The finding, published in The Holocene, provide more evidence that humans impacted global climate long before the modern industrial era.
"They had achieved a pretty sophisticated level of living that I don't think people have fully appreciated," said Gregory Springer, an associate professor of geological sciences at Ohio University and lead author of the study. "They were very advanced, and they knew how to get the most out of the forests and landscapes they lived in. This was all across North America, not just a few locations."
This stalagmite, found in a West Virginia cave, showed a major change in the carbon record at about 100 B.C.
(Photo Credit: Courtesy Gregory Springer, Ohio University)
Initially, researchers were studying historic drought cycles in North America using carbon isotopes in stalagmites. To their surprise, the carbon record contained evidence of a major change in the local ecosystem beginning at 100 B.C. This intrigued the team because an archeological excavation in a nearby cave had yielded evidence of a Native American community there 2,000 years ago.
The team found very high levels of charcoal beginning 2,000 years ago, as well as a carbon isotope history similar to the stalagmite.
This evidence suggests that Native Americans significantly altered the local ecosystem by clearing and burning forests, probably to make fields and enhance the growth of nut trees. This picture conflicts with the popular notion that early Native Americans had little impact on North American landscapes. They were better land stewards than the European colonialists who followed but they apparently cleared more land and burned more forest than previously thought.
"Long before we were burning fossil fuels, we were already pumping greenhouse gasses into the atmosphere. It wasn't at the same level as today, but it sets the stage," Springer said.
Citation: Springer et al., 'Multiproxy evidence from caves of Native Americans altering the overlying landscape during the late Holocene of east-central North America The Holocene, April 2010, 20(2) 275-283; doi:10.1177/0959683609350395