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Wednesday, March 28, 2018

In findings published Tuesday in Nature Communications, scientists report that the Amazon forest of the 1200s to 1500s c.e. may have been home to as many as a million more humans than has previously been thought and an area that many think of as untrammeled jungle may have been crisscrossed by canals, roads and other infrastructure.

The researchers used satellite imagery of much of Brazil and Bolivia taken by Google Earth to detect probable earthworks, such as partial walls, canals, and the dug-out portions of roads. This evidence, the study says, was visible from space not only because of improvements in imaging technology but also the extensive deforestation that has removed the vegetation that concealed it from previous efforts.

The researchers identified 81 sites and selected 24 to visit on foot. At every one, they found signs of human activity, such as charcoal and ceramics. They estimate as many as 1500 such sites may exist, spread out over a total of 400,000?square kilometers (150,000 square miles). This area, previously thought to be uninhabited, appears to have held fortified villages and agricultural operations supported by the Amazon’s many smaller creeks and tributaries. Earlier predictions had placed the population of the entire Amazon basin at 1.5 to 2 million, with most of it concentrated on flood plains and along major rivers. This is some of the first evidence supporting a belief that has emerged among archaeologists over the past several years that the earth-building cultures of the Amazon were relatively populous and contradicts the popular image of the pre-Columbian Amazon as an unconquered forest.

“The idea that the Amazon was a pristine forest, untouched by humans, home to scattered nomadic populations … we already knew that was not true,” first author Dr. Jonas Gregorio de Souza of the University of Exeter told The Guardian. “The big debate is how populations were distributed in pre-Columbian times in the Amazon.”

Previous models of Amazonian humans have presupposed that most communication and trade took place along waterways, but these findings suggest that inhabited areas with roads may have been contiguous along land as well, with some networks stretching nearly 1800 km (1100 miles). Evidence indicated the presence of causeways, reservoirs, canals, fish preserves, roads, and what researchers have called ceremonial sites based on the presence of votives and similar objects. Although the satellite and in-person investigations only showed earthen structures, researchers report there would have been wooden buildings at these sites, and the circular walls surrounding the raised villages may have been topped with timber fence-walls called palisades.

Researchers speculate that the seasonal climate in this part of the Amazon—there was a regular dry season that would have made the vegetation easier to clear and would have provided less rainfall to leach nutrients out of the soil—may have made the area more friendly to farming than rainier parts of the basin.

The researchers say their work has implications for the protection of the Amazon ecosystem in modern times, that it can be used to estimate how well it grows back after humans have cleared large tracts, but, as de Souza points out, large numbers of humans may have been cut down as well. Reports from the 1600s and 1700s, such as the writings of Bartolomé de las Casas, cite dense populations of people that were wiped out after contact with the Conquistadors. “We know that diseases travelled much faster than people and probably this population was already weakened by diseases brought by Europeans even before the Europeans set foot on the area,” de Souza told reporters.

The study was funded by the European Research Council and National Geographic.

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