Ecological Enigmas of Easter Island and Namibia’s Desert

Haunting photos and mysterious stories of the stone statues—or moai (pronounced mo-eye)—on Easter Island have probably fascinated you since you were a child. You most likely learned in school that about 1,000 years ago, a small band of Polynesians sailed thousands of miles across the Pacific Ocean to settle a small, previously uninhabited island that was one of the world’s most isolated places. In 1722, the Dutch explorer Jacob Roggeveen named this tiny spit of volcanic rock “Easter Island,” since he first spied it on Easter Day in that year. Unfortunately, this tale doesn’t end well. You were taught that, eventually, the number of people living on the island, who called their home Rapa Nui, ballooned to unsustainable levels, and they wrecked their environment by cutting down all the trees. Then, their civilization collapsed.

Now, however, a new study is challenging this narrative of ecocide, and the new thinking about what happened on Rapa Nui may surprise you.

Another ecological myth has recently been turned on its head. This one comes from Namibia and concerns the country’s “fairy circles,” the rings of grass up to 15 feet in diameter that have a distinctly different color or texture than the grass inside or outside the rings. Depending on conditions, grass within fairy circles can be denser, greener and faster growing; or, alternatively, browner and drier than the surrounding grass. On the edges of the Namib Desert in the dry grasslands, the formation of such fairy circles has been researched for decades and has been the subject of much debate. How do the “death zones” inside the circles develop? The long-standing theory is termite damage. New, extensive fieldwork, however, reveals that termites have nothing to do with it.

Easter Islanders did not commit ecocide

Just 14 miles long and seven miles wide, Rapa Nui is more than 2,000 miles off the coast of South America and 1,100 miles from its nearest Polynesian neighbor, Pitcairn Island, where mutineers from the HMS Bounty hid in the 19th century. The widely accepted human history of the island that’s told in academic studies and popular books like American author and historian Jared Diamond’s 2005 Collapse is that after the Polynesians settled on the island, their numbers ballooned to unsustainable levels. They chopped down all the trees, killed off the seabirds, exhausted the soils and, in the end, ruined their environment. Their civilization collapsed, with just a few thousand people remaining when Europeans landed on the island in the 18th century. The many moai now stand as emblems of a vanished civilization.

But a new study that was published in the journal Science Advances in June 2024 by archaeologists from New York’s Columbia University and other researchers from the University of Arizona, New York’s Binghamton University and independent researchers on Rapa Nui challenges this narrative of ecocide.

Rapa Nui’s population never spiraled to unsustainable levels, say the scientists; instead, the Polynesian settlers found ways to cope with the island’s severe limits and maintained a small, stable population for centuries. The evidence for this, the researchers state, can be found in a new, sophisticated inventory of ingenious “rock gardens,” where the islanders raised highly nutritious sweet potatoes, a staple of their diet. The gardens covered only enough area to support a few thousand people. It’s the opposite of the collapse theory; it suggests that the population could never have been as big as some of the previous estimates. In fact, conclude the scientists, people were able to be very resilient in the face of limited resources by modifying the environment in a way that helped.

The 63-square-mile island of Rapa Nui is made entirely of volcanic rock; but unlike lush tropical islands such as Hawaii and Tahiti, eruptions ceased hundreds of thousands of years ago. Mineral nutrients brought up by lava have long since eroded from the soils. Located in the subtropics, the island is also dryer than its tropical counterparts. To make things more challenging, surrounding ocean waters drop off steeply, meaning islanders had to work harder to harvest marine creatures than those living on Polynesian islands ringed with accessible and productive lagoons and reefs.

To cope, the settlers used a technique called “rock gardening,” or lithic mulching. This consists of scattering rocks over low-lying surfaces that are at least partly protected from salt spray and wind. In the gaps between rocks, they planted sweet potatoes. Research has shown that rocks from golf-ball-size to boulders disrupt drying winds and create turbulent airflow, reducing the highest daytime surface temperatures and increasing the lowest nighttime ones. Smaller bits of rock, broken up by hand, expose fresh surfaces laden with mineral nutrients that get released into the soil as they weather. The technique has also been used by Indigenous peoples in the Canary Islands, in New Zealand and in the U.S. Southwest, among other places.

Some scientists have argued that the island’s population had to have once been much larger than the 3,000 or so residents first observed by Europeans, in part because of the massive moai. The reasoning goes that it would have taken hordes of people to construct and move them. But investigations into the rock gardens’ extent and production capacity doesn’t jell with that idea.

Early Europeans estimated that the rock gardens covered 10% of the island. A 2013 study based on visual and near-infrared satellite imagery came up with 2.5% to 12.5%; a wide margin of error because these spectra distinguish only areas of rock versus vegetation, not all of which are gardens. The authors of another study in 2017 identified about 7,700 acres, or 19% of the island, as suitable for sweet potatoes. Making various assumptions about crop yields and other factors, historians have estimated past populations might have risen as high as 17,500 or even 25,000, though they also could have been much lower.

