![Drone image of a car driving through the NamibRand Nature Reserve, one of the fairy circle regions in Namibia.](https://oponame.com/wp-content/uploads/2022/10/Myth-busted-the-formation-of-fairy-circles-in-Namibia-is.jpg)
Stephane Getzin
So-called “fairy circles” are bare, reddish-hued circular spots found especially in the Namibian grasslands and northwestern Australia. Scientists have long wondered if these unusual patterns are due to termites or an ecological version of a self-organizing Turing mechanism. A few years ago, Stephan Getzin from the University of Göttingen found strong evidence for the latter hypothesis in Australia. And now his team has found similar evidence in Namibia, according to a new paper published in the journal Perspectives in Plant Ecology, Evolution and Systematics.
“We can now definitively reject the termite hypothesis because termites are not a prerequisite for forming new fairy circles,” Getzin told Ars. This goes for both Australian and Namibian fairy circles.
As previously reported, the Himba Bushmen of the Namibian grasslands have passed down legends of the region’s mysterious fairy circles. They can reach several feet in diameter. Nicknamed “footprints of the gods”, they are often said to be the work of the deity Himba Mukuru, or an underground dragon whose poisonous breath kills anything that grows inside these circles.
Scientists have their own ideas, and over the years two different hypotheses have emerged about how circles form. One theory attributed the phenomenon to a particular species of termite (Psammmotermes allocerus), the burial of which damages plant roots, causing extra rainwater to seep into the sandy soil before the plants can suck it up, giving termites a handy water trap like resource. As a result, plants die in a circle from the site of an insect nest. The circles get larger in diameter during droughts because termites have to venture farther to feed.
The other hypothesis – the one adopted by Getzin – holds that the circles are a kind of self-organizing spatial growth pattern (a Turing model) that arises when plants compete for scarce water and soil nutrients. In his seminal 1952 paper, Alan Turing attempted to understand how natural, non-random patterns emerge (like the stripes of a zebra), and he focused on chemicals known as morphogens. He devised a mechanism involving the interaction between an activating chemical and an inhibiting chemical that diffuse throughout an entire system, much like gas atoms would in a closed box.
It is like injecting a drop of black ink into a beaker of water. Normally, this would stabilize a system: the water would gradually turn a uniform gray. But if the inhibitor diffuses faster than the activator, the process is destabilized. This mechanism will produce a Turing pattern: spots, stripes or, when applied to an ecological system, clusters of ant nests or fairy circles.
A researcher investigates the death of grasses inside fairy circles in a plot near Kamberg in the Namib. The recording was made about a week after the March 2020 rains.
In 2019, Getzin’s team conducted a study of fairy rings in northwest Australia, near an old mining town called Newman. The team dug more than 150 holes in nearly 50 fairy circles in the area to collect and analyze soil samples, particularly to test the termite hypothesis. They also used drones to map larger areas of the continent to compare gaps in vegetation typically caused by harvester termites in the region, with the fairy circles that sometimes form.
The gaps in vegetation caused by harvester termites were only about half the size of fairy circles and much less orderly, so they found no hard subterranean termitaria that would prevent the growth of grasses. But they found heavy soil compaction and high clay content in the circles, evidence that heavy rains, extreme heat and evaporation contributed to their formation. “Termite constructions may occur in the fairy circle area, but the partial local correlation between termites and fairy circles has no causal relationship,” Getzin said at the time. “Thus, no destructive mechanisms, such as those of termites, are necessary for the formation of the distinct fairy circle patterns; hydrological plant-soil interactions alone suffice.”
Having effectively disproved the Australian termite origin hypothesis, Getzin focused on testing the termite hypothesis specifically for Namibia, using a similar methodology. While his previous work on Namibian fairy circles did not specifically address plant root research, this new study shows that plant roots are not affected by herbivorous insects.
Investigation of a fairy circle in Brandberg, Namibia 35 days after the March 2021 rains.
“For the first time, we went right after the rain into the fairy circles and checked the new grasses for termite herbivory,” Getzin told Ars. “Our excavations show that termites certainly did not cause the grasses to die. If you get to fairy circles too late, the grasses are long dead and scavengers like termites may have already fed on the grass. ‘lignified grass. But they did not kill the We show unambiguously that the grasses die before and completely independently of any action of the termites.’
What’s next for Getzin? He thinks more research is needed on plant swarm intelligence, comparing plants to beavers in that they can act as “ecosystem engineers” that alter their environment. “Most people can’t believe this or don’t want to believe it because plants don’t have brains,” Getzin said. “But plants act like the beaver as engineers of the ecosystem because their only way to survive is to form optimal, strictly geometric patterns” – in other words, Turing patterns.
DOI: Perspectives in Plant Ecology, Evolution and Systematics, 2022. 10.1016/j.ppees.2022.125698 (About DOIs).
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