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Double trees

A popular tree grows twice as well in the New York metropolitan sprawl as in rural New York State, according to a new test. Clones of an Eastern cottonwood (Populus deltoides) in the Bronx and other city spots grew to double the biomass of clones outside small towns upstate or on Long Island, says Jillian Gregg, now of the Environmental Protection Agency's western-ecology division in Corvallis, Ore.

The growth gap comes from damage, she and her New York colleagues report. Ozone chemists have known that concentrations may spike skyscraper high in city air, but during a full 24 hours, rural trees actually get a higher cumulative ozone exposure from pollution that in and lingers. A series of new experiments now shows that this hang-around ozone is the factor in tree growth, the researchers say in the July 10 Nature.

"This study has profound importance in showing us most vividly that rural areas the price for urban pollution," says Stephen P. Long of the University of Illinois at Urbana-Champaign. "This work should be a wake-up call," he adds.