The Namib desert is covered in a mind-bending pattern of fairy circles, the origin of which has been heatedly debated by scientists – but now the mystery appears to have been solved.
In southern Africa, the extraordinary Namib Desert’s vast grasslands are dotted with what look like a set of “fairy circles” – circular patches of land barren of plants, surrounded by vegetation. The otherworldly looking circles range from 10 to 65 feet in diameter and stretch for hundreds of miles across the desert. According to local legend, they were created by the gods who left behind their footprints on the red earth, but the truth has more to do with math and biology than folklore. In fact, what looks like a random arrangement may not be random at all.
“The whole landscape looks like a polka dot dress,” says mathematician Corina Tarnita, who has been studying the Namibian fairy circles for some time. The dots are like islands in a sea of short grass that are “very, very regularly spaced.”
For decades, researchers have puzzled over the mystery of the fairy circles in Namibia (and also in Pilbara, Western Australia, where a similar phenomenon was confirmed in 2014), proposing various theories explaining the strange pattern. There have been two major hypotheses that these theories have coalesced around:
First, the Namib Desert is a very arid system, and plants therefore compete fiercely for resources. While they help their nearest neighbors by creating shade and retaining water on the soil’s surface, they also hinder those further away by growing long roots that extract water from the soil. In this way, vegetation tends to thin or disappear at the edges of the patch, forming regular distanced gaps.
“You look at them from a satellite image and you think, ‘oh, they fit beautifully with this theory of the plants competing for water,'” Tarnita says. “But then you go underground and you find that under each one of these spots, there’s a termite colony.”
And indeed, the other theory has to do with termites. This camp claims the empty patches are created by termite colonies under the ground that wipe out the vegetation in the area around their nests. All this makes the surrounding soil porous, establishing permanent reservoirs of rainwater about 50 centimetres below the surface. This water then sustains the colony and the surrounding ecosystem.
Although the termite theory has been backed up by scientific observations of termites within the fairy circles, no one could explain why the patterns are so regular.
To find out, Tarnita collaborated with ecologist Rob Ringle of Princeton University, who pointed out how eusocial insects (insects that are divided into specialized castes to support the overall success of the colony) burrow a large network of underground tunnels to forage for food, decimating the vegetation above them. However, when one colony intrudes the territory of another, the two colonies fight until one is completely destroyed, Tarnita explains. The result? A series of colonies, about the same size, with a “no-termite’s land” between them.
Tarnita and her team decided to draw up a computer model of the two hypotheses and found that plant competition and termite colonies could both independently be responsible for the fairy circles. That said, only when combining the two together were the researchers be able to create the entirety of the landscape. Their findings were published in Nature in January 2017. The team is now looking to test the hypotheses in other ways, for example by concluding small scale manipulation studies in the field that compare the presence and absence of termite colonies.
But there’s even more to grasp though. The Namibian fairy circles are a very complex ecosystem, and as such, it has many different factors at play, Tarnita explains. You have to take many different things into account, like the various species interacting with the vegetation, the level of precipitation in the area, or the microbes growing in the soil. Drawing up a mathematical model by altering the availability of one variable and modeling the subsequent patterns, one can take into consideration all of these biological and ecological processes. This can help researchers better evaluate the conditions of an ecosystem – and even make predictions of an impending collapse.
“If we think that patterns might not just be something beautiful, but something meaningful, they might tell us something about the ecosystem’s health and how it functions,” Tarnita concludes.