Carbon Dioxide Escalation Alters Amazon Rainforest

BALBOA, Panama, March 12, 2004 (ENS) - A team of U.S. and Brazilian scientists has shown that undisturbed, old growth rainforests in central Amazonia are experiencing rapid changes in dynamics and species composition. While these forests are located far from human settlements, their changes are the result of rising levels of carbon dioxide (CO2) in the atmosphere caused by human activities, the scientific team has found.

Carbon dioxide levels have risen by 30 percent in the last 200 years as a result of industrial emissions, automobiles, and rapid forest burning, and much of this increase has occurred since 1960.

"The changes in Amazonian forests really jump out at you," said William Laurance, a U.S. scientist with the Smithsonian Tropical Research Institute in Balboa and lead author of the study. "It is a little scary to realize that seemingly pristine forests can change so quickly and dramatically."

The paper appears this week in the scientific journal "Nature."

An untouched portion of the Amazon rainforest is nevertheless affected by rising carbon dioxide levels in the atmosphere. (Photo courtesy NOAA)

For the past two decades, the research team studied the life patterns of nearly 14,000 trees in the central Amazon, scattered across a landscape of 120 square miles in area.

The scientists noticed the trend while documenting the effects of clearing the rainforest. They surveyed tree growth in 69 remote one hectare plots, intended as pristine controls to compare to changes in other areas, where humans are active.

"But suddenly the controls weren't acting like controls," Laurance says.

During the course of the study, most species of trees began growing faster. The forests also became more dynamic, with existing trees dying faster and being replaced by young new trees.

Even more important is that the species composition of the forest is changing.

"There clearly are winners and losers," said Alexandre Oliveira of the University of São Paulo, Brazil, another team member. "In general, large, fast growing trees are winning at the expense of smaller trees that live in the forest understory."

Amazonian central plain, Negro River watershed (Photo courtesy UNESCO)

Under these conditions, big, fast growing species of trees probably have an advantage over smaller trees and slower growing trees.

"Sadly, this could be a signal that the forest's ecology is changing in fundamental ways," Laurance said. "Tropical rainforests are renowned for having lots of highly specialized species. If you change the tree communities then other species - especially the animals that feed on and pollinate the trees - will undoubtedly change as well."

The problem could extend beyond loss of biodiversity, warns Laurance. The future lack of slower growing trees, which produce denser wood and foliage, could eventually lead to a drop in the amount of carbon dioxide that the rainforest removes from the atmosphere.

The scientist says his findings underline the importance of measures such as the Kyoto Protocol, which limits the emission of carbon dioxide and other greenhouse gases by industrialized countries. Laurance told "Nature" that he is angry at the United States' failure to ratify the treaty. "As a U.S. citizen, I am chagrined," he said. "We have enough information to know that we have to do something."

When President George W. Bush took office in 2001, he backed the United States out of the Kyoto Protocol originally signed under President Bill Clinton, saying it would be too expensive for the U.S. economy. With about five percent of the world's population, the United States emits some 25 percent of the world's greenhouse gases.