Backpacker Magazine – September 2007

Super Poison Ivy is Coming

More potent poison ivy is on the way, plus fast-growing weeds that will change the face of Eastern forests.

by: The Backpacker Editors

Picture poison ivy growing like it's jacked on steroids. Or kudzu sprouting like a mutant monstrosity in a Japanese horror flick, strangling the trees all around it. Sound far-fetched? Not if carbon dioxide levels keep rising. A sweeping prognosis for eastern woodlands can be tricky, but one important 2006 study hints at what could be in store.

Jacqueline Mohan, an ecologist with the Ecosystems Center at the Marine Biological Laboratory in Woods Hole, MA, used a duct network to boost CO2 levels in a North Carolina forest by 200 parts per million, 50 percent higher than present levels. Her goal was to mimic the concentration expected by the year 2050 if current emission rates continue worldwide.

In her study, poison ivy grew 150 percent faster and three times larger than normal, and its rash-causing oil, urushiol, increased in potency. And if that's not nightmarish enough, the evil weed grew five times faster than most of the area's trees. Kudzu (below) is another big winner in a CO2-dense forest. This exotic Japanese vine has already overgrown many Southeast forests, burying even tall trees under thick mounds of green and wreaking havoc for trail crews. Lacking a tree's trunk-and-branch network, the vines' carbon intake is spent mainly on growing new leaves, which collect yet more carbon and sunlight. Cold-sensitive kudzu has marched north with this advantage, following changing frost zones, and is now firmly entrenched as far north as Delaware.

"It's sobering that carbon dioxide increases can favor pests and weeds, those plants we'd least like to see succeed," comments ecologist Bruce Hungate of Northern Arizona University. The big worry for backpackers: that kudzu and other woody vines like English ivy will monopolize soil nutrients, choke out new tree growth, and alter Eastern forests forever.