Rain forest plants may change radically

Rain forest plants may change radically

By Teresa Riordan

WASHINGTON (Reuter): Plant life in virgin tropical forests may be changing radically, according to a report by a leading biodiversity expert.

Some scientists theorize that the changes may result from rising carbon dioxide levels in the Earth's atmosphere.

Studying changes over time in the plant inventories of 19 remote tropical rain forests worldwide, Alwyn Gentry found the rate at which trees are dying and growing is accelerating.

A more rapid turnover rate would favor fast-growing, light- loving trees and vines and nudge out shade-tolerant hardwoods, according to the report.

It was drawn up by Gentry and his former graduate student Oliver Phillips, a postdoctoral researcher at the Missouri Botanical Garden in St. Louis.

Gentry, the world's foremost expert on Amazonian tropical plants, died in a plane crash in Ecuador last August with Ted Parker, the leading expert on the birds of South America.

Commenting on the study's findings, Phillips told Reuters: "We speculate that if turnover rates continue to increase, we will see a dramatic transformation of these forests."

He said such a transformation could endanger species which depend on the hardwoods for food or shelter and would have repercussions for already increasing carbon dioxide levels.

All trees absorb carbon dioxide through photosynthesis, the process by which plants use light to manufacture food, but trees with light wood absorb much less than dense wood trees.

Carbon dioxide is a greenhouse gas that can trap heat in the earth's atmosphere and which is thought to contribute to global warming.

The study by Gentry and Phillips appeared in a recent issue of the journal Science.

Old forests

Previously links have been made between the cutting down of old rain forests, which because of their slow-growing hardwoods absorb lots of carbon dioxide, and increases in carbon dioxide levels, which have gone up 15 percent since 1950. When trees die they release their carbon back into the atmosphere.

This is the first study to chronicle a change in the composition of old forests that have been physically undisturbed by human beings.

Scientists cautiously point out that the increasing turnover of tropical forest trees coincides with the carbon dioxide buildup.

"The change of carbon dioxide in the atmosphere is a likely cause" of this acceleration in the natural process of tree death and tree growth, Peter Raven, director of the Missouri Botanical Garden in Saint Louis, said.

The scientists found that among 14 of 19 sites the turnover rate was higher than it had been over the course of an average span of 15 years. At four of the sites, all in Amazonia, the turnover rate increased by at least one and a half times.

Stuart Pimm, a zoologist at the University of Tennessee, and Andrew Sugden, editor of the British-based Trends in Ecology and Evolution, speculate in a related Science article that old forest transformations threaten biodiversity of plant and animal species.

"A decrease in diversity over large areas is the most likely outcome," they wrote.