If you think the Amazon jungle is completely wild, think again

Welcome to the somewhat civilized jungle. Plant cultivation by native groups has shaped the landscape of at least part of South America’s Amazon forests for more than 8,000 years, researchers say.

Of dozens of tree species partly or fully domesticated by ancient peoples, 20 kinds of fruit and nut trees still cover large chunks of Amazonian forests, say ecologist Carolina Levis of the National Institute for Amazonian Research in Manaus, Brazil, and colleagues. Numbers and variety of domesticated tree species increase on and around previously discovered Amazonian archaeological sites, the scientists report in the March 3 Science.

Domesticated trees are “a surviving heritage of the Amazon’s past inhabitants,” Levis says.

The new report, says archaeologist Peter Stahl of the University of Victoria in Canada, adds to previous evidence that “resourceful and highly developed indigenous cultures” intentionally altered some Amazonian forests.

Southwestern and northwestern Amazonian forests contain the greatest numbers and diversity of domesticated tree species, Levis’ team found. Large stands of domesticated Brazil nut trees remain crucial resources for inhabitants of southwestern forests today.

Over the past 300 years, modern Amazonian groups may have helped spread some domesticated tree species, Levis’ group says. For instance, 17th century v­oyagers from Portugal and Spain established plantations of cacao trees in southwestern Amazonian forests that exploited cacao trees already cultivated by local communities, the scientists propose.

Their findings build on a 2013 survey of forest plots all across the Amazon led by ecologist and study coauthor Hans ter Steege of the Naturalis Biodiversity Center in Leiden, the Netherlands. Of approximately 16,000 Amazonian tree species, just 227 accounted for half of all trees, the 2013 study concluded.

Of that number, 85 species display physical features signaling partial or full domestication by native Amazonians before European contact, the new study finds. Studies of plant DNA and plant remains from the Amazon previously suggested that domestication started more than 8,000 years ago. Crucially, 20 domesticated tree species — five times more than the number expected by chance — dominate their respective Amazonian landscapes, especially near archaeological sites and rivers where ancient humans likely congregated, Levis’ team says.

Archaeologists, ecologists and crop geneticists have so far studied only a small slice of the Amazon, which covers an area equivalent to about 93 percent of the contiguous U.S. states.

Levis and her colleagues suspect ancient native groups domesticated trees and plants throughout much of the region. 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. In the new study, only Brazil nut trees show clear evidence of expansion into surrounding forests from an area of ancient domestication, McMichael says. Other tree species may have mainly been domesticated by native groups or Europeans in the past few hundred years, she says.

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Editor’s note: This story was updated March 15, 2017, to correct the Amazonian regions with the greatest numbers and diversity of domesticated tree species.