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Areas with Heavy Tree Cover Drop - Dramatic Tree Loss Costs DC Millions

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Fashington DC has experienced a dramatic loss of tree cover since 1973, including a 64 percent decline in the most ecologically valuable areas with heavy tree cover, according to a new report by the national conservation group American Forests.

This decline, according to the American Forests study, represents more than a quarter billion dollars worth of ecological services. The analysis also found the District is losing trees at a faster rate than the region as a whole, and recommends conserving and increasing the

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city's remaining tree cover as a cost-effective way to capitalize on the economic value of this natural resource.

The analysis compared satellite images from 1973, 1985, and 1997 and found that areas with high vegetation and tree canopy coverage dropped from 37.4 percent (16,440 acres) to 13.4 percent (5,871 acres) of the total area (43,938 acres). During the same 24-year period, areas with very low tree cover increased from 51 to nearly 72 percent of the total study area. High canopy coverage was defined as 50 percent tree cover or more. Very low canopy coverage was defined as less than 20 percent tree cover.

"We measure tree cover using satellite imagery because trees provide a good measure of the ecological health of a community. Washington is like other cities we've studied, which are losing their urban forests at an alarming rate. This national trend can be reversed if people realize the value of our cities' green infrastructure. Planting and caring for trees and forests will save money and make our communities greener, healthier, and more livable," said Gary Moll, vice president of American Forests' Urban Forest Center.

The loss of tree cover and increase in impervious surfaces, such as roads and buildings, significantly increased the impacts of stormwater runoff. The study found that stormwater flow during a peak storm event increased by an estimated 29 million cubic feet, or 34 percent. Replacing this lost stormwater retention capacity with reservoirs,

"This decline represents more than a quarter billion dollars worth of ecological services."

sand filters and other engineered systems would cost $226 million ($7.80/square foot). This service was provided previously by trees, vegetation and natural soils, which slow stormwater movement, lower total runoff volume, reduce flooding, and improve water quality.

Air quality also declined. The lost tree canopy had been removing about 354,000 pounds of pollutants from the atmosphere annually at a value of approximately $996,000. Urban forests improve air quality by removing nitrogen dioxide (NO2), sulfur dioxide (SO2), carbon monoxide (CO), ozone (O3), and particulate matter 10 microns (PM10) or less.

American Forests used satellite images and Geographic Information Systems (GIS) technology to measure the Districtís change in tree cover. The data came from a larger, Regional Ecosystem Analysis of the southeastern Chesapeake Bay watershed, which American Forests performed last spring. Average tree cover throughout the District declined from 37 percent to 21 percent for a net loss of 16 percent, compared to a net loss of 12 percent during the same period in the Chesapeake Bay region. Healthy cities should have an average tree canopy coverage of 40 percent to ensure their ecological, economic and social sustainability. Rural areas should have at least 50 percent.

American Forests also evaluated in detail twelve sites of 1 to 4 acres to determine stormwater runoff, air pollution, and other values. Low level aerial photographs and field surveys of the sites were analyzed along with additional data on soil types, rainfall patterns, and land-use configurations. The results provided the basis to estimate the value of the District's ecology.

"Our satellite data is available to other cities and counties in the region, and we recommend they conduct their own analyses to understand the costs of urban sprawl," said Deborah Gangloff, American Forests' executive director. "Local decisionmakers who know the value of their urban forests can plan for tree-smart development and still accommodate the growth of their communities."

The District of Columbia Urban Ecosystem Analysis can be downloaded from American Forests' website here.

American Forests, founded in 1875, is the oldest national nonprofit citizen conservation organization. Its three Centers - Global ReLeaf, Urban Forests, and Forest Policy - mobilize people around the world to improve the environment by planting and caring for trees.

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