Branching out

October 17, 1997|By Edward Flattau

WASHINGTON -- A national conservation organization has conducted a study of how much tree cover an urban center needs to sustain a high quality of life -- and guess what? Nary a city (with the possible exception of Minneapolis) approaches the arboreal goal.

With the aid of urban silviculturists, the organization American Forests developed a minimum healthy tree-cover standard: At least 40 percent of a metropolitan area's acreage should have a tree canopy.

Few cities come even close to meeting this leafy standard. Of those "urban areas" (extending about three miles beyond city limits) that American Forests charted, Austin, Texas, was the greenest with a 34 percent tree cover score.

Greater Baltimore followed with 31 percent.

Most large American cities, however, are much further away from the 40 percent goal.

Downtown districts are a particular problem in most urban areas. American Forests recommends a minimum 15 percent tree cover for the center city (as opposed to 25 percent in urban residential areas and 50 percent in the suburbs proper).

Yet the survey found most downtown districts have no more than 6 percent to 10 percent tree cover. Further complicating matters is the short life span (seven to 10 years) of trees in the city center, mostly the result of poor soil and inadequate space for root systems. In a rural location, these same trees might live for 200 years.

All is not lost, however. Gary Moll, coordinator of the study, says if the soil and space deficiencies are corrected in the business district, trees could last at least 70 years despite air pollution from traffic congestion. Another opportunity comes from urban renewal. City planners should provide more treed open space.

One might wonder why the goal for tree cover downtown shouldn't be more ambitious than 15 percent. The response from urban planners is that 15 percent is a realistic level, given the amount of space normally available in these commercial neighborhoods.

Of course, the bottom line is the trees' actual value to the urban environment. Aesthetics are an obvious plus, as are the air conditioning properties of shade.

But as the American Forests study points out, there is far more. The urban forest produces quantifiable benefits through its favorable impacts on air quality and storm-water management.

By capturing and filtering harmful air pollutants, trees render a service currently worth approximately $31 million a year in Baltimore, $15 million in Atlanta, and $11 million in Milwaukee, according to the study.

In regard to storm-water runoff, which is the most insidious form of water pollution, trees perform a function that will save Austin $1.4 billion over time, Atlanta $883 million, Baltimore $340 million and Milwaukee $305 million. That's because a moderately sized tree's roots can absorb up to 400 gallons of water daily.

American Forests forecasts that environmental benefits would grow substantially if these cities reached the 40 percent tree-cover target.

Milwaukee would experience $10 million worth of additional annual air quality improvements, Atlanta $7 million, Austin $6 million and Baltimore $3 million. Storm-water benefits would be even greater: from $358 million for Atlanta to $102 million for Baltimore.

Cities need to promptly take heed. Urban areas in this country have been expanding at an estimated 2 million acres a year. Trees can get lost in the developmental frenzy. If these new communities are to be desirable, environmentally sustainable places to live, trees must also take root.

Edward Flattau writes on environmental issues.

If you're interested in seeing more trees planted in the city, you may contact Beautiful Baltimore, Inc., 303 Oakdale Rd., Baltimore, MD 21210.)

Pub Date: 10/17/97

Baltimore Sun Articles
Please note the green-lined linked article text has been applied commercially without any involvement from our newsroom editors, reporters or any other editorial staff.