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updated: 2/8/2011 10:20 AM

Plants gone wild: How vines spread, grow and take over

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By Valerie Blaine

Some plants are famous for their breathtakingly beautiful flowers. Some draw attention by their height or their girth. But some plants go largely unnoticed. That is, until something goes awry.

Vines are plants that are going awry. It's not your imagination: that wild grape vine really is smothering your hedge. That bittersweet is really choking your oak tree. Those poison ivy leaves really are enormous.

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Ecologists have taken notice of the vines-on-steroid symptoms, and there's a growing body of evidence that many vines are getting "bigger and badder." The culprit appears to be increased levels of carbon dioxide.

Take poison ivy, for example. A study conducted at the Ecosystems Center in Woods Hole, Mass., looked at poison-ivy growth in response to carbon dioxide levels from 1999 to 2004.

"We went out and measured poison ivy for six years and found that poison ivy shows a tremendous, big growth enhancement from the elevated CO2," said research scientist Jacqueline Mohan. "Poison-ivy grows 149 percent faster (with increased levels of CO2)."

As if that weren't discomforting enough, the Woods Hole study found that in addition to increased growth, the chemical that causes the nasty reaction on human skin, urushiol, became more virulent.

United States Department of Agriculture plant physiologist Lewis Ziska reported results this year from additional data on poison ivy. The new data support the hypothesis that poison ivy is spreading more vigorously, appearing in new habitats, and is increasingly allergenic.

"The plants are spreading faster, growing larger, showing up in new places and becoming more toxic," reported National Public Radio's Michele Norris in a July 2010 interview with Ziska. "It's the kind of thing that's so scary, it almost deserves its own soundtrack."

What about other vines in our area? Oriental bittersweet, an invasive nonnative plant, has made its way into many of our woodlands, spreading readily by berry-loving birds and unwitting people who use bittersweet for decorations in the fall. Oriental bittersweet is a vigorous vine that grows so large it can be mistaken for the tree it grows on. The sheer weight of the vine causes trees to be uprooted and makes them more susceptible to windfall in storms. It also girdles the trunks of large trees, thereby hastening their decline.

Trumpet vine, Japanese honeysuckle, and the notorious kudzu have also shown an increase in growth lately. These vines have a more southerly distribution but their ranges may extend northward with a warming climate. Elevated CO2 combined with longer and warmer growing seasons appear to be a boon to these pernicious plants.

The prevalence of increasingly vigorous vines in the south is a cause for much concern and consternation. A study conducted by The Ohio State University published in 2007 reported "that vines are indeed growing at unprecedented rates in the Southern United States," according to Science Daily. "Researchers charting the growth of vines in two forests in South Carolina found up to a 10-fold increase in the number of vines in just two decades."

In 2008 a research report published by University of Wisconsin-Milwaukee ecologist Stefan Schnitzer produced similar results. Schnitzer looked at growth rate of tropical vines at higher levels of CO2 and during droughts. His research supported other studies correlating increased vine growth with increased CO2. But he also found that tropical vines grew vigorously during seasonal droughts, giving them a competitive advantage over trees.

"In fact," reported Science Daily, "he found the growth rate of (vines) is seven times that of trees in dry conditions."

And, because vines do not sequester, or store, CO2 as well as trees do, "vines may cause a net forest-wide loss in carbon."

The phenomenon of vine growth is changing the makeup of our woodlands. Ever larger and stronger vines are altering habitat, particularly along the edges of woods and trails. This may be helpful to some species of birds, the "skulkers" like migrating Connecticut warblers, but it may be a detriment to other species that need easy ingress and egress along the forest edge.

The changing growth patterns of vines presents a challenge to both natural areas managers and laymen alike. What can you do? Take extra care to avoid poison ivy. Eradicate invasive vines from your fence or hedgerow. Refrain from buying Oriental Bittersweet for fall decorations.

These vines will not wind their way under your doors and window sills as did "The Blob" in the '50s sci-fi flick. They won't grow overnight like Jack's beanstalk up to the land of a cantankerous giant in the sky. But you've heard it through the grapevine, the uprising of the vines is here.

• Valerie Blaine is a naturalist with the Forest Preserve District of Kane County. You may reach her at blainevalerie@kaneforest.com

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