In this six-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.

—J. E. Mohan, L. H. Ziska, W. H. Schlesinger, R. B. Thomas, R. C. Sicher, K. George, & J. S. Clark, “Biomass and toxicity responses of poison ivy (Toxicodendron radicans) to elevated atmospheric CO2”, Proceedings of the National Academy of Sciences U.S.A. 103 (24) 9086-9089, (2006).

Very early spring: half-inch shoots of bloodroot appeared this morning near the creek, and two shy half-open hepatica blooms. The maples are awash in burnished flowers. The bugs are back. And soon the new leaves of poison ivy, narrow and red, will appear like snakes’ tongues among the rocks and roots.

It looks to be a good year for poison ivy—actually, a good century. With carbon levels in the atmosphere increasing, research by J. E. Mohan and colleagues suggests that poison ivy, already an abundant plant, will become even more so. And that it will become, alas, more poisonous: that is, it will contain a more potent form of urushiol, the chemical that irritates human skin. . . .