“Empty” Amazon was densely populated

Researchers have discovered an 1800 kilometre stretch of Pre-Columbian settlements in the Amazon, potentially rewriting both the history of the region and the conservation strategies for the largest wilderness on Earth.

The discovery, reported in the journal Nature Communications, suggests that areas of Amazonia previously thought to be free of human influence (at least prior to Spanish colonisation) were in fact densely populated. The role of human activity in shaping the environment must therefore be re-evaluated.

To make the finding, a team led by Jonas Gregorio de Souza of the University of Exeter, UK, used a combination of remote sensing, excavation and survey data to examine landscapes in the Upper Tapajós Basin – an area of about 492,000 square kilometres in Brazil that accounts for around 7% of the Amazon basin.

Much of the area comprises interfluvial forests – that is, vegetation growing on ridges and plateaus situated between narrow valleys. This type of landform has been largely ignored by archaeologists, de Souza and colleagues explain, because of “traditional views that Pre-Columbian people concentrated on resource-rich floodplains”.

Areas such as the Upper Tapajós Basin, therefore, were thought to be marginal.

The assumption has now been shown to be wrong. Citing earthworks such as ditched enclosures, the researchers confidently identify 81 settlements along tributaries and interfluvial zones, dating them between approximately 1250 and 1500 CE.

Extrapolating, the team estimates that a similar population density existed during the period across about 400,000 square kilometres of southern Amazonia.

The finds provide evidence that link Pre-Columbian populations across the Amazon basin from east to west, suggesting that different cultures and language groups are interconnected despite “a diversity of traditions and socio-political trajectories”.

De Souza and his colleagues dismiss the standard idea that holds Pre-Columbian society to have been focussed on major waterways, and show that there were also “parallel networks of complex societies” that formed regional systems as well.

The discoveries are of clear interest to archaeologists and historians, but also carry significant implications for biologists and ecologists. Far from being a wilderness untouched by human activity, the Upper Tapajós Basin is at least to some extent the product of intensive human settlement and intervention.

“An understanding of the historical role of humans in shaping Amazonian landscapes, and to what extent these forests were resilient to historical disturbance, is critical to making informed policy decisions on sustainable futures,” the researchers advise.