Sunrise at the Ahu Tongariki on Easter Island

Sunrise at the Ahu Tongariki on Easter Island. (Photo by Focus Fusion on Shutterstock)

For decades, the story of Easter Island (Rapa Nui) has captivated the world as a cautionary tale of environmental collapse and societal downfall. Popular narratives painted a picture of a civilization that grew too large, exhausted its resources, and crumbled under its own weight. It’s long been believed that the island’s inhabitants had extensively modified the landscape with innovative “rock gardens” to boost food production and support a burgeoning population. However, a fascinating new study turns this narrative on its head.

What is Easter Island?

This remote speck of land in the southeastern Pacific Ocean, about 2,200 miles from Chile, is known for its enigmatic giant stone statues called moai. The history of the 63-square-mile island made entirely of volcanic rock and its incredible statues have long been shrouded in mystery.

Easter Island was first settled by Polynesian voyagers around 800-1200 CE, who established a complex society that flourished for centuries. The island’s inhabitants, known as the Rapanui, developed a unique culture characterized by monumental stone architecture, a complex social structure, and innovative agricultural practices. However, by the time European explorers first arrived in 1722, the island’s ecosystem had undergone significant changes, with its once-lush palm forests largely gone and its population seemingly in decline.

Central to this study are the unique agricultural features known as “rock gardens” or “lithic mulch gardens.” These innovative cultivation techniques were developed by the ancient Rapanui to overcome the challenges of farming on an island with relatively poor soil and limited freshwater resources.

The primary crop grown in these rock gardens was sweet potato (Ipomoea batatas), a staple of the Rapanui diet. Other crops likely cultivated using these methods included yams, taro, and bananas.

Today, Easter Island is a major tourist destination, attracting about 100,000 visitors each year who come to marvel at the moai and experience the island’s unique culture. Approximately 8,000 people now call the island home. Tourism has become a crucial part of the local economy, but it has also brought challenges in terms of preserving the island’s fragile ecosystem and archaeological heritage.

The story tour guides tell of the Rapanui appears to now need a major update thanks to this new study. Using cutting-edge satellite technology and machine learning, researchers have discovered that the extent of ancient agricultural infrastructure on Easter Island was dramatically smaller than previously believed.

Today, about 8,000 people inhabit Easter Island, or Rapa Nui.
Today, about 8,000 people inhabit Easter Island, or Rapa Nui. (Photo by Sergey-73 on Shutterstock)

What Did the Study Find?

The study, led by Dylan S. Davis of Columbia University, reports that rock gardens covered only about 0.76 square kilometers of the island – roughly one-fifth of the most conservative previous estimates. This finding has profound implications for our understanding of Easter Island’s past population size, agricultural practices, and the island’s alleged “collapse.”

The research team utilized high-resolution shortwave infrared (SWIR) satellite imagery, a technology that can detect subtle differences in soil composition and moisture levels. By training machine learning algorithms on known rock garden locations, they were able to identify these features across the entire island with unprecedented accuracy. The results, published in Science Advances, paint a picture of a much more modest agricultural system than earlier studies had suggested.

“This shows that the population could never have been as big as some of the previous estimates,” says Davis, a postdoctoral researcher in archaeology at the Columbia Climate School, in a statement. “The lesson is the opposite of the collapse theory. People were able to be very resilient in the face of limited resources by modifying the environment in a way that helped.”

This revelation challenges long-held assumptions about Easter Island’s carrying capacity and the size of its pre-European contact population. Previous estimates, based on less accurate assessments of agricultural extent, had suggested the island could have supported up to 17,500 people. However, the new data indicates that the population was likely much smaller, aligning more closely with early European estimates of around just 3,000 inhabitants.

The ancient moai of Ahu Togariki, on Easter Island, some 2,000 miles off the coast of Chile.
The ancient moai of Ahu Togariki, on Easter Island, some 2,000 miles off the coast of Chile. (Photo by Kristopher Kettner on Shutterstock)

Methodology: Harnessing the Power of SWIR

The key to this study’s success lay in its innovative use of SWIR satellite imagery. Unlike traditional visual or near-infrared imagery, SWIR can detect subtle variations in soil moisture and mineral composition. This makes it particularly well-suited for identifying archaeological features that might be invisible to the naked eye or other remote sensing technologies.

The researchers obtained high-resolution SWIR imagery of Easter Island from the WorldView-3 satellite, covering the entire island with minimal cloud cover. They then collected ground-truth data by conducting surveys of known rock garden locations on the island between 2019 and 2023. This information was used to train three different machine learning algorithms: maximum entropy (MaxEnt), random forest (RF), and maximum likelihood classification (MLC).

The team compared the performance of these algorithms using both SWIR data and more traditional visual and near-infrared (VNIR) imagery. In all cases, the SWIR data outperformed VNIR in accurately identifying rock gardens. The MaxEnt model applied to SWIR imagery proved to be the most effective, achieving an overall accuracy of 82.44% – a significant improvement over previous attempts to map these features.

