Fairy Circles in African Grassland Not Made by Termites – So What's Causing Them?

Some of the grassland regions in Africa are peppered with what are colloquially called fairy circles, describing areas that are round and free of any vegetation. But what's causing these formations has long baffled scientists.

So-called fairy circles spotted in the Nambi Desert. (Image source: Stephan Getzin/UFZ)

For a while, scientists hypothesized that termites might be creating the patchwork. Another idea included gases rising from the ground to the surface, while a third suggested competition for water resources among the plants.

Scientists at the Helmholtz Centre for Environmental Research in Leipzig, Germany, investigated all three options.

"Although scientists have been trying to answer this question for decades their mystery remains as yet unresolved," Dr. Stephan Getzin said in a statement.

"We have adopted an entirely novel approach in this research," Getzin, who has been studying the fairy circles for more than a decade, continued.

Using aerial images from northwest Nambia, the researchers analyzed the circles' spatial location and distribution. Were they arranged or scattered? What was their relation to their neighbors?

They found the circles had a regular distribution over large areas.

This fairy circle in the Marienfluss Valley measured six meters across. (Image source: Stephan Getzin/UFZ)

"The occurrence of such patterning in nature is rather unusual," Getzin said. "There must be particularly strong regulating forces at work."

This finding, Getzin said, rules out the termite theory, which was the most popular hypothesis for a while, especially after a  sand termite species was present at the circles. What's more, he pointed out that no one has shown that these critters were eating the plants or causing other disruptions that would create the pattern.

The most likely cause, Getzin said, is resource competition. Consider how a growing tree will cause smaller vegetation nearby to adapt to its use of water, light and other resources. Getzin thinks the same thing could be happening in the grasslands when some vegetation grows too close to each other. 

To confirm this idea, Getzin and other researchers from Israel simulated groundwater competition using a computer model and found that it resulted in similar distribution patterns as the fairy rings.

"We consider this at present being the most convincing explanation," the researchers said.

The study was published in the journal Ecography.