Magazine article American Forests

Money in the Tree Bank: New Mechanisms for Measuring Ecosystem Values Make It Possible for Cities to Be Both Environmentally Green and Financially Savvy

Magazine article American Forests

Money in the Tree Bank: New Mechanisms for Measuring Ecosystem Values Make It Possible for Cities to Be Both Environmentally Green and Financially Savvy

Article excerpt

John Wimberly lives in the tree-covered neighborhood of Chevy Chase in Washington, DC. Trees dominate the landscape there, reaching high into the sky to form a green canopy and protective umbrella over the community. Without the trees, the neighborhood would change completely.


That possibility became very real when a senior care facility in the neighborhood proposed removing 30 percent of the tree cover on its 16-acre site as part of an expansion. The proposed building would be placed on a wooded portion of the site rather than on a grassy area.

The impact, while felt most heavily in Chevy Chase, would actually be felt citywide. With an existing tree canopy of 28 percent, the District of Columbia is already trying to address its tree deficit. A previous study by AMERICAN FORESTS recommended the city enact policies that lead to a net gain in trees. Setting a canopy cover goal is a first step.

"The District could realistically increase canopy cover 7 percent to maximize benefits from this natural capital," says Gary Moll, vice president of urban forestry for AMERICAN FORESTS.


The problem is not unique to Washington, DC; in fact, it's a story often repeated in communities across the country. Incremental, project-by-project changes add up to citywide tree deficits. The momentum of growth and development is plowing down urban forests--and eroding natural capital. Urban land cover is expanding by about 20 percent every 10 years while the urban tree deficit increases by about 30 percent during the same time period. Even more frustrating, citizens--as individuals--are unsure how to change this trend.

That's where AMERICAN FORESTS hopes people will take advantage of its CITYgreen software, which allows individuals or communities to calculate the magnitude of a community's tree deficit and the corresponding impact of air, water, and energy. Different versions are geared toward different skill levels. Novices can get a fast, free tree analysis of their city, town or watershed from AMERICAN FORESTS' website ( GIS professionals can use CITYgreen for ArcGIS to perform an advanced analysis.

Satellite images and GIS tools make it easy for officials to begin to consider trees as part of a community's tangible financial assets. Think of an urban forest as the principal of an investment. When it's large enough, that principal provides many environmental benefits, among them cleaning air, slowing stormwater and recharging groundwater, filtering pollutants from city streets before they enter waterways, and cooling communities.

These "ecosystem services" are like the interest that flows from the principal. Without a sufficient urban forest to work for cities, ecosystem services will dwindle. The goal is to protect the principal and use the interest. Yet cities too often install costly built infrastructure rather than allow nature to help manage air and water systems.

What constitutes a "sufficient" urban forest? While ideal canopy amounts vary by region, AMERICAN FORESTS recommends that every community set tree canopy goals and offers general guidelines for different regions of the country on its website. Communities that don't meet federal clean air and water regulations need to first determine their tree canopy cover, then set canopy goals with an eye toward using the ecosystem services trees provide to help them reach compliance. The real trick is enacting policies and programs that allow a community to achieve its canopy goal.

In Leesburg, Virginia, for example, urban forester Jay Banks has watched tree canopy dwindle since 1997. The city didn't balance its "green" and "gray" infrastructure and so had to engineer a stormwater system to handle all the flow, he recalls. Residents learned just how big those stormwater culverts were when Hurricane Isabel flushed so much stormwater into the drains that a van got caught in the flooding and washed through a culvert under a four-lane road. …

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