The Heat Is Online

CO2-driven Vine Growth Seen Choking Trees in Amazonia

Vines Spread, Choke Trees in Deepest Amazon Jungle

Reuters News Service, Aug. 14, 2002

LONDON (Reuters) - Jungle vines are spreading faster in South America's Amazon rainforest than before, choking trees and potentially slowing the forests' ability to soak up damaging greenhouse gases, scientists say.

The spread of woody vines -- like the ones Tarzan swings from in the movies-- is the first change in plant composition that scientists have recorded in the deepest virgin jungle, and suggests mankind is having more impact on delicate ecosystems than previously shown. A team of researchers from Bolivia, Ecuador, Peru and the United States, led by Oliver Phillips of Leeds University in Britain, counted and measured the vines, called lianas, in the primary rainforests of the Amazon.

They found that the "dominance" of lianas over trees had increased by between 1.7 and 4.6 per year over the last two decades of the twentieth century. "It's the first time that a changing composition has been observed in mature forests," Phillips told Reuters in a telephone interview. His team's findings are published in the British science journal Nature.

He said the growth in vines appeared to have been caused by greater concentrations of carbon dioxide, the "greenhouse" gas that most scientists believe is causing global temperatures to rise as a result of human activity. Plants absorb carbon dioxide in photosynthesis and scientists have predicted that as humans produce more of the gas, forests would grow to soak some of it up, a phenomenon called the "carbon sink," which could help ease global warming.

But Phillips said the additional carbon appears to benefit resource-hungry vines more than slower-growing trees, throwing off the balance in jungle forests. "What we think we were finding is the ecosystem responding, not just in growth but in a change in its composition. If you change an environmental driver like carbon dioxide concentration, some plants will do better than others," he said. As the vines weigh down trees and kill them, they can reduce the ability of the forest to soak up more carbon, making the problem of global warming even worse.

Other plant and animal species are also likely to have been affected by the increase in vines relative to trees. Different insects may pollinate vines rather than trees, different birds may eat the insects, and so on.

"The ecosystem's connected. You change one part and other parts are likely to change too," Phillips said. "It's a kind of example of how we can't predict how the world is going to respond to the changes we're causing."