How'd They Do That?: Poison Ivy and Carbon Dioxide Studies

When I was visiting BoingBoing last spring, I told y'all about some research being done by Lewis Ziska from the USDA and Jackie Mohan from the University of Georgia on how poison ivy responds to rising levels of carbon dioxide in the atmosphere. (Answer: In a way that kind of sucks for people.)

What I didn't tell you was how the scientists figured out that CO2 makes ivy grow incredibly fast, and problematically poisonous. While some of the evidence comes from controlled studies done in a tidy, little lab, there's more to it than that.

These look a bit like high-voltage electricity transmission towers, or a Stonehenge-style monument built for some forest-dwelling version of Burning Man. Suffice to say, they are neither. Instead, they're actually giant structures of PVC pipe that Ziska, Mohan and their colleagues built to test the effects of CO2 on wild forest. The base rings are a 100 feet in diameter and vertical piping goes up to the very top of the forest canopy. Six towers total, in use from 1998 until 2004. Three blowing air. And three blowing a heady mix of air and carbon dioxide that pumped parts of the forest up to the ambient CO2 levels predicted for the year 2050.

And that was how the team learned something really neat. When I posted about this research before, somebody here asked whether other plants, besides poison ivy, got the same growth spurt from CO2 exposure. At the time, I didn't know. But talking to Mohan more, I found out that there's at least some basis for comparison. In particular, let's talk trees, turkey.

Both trees and poison ivy grew faster, when exposed to higher concentrations of CO2, than their oxygen-only counterparts. But poison ivy grew faster than the trees--150% faster, in fact, compared to a 20% increase in tree growth. The difference, according to Jackie Mohan, is that poison ivy, like all vines, is a bit lazy.

"Vines don't need to devote so much of their CO2 resources to growing these big, woody trunks," she says. "Instead, they can devote that to growing more green leaves, which increase photosynthesis some more. And it becomes a cycle."

This study was the first time the effects of CO2 had been researched like this in the wild. The next step will be to see how the growth of poison ivy differs between rural areas and cities, where CO2 levels are naturally higher thanks to a higher concentration of cars and industrial pollution. Mohan is working on that now. It's too early to tell, but she expects to find that the urban ivy is bigger and tougher than its country mouse cousin.

All images courtesy Jackie Mohan and Duke University.