More than 10,000 pre-Columbian archaeological sites remain unexplored in the Amazon rainforest
JUAN MIGUEL HERNÁNDEZ BONILLA
New research combines a remote sensing system with a predictive spatial distribution model and concludes that between 10,272 and 23,648 large-scale archaeological sites remain to be discovered in the Amazon jungle
Archaeological sites in the Amazonian landscape.DIEGO LOURENÇO GURGEL
Under the trees of the Amazon rainforest, the archaeological remains of what was once a large village built by Indigenous communities before the arrival of Europeans in America are hidden. The ancient city had elevated causeways, artificial ponds, dams, ditches, cemeteries, roads with sidewalks, fish dams, and was located in what is now known as the Xingu River basin, in the southern Brazilian Amazon. These ruins, which remain hidden by the dense vegetation of the forest, were discovered by a group of scientists thanks to a special remote sensing system called LiDAR, which uses laser beams to map small changes in the topography of the jungle floor and allows reconstructing what is on the surface in three dimensions.
Vinicius Peripato and Luiz Aragão, of Brazil’s National Institute for Space Research, led a five-year study in which they flew over 5,315 square kilometers in a region of the Amazon with drones and airplanes equipped with the LiDAR system. In that small area of land alone, which represents 0.08% of the seven million hectares of the world’s largest tropical forest, they found 24 new archaeological sites similar to the ancient village. They decided to combine their findings with a predictive spatial distribution model that made it possible to establish an estimate of soil displacement produced by communities throughout the rainforest more than 500 years ago. The results of the study, published Thursday on the cover of Science, reveal that between 10,272 and 23,648 large-scale pre-Columbian archaeological sites remain to be discovered in the Amazon.
LiDAR data from outings to investigate terraces under the forest canopy. From top to bottom, the first is the set of LiDAR points colored by height. Followed by terrain slope, hill shading and elevation of a set of embankments, all obtained after digital removal of surface elements (forest).VINICIUS PERIPATO
The origin of the project was a question which would be impossible to answer without today’s technology: where and how many pre-Columbian sites are hidden under the canopy of the Amazon forest? Up to the time of the research, scientists from the nine countries that are part of the rainforest (Brazil, Peru, Colombia, Bolivia, Venezuela, Ecuador, Guyana, Suriname, and French Guiana) had discovered about 950 archaeological sites using the high-resolution satellite data provided by Google Earth. The problem was that only deforested areas were visible. What is still under trees remained hidden. The LiDAR system, which stands for “Light Detection and Ranging,” changed everything.
In an interview with EL PAÍS, Peripato explains that this aerial sensor is an advanced remote sensing technology that “has revolutionized the way in which we obtain information about the Earth’s surface and its three-dimensional characteristics”. You no longer have to cut down the forest to know what is underneath it. In recent years, LiDAR has also been used to discover the complex urban and rural network that the Maya had throughout Mesoamerica: “Mesoamerican archaeological sites have very different characteristics from those in the Amazon because of the variety of construction materials: the Maya used stone and the Amazonians used earth. LiDAR technology has substantially improved our spatial understanding of archaeology at sites with forested landscapes,” reads the scientific article.
Peripato says that among the 24 archaeological sites they found defense and ceremonial areas in the southwestern Amazon, known as geoglyphs. “The presence of funerary urns within this type of sites, and the absence of soils and anthropogenic ceramics, are evidence that the use of these structures was limited to religious and community meetings,” the researcher says. They also found mountains conquered by Indigenous communities in the Guiana Shield that were used for ceremonial and domestic functions, and riverside sites in the central Amazon plains that were used to collect fish during the rise and fall of water levels.
Carolina Levis, co-author of the study and professor at the Federal University of Santa Catarina in Brazil, explains in a press release that this research helps to disprove the widespread idea that the Amazon is a vast virgin forest. “The research shows us that there are many areas of the forest that have already been subject to extensive engineering, cultivation and domestication of plants by pre-Columbian societies,” Levis says. And she adds: “these archaeological sites are proof that Indigenous communities mastered sophisticated land and plant management techniques, which, in some cases, are still present in current knowledge and practices that can inspire new ways of living with the forest without the need for its destruction”.
