The Amazon has long been held up as an example of untamed wilderness. But people have lived in the world’s largest rainforest for thousands of years, hunting, gathering and farming1. For years, researchers have debated how much of an influence human activities have had on the Amazon. And now, a study describes the extent to which ancient peoples changed the distribution of trees in the forest around them.
The paper2, published on 2 March in Science, finds that many domesticated trees and palms are five times more likely to be over-represented in the Amazon than are non-domesticated ones. The researchers also found that the domesticated plants tended to cluster around the remains of pre-Columbian settlements — or areas where people lived prior to the arrival of Christopher Columbus. They suggest that this pattern could help other scientists to discover as yet unknown ancient settlements in the Amazon.
Levis and her team used data from the Amazon Tree Diversity Network — a group of researchers who share information on palms and trees in the Amazon — to estimate biodiversity in the rainforest. So far, scientists in the network have identified 4,962 palm and tree species in the Amazon. Of the 85 domesticated woody species, Levis discovered that about 20 of them, such as Brazil nuts (Bertholletia excelsa) and cocoa plants (Theobroma cacao), were over-represented.
The researchers wanted to know whether this was because of human influence or the environment. So they compared the distribution of domesticated species to more than 3,000 known pre-Columbian archaeological sites and likely settlement areas, including near the banks of rivers. Domesticated species were much more likely to thrive where ancient people had lived than were non-domesticated species.
All told, about 20% of the distribution of domesticated species across the Amazon seemed to be driven by human influences, while 30% was likely due to environmental factors such as soil composition. However, in the southwestern Amazon — which hosted large pre-Columbian populations — about 30% of the distribution of domesticated species stemmed from human activities. Less than 10% was due to environmental conditions.