Popular tree growth

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 planted 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 ozone damage, she and her New York colleagues report. Ozone chemists have known that concentrations may spike skyscrapers high in city air, but during a full 24 hours, rural trees actually get a higher cumulative ozone exposure from urban pollution that blows in and lingers. A series of new experiments now show that this hang-around ozone is the overwhelming 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 pay 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. Earlier studies had fingered car fumes, heavy metals in soils, and other cityscape menaces to plant life. Yet some urban quirks, such as extra warmth and increased concentrations of carbon dioxide, may boost plant growth.