Discovery Magazine

Photo Credit: Crystal McMichael

Pre-Columbian Human Impacts on Amazonian Rainforest Ecosystems

How natural are the Amazonian rainforest ecosystems? A growing case is being made among anthropologists and archaeologists that prior to European contact in 1492, native people manipulated much, perhaps most, of Amazonia. If fire was used across the Amazon basin to clear land for agriculture then Amazonian rainforest ecosystems that ecologists have assumed were mature may in fact be only one-to-several generations removed from intensive management. Fire does not occur naturally in the western Amazon and so charcoal in the soil is a sure sign of human activity. Given that the Amazonian rainforest ecosystems support Earth's largest rainforest and are home to unparalleled biodiversity, understanding the extent to which wildlife and people have interacted in the past is vital for effective planning and management. A further aspect of this debate is that if much of Amazonia is truly the product of disturbance, the forest must be considered to be relatively young and is probably not at equilibrium with respect to carbon cycling. To test the hypothesis of widespread disturbance, this project will conduct the first systematic survey of soils in Amazonian rainforest ecosystems for charcoal. Fires in Amazonia are almost always human-induced, and each burn leaves ash and charcoal that become incorporated into soil. Over 400 soil pits have been sampled on transects across western Amazonia, to determine the distribution and age of buried charcoal. Prior soil descriptions also will be used to determine where other scientists have located charcoal and data gathered in this project will be compared with a new model for pre-Columbian settlement of Amazonia. Through these analyses, the collaborating team from Florida Tech, Wake Forest, University of Florida, The National History Museum and Guarulhos University, Brazil, hope to inject real data into the policy arena of Amazonian development and conservation.

Other indicators of human presence in Amazonian rainforest ecosystems will also be mapped such as the presence of pot fragments or black earths (soils created by mixing charcoal into the soil). The study will be based on a randomized design, but care will be taken to collect data from areas known to have supported pre-Columbian populations as well as those where there is nothing known of past occupation.

The first results from this study of sparse human occupation in Amazonian rainforest ecosystems have now been published in Science.