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Hundreds of monumental stone heads dot the coastline of the remote Pacific island of Rapa Nui, or Easter Island. Settled by a small band of Polynesian sailors nearly 900 years ago, it is a fascinating place that is the subject of fierce debate about how complex societies can sometimes fail catastrophically.
Some experts, such as geographer Jared Diamond in his 2005 book “Collapse,” used Easter Island as a cautionary example of how exploitation of limited resources can lead to catastrophic depopulation, ecological destruction and the extinction of a culture through civil conflict.
Other researchers suggest the opposite; He suggests that Easter Island is a story of how an isolated people created a sustainable system that allowed a small but stable population to thrive for centuries until first contact with European colonial powers in the early 18th century.
Now research involving remote sensing data and machine learning to map evidence of island farming offers a new clue that could help elucidate the mysterious demise of the island’s original civilization. The new finding suggests that the island is not densely populated and ecological collapse is a less likely scenario.
The lead author of the study, published Friday in the journal Science, said Dr. “All this evidence that’s been collected over the past 15 or 20 years is starting to kind of throw a monkey wrench in the story of the collapse,” Dylan Davis said. Improvements.
“And that’s what this article is built on.”
Easter Island residents used rock gardens
Rapa Nui, today part of Chile, is more than 2,000 kilometers (1,242 miles) from the nearest inhabited island of Pitcairn and about 3,700 kilometers (2,300 miles) from the South American mainland, according to the study.
Davis, a postdoctoral research fellow at the Columbia Climate School’s Lamont-Doherty Earth Observatory, and his team focused on agricultural practices to understand how large a population the island could support. It is slightly smaller than Washington, DC, at 163 square kilometers (63 square miles).
Previous research suggested that rock gardens cover an area of 21.1 square kilometers (8.1 square miles) and could house up to 17,000 people. This finding in February 2013 reinforced the idea that humans were depleting Rapa Nui’s limited resources.
Archaeologists have identified the remains of rock gardens where islanders could grow sweet potatoes and other crops. Scattered and pulverized rocks make the soil more fertile by adding and sealing nutrients and moisture and protecting young plants from winds; This is an ancient agricultural technique also known as rock mulching.
But in the new study, Davis and colleagues found that the maximum number of people on Rapa Nui was about 4,000, less than a quarter of that high estimate.
The team identified significantly smaller population numbers using a machine learning model trained to identify rock gardens from high-resolution shortwave infrared and near-infrared data collected by satellite.
“What we’re using in this paper is called shortwave infrared imagery,” Davis said, “and it’s really good at detecting very subtle differences in moisture content and mineralogical changes in soil.”
The researchers found that rock gardens, which can be identified by patterns of vegetation and soil composition, cover about three-quarters of 1 square kilometer (0.4 square miles), and that rock garden cultivation alone can only support about 2,000 people. Combined with estimates of fisheries and other seafood availability, the team believes Rapa Nui could sustain a population of 3,901 people.
Davis said the team manually validated the model and it was 83% accurate. “That’s good right now because of the data available,” he said. “If there were obvious errors, we removed them.”
Another limitation of the approach was the possibility that rock gardening features may have been destroyed over the centuries.
What really happened on Easter Island?
Thegn Ladefoged, an archeology professor at the University of Auckland, New Zealand, who conducted a similar study published in February 2013 that resulted in a higher population estimate, said the latest research provides “new information about the carrying capacity and possible population of ancient Rapa Nui.” predictions.”
“Analysis of newly obtained high-resolution shortwave infrared remotely sensed data revealed that the total area of rock gardening is 5 to 20 times lower than previous estimates,” Ladefoged said via email. “This finding was the result of integrating new remotely sensed data that was not available when we conducted our original study.” He was not involved in the new research.
“I agree with the authors that no pre-colonial ecocide occurred on Rapa Nui and the population did not experience a collapse.”
But Christopher Stevenson, an anthropology professor at Virginia Commonwealth University’s School of Earth Studies, said the machine learning methodology “is far from clear and has not been well evaluated.”
“The authors are trying to say that their approach is much better than past work without actually showing how they addressed the complexity of the dataset,” Stevenson said via email.
The view that the island once hosted a population of several thousand people stems from the assumption that large numbers of people would have been required to build and move the more than 800 colossal stone statues, or moai, erected across the island.
However, a January 2022 study suggested that this may not require as much muscle strength as previously thought. Moreover, while it was initially thought that the islanders partially felled the trees to move the carved heads, a January 2017 study suggested that native palm vegetation was burned to make the soil more fertile.
“As a result, we have no evidence that thousands and thousands of people lived there. In fact, when Europeans first came into contact with the Rapa Nui people, they reported seeing only 3,000 or 4,000 people, and the people were in good spirits,” Davis said.
“And the real population collapse occurs after that, and that’s probably due to exposure to disease.”
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