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Dueling Theories on the Cause of “Fairy Circles” Could Both Be Right

New research brings together competing concepts to describe how the mysterious features form

This aerial view shoes the weird wonder of "fairy circles" in the Namibian desert. (Justinreznick/iStock)
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What’s the secret behind the weird, perfectly round patches of bare ground in the grasses of the Namibian desert? Known as “fairy circles,” these pockmarks are the source of inspiration for both local legends and warring scientific theories alike. But one of science’s most magical debates could soon be laid to rest. As The Guardian’s Ian Sample reports, a new study has fused two possible explanations for the circles to come up with a new take on what could cause Namibia's fairy circles.

The paper, recently published in the journal Nature, is the latest salvo in a sometimes vicious debate about what causes the strange circles. As Smithsonian.com reported last year, two main theories have emerged over the years. One contends that the grass formed fairy rings itself in an attempt to survive and take advantage of limited resources in arid desert environments. The other argues that some kind of underground animal—likely sand termites—gnaw at the roots of desert vegetation, leaving behind dead patches above the ground.

In an attempt to learn more about those oft-debated patterns, the team decided to layer both theories together with computer modeling. First, they simulated how sand termites would impact desert grasses. Their model showed that dead areas might crop up where termite colonies eat the roots of desert grass. Round boundaries would form that stop where other, similarly-sized colonies begin. Then, they added another layer of competition to the mix, simulating how grass growing in the midst of a termite territorial conflict might respond.

Like the termites, grass itself has to compete to survive. Since the desert is so inhospitable and dry, grasses need to hog as much water as possible to live. When grass is spread out, it’s not too much of a problem to gather water, but as more grass grows, plants must compete for the precious few drops of water, especially as they grow larger. In these situations, the long roots of the plant draw water from farther away, making it hard for distant plants to grow. These large grasses also foster nearby vegetation, providing moisture and shade for their neighbors, Sample reports. So, when the team added grass competition to the termite model, their simulation produced fairy circle-like dry patches with grasses growing in between.

Corina Tarina, an evolutionary biologist from Princeton University and the first author of the paper, tells Sample that when the team went to Namibia to take photographs, they found just what their model predicted. “We found an exact agreement,” she says.

Namibia isn’t the only place where fairy circles (don’t) grow—just last year, similar formations were found in the arid grasses of the Western Australian outback. Since the simulations focused on the Namibian fairy circle instead, it’s still unclear if those circles formed for the same reasons.

It just goes to show that many processes shape the beautiful and often perplexing patterns found in nature. Similarly, weaving two theories together seems to have revealed an answer that is as complex as it is agreeable—and that harmony between two dueling theories is just as satisfying as the fairy circles themselves.

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