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For more than 50 years, conservationists have studied and debated the mystery of the Namib Desert’s “fairy circles,” circular patches of mostly barren grasses that have spread 1,100 miles across South Africa’s arid grasslands.
Despite their whimsical name, similar to the term “fairy rings” for circular patterns of fungi found in woodland areas, no fairies play here. Many theories have been advanced, but two have the greatest merit. One theory appeared to blame termites for these dry patches, while the other considered the evolution of grasses. Scientists have gone back and forth for decades, but a new study offers what may finally be evidence for a clear explanation.
Stephan Getzin, an ecologist at the University of Göttingen in Germany and lead author of the study, began his research on fairy circles in 2000. Over the years, he has published more papers on the circles and their origins than any other expert. .
What makes the fairy circles stand out are the barren patches within them, but the growth of grasses around them is also remarkable – they have found a way to thrive in what is considered one of the driest places in the world. In previous research, Getzin and his team hypothesized that the plants in the outer rings of the rings had evolved to maximize their limited water in the desert.
And for the past three years, he has spent time in Namibia monitoring the growth of grasses to find more evidence for this theory. During the 2020 drought, Getzin and his team of researchers installed sensors that could record soil moisture to a depth of about 7.9 inches (20 centimeters) — and monitor the grasses’ water uptake.
“We were really lucky, because in 2020 there wasn’t a lot of vegetation, or in fact, hardly any grass in the fairy circle area,” Getzin said. “But in 2021, and this year, 2022, there was a very good period of rainfall, so we could really watch how the growth of the new grasses redistributes the soil water.”
Analyzing the data from these periods of rainfall, Getzin’s team found that the water from the circles was running out quickly, even though there was no grass to use it, while the outfield grasses were as strong as ever. Under the intense heat in the desert, these well-established grasses had evolved to create a vacuum system around their roots that drew any water toward them, according to Getzin. The grasses through the circles, which try to grow right after the rains, meanwhile, could not get enough water to live.
“A circle is the most logical geometric formation you would create as a plant suffering from a lack of water,” Getzin said. “If these circles were square, or low, complex structures, then you would have a lot more individual greens along the circumference. … The proportional area is smaller than if you grow in a circle. These grasses end up in a circle because that’s the most logical structure for maximizing the water available to each individual plant.”
The study called this an example of “ecohydrological feedback,” in which barren circles become reservoirs that help sustain grasses at the edges—albeit at the expense of grasses in the middle. This self-organization is used to protect against the negative effects of increasing drought, Getzin said, and is also seen in other harsh arid regions of the world.
The termite hypothesis, meanwhile, proposed that fairy circles are created by sand termites damaging grass roots, and was accepted among other scientists. However, a 2016 study of similar fairy circles in Australia found no clear links to the parasites. Getzin’s latest research came to similar conclusions.
“We have one example where it rained just once, the grasses came up, and after eight or nine days, the grasses just inside the fairy circles were starting to die,” Getchin said. “When we (excavated) these grasses carefully and looked at the roots, none of these grasses had termite root damage — but they still died. Our results clearly state, no, these grasses die without termites.”
Getzin and his team also found that roots from young plants inside the circles were longer than those outside. This suggests, according to Getzin, that the grasses had created longer paths in an attempt to find water—further evidence of their competition with the outer ring grasses in the desert where it was scarce.
While the evidence from the study is a step forward, scientists — including Getzin — believe there is still more research that could be done. That said, Getzin told CNN it was time to move on to a new challenge.
“With the fairy cycles in Namibia, as well as those observed in Australia, plants modify the distribution of soil moisture and thus increase their chances of survival, and we can call this kind of ‘swarm intelligence’,” said Getzin. “Plants create clever patterns and geometric formations and I will continue to work in this direction.”
Near the fairy circle area in Namibia, for example, researchers also found a different type of grass that forms in large, circular rings after rainfall. “It’s a completely different genus of grass, but it forms identical circular formations,” Getzin said. He is looking to investigate this process during Namibia’s next rainy season in 2023.
