Every tree that's subtracted from a city's ecosystem means some particulate pollution that should have been filtered out remains. In Washington, that amounts to 540 extra tons each year.

Tree-cover Benefits

Urban canopy helps absorb carbon dioxide, pull particulate matter from the air, prevent floods and keep temperatures at livable levels. How much tree cover a city needs depends on local climate, but in the U.S., the guidelines divide roughly along the Mississippi River, with cities to the east needing a 40 percent cover and cities to the west a less-leafy 25 percent.

Pollution Increases

All this hits the environment hard, starting with air quality. Every tree that?EUR??,,????'?????<

Stormwater Increases

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In 2006, Los Angeles volunteers kicked off a campaign to plant 11 million trees over the next 30 years. Tree advocates are calling for similar efforts across the country.
Photo: City of Los Angeles

Heat Island Increases

In Atlanta, where developers bulldozed 380,000 acres from 1973 to 1999 ?EUR??,,????'?????<

Keep the Trees You Have

Local governments are finally responding to the problem. More than 2,000 big and small cities have launched long-term planting and preservation programs. For now, the most immediate answer is less the planting strategy than the preservation one, something that can best be achieved by curbing sprawl and downsizing our taste for too-big homes.

Source: Time magazine