News Archive

Hundreds of ancient earthworks built in the Amazon without large-scale deforestation

The Amazonian rainforest was transformed more than two thousand years ago by ancient people who built hundreds of mysterious earthworks, new research has revealed.

Findings by Brazilian and UK experts, including from the University of Reading, provide new evidence for how indigenous people lived in the Amazon before European people arrived in the region. The research was published in PNAS (Proceedings of the National Academy of Sciences) on 6 February 2017.

The ditched enclosures, in Acre state in the western Brazilian Amazon, were concealed for centuries by trees. Modern deforestation has allowed the discovery of more than 450 of these large geometrical geoglyphs.

Professor Frank Mayle, a co-author of the study and professor in Tropical Palaeoecology in the University of Reading’s Geography and Environmental Science department, said: “This research builds upon our previous work that challenges the assumption that geoglyph construction entailed extensive deforestation.

“Our earlier study from Amazonian Bolivia revealed construction of these monumental earthworks in open savanna under past climate conditions too dry to support rainforest. However, this latest study further north in the Brazilian Amazon shows that this geoglyph culture instead made small-scale clearings in bamboo forest to build these earthworks.

“Both studies refute the notion of Amazonia as a pristine wilderness and instead reveal a strong legacy of forest management spanning several millennia.”

Mystery

The function of these mysterious sites is still little understood – they are unlikely to be villages, since archaeologists recover very few artefacts during excavation. The layout doesn’t suggest they were built for defensive reasons. It is thought they were used only sporadically, perhaps as ritual gathering places.

The structures are ditched enclosures that occupy roughly 13,000km². Their discovery also challenges assumptions that the rainforest ecosystem has been untouched by humans.

Using state-of-the-art methods, the team members were able to reconstruct 6,000 years of vegetation and fire history around two geoglyph sites. They found that humans heavily altered bamboo forests for millennia and small, temporary clearings were made to build the geoglyphs.

Instead of burning large tracts of forest – either for geoglyph construction or agricultural practices – people transformed their environment by concentrating on economically valuable tree species such as palms, creating a kind of ‘prehistoric supermarket’ of useful forest products. The team found evidence to suggest the biodiversity of some of Acre’s remaining forests may have a strong legacy of these ancient ‘agroforestry’ practices.

To conduct the study, the team extracted soil samples from pits dug within and outside of the geoglyphs. By analysing these soils, they were able to reconstruct ancient vegetation and assess the amount of ancient forest burning through charcoal quantities, to assess the amount of ancient forest burning; and carbon stable isotopes, to indicate how ‘open’ the vegetation was in the past.

Learning from the past

The research was led by Jennifer Watling, post-doctoral researcher at the Museum of Archaeology and Ethnography, University of São Paulo, when she was studying for a PhD at the University of Exeter.

Dr Watling said: “Despite the huge number and density of geoglyph sites in the region, we can be certain that Acre’s forests were never cleared as extensively, or for as long, as they have been in recent years.

“Our evidence that Amazonian forests have been managed by indigenous peoples long before European Contact should not be cited as justification for the destructive, unsustainable land-use practiced today. It should instead serve to highlight the ingenuity of past subsistence regimes that did not lead to forest degradation, and the importance of indigenous knowledge for finding more sustainable land-use alternatives”.

The study was published in PNAS (Proceedings of the National Academy of Sciences) and also involved researchers from the universities of Swansea, and São Paulo, Belém and Acre in Brazil. The research was funded by the Arts and Humanities Research Council, National Geographic, and the Natural Environment Research Council Radiocarbon Facility.

Full reference:

J. Watling, J. Iriarte, F. Mayle, D. Schaan, L. Pessenda, N. Loader, F. Street-Perrott, R. Dickau, A. Damasceno, A. Ranzi (2017). ‘Impact of pre-Colombian ‘geoglyph’ builders on Amazonian forests’. DOI: 10.1073/pnas.1614359114

Photo credit: 'Cachimbo' (2009) Diego Gurgel