Resilient Rainforests

“How ‘Virgin’ Is Virgin Rainforest?” by K.J. Willis, L. Gillson, and T. M. Brncic, in Science (Apr. 16, 2004), American Assn. for the Advancement of Science, 1200 New York Ave., N.W., Washington, D.C. 20005.

The plight of Earth’s tropical rainforests—disappearing at a rate of almost 15 million acres a year, with up to two-thirds of the loss due to slash-and-burn farming—may not be as dire as everyone supposes. Evidence has begun to accumulate that many of these rainforests suffered the destructive intrusion of humans in the past, yet managed to recover.

Case studies in the three largest blocks of undisturbed rainforest—in the Amazon basin, the Congo basin, and Southeast Asia—“now suggest that prehistoric human activities were far more extensive than originally thought,” report the authors, all affiliated with the University of Oxford’s Long-Term Ecology Laboratory.

In the Amazon basin, recent studies indicate that the most fertile regions in the lowland rainforest have a type of soil that was formed by burning and agricultural activities 2,500 years ago. Such “terra preta” soils cover as much as 123,550 acres in central Amazonia. Emerging archaeological evidence from the Upper Xingu region of Brazil—which “now comprises the largest contiguous tract of tropical forest in the southern peripheries of the Amazon”—also shows extensive settlements between 400 and 750 years ago. “These were complex regional settlements indicating intensive management and development of the landscape and resulting in large-scale transformation of the forest to agricultural land and parkland,” Willis and her coauthors write. But after “catastrophic depopulation” during the 17th century, “extensive reforestation” took place.

Recent studies in the Congo basin and the Indo-Malay region of Southeast Asia tell similar stories of early human disturbance and subsequent forest regeneration.

The rate and extent of forest clearing today may be much greater, but “the process is comparable to prehistoric losses” in many cases, say the authors. “These tropical ecosystems are not as fragile as often portrayed and in fact are quite resilient.”