| STUDY |
City trees outdo country trees Jillian W. Gregg at Cornell university and the Institute of Ecosystem Studies, Millbrook, N.Y., along with colleagues Clive G. Jones and Todd E. Dawson, grew cottonwood clones for three consecutive seasons at urban and rural sites around New York City and found that urban plant biomass was twice that at rural sites [Nature, 424, 183 (2003)]. The authors note that plants in cities are exposed to many pollutants and higher temperatures, carbon dioxide, and nitrogen deposition than plants in rural areas. Each such factor may harm or help plant growth, they say, but "the net effect of all factors and the key driving variables were unknown." Gregg and her coworkers in their research used soil transplants, nutrient budgets, chamber experiments, and multiple-regression analyses. With such tools, they showed that "soils, temperature, CO2, nutrient deposition, urban air pollutants, and microclimatic variables could not account for increased growth in the city." Nor could they account for reduced growth in the country. The scientists find, rather, that lower growth in rural areas results from higher cumulative ozone exposure in those areas. Urban precursors, they say, lead to formation of ozone, but scavenging by nitrogen oxides leads to the continued production and depletion cycles within the city center. Once outside the city, where nitrogen oxides are low in concentration, ozone remains in the air for longer periods of time. A pretty kettle of fish! Their results, say Gregg and colleagues, go against extensive research suggesting that ecological differences between city and country are the result of higher urban ozone exposures. The results also contradict "the pervasive perception that rural environments are safe havens from urban pollutant emissions." Gregg and colleagues think their work "highlights the need to reconsider relative pollutant impacts in urban and rural environments as air sheds merge throughout the globe. Although extensive global change research has studied potential impacts of temperature, CO2, and N deposition, this study shows overriding O3 impacts amid these other factors." |
| UPDATE | 04.08.03 |
| AUTHOR | Jillian W. Gregg at Cornell university and the Institute of Ecosystem Studies, Millbrook, N.Y., along with colleagues Clive G. Jones and Todd E. Dawson |
| LITERATURE REF. |
[Nature, 424, 183 (2003)]. |
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