Poison Ivy on Steroids?

If you’ve noticed anything different about the poison ivy you encounter while hiking or working on a trail, you’re not dreaming. Reports issued last year (2007) provide documentation on increases in:

• Poision ivy growth
• The average size of poison ivy leaves
• The potency of urushiol oil in poison ivy

Further, each of the separate studies quoted in the New York Times article¹ point to the same culprit as the responsible agent for these issues.

The Noxious Weed

Poison ivy plants—the stem and leaf size as well as the amount of oil (urushiol) in them—have significantly increased in average size since the 1950s. According to a study published in Weed Science (yes, that’s the title of this scholarly online review):

After about eight months, leaf size, stem length and weight and oil content of the plants raised at current carbon-dioxide levels were, on average, 50 percent to 75 percent higher than the plants under the 1950’s conditions, according to the study … Not only did the higher CO₂ level double the growth rate, but it made for hardier plants that recovered more quickly from the ravages of grazing animals.²

Urushiol

Study results don’t appear to be conclusive as yet, but a Duke University³ study points to the probability of increased potency of the urushiol oil, to which most of us are allergic, within the past decade.

Not Steroids: CO₂

Despite my pathetic attempt to write an attention-grabbing title slug for this article, steriods are not responsible for these issues. Rather, the studies presented so far point to the increase in atmospheric CO₂ and its ability to stimulate growth in poison ivy, poison oak, poison sumac, and other weeds commonly found in both Europe and North America. Of course, rising CO₂ levels are also attributed to the phenomena of global warming.

Sources

¹Poison Ivy, Now With Stronger Poison by Mike Nizza, The Lede (New York Times), June 27, 2007

²Biomass and toxicity responses of poison ivy (Toxicodendron radicans) to elevated atmospheric CO2, Jacqueline E. Mohan, Lewis H. Ziska, William H. Schlesinger, Richard B. Thomas, Richard C. Sicher, Kate George, and James S. Clark. Contributed by William H. Schlesinger, April 22, 2006 (Download the article: Duke University article on Poison Ivy<)

³Rising Atmospheric Carbon Dioxide and Potential Impacts on the Growth and Toxicity of Poison Ivy (Toxicodendron Radicans), L.H. Ziska, R.C. Sicher, K. George, and J.E. Mohan
Author affiliations. USDA-ARS, Crop Systems and Global Change Laboratory, Beltsville, MD 20705; third author: Ecosystems Center, Marine Biological Laboratory, Woods Hole, MA 02543. Weed Science, Volume 55, Issue 4 (July 2007) pp. 288–292 DOI: 10.1614/WS-06-190