How Has Climate Change Affected Poison Ivy? Ask this Chatham Grad.
Some of the poison ivy specimens used by Alyssa McCormick for her research into how climate change has affected the plant. (Courtesy of Alyssa McCormick)
Alyssa McCormick ’22 had never gotten a rash from poison ivy until she started touching the three-leaf plant every day for a whole summer—on purpose.
“I actually wasn’t using gloves,” she said. “It would have made what I was doing a lot harder. I just was not concerned, but eventually... I did start being concerned.”
Gloves initially seem like they would have been the minimum precaution against urushiol, the resin that oozes from this woody vine and causes the itchy, red, blistered skin that has dampened countless summer vacations. But McCormick couldn’t wear gloves for fear of damaging her poison ivy specimens, some of which dated back to the 1830s and were housed in the Carnegie Museum of Natural History’s herbarium records.
By comparing those old samples against others from the 20th and 21st centuries, McCormick – along with Carnegie Museum researchers Molly Ng and J. Mason Heberling, plus Falk School of Sustainability & Environment Professor Ryan Utz – was able to learn how rising carbon dioxide levels in the atmosphere caused by human activity affected poison ivy in the post-industrial age.
What McCormick found was that poison ivy has changed in the past two centuries. Leaves were larger in area. Pores under the leaves, which aid in the absorption of CO2, were more densely packed together. And the plant couldn’t use water as efficiently as it once could.
These findings, published last month in the American Journal of Botany, confirmed some of the ideas formed in a 2006 study published in Proceedings of the National Academy of Sciences, which put poison ivy plants in a controlled growth chamber and supplied them with CO2. What that study concluded was poison ivy would become “more abundant and more ‘toxic’ in the future” due to rising CO2 levels in Earth’s atmosphere.
What that study lacked, however, was an answer to how poison ivy has already changed in a world that currently has higher levels of atmospheric carbon dioxide than it did 200 years ago. That’s where McCormick’s research came into play.
“The big take-home message of our paper is that herbarium specimens allow us to explore questions that we wouldn’t be able to explore just by going out into the woods and doing field work, because it spans over such a great period of time,” she said.
During her summer internship at the Carnegie Museum of Natural History, McCormick was able to look at hundreds of poison ivy specimens, upon which she made a one-centimeter mark with clear nail varnish on the underside of the leaf. Then, she allowed it to dry before she viewed the area under a microscope.
“I was surprised how much I grew attached to my microscope slides,” she said. “I really became very invested in something that would seem very mundane to other people.”
Stomata magnified 400 times under a microscope. (Courtesy Alyssa McCormick)
By looking under a microscope, which magnified the specimens by 400 times, she was able to take images to closely study poision ivy and other similar plants, such as poison sumac, staghorn sumac, and Virginia creeper. She took four images of each of the 500-plus specimens.
“I thought it was really, really cool to see how old the specimens were. It was crazy just to touch a plant that existed in the 1860s,” she continued, before adding with a laugh: “And I think I grew attached to my microscope slides because they were my best friends for the whole summer.”
Mick Stinelli is a Writer and Digital Content Specialist at Chatham University. His writing has previously appeared in the Pittsburgh Post-Gazette and 90.5 WESA.