Has increased CO2 impacted the northerly limit of Eastern Climbing Poison Ivy over the last 50 years?

Background/Question/Methods

On August 31, 1960, Dr. William T. Gillis collected Eastern Climbing Poison Ivy (Toxicodendron radicans subsp. radicans) in Grafton County New Hampshire slightly south of the 44th latitude.  Gillis noted that this poison ivy plant climbing an American Elm (Ulmus americana) “…was probably the farthest north the climbing form occurs.”

A 2007 study by Dr.L.Ziska and Dr.J.Mohan, et al entitled Rising Atmospheric Carbon Dioxide and Potential Impacts on the Growth and Toxicity of Poison Ivy (Toxicodendron radicans) found that poison ivy growth and density has accelerated due to increased atmospheric CO₂.  According to a 2009 report in the journal Environmental Health Perspectives, “the concentration of atmospheric carbon dioxide has increased by 22% since 1960…”

 The question examined: What affect does the increased atmospheric CO₂ have on the northern limit of Eastern Climbing Poison Ivy growth as documented by Gillis in 1960?

Results/Conclusions

After obtaining an image of the sample collected by Gillis from the Beal Darlington Herbarium at Michigan State University (New Hampshire. GRAFTON CO: West Thornton, Gillis 4097;162991 MSU), I traveled from Philadelphia, PA to West Thornton, NH looking for the most northerly occurring Eastern Climbing Poison Ivy.

On September 24, 2010, I found a rhizome of the Eastern Climbing Poison Ivy plant found in 1960 which is now growing on a Common Chokecherry tree (Prunus virginiana)  2 meters north of the Elm observed by Gillis.  The Elm has been reduced to 1 meter tall root water sprouts. I collected a sample of this poison ivy plant which has been entered in to the Herbarium at Michigan State University (New Hampshire. GRAFTON CO: West Thornton, Mycka 398487 MSU).

Between September 25 and 28, 2010, I searched north of this site and beyond the 45th latitude but could not find Eastern Climbing Poison Ivy. However, as expected I did find Ryberg’s Prostrate Poison Ivy (Toxicodendron rydbergii) plants growing in both Lancaster and Colebrook, NH.

Despite the increased atmospheric CO₂’s affect on the growth and density of poison ivy, no significant change on the northern range limit of Eastern Climbing Poison Ivy was observed from 1960 to 2010.  It appears that the northern range of Eastern Climbing Poison Ivy has not been affected by the atmospheric CO₂ increase.