The investigation is also an important step towards thinking of the Amazon rainforest not only as a space of animal and plant biodiversity, but also as a great source of archaeological research. Before, we were certain that the Amazon River basin was home to 427 species of mammals, 1,300 species of birds, 378 species of reptiles and more than 400 species of amphibians. Now we know that on the surface covered by the forest there are more than 10,000 large-scale archeological earthworks that may hold the keys to a better understanding of the customs and culture of the Indigenous communities that inhabited the jungle for thousands of years.
Luiz Aragão tells EL PAÍS that the map also makes it possible to demonstrate that in regions with a high probability of finding archaeological sites, there is an increase in the density of domesticated tree species. “This was an interesting result because it shows that pre-Columbian populations had a very close relationship with species that provided them with well-being, especially food and fibers. From this, it can be concluded that they manipulated the ecosystem to increase the density of these species.” In fact, the research shows that the number of plants and trees of edible fruits and nuts increased significantly in the places where the archaeological sites are believed to be located. The authors identified relationships between the predicted probability of archaeological sites and the occurrence and abundance of domesticated tree species. “This suggests that active pre-Columbian Indigenous forest management practices have long shaped the ecology of modern forests throughout the Amazon,” says the article.
Despite the novelty of the research, Aragão is also cautious, pointing out its limitations. When asked if it is possible to conclude that there are more than 10,000 unexplored pre-Columbian archaeological sites in the Amazon, he answers with a strong yes, but is clear that it is an estimate. “Based on the existing number of known structures and our prediction model, we expect that many sites are still hidden under the canopy. Of course, this is an estimate based on statistical methods and has uncertainties. But it is very likely that there are thousands of archaeological sites that are there to be discovered,” he explains to EL PAÍS.
Hans ter Steege, co-author of the paper and researcher at the Naturalis Biodiversity Center and Utrecht University, says that these archaeological sites must be concentrated in specific areas of the forest: “We predict that 90% of the Amazon forest has very little chance of having earth movements, so this type of alteration may have occurred mainly in 10% of its area,” says the scientist in a statement.
Although neither the size nor the characteristics of the thousands of archaeological sites in the rainforest are yet well known, this work opens up new avenues of research so that future scientists will be equipped with a compass to know where to explore. “Amazonian forests deserve protection not only for their ecological and environmental value but also for their high archaeological, social and biocultural value, which can teach modern society how to sustainably manage its natural resources,” the research concludes.
More than 10,000 pre-Columbian earthworks are still hidden throughout Amazonia
Indigenous societies are known to have occupied the Amazon basin for more than 12,000 years, but the scale of their influence on Amazonian forests remains uncertain. We report the discovery, using LIDAR (light detection and ranging) information from across the basin, of 24 previously undetected pre-Columbian earthworks beneath the forest canopy. Modeled distribution and abundance of large-scale archaeological sites across Amazonia suggest that between 10,272 and 23,648 sites remain to be discovered and that most will be found in the southwest. We also identified 53 domesticated tree species significantly associated with earthwork occurrence probability, likely suggesting past management practices. Closed-canopy forests across Amazonia are likely to contain thousands of undiscovered archaeological sites around which pre-Columbian societies actively modified forests, a discovery that opens opportunities for better understanding the magnitude of ancient human influence on Amazonia and its current state.
Fig. 1. Geographical distribution of known and newly discovered pre-Columbian geometric earthworks in Amazonia.
(A) Map of previously reported and newly discovered earthworks (purple circles and yellow stars, respectively) reported in this study across six Amazonian regions: central Amazonia (CA), eastern Amazonia (EA), Guiana Shield (GS), northwestern Amazonia (NwA), southern Amazonia (SA), and southwestern Amazonia (SwA). (B) Newly discovered earthworks in SA. (C to F) Newly discovered earthworks in SwA. (G to I) Newly discovered earthworks in GS. (J and K) Newly discovered earthworks in CA. Scale bars, 100 m.