The Amazon rainforest has always been viewed as a parcel of nature untouched by humans.

A new study, however, shows otherwise. It has revealed that the forests may have been largely shaped by trees cultivated by indigenous groups thousands of years earlier.

Influenced By Human Settlements

The new research discovered that many domesticated trees are five times more likely to be overrepresented in the region than non-domesticated ones. These domesticated plants were also more likely to be concentrated around the remains of pre-Columbian settlements, where people lived before the arrival of Italian explorer Christopher Columbus.

“That’s even the case for some really remote, mature forests that we’d typically assumed to be pristine and undisturbed,” said study coauthor Nigel Pitman of Chicago’s Field Museum in a statement.

Some prevalent tree species in the Amazon today, including cacao, acai, and Brazil nut trees, tend to be common as they were planted by settlers long before European conquerors arrived, according to Pitman.

The team used data from the Amazon Tree Diversity Network, a group of researchers sharing information on trees and palms in the Amazon, to estimate biodiversity in the area. The data emerged from over 1,000 forest surveys on a map of more than 3,000 pre-Columbian archeological sites.

The scientists have so far analyzed 4,962 species. Of the 85 domesticated species, they found that around 20 were overrepresented.

Was this due to human influence? To find out, the team compared the domesticated species’ distribution to the known archeological sites and likely settlement locations, such as near riverbanks. They saw that domesticated species were much more likely to grow where ancient groups lived once.

Around 20 percent of the domesticated species’ distribution across the rainforest appeared to be propelled by human influence, while 30 percent tended to be due to ecological factors like soil composition. In the southwest where large pre-Columbian peoples thrived, around 30 percent of the domesticated species’ distribution rooted from human activity, and less than 10 percent was because of the environment.

Study Implications

The Amazonian forests have always offered the impression of being an untouched landscape. In recent years, though, new archeological sites have emerged.

The new findings, according to lead author and PHD student Carolina Levis, indicate that the flora in the area is partly the “surviving heritage” of former dwellers.

“We need to ask ‘What are the human influences in these communities?’” said Levis, a paleoecologist at the Netherlands’ Wageningen University.

These findings, however, should not attribute the distribution of domesticated plants solely to human influence. Ancient and modern people, for instance, tend to settle in similar locations, making it possible for modern groups to influence the ecosystems as much as ancient ones did.

In addition, domesticated species may have also re-colonized pristine areas more quickly than their non-domesticated counterparts did — without human help.

Ecologist Mark Bush cited a Central America example: when humans left Mayan sites, Brosimum trees re-colonized the site when scientists thought for years that Mayans deliberately planted them.

The findings were discussed in the journal Science.

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