After running the best-performing model on the entire island, the researchers manually reviewed the results to remove any obvious errors, such as misclassifications of modern roads or natural lava flows. They also excluded any identified areas smaller than 10 square meters, as these were likely artifacts of the analysis rather than actual garden features.

Study coauthor Robert DiNapoli inspects a rock garden on Easter Island.
So-called rock gardens were key to feeding the population of Rapa Nui, today commonly known as Easter Island. Robert DiNapoli, coauthor of a new study on the gardens, inspects one. (Photo by Carl Lipo)

Results: A Dramatically Different Picture Emerges

The study’s findings are striking. While previous estimates had suggested that rock gardens covered between 4.9 and 21.1 square kilometers of Easter Island, this new analysis found only 0.76 square kilometers of these agricultural features. This represents a reduction of 80% compared to even the most conservative prior estimates.

The distribution of rock gardens also provided insights into ancient land use patterns on the island. The majority of identified gardens were clustered along coastal regions, with fewer found at higher elevations inland. This pattern aligns with archaeological understanding of settlement patterns on the island, where most habitation was concentrated near the coast.

To account for the possibility that modern development might have destroyed some ancient rock gardens, the researchers also analyzed areas of the island that have been disturbed by urbanization or modern agriculture. They found that approximately 25 square kilometers of the island have been affected by these activities. However, more than 5 square kilometers of this disturbed area are in zones where no rock gardens have been discovered through either ground investigations or remote sensing surveys.

Moai statues under a blue sky at Rano Raraku on Easter Island
Moai statues under a blue sky at Rano Raraku on Easter Island. (Photo by Aeonian Photography on Shutterstock)

Limitations: Acknowledging Uncertainties

The study represents a significant advance in our understanding of Easter Island’s agricultural past, but the researchers acknowledge several limitations to their approach. One key consideration is the potential for rock gardens to have been destroyed or obscured by modern development, particularly in and around the island’s main settlement of Hanga Roa. The study attempted to account for this by analyzing disturbed areas, but some uncertainty remains.

Another limitation is the resolution of the SWIR imagery used (3.7 meters per pixel). While this represents the highest resolution commercially available SWIR data, it may still miss very small garden features. The researchers addressed this by excluding identified areas smaller than 10 square meters, but it’s possible that some legitimate small gardens were overlooked.

Finally, the study provides a snapshot of rock garden extent at a single point in time. It’s possible that the total area under cultivation varied throughout the island’s history, with some gardens being abandoned and new ones created over time. Further archaeological work would be needed to establish a more detailed chronology of agricultural development on the island.

Discussion and Takeaways: Rewriting Easter Island’s Story

The implications of this study extend far beyond a simple adjustment of numbers. By dramatically reducing the estimated extent of intensive agriculture on Easter Island, it forces a reevaluation of many assumptions about the island’s past.

First and foremost, it challenges the idea that Easter Island’s population grew to unsustainable levels before European contact. Using the same methods as previous studies but with the new, more accurate data on agricultural extent, the researchers calculated that the maximum population that could have been supported by the identified rock gardens was around 3,900 people. This aligns much more closely with early European estimates of the island’s population than with the higher figures of 15,000 or more that have been proposed by some researchers.

The iconic Moai heads at a Unesco Heritage National Park from Easter Island, Chile.
The iconic Moai heads at a Unesco Heritage National Park from Easter Island, Chile. (Photo by Yoko Correia Nishimiya on Unsplash)

This finding lends support to a growing body of archaeological evidence that suggests Easter Island did not experience a dramatic “collapse” before European contact. Instead, it paints a picture of a society that successfully adapted to the challenges of living on a remote, resource-poor island through innovative agricultural techniques and careful resource management.

“People’s lifestyle must have been incredibly laborious,” says co-author Carl Lipo, an archaeologist at Binghamton University. “Think about sitting around breaking up rocks all day.”

The study also highlights the potential of new remote sensing technologies, particularly SWIR imagery, for archaeological research. By providing a way to detect subtle landscape modifications over large areas, this approach could revolutionize our understanding of ancient land use patterns in many parts of the world.

The narrative of Easter Island as an example of societal collapse due to resource overexploitation has been widely popularized and used as a parable for modern environmental concerns. While there are certainly lessons to be learned from the island’s history, this study suggests that the reality was far more complex – and perhaps more hopeful – than previously thought.

As Davis and his colleagues conclude, “Our results add to a growing body of empirical research showing that Rapa Nui represents a prime example of how an isolated population with limited natural resources created a sustainable subsistence system, maintaining their numbers within the limitations of environmental carrying capacity.”

In rewriting the agricultural history of Easter Island, this study sheds new light on a fascinating chapter of human history. It’s a reminder that with careful management and innovation, even the most resource-poor environments can support thriving human communities for centuries.

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