Carbon dioxide boosts poison ivy

Poison ivy, the bane of gardeners, hikers and little kids, may be on its way to becoming a more serious problem in the future.

It sounds like something out of a horror movie -- a stronger, more potent poison ivy rising in the wake of man-kind's environmental folly, like Godzilla born of a nuclear flash.

Recent studies have discovered that rising atmospheric carbon-dioxide levels favor some plants over others, among them such vines as poison ivy.

In studies conducted by U.S. Department of Agriculture Research Service, Lewis Ziska, a plant physiologist, compared the poison ivy growth rates between 1950 and today. The growth rate today was found to be 50 percent to 75 percent higher.

Additionally, urushiol, the chemical component in poison ivy that causes the rash, was found to be more virulent.

"There are essentially two kinds of urushiol, and higher CO2 levels favor the more virulent form," Ziska said.

Other factors in modern-day environmental degradation also favor the growth of poison ivy.

"It is rare to find poison ivy in an old-growth forest," Ziska said. "It cannot compete with the established tree canopy. Fragmented landscapes favor the growth of vines," he said.

As a consequence, poison ivy is more likely to spring up in urban areas -- those environments where humans are most likely to encounter it. Carbon-dioxide levels also are generally higher there, and nearby woodlands tend to be fragmented, supplying large areas of "edge habitat" where the vine thrives. The effects of an increase in temperature have not yet been explored.

Why vines are better able to utilize the increased carbon dioxide levels is one of the important questions the study has spawned.

"This is what we really want to find out," Ziska said. "We think and speculate that if you give vines more CO2 they can use it to make more leaves, while trees have to put their energy into producing wood. Vines can piggyback onto trees for support," Ziska said. "If you look at the growth rings, vines are growing 10 times faster."

Poison ivy is not the only vine behaving in this fashion. Consider that many of our most competitive weed species are vines: wisteria, ampelopsis, Japanese honeysuckle and that Southern icon, kudzu.

A study published in May 2006 that involved Duke University's Free Air CO2 Enrichment area in Duke Forest, where researchers pumped in elevated amounts of carbon dioxide over an extended period to study the effect on plants, found that poison-ivy vines in the carbon-enriched area grew 149 percent faster and had an urushiol concentration that was 153 percent higher than the control plants.

Ziska said another finding in the recent study was that the plant is better able to recover from grazing by deer and rabbits after it has been exposed to higher carbon-dioxide levels. Poison ivy is an important wildlife food. Birds and squirrels eat the highly toxic material without consequence.

"Giving carbon dioxide to plants is like giving them junk food," Ziska said. "They grow starchy and their chemistry changes."

A change that means those who enjoy the outdoors should sharpen their eyes for the "leaves of three."