For the new, 2024 Science Advances study, members of the research team did on-the-ground surveys of rock gardens and their characteristics over a five-year period. Using this data, they then trained a series of machine-learning models to detect gardens through satellite imagery tuned to newly available shortwave-infrared spectra, which highlights not just rocks, but places of higher soil moisture and nitrogen, which are key features of the gardens.

The researchers concluded that rock gardens occupy only about 188 acres, which is less than one-half of 1% of the island. While they admit they may have missed some small rock gardens, they wouldn’t have been enough to make a big difference. If the islanders’ entire diet were based on sweet potatoes, these gardens could have supported about 2,000 people. However, based on isotopes found in bones and teeth and other evidence, people in the past probably managed to get 35% to 45% of their diet from marine sources and a small amount from other less nutritious crops, including bananas, sugarcane and taro. Factoring in these sources would have raised the population carrying capacity to about 3,000, the number observed upon first European contact.

Previously, the island’s numerous natural rock outcrops were misidentified as rock gardens. The satellite imagery provides a different picture. And although the population boom-and-bust idea is still popular with the public and some ecologists, archaeologists are quietly retreating from it. Accumulating evidence based on radiocarbon dating of artifacts and human remains also does not support the idea of huge populations.

The lives of the people of Rapi Nui must once have been incredibly laborious. Most of their time would have been spent breaking up rocks. Today, the island’s population is nearly 8,000 (plus about 100,000 visitors a year). Most food is now imported; but some residents still grow sweet potatoes in the ancient gardens, a practice that grew during the 2020–2021 lockdowns of the COVID-19 pandemic, when imports were restricted. Some also turned to mainland farming techniques, plowing soils and applying artificial fertilizer. But this is not likely to be sustainable, as it will further deplete the thin soil cover.

Some anthropologists now see the island as a classic case study in human behavioral adaptation in the face of a dynamic environment. The Science Advances study and others like it provide an opportunity to better document the nature and extent of strategies of adaptation.

Namibia’s gaps in grass are not fairy creations

Namibia’s legendary fairy circles are mysterious, circular, bald patches in the dry grasslands on the edge of the Namib Desert. It’s long been thought that sand termites create fairy circles by consuming vegetation and burrowing in the soil to create the rings. The barren circles allow water to percolate down through the sandy soil and accumulate underground, allowing the soil to remain moist even under the driest conditions. Now, however, researchers at Germany’s University of Gottingen and Israel’s Ben-Gurion University of the Negev believe they’ve discovered how freshly germinated grass dies inside fairy circles—and their idea doesn’t involve termites at all.

In an article published in the journal Perspectives in Plant Ecology, Evolution and Systematics in June 2024, the scientists explained how they used measurements of the lengths of leaves and roots—along with photographs—to analyze 500 individual grass plants in four regions of the Namib Desert. They also took several hundred measurements of soil moisture during and after the 2023 and 2024 rainy seasons.

Their results showed that the Namib topsoil is very susceptible to drying out. Throughout and after the rains, the soil moisture here is three to four times lower than the soil at a depth of around eight inches. In addition, the topsoil is significantly drier within the fairy circle than outside during the period of grass growth after ample rainfall. Under these conditions, freshly germinated grasses cannot survive in the fairy circle: they dry out because they cannot reach the deeper, more moist layers of soil with their roots, which are, on average, four inches long.

In contrast, the large, perennial clumps of grass that grow at the edges of the fairy circles benefit from being able to access the soil water to a depth of 7.8 to 11.8 inches and below. With their well-developed root system, these clumps of grass soak up the water particularly well and turn green after the rains. Then, they have a huge competitive advantage over the freshly germinated grasses inside the fairy circles, which only lose a small amount of water via transpiration from their small leaves, resulting in insufficient “suction power” to pull new water from deeper soil layers.

The measurement data also show that the physical conductivity of the water is high in the first 20 days after the rains, particularly in the upper soil, and decreases with depth. As a result, the clumps of grass at the edges of the fairy circles primarily draw water from the top four to eight inches of the soil. This causes the new grass inside the fairy circles to die. The proof is that the soil water in the fairy circles only decreases noticeably quickly with the strengthening and regrowth of the surrounding grasses after the rains.

According to the researchers, this testifies to the basic function of the fairy circles as water sources for the drought-stressed grass of the Namib. The round shape of the fairy circles is formed by the grass itself, as this creates the maximum supply of soil water. This self-organization can be described as “swarm intelligence”; a systematic adaptation to a lack of resources in this arid region.

The scientific truth is not humdrum

Due to their mysterious, ring-like appearance, fairy circles have been of interest since ancient times. According to medieval lore, they were thought to appear after a band of fairies had danced in an area. And the most popular theory about Easter Island is that this remote civilization destroyed itself, cutting down all the trees to make contraptions for moving the huge statues, akin to Dr. Seuss’s tale of The Lorax.

Quite frankly, I’d like to believe that fairies dance in remote Namibian deserts and that ancient peoples of Rapa Nui lived to decry their deforested land and the error of their ways. But those are just enchanting, entertaining and somewhat educational fables.

Still, the truth—although not as charming—is just as wondrous. The ingenuity of the Rapa Nui people and the inventiveness of the Namibia soils are recitations in eco-resilience.

Here’s to finding your true places and natural habitats,

Candy