A “fan” of World Climate Report sent us an email insisting that we feature too many articles showing biological benefits of elevated atmospheric carbon dioxide (CO2) levels. We were accused of featuring forests, grasslands, and agricultural crops, with no discussion of how elevated CO2 might enhance noxious members of the biosphere. The “fan” challenged us to do a feature on poison ivy, so in the spirit of fairness, we accepted the challenge and explore the world of higher levels of CO2, higher temperatures, and the impact on poison ivy. We imagine that just like plants the world over, poison ivy, too, will greatly benefit from an enriched atmospheric CO2 concentration.
We began with a quick web search on “Global Warming and Poison Ivy” and sat back and found over 90,000 sites! The first page of “hits” includes “Itchier Poison Ivy Tied to Global Warming,” “Poison Ivy Itchier, More Plentiful with Warming,” “Poison Ivy, Now With Stronger Poison,” “Unlikely Fan of Global Warming: Poison Ivy,” “With Global Warming Comes a Rash of Poison Ivy,” “Global Warming Causes Record Poison Ivy Season,” “Fire Ants, Poison Ivy, Deer Ticks: Global Warming’s Big Winners,” “Another Reason to Worry about Global Warming: More and Itchier Poison Ivy,” and on and on for 90,000 variations of the same theme. Someday we might look into the link to fire ants and deer ticks, but for now, poison ivy is the plant in the spotlight.
Poison ivy (Toxicodendron radicans) is a poisonous plant (not really a true “ivy”) that is well known for its production of urushiol, a clear liquid compound found within the sap of the plant that causes an itching rash in most people who touch it. Poison ivy is extremely common in New England, the Mid-Atlantic states, and throughout the Southeastern states. Although closely related to mango and cashews, poison ivy’s berries are toxic for almost all human beings but they are eaten and apparently enjoyed by different woodpeckers. Mother Nature has her reasons for creating poison ivy, but from a human perspective, Mother Nature did us no favor spreading this plant throughout the forests.
Sing along – “you can look but you better not touch … Poison Ivee-ee-ee-ee-ee”
Two major articles appeared in the literature providing a glimpse of how poison ivy will respond to a world of higher levels of atmospheric CO2 and potentially higher temperatures. The first is by seven scientists with Duke University, Harvard University, the Marine Biological Laboratory at Woods Hole, U.S. Department of Agriculture, and West Virginia University; the research was funded by U.S. Department of Energy (go figure their interest) and the National Science Foundation. Mohan et al. grew poison ivy (Toxicodendron radicans) for six years in an intact forest system in North Carolina with ambient (370 ppm) and elevated (570 ppm) atmospheric CO2 levels. The authors report
“Here we show that CO2 enrichment increased T. radicans photosynthesis by 77%, and increased the efficiency of plant water usage by 51% by reducing stomatal conductance. Elevated CO2 also stimulated the growth of poison ivy during the five growing seasons at the Duke FACE experiment. Although the average plant biomass in 1999 did not differ significantly between treatments, poison ivy grew faster with CO2 enrichment so that by 2004, ambient plants averaged 5.0 ± 0.6 g of dry weight and elevated CO2 plants averaged 8.1 ± 0.8 g, representing an average annual growth increase of 149% in elevated compared to ambient plants. This increase is notably larger than the 31% average increase in biomass observed for woody plants grown at two times the ambient CO2 concentration under controlled conditions (compared to 1.5 times ambient CO2 at the Duke FACE experiment), and the ~21% stimulation of overall net primary productivity in the first 5 years of the Duke FACE experiment.”
Mohan et al. summarize their research stating
“In this 6-year study at the Duke University Free-Air CO2 Enrichment experiment, we show that elevated atmospheric CO2 in an intact forest ecosystem increases photosynthesis, water use efficiency, growth, and population biomass of poison ivy. The CO2 growth stimulation exceeds that of most other woody species. Furthermore, high-CO2 plants produce a more allergenic form of urushiol. Our results indicate that Toxicodendron taxa will become more abundant and more ‘toxic’ in the future, potentially affecting global forest dynamics and human health.”
The global warming alarmists will love to learn that
“If Toxicodendron becomes both more abundant and more irritating to sensitive individuals, which include ~80% of the human population, it is likely that this plant will become a greater health problem in the future.”
“when you’re a sleepin’ Poison ivy comes a creeping all around”
The second article was published by Weed Science (who knew?) and was written by four of the six scientists from the previous piece. Ziska et al. grew poison ivy in controlled chambers with atmospheric CO2 maintained at 300, 400, 500, and 600 ppm. They found that after 250 days, “increasing CO2 resulted in significant increases in leaf area, leaf and stem weight, and rhizome length relative to the 300 ppm baseline with the greatest relative increase occurring from 300 to 400 ppm. There was a nonsignificant increase in urushiol concentration in response to CO2; however, because of the stimulatory effect of CO2 on leaf biomass, the amount of urushiol produced per plant increased significantly for all CO2 above the 300 ppm baseline.” They concluded
“Overall, these data confirm earlier, field-based reports on the CO2 sensitivity of poison ivy but emphasize its ability to respond to even small changes in CO2 above the mid-20th century carbon dioxide baseline and suggest that its rate of spread, its ability to recover from herbivory, and its production of urushiol, may be enhanced in a future, higher CO2 environment.”
“You’re gonna need an ocean of calamine lotion”
So there you have it—poison ivy will benefit from elevated CO2, and 90,000 websites and countless news reports have made sure people link higher levels of CO2 with pumped-up poison ivy. The next time you are at the health food store, have a look at all the medicinal plants that seem to benefit humans, and in virtually every case, those plants benefit from higher CO2 levels. Next head over to the grocery store produce section and the story is the same—all of those fruits and vegetables benefit from more CO2. Forests benefit, grasslands benefit, plants in the sea benefit, plants in the desert benefit, and on and on.
Keep that in mind as you read through the 90,000 sites on the future of poison ivy in a CO2 enriched world.
Mohan, J.E., L.H. Ziska, W.H. Schlesinger, R.B. Thomas, R.C. Sicher, K. George, and J.S. Clark. 2006. Biomass and toxicity responses of poison ivy (Toxicodendron radicans) to elevated atmospheric CO2. Proceedings of the National Academy of Sciences, 103, 9086-9089.
Ziska, L.H., R.C. Sicher, K. George, and J.E. Mohan. 2007. Rising atmospheric carbon dioxide and potential impacts on the growth and toxicity of poison ivy (Toxicodendron radicans). Weed Science, 55, 288-292.