From the subtropical forests of South Carolina, to the tropical forests of Panama, and the rainforests of South America, vines are taking hold. The proportion of liana vines to trees in Panama has more than doubled in the last 40 years and in French Guiana, the concentration of vines increased 60 percent more than trees between 1992 and 2002. Similar reports have come from Brazil, Bolivia, and elsewhere.
The trend indicates that the tropical forests of the Americas are undergoing a fundamental structural shift, one that has serious implications for the water cycle and carbon storage processes.The question of whether vines were actually becoming more common in the American tropics is a contentious one. The idea was first suggested in a study by Oliver Phillips, a professor at the University of Leeds in the UK, that claimed vines were becoming more common in the Amazon. However, more comprehensive research was needed to provide definitive evidence of the alarming trend.
Stefan Schnitzer, a research associate at the Smithsonian Tropical Research Institute in Panama and associate professor at the University of Wisconsin at Milwaukee, conducted just such an inquiry. "By pulling together data from eight different studies," he explains, "we now have irrefutable evidence that vines are on the rise not only in the Amazon, but throughout the American tropics."
Still, there is no consensus as to why vines seem to be outpacing trees in the region. Some research has suggested that they are better able to weather drought, climactic events like hurricanes and El Niño, and disturbances from humans. At the same time, vines in North American forests and Africa, research has shown, do not have the same advantage they do in the tropical forests of the Americas.
Regardless of its cause, the consequences of this trend are severe. "We are witnessing a fundamental structural change in the physical make-up of forests," Schnitzer says, "that will have a profound impact on the animals, human communities and businesses that depend on them for their livelihoods."
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