Unlikely Fan of Global Warming: Poison Ivy

Global warming may spell bad times for polar bears but it seems to be a boon to poison ivy. A six-year experiment to find out how increased levels of carbon dioxide affect forests uncovered a surprising result: In the area used for the experiment, poison ivy grew like crazy. Melissa Block talks with ecologist Jacqueline Mohan is a scientist at the Ecosystems Center in Woods Hole, part of the Harvard Forest in central Massachusetts.

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MELISSA BLOCK, host:

You know the saying, leaves of three, let them be? The memory device to help you steer clear of poison ivy. Well, global climate change may make it harder to steer clear. A new report says poison ivy thrives on global warming. And researcher Jacqueline Mohan joins us to explain why.

Ms. Mohan, you spent six years on an experiment measuring all this. What did you do?

Ms. JACQUELINE MOHAN (Ecosystems Center in Woods Hole): I measured the growth and the survivorship as well as the population biomass of the growth of the whole group of poison ivy at the Duke Forest face experiment. That's where we raised carbon dioxide concentrations to simulate what we expect the globe to reach towards the middle of this century.

BLOCK: Now, how do you raise the carbon dioxide concentrations?

Ms. MOHAN: What it basically involves is laying giant PVC piping on the ground around chunks of forests or plots of forests. So we have three control plots where we just blow in normal air and three elevated plots where the air simulates what the globe will reach, again, about the middle of this century.

BLOCK: Ok, and you were particularly looking at what would happen with poison ivy. What'd you find out?

Ms. MOHAN: So, we went out and measured poison ivy for six years and found that poison ivy shows a tremendous, big growth enhancement from the elevated CO2. Poison ivy grows 149 percent faster.

BLOCK: So, 149 percent faster when you boosted the carbon dioxide levels?

Ms. MOHAN: That's correct.

BLOCK: And was that something you could see? You could actually look at it and say, wow, this stuff is really going crazy?

Ms. MOHAN: You could see - a trained scientist could definitely see it. It was quite noticeable. My colleagues did work on the phytochemical, the sort of poison response. And they found, rather surprisingly, that the carbon-based compound, called urushiol, that makes the poison ivy poisonous, actually reverts to a more poisonous form under high CO2.

BLOCK: So what you're ending up with is more poison ivy, healthier poison ivy and then it's also more toxic?

Ms. MOHAN: That's correct.

BLOCK: That sounds like a pretty scary scenario.

Ms. MOHAN: Yeah. It's nasty. I, myself, am very sensitive to poison ivy now. I wasn't before I began this research, but a U.S. Forest Service study estimates that about 80 percent of humans are allergic to urushiol. I caution people, even if you think you're not allergic to poison ivy because you haven't gotten it yet, you probably are allergic. It's just a matter of time before you're exposed to it enough.

BLOCK: You know we're now in full poison ivy season and I'm betting that you and your colleagues have come up with some strategies for dealing with the reactions when you come into contact with it.

Ms. MOHAN: Well, my first strategy is always prevention. I wear latex gloves, multiple layers of latex gloves, which I would duct tape to the sleeves of my shirts. When I do get poison ivy, as I do now, I personally just use vitamin E. I find that that's a pretty effective treatment. But I have many colleagues who've gotten so allergic to it over the years, if they get poison ivy they have to be rushed to the hospital.

BLOCK: Wow.

Ms. MOHAN: Yeah. And they started out not so allergic to it.

BLOCK: And the vitamin E, you just put it right on the blisters themselves?

Ms. MOHAN: I put it right on the blisters, yes.

BLOCK: And it works?

Ms. MOHAN: It seems to work. I mean, for me it's better than doing nothing. And then I cover it, of course, with a bandage.

BLOCK: Well, Jacqueline Mohan, thanks very much for talking with us.

Ms. MOHAN: Thank you very much. I appreciate your interest in this work.

BLOCK: Jacqueline Mohan was lead investigator for the study Biomass and Toxicity Responses of Poison Ivy to Elevated Atmospheric CO2, published this week in the proceedings of the National Academy of Sciences.

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