Scientists have identified long-standing concentrations of cacao, acai, and brazil nut trees near archaeological sites in the Amazon rain forest—a discovery that suggests pre-Columbian peoples were cultivating useful species for a very long time, in some cases more than 8000 years ago. The researchers published their findings today, March 2, in the journal Science.

The study is the result of work by hundreds of ecologists and social scientists from around the world. The team overlaid more than 1000 forest surveys with a map of more than 3000 archaeological sites across the Amazon, focusing on 85 species that are currently or have historically been used by Amazon peoples for food and shelter.

Hatahara Site with Manacapuru phase urns and anthropogenic dark soils, ca 600 CE © Val Moraes—Central Amazon Project

 
Those 85 domesticated species appeared to have a real edge over their fellow trees. In particular, 20 of them were five times more likely to appear on the surveys than other species, and were both more common and more diverse than other trees in the regions surrounding ancient archaeological sites. From these trees, people took food and shelter. To these trees, they gave dominion over other species.

Forest with domesticated hyperdominant species (Bertholletia excelsa and Euterpe precatoria) on anthropogenic dark soils. Both species have a long history of human use (c) Carolina Levis.

 
Was human cultivation of these trees responsible for the trees’ success? Or was the trees’ success what made them attractive targets for domestication? The researchers admit that it’s sort of a “chicken-and-egg question.” Still, they write, “the first alternative is more probable, given the sum of other evidence that also supports the influence of past societies in increasing domesticated species abundance and richness in forests.”

Team leader Carolina Levis is a Ph.D. student at Brazil's National Institute for Amazonian Research (INPA) and at Wageningen University and Research Center in the Netherlands. “For many years, ecological studies ignored the influence of pre-Columbian peoples on the forests we see today,” she said in a statement. Yet domesticated species “are vital for the livelihood and economy of Amazonian peoples and indicate that the Amazonian flora is in part a surviving heritage of its former inhabitants."

The long-standing relationship between local people and domesticated trees continues to this day. Co-author Flávia Costa of INPA noted that the forest regions with the highest concentrations of domesticated trees are also the same ones losing the most ground to deforestation and development.

“Southwestern and eastern Amazonia may not be considered classical biodiversity hotspots,” she said, “but should be top conservation priorities as reservoirs of high value forests for human populations.”