Ancient people had minimal, if any, impact on the outlying forests of South America's Amazon Basin, and settlements near rivers were likely limited, indicates a new study of soil collected from the western and central Amazon.
Previous research has suggested that, prior to the arrival of Christopher Columbus and Europeans, indigenous people built dense, complex settlements in eastern Amazonia and near some riverbanks in central Amazonia. And it is believed that human changes to the landscape, such as removing forests and planting crops, contributed to the incredible diversity of living things found in this region.
The new research, however, indicates ancient humans' impacts were quite limited, particularly in the outlying forests of western Amazonia. Evidence of fire and agriculture suggests people lived in small groups, leaving little mark on the landscape, except for some larger settlements near rivers.
The researchers, led by Crystal McMichael of the Florida Institute of Technology, reconstructed the history of human occupation using 247 soil samples collected from 55 locations, including sites known to have been occupied by people in western and central Amazonia.
Within the soil samples, they looked for microscopic pieces of silica called phytoliths left by crops and other plants associated with human changes to ecosystems. They also looked for charcoal, which would signal fires and evidence of humans, since natural fires are rare in the Amazon.
Even archaeological sites and sites with dark soils clearly modified by humans in western and central Amazonia bore only limited evidence of forest clearing or agriculture.
In the soils tested, charcoal was most commonly found on river bluffs, especially in the central basin. Meanwhile, nearly all phytoliths found were left by forest plants, rather than plants associated with humans, and signs of forest clearing were scarce.
The findings imply that the diversity of plants and animals living in the Amazon are more a result of natural evolution than humans' modifications to the landscape, the researchers conclude. What's more, they write, "we cannot assume that Amazonian forests were resilient in the face of heavy pre-Columbian disturbance, because vast areas were probably never heavily disturbed."
The results of the research were detailed in the June 15 issue of the journal Science.