New Theory Explains Africa’s Mysterious Fairy Circles

Fairy circle
This fairy circle in the Namib Desert in Namibia is made of Stipagrostis ciliate grass–perhaps in response to water scarcity? Photograph by Norbert Juergens, National Geographic Stock

A few months ago we brought you the latest explanation of Africa’s mysterious “fairy circles”—circular patterns in the earth that appear across the grasslands of southern Africa and which have intrigued and baffled scientists, earning their rather ethereal name.

The newest findings at the time suggested the fantastical formations were the result of termites eating away grass roots to create the fairy circles’ iconic sandy centers. Now a new study recently published in PLoS ONE posits that rather than relying on the landscaping skills of insects, the grasses are doing it themselves; in a phenomenon with the very sexy name of “Self-Organizing Spatial Vegetation Patterning.”

Luckily it’s simpler than it sounds. Basically the theory is this:

In dry ecosystems like Namibia, where fairy circles are common, competition for water is fierce. Therefore, while we may see a calm savannah landscape, fierce resource competition is actually being waged below the surface, at root level.

“We hypothesize that these barren spots arise due to below-ground resource competition between grasses,” states the report. “Enhanced growth in individuals that are strong competitors for below-ground resources results in the decline in growth of neighboring individuals, thus forming larger interspaces or barren patches.”

In other words, whoever wins the water war essentially condemns his neighboring grasses to death by dehydration, creating a barren patch—the nexus of the fairy circle.

Beneficial Rings

But rather than killing off all the competition and just leaving it at that, the newly sandy patch actually benefits a radius of surrounding plants. The study confirms that, as previously theorized, the resulting barren patch acts as a reservoir for moisture and nutrients, trapping those life-giving resources to the boon of surrounding plants and creating the neat rings of thriving grass that have made fairy circles such an object of curiosity and speculation over the years.

The report also suggests that the increased moisture and nutrient levels generated by the circle’s reservoir center and spread through “water runoff or sub-surface seepage” enable bigger grasses to grow around the circle’s edge, and help the ring of flora survive periods of extended drought.

The study employed extensive modeling to show that the occurrence and spacing of fairy circles can be accurately predicted based on a few environmental factors, including vegetation biomass, precipitation, and temperature seasonality, thereby “indicating that fairy circles are likely a climate-dependent emergent phenomenon.”

The Termite Connection

However, the report allows that other factors, including the previously discussed termites, may be contributing factors that share responsibility for keeping fairy circles clear of invading grasses and other vegetation. The report theorizes that the termite P. allocerus and other insects “…may contribute to grass mortality within fairy circles. Indeed, dead grass tussocks on some circles frequently have symptoms of termite damage.”

Therefore, although the theory is that resource-competition among grasses is what creates fairy circles “…a complex set of constraints including competition, nutrient availability, lack of propagules and faunal activity may all contribute to fairy circle maintenance,” according to the report.

Perhaps time will show this to be the definitive analysis of how fairy circles come into being, or perhaps a new theory will come along involving yet-unknown factors.

Until then, fairy circles are the mystery that keeps on giving.

Follow Stefan Sirucek on Twitter.

Stefan Sirucek is a writer and journalist who reports from both sides of the Atlantic. He's written for the Huffington Post and Wall Street Journal. Follow him on Twitter at @sirstefan.

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