Humans Shaped the Amazonian Rainforest

"For many years, ecological studies ignored the influence of pre-Columbian peoples on the forests we see today". Left behind was a verdant, leafy legacy in the untold numbers of palms and other trees that had been cultivated across the Amazon.

This suggests that it's more likely that humans planted the trees where they would be convenient rather than basing their communities around where they naturally grew. They found the species were not only more likely to be present in general, but much more likely to be found close to ancient archaeological sites.

"So the Amazon is not almost as untouched as it may seem", said study researcher Hans ter Steege, a forest community ecologist at the Naturalis Biodiversity Center in the Netherlands and Free University of Amsterdam. These species dominated the mature Amazon forests as compared to the undomesticated species.

Led by Carolina Levis, a PhD candidate at Brazil's National Institute for Amazonian Research (INPA) and Wageningen University and Research Center in the Netherlands, researchers found strong evidence that tree species domesticated and distributed throughout the Amazon basin prior to the arrival of Europeans in 1492 are still playing a strong role in the Amazon's ecosystem. Southwestern Amazonia, where large stands of Brazil nut trees remain a foundation of local residents' livelihoods, is one such example.

The researchers reached the conclusion after analyzing trees at almost 1,170 sites across the Amazon and compared the data to a map of over 3,000 known archaeological sites representing former human settlements in the region.

The study focused on 85 tree species known to have been domesticated by Amazonian peoples for food, shelter, or other uses over the last several thousand years. Over the past 8,000 years, these trees were five times more likely to become the dominant species in the Amazonian forest than the species the humans had not domesticated.

"This lays to rest the long-standing myth of the "empty Amazon", says Charles Clement, senior researcher at INPA, Manaus, and a coauthor of the study. Early European naturalists reported scattered indigenous populations living in huge and apparently virgin forests, and that idea has continued to fascinate the media, policy makers, development planners and even some scientists. "But today the species is most prevalent in the southern areas of the rainforest". Numerous species are distributed widely today and dominate large swaths of the rainforest - a living legacy to the region's indigenous peoples.

They compared the results to a map of about 3,000 archaeological sites which represented ancient indigenous settlements.

Nevertheless, human activities influenced 30 percent of the plant distribution in the area which was largely inhabited by pre-Columbian populations which is the southwestern Amazon. But some researchers, including ecologist Crystal McMichael of the University of Amsterdam, say it's more likely that ancient South Americans domesticated trees just in certain parts of the Amazon. "Results of this study have important implications for conservation".

Over the past 300 years, modern Amazonian groups may have helped spread some domesticated tree species, Levis' group says. Two possible factors that were considered by the researchers were human influence or environmental conditions.

  • Carolyn Briggs