How might fairy circles be created?

Our primary goal for heading to Namibia in just a few days is to learn how fairy circles are created and maintained. What processes actually create fairy circles remains a highly debated mystery with multiple competing hypotheses, despite years of scientific research. We’ll cover a few of the key scientific possibilities in this post and creation stories for the fairy circles a bit later (so stay tuned)!

These regularly spaced bare circles of ground in arid grasslands have several highly perplexing qualities. The first, and most fascinating to me, is how evenly spaced they are. They have a honeycomb-type pattern that extends for hundreds of miles. This pattern is the result of self-organization–meaning that it isn’t designed but rather arises from the interaction of different parts of the system. Classic self-organization examples include birds flocking together, ant colonies, beehives, or even the creation of human society! All of these classic examples, however, involve individuals with behavioral choices, and these choices tend to be a critical component necessary for self-organization. Fairy circles, though, are the result of individual grasses–so no behavior here. This makes fairy circles a really interesting, and pretty unique, example of a complex system self-organizing.

One hypothesis is that fairy circles might arise from individual plants competing with one another. The Namib desert is an extremely harsh environment with very little rainfall (less than 4 inches a year), so competition between plants is fierce. Specifically, these plants have to compete for precious resources, such as nitrogen, other nutrients, and especially water. So, this intense competition for water and nutrients leads to individuals that win and lose–all within a small area. The individuals that lose die-off, creating a small blank area in the grassland. Rainfall and nutrients in this newly blank soil can then be used by the neighboring individuals, or the ones on the outside of the fairy circles. These individuals then grow larger (a pattern we do, indeed, observe in fairy circles), making them even better competitors. Any seedling that manages to establish in a fairy circle will then very likely be outcompeted by these larger individuals that form the outside of the ring.

 

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Difference in biomass between the edge of the fairy circles and the surrounding grasses.

Alternatively, a common pattern in the Namib desert are termite nests in the center of fairy circles. So, perhaps termites actually create the circles? Termites act as ecosystem engineers–meaning they are well known for modifying their environments. Termites may eat the vegetation in the middle of the circles, creating the bare spots we see. As termites consume all the vegetation in the center, this produces more moisture in the center of the circle. Similarly to the previous hypothesis, the grasses at the edge of the circles can then access this water to grow larger. Other studies have, indeed, observed termite nests in 80% to 100% of all circles, but it is unclear if the termites are taking advantage of the fairy circles or, rather, creating the fairy circles.

Clearly, the verdict is still out! We are going to be examining fairy circles that have been manipulated to help us distinguish between hypotheses. In 2015, Nichole and her collaborators added water and nutrients to some fairy circles and removed termites from other circles. Now, we have the opportunity to go back and see how the circles have responded to the various treatments, hopefully allowing us to better understand how they are created in the first place. Fingers crossed!

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