Increased carbon in atmosphere may explain bumper crop of poison ivy
Tuesday, August 31, 2010
It started with a slightly puffy eyelid in early summer, which I waved off as an inconsequential bug bite. The next morning, I couldn't ignore my son's symptoms when he appeared with two eyes swollen to slits, a bloated face and an itchy rash raging over his body.
Ah, poison ivy. How it torments with weepy rashes and maddening itchiness -- and may do so more and more.
That is what the experts say, and I can offer supporting testimony, at least for this season's crop.
"It is a good year for poison ivy," said Alonso Abugattas, the acting director of the Long Branch Nature Center in Arlington. "We've noticed it more in our park. I think it's the timing of the rain."
Or it may have to do with increasing carbon dioxide, or CO2, levels in the atmosphere, said Jacqueline Mohan, an assistant professor at the University of Georgia's Odum School of Ecology. According to a report in the journal Environmental Health Perspectives last year, the amount of CO2 in the atmosphere has grown by 22 percent since 1960, which may not be so good for humans but is great for poison ivy and other vines.
Mohan has been tracking poison ivy since 1998. In a study in the Duke Forest in Durham, N.C., she simulated the carbon dioxide content in the air 50 years ago, today and using projections for the year 2050. "Tree seedlings grew 8 to 12 percent more, with more C02," said Mohan. "Poison ivy grew 149 percent more. Poison ivy is getting bigger, faster and nastier."
Plants survive by converting carbons from carbon dioxide into carbohydrates through sunlight-fueled photosynthesis.
"Vines are particularly adapted to take advantage of higher CO2 in the atmosphere," said Mohan, since they "can increase their rate of photosynthesis to make more green leafy tissue," which allows them to grow more and put out even more leafy tissue. Trees, on the other hand, "have to devote much of their photosynthetic carbohydrate to creating woody, non-photosynthetic support tissues such as trunks and branches, which do not lead to further increases in photosynthesis."
Poison ivy is in the same plant family as cashews, pistachios and mangoes, which also cause skin reactions in some people. Native to the East Coast, the vine has shiny, dark-green leaves, often serrated and clustered in threes. In the fall, the leaves turn a handsome scarlet, prized by some botanical gardens. And birds are fond of its berries, which start out green and turn white. The vine grows along the ground, climbs up trees and can become a massive, hairy rope; in some cases, it buds into a bush.
"It can sprout and grow just about wherever seeds contact soil," said Jon Traunfeld of the University of Maryland Extension Service. "It can grow in deep shade or full sun."
Most people are allergic to the oil poison ivy produces, urushiol. The oil is present in all parts of the plant -- stems, berries and leaves -- during any season, which means that if you are working in the garden in the middle of November or bushwhacking through the woods in winter, you could develop a rash from coming into contact with poison ivy roots or some other remnant of the plants. Burning logs that are covered in poison ivy can cause respiratory problems for people who breathe in the smoke.
"Even in dead poison ivy the oil is still active," said Georgetown University professor of nursing and health studies Laura Anderko, a registered nurse with a PhD in public health. The age of the plant doesn't matter. "The Japanese have a 500-year-old poison ivy specimen that can induce a rash," said Lewis Ziska, a plant physiologist with the U.S. Department of Agriculture.