As handy as a tree

Bay watershed: As forests fall, lost impact on pollution and erosion control is worth millions.

June 02, 1999

TREES ARE an economic miracle. They filter pollutants from air and water, provide cooling and shade in summer, protection from winter cold, wildlife habitat and storm-water control against erosion and pollution runoff, absorb carbon dioxide and retard global warming.

Yet tree cover in the Chesapeake Bay watershed is rapidly disappearing, with development the prime cause. Nonurban areas are losing trees at the same rate as the highly developed Baltimore-Washington corridor.

Between 1973 and 1997, high-canopy tree cover in the heart of the watershed plummeted from 55 percent to 38 percent, according to satellite maps analyzed by American Forests, a nonprofit conservation group. Low-vegetation cover (developed areas) rose from 35 percent to 50 percent; average tree cover dropped from 51 percent to 38 percent.

In the Baltimore-Washington area, the group calculates the loss of tree cover over 24 years would require $1 billion of engineered projects to compensate for the runoff and storm-water retention those trees would have provided. It costs us $24 million a year to remove pollutants that these lost trees would have sucked from the air for free.

The loss of fully functioning forest ecosystems cannot be entirely replaced, leaving fragmented patches that do not have the environmental value of larger healthy forests. Likewise, forested wetlands can't be sufficiently replaced by more man-made marshes.

Planting more trees and directing development to minimize destruction of woodlands are two answers to the accelerated loss. The new Chesapeake Bay Program agenda, to be adopted by state and federal officials next year, must give priority to these forest restoration and preservation measures.

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