Environmental impact of geometric earthwork construction in pre-Columbian Amazonia

• Published in: Proceedings of the National Academy of Sciences - PNAS 2014-07, Vol.111 (29), p.10497-10502
• Main Authors: Carson, John Francis, Whitney, Bronwen S., Mayle, Francis E., Iriarte, José, Prümers, Heiko, Soto, J. Daniel, Watling, Jennifer
• Format: Article
• Language: English
• Subjects: Amazonia; biogeochemical cycles; Biological Sciences; Bolivia; burning; Charcoal; Deforestation; Ditches; Earthworks; Ecosystem; ecosystems; Environment; Environmental impact; Geography; Lakes; Land use; landscapes; Paleoclimatology; paleoecology; Pollen; Precolumbian era; Rain; rain forests; Rainforests; savannas; Social Sciences; Stone Age; Time Factors; Trees - physiology; Tropical forests; Tropical rain forests; Vegetation
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1321770111

There is considerable controversy over whether pre-Columbian (pre-A.D. 1492) Amazonia was largely “pristine” and sparsely populated by slash-and-burn agriculturists, or instead a densely populated, domesticated landscape, heavily altered by extensive deforestation and anthropogenic burning. The discovery of hundreds of large geometric earthworks beneath intact rainforest across southern Amazonia challenges its status as a pristine landscape, and has been assumed to indicate extensive pre-Columbian deforestation by large populations. We tested these assumptions using coupled local- and regional-scale paleoecological records to reconstruct land use on an earthwork site in northeast Bolivia within the context of regional, climate-driven biome changes. This approach revealed evidence for an alternative scenario of Amazonian land use, which did not necessitate labor-intensive rainforest clearance for earthwork construction. Instead, we show that the inhabitants exploited a naturally open savanna landscape that they maintained around their settlement despite the climatically driven rainforest expansion that began ∼2,000 y ago across the region. Earthwork construction and agriculture on terra firme landscapes currently occupied by the seasonal rainforests of southern Amazonia may therefore not have necessitated large-scale deforestation using stone tools. This finding implies far less labor—and potentially lower population density—than previously supposed. Our findings demonstrate that current debates over the magnitude and nature of pre-Columbian Amazonian land use, and its impact on global biogeochemical cycling, are potentially flawed because they do not consider this land use in the context of climate-driven forest–savanna biome shifts through the mid-to-late Holocene.