ecology: “undisturbed” rainforests disturbed after all

The Amazonian rainforests are changing, even in areas untouched by human activities such as logging, clearing, or burning — and rising levels of carbon dioxide may be to blame. Over the past 20 years, the species composition of the “pristine” Amazon has altered to favor tall, fast-growing trees, a team of US and Brazilian researchers reported in the March 11 Nature. They suspect that the carbon dioxide, which plants use for growth, is fertilizing the rainforest, giving the faster-growing species the advantage over slower-growing neighbors, which are in decline. The authors warn that this composition change may affect the rainforests’ ability to absorb carbon dioxide,implicated in global warming: Faster-growing trees produce wood less dense than slower-growing varieties, meaning they’ll store less carbon. “The changes in Amazonian forests really jump out at you,” lead author William Laurance of the Smithsonian Tropical Research Institute in Panama stated in a press release. “It’s a little scary to realize that seemingly pristine forests can change so quickly and dramatically.” He added: “If you change the tree communities, then other species — especially the animals that feed on and pollinate the trees — will undoubtedly change as well.”

This news brief appeared in the Discoveries column of the Boston Globe’s Health/Science section on 3/16/2004.