Why poison ivy loves climate change

A MARTÍNEZ, HOST:

When it comes to climate change, poison ivy seems to be a big winner. WBUR's Gabrielle Emanuel reports.

PETER BARRON: So here I'm just using two garden forks, sticking them in the ground. It's a slow aerobic kind of exercise.

GABRIELLE EMANUEL, BYLINE: Peter Barron's job is removing poison ivy, and his promise is he'll do it with no chemicals. His clients know him by his nickname, Pesky Pete. Today he's working in a wooded back garden in central Massachusetts, using just his hands, a few tools and gloves that go up over his elbows.

BARRON: Someone said to me, cow-birthing gloves. I was like, oh, yeah, cow-birthing gloves - that's what I'll call them from now on.

EMANUEL: Even with the gloves, Pesky Pete says he gets that itchy, blistering rash about 10 times a year. But unlike most, he loves this plant. Every year, he takes pictures of the first poison ivy leaves he sees. At that stage, it's three tiny red, shiny leaves.

BARRON: When I first started, it was May 10 or May 11, and I was so excited. I was like, wow, this is going to be great. I'm going to do this.

EMANUEL: Fourteen years later, he says, the season starts almost a month earlier.

BARRON: In 2023, my first sightings of poison ivy was on April 18.

EMANUEL: His guess is that warmer weather explains the shift. Scientists have also noticed changes. In the late '90s, some researchers hatched an ambitious plan - pump carbon dioxide into the air around large circular forest plots to simulate what they thought 2050 would be like.

WILLIAM SCHLESINGER: Sort of a cylinder of the future is the way I like to call it.

EMANUEL: William Schlesinger is now an emeritus professor at Duke University. His team watched over this forest laboratory for years. They found that almost everything grew faster with more CO2. But poison ivy was the speediest of all, growing 70% faster than without the extra carbon dioxide.

SCHLESINGER: Oh, it's - it was the max. It topped the growth of everything else.

EMANUEL: And that's not all. The CO2-enhanced poison ivy became more toxic, and the individual leaves got bigger. In another ongoing study, Jackie Mohan of the University of Georgia is looking at how poison ivy responds to warmer soil.

JACKIE MOHAN: My heavens to Betsy, it's taking off in terms of growth.

EMANUEL: She says it has to do with a fungus by the vines' roots that likes the warmth and helps feed poison ivy. Plus, the vines don't need a sturdy trunk or branches. They can put all their energy into getting bigger.

MOHAN: Bigger and nastier.

EMANUEL: In the suburbs west of Boston, Dr. Louis Kuchnir sees just how nasty it can be.

LOUIS KUCHNIR: Some people will have a tremendous allergic reaction to poison ivy, and others just don't seem to mount any allergic reaction at all.

EMANUEL: He works with a team of 10 dermatologists.

KUCHNIR: Every one of us sees it every week. And I mean the kind of cases where people can't sleep and are covered with blisters.

EMANUEL: Kuchnir's noticed an uptick in the past few years.

KUCHNIR: The kind of poison ivy that takes people to the emergency rooms - that has been getting more common.

EMANUEL: He suspects that's due to the pandemic nudging people into their gardens and onto trails. Gwyn Loud is on the board of the Lincoln Land Conservation Trust, and she's been paying close attention to the plants and animals for decades. With gloves on, she pulls a bit of poison ivy, now deep green since it's later in the summer.

GWYN LOUD: So here's some right here.

EMANUEL: Are you able to quantify how much it's grown in the 55 years you've lived here?

LOUD: There is a lot more all over the place.

EMANUEL: And she's noticed another change too. The leaves can be the size of a book.

LOUD: Look at these huge leaves down here - huge.

EMANUEL: Loud says she wishes there was hard data, but from what she sees, it's not good news for the roughly 80% of people who are allergic to poison ivy. And scientists worry it could disrupt the delicate balance in the forest.

For NPR News, I'm Gabrielle Emanuel. Transcript provided by NPR, Copyright NPR.

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