Vines are crowding out trees in tropics
Published 4:00 am Wednesday, February 23, 2011
LOS ANGELES — Vines may be proliferating at the expense of trees in tropical forests across the Americas, scientists have found. This shift in abundance could affect the water in the ecosystem and how carbon is stored in the plants, potentially drying out forests and resulting in more carbon dioxide in the Earth’s atmosphere.
The report, published online last week in the journal Ecology Letters, surveyed eight studies on the state of woody vines in tropical forests from the Savannah River system and the Congaree National Park in South Carolina to an area in the central Amazon about 50 miles north of Manaus, Brazil. They found that in all forests, vines were increasing in abundance, biomass or both.
“Global change is happening everywhere — and this is one of the first signs for tropical forests,” said Stefan Schnitzer, an ecologist with the Smithsonian Tropical Research Institute in Panama, who conducted the review with Frans Bongers of Wageningen University in the Netherlands.
Woody vines evolved to escape the dimly lit confines under the trees in tropical forests by climbing up tree trunks and branches, then spreading their network of leaves over the dense treetops that make up the forest canopy. They block sunlight from the tree leaves they cover and compete with the trees for water and nutrients.
Generally, Schnitzer said, about a quarter of the plants in a tropical forest will be vines. Several studies in the last decade suggested that vines are growing faster and becoming more abundant. Before this study, Schnitzer added, no one had compiled the data to carefully look at the issue.
The scientists noted, for example, that a 2010 study on Panama’s Barro Colorado Island found that vines infested 75 percent of the crowns of trees in 2007, more than double the 32 percent rate in the late 1960s. A 2008 study of a forest in French Guiana found that from 1992 to 2002 vine abundance rose 1.8 percent while tree abundance dropped by 4.6 percent.
Several factors may be working in the vines’ favor, Schnitzer said. During the dry season, trees slow their rate of photosynthesis, using sunlight to create energy out of water and carbon dioxide. Vines don’t, and can therefore keep growing.