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Poison ivy seen as thriving on carbon dioxide

Bob Tippee

As if rising sea levels and malaria plagues weren't frightening enough, the world has another malign effect of global warming over which to panic: poison ivy.

News media recently reported a Duke University study showing that rising concentrations of carbon dioxide accelerate growth of the obnoxious vine through aerial fertilization. Worse, they increase potency of the substance that causes itchy rashes.

Until now, supporters of aggressive warming prevention have scoffed at suggestions that CO2 enrichment of the atmosphere might promote plant growth. Their political agenda treats CO2 as a thoroughgoing scourge and resists hints of potential benefits.

But aerial fertilization suits that agenda when the main beneficiary is a plant nobody likes.

The Duke study controlled CO2 levels in an experimental plot of a North Carolina forest. At rising levels, poison ivy grew faster and nastier. As another reason to fear global warming, the results became news.

As usual, however, things aren't that simple.

A study by Ronald Londre and Stefan Schnitzer of the University of Wisconsin-Milwaukee examined 45 years of data from 14 deciduous forests in southern Wisconsin to test the hypothesis that warming and CO2 enrichment should push lianas—woody vines such as poison ivy—toward Earth's poles. In that study liana growth decreased in forest interiors, with the decline accelerating as a function of distance from forest edges.

"Our findings suggest that forest fragmentation, not climate change, is likely resulting in the increase in liana abundance in northern deciduous temperate forests and that lianas may further increase in abundance and impact if the severity of forest fragmentation intensifies," the researchers said.

CO2 Science, an online magazine published by the Center for the Study of Carbon Dioxide and Global Change—which opposes aggressive prevention—opined on July 4 that the warming and increased CO2 fertilization of the Londre and Schnitzer study period accelerated tree growth in forest interiors enough to deprive lianas of light.

If so, poison ivy would seem not to be the only plant able to benefit from rising CO2 levels. But the implications for, say, global food supply are hardly frightening. They probably won't make the news.

(Online July 6, 2007; author's e-mail:

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