's fun and easy to get the public involved," says Steve Cothrel, president of the Society of Municipal Arborists. "But if you don't maintain the trees, you can end up with a lot of headaches and potential hazards."

Education, therefore, is a priority for organizations like The Greening of Detroit and Trees Atlanta, which teach neighborhood volunteers proper aftercare, from pruning to watering.

In both cities, the goal is to maintain each tree three or four years after being planted, while it's getting established. Ideally, community groups that plant trees shoulder this responsibility.

"We ask our planting partners to sign maintenance agreements," says Ms. Witt, "but practically speaking, it doesn't always get done."

The effort is backstopped, therefore, by a small full-time staff and by the Green Corps, trained high school summer workers.

In order to have trees planted, neighborhood groups must have a water supply (even if it's just permission to use someone's garden hose), and generally a willingness to do some modest fundraising. "We find that encourages them to take better care of the trees," Witt says.