In the tropics of the Western Hemisphere, ecologists had the impression that native vines were choking the daylights out of the trees. Now they know the vines are indeed taking control.
"By pulling together data from eight different studies, we now have irrefutable evidence that vines are on the rise not only in the Amazon, but throughout the American tropics," said Stefan Schnitzer of the Smithsonian Tropical Research Institute in Panama, in a press release by that organization. Schnitzer's work, published in Ecology Letters, appeared online on Feb. 14.
Woody vines, called lianas, compete with trees for water, nutrients and sunlight. The native vines grow high into the canopy by exploiting trees' height and strength for support. So an increase in their numbers could mean trouble for the trees -- shifting the dynamics of forest life.
"We are witnessing a fundamental structural change in the physical make-up of forests that will have a profound impact on the animals, human communities, and businesses that depend on them for their livelihoods," said Schnitzer, who is also an associate professor at the University of Wisconsin at Milwaukee.
The proportion of vines in tree crowns has more than doubled over the past 40 years on Panama's Barro Colorado Island. In French Guiana, the amount of vines increased 60 percent faster than trees from 1992 to 2002. Similar observations were made in Brazil, Bolivia, and even subtropical forests of South Carolina.
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On the other hand, studies in Africa did not observe increased vine growth.
The U.S. National Science Foundation last yearawarded Schnitzer $890,000 to help investigate the distribution and dominance patterns of lianas and trees.
Schnitzer explains that there are several possible explanations for why the vines are turning the forests into jungles. Vines have a high tolerance for droughts; they recover quickly from natural disturbances, such as hurricanes and El Niño events, and are among the first to return to the scene after logging, agriculture and road construction tears into the environment.
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Increased carbon dioxide levels may also be giving vines growth spurts that they can use more advantageously than the trees. But whatever the reason for the vine take-over, the outcome is looking dim for trees.
IMAGE 1: Bauhinia is a common tropical vine. (Beth King, Smithsonian Tropical Research Institute)
IMAGE 2: Stefan Schnitzer studies lianas, or woody vines. (Marcos Guerra, Smithsonian Tropical Research Institute)
Tags: Plants
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