CITY TREES VERSUS COUNTRY COUSINS. Dug up after a growing season in two kinds of air pollution, cottonwood trees show the retardant effects of ozone. From left, five city trees from the Bronx, where nitric-oxide pollution reduced the ozone exposure period; Cornell ecologist Jillian Gregg; and five country trees that grew in a high ozone rural environment in Riverhead, Long Island. Photo provided by Jilian Gregg. Copyright © Cornell University
NOT SO LUCKY. Examining tree growth in New York City, Cornell ecologist Jillian Gregg says low-ozone "footprints" in urban areas occur because high nitric-oxide concentrations scavenge ozone from the urban atmosphere. But rural areas arent so "lucky". These same nitric oxide compounds are one of the primary precursors that react to form high ozone concentrations that are blown to rural environments. Once there, nitric oxide is very low in concentration so ozone remains in the atmosphere for a longer period. While individual one-hour peak ozone concentrations are often higher in urban environments, the extended exposure period outside the urban center cause some rural trees to grow only half as fast as their city cousins. Photo provided by Jillian Gregg.Copyright © Cornell University
A tree grows in Brooklyn -- despite big-city air pollutants. Meanwhile, identical trees planted downwind of city pollution grow only half as well -- a surprising finding that ecologists at Cornell University and the Institute of Ecosystem Studies (IES) reported in the current issue of Nature (July 10, 2003). They attribute the effect to an atmospheric-chemistry "footprint" that favors city trees.
"I know this sounds counterintuitive but it’s true. City-grown pollution -- and ozone in particular -- is tougher on country trees," says Jillian W. Gregg, lead author of the Nature cover article, "Urbanization effects on tree growth in the vicinity of New York City." Other authors of the Nature report are Clive G. Jones, an ecologist at the Institute of Ecosystem Studies in Millbrook, N.Y., where some of the field studies were conducted, and Todd E. Dawson, professor of integrative biology at the University of California, Berkeley, and a professor at Cornell when the study began.
Gregg was a joint Cornell/IES graduate student, pursuing a Ph.D. in ecology, when she started planting identical clones of cottonwood trees (also known as poplars, or by the scientific name Populus deltoides ) in and around New York City. Test sites included the New York Botanical Garden and the Hunts Point water works in the Bronx; a Consolidated Edison fuel depot in Astoria, Queens; as well as Long Island’s Brookhaven National Laboratory in Upton; Eisenhower Park in Hempstead; and the Cornell Horticultural Research Laboratory in Riverhead. About 50 miles north of Manhattan, in the Hudson River valley, she also planted cottonwood clones at the Millbrook institute.
Roger Segelken | Cornell University
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