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Arid desert ‘fairy circles’ caused by … rain?

The Australian fairy circles (viewed from above) forms an additional source of water in this dry region, because the rainwater flows in the direction of the grasses at the edge.
(Stephan Getzin)

Unusual bare circles in the grasslands of Australia and the Namib Desert called “fairy circles” are not the work of termites, new research suggests.

Fairy circles are a long-standing mystery. Some scientists have argued that they mark termite nests, or are the result of plants compete for scarce resources. Some say that a combination of termites and plant activity resulted in the odd spots. But now, a new study suggests that the circles are not the result of something alive. On the contrary, they are a result of erosion caused by heavy rainfall, and evaporation.

Termites nest sometimes within fairy circles, study researcher Stephan Getzin, of the University of Göttingen in Germany, said in a statement. But there is no evidence that the termites are actually the creation of the bald spots. [Photos: Mystical Fairy Circles Grace African Desert]

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Getzin and his colleagues focused on the fairy circles in the Australian desert near the town of Newman. They used drones for the visualization of the circles from the top and the excavated samples of 48 separate fairy circles spread over 7.4 miles (12 km). They compared the aerial photos of fairy circles with bird’s-eye views of famous harvester termites nesting .

“The vegetation gaps caused by harvester termites are only about half the size of the fairy circles and much less ordered,” Getzin said.

When the team went digging in the circles, they found only a few “termitaria, or termite colonies. They were small, not the large, paved dirt that prevents the plants to grow over large areas and can ensure that the bare circles. What the fairy circles contain, Getzin said, was a lot of clay and compacted soil. Most likely, he and his team have closed, forming the circles into cycles of heavy rain and evaporation in the extreme heat of the desert. In unvegetated soil, they wrote in the open-access journal of the Ecological Society of America, heavy rainfall washes fine clay in the empty spaces in the soil, essentially sealing it off with a hard “crust” is insensitive for new growth of the plant.

“[N]o destructive mechanisms, such as those of termites, are necessary for the formation of different fairy circle patterns,” Getzin said. “Hydrological plant-soil interactions along are sufficient.”

Namibian mystery

In a second study published in the Journal of Arid Environments, Getzin and his colleagues Hezi Yizhaq of the Ben-Gurion University of the Negev in Israel used satellite images to examine the patterns of fairy circles in Namibia. Most of the research on Namibian fairy circles has focused on the peculiar ordered, almost hexagonal pattern seen in fairly flat grassland conditions, they wrote. But in places where the topography is more varied, or conditions are unusual, the fairy of the circles, forming different patterns. [Image Gallery: Amazing ‘Fairy Circles’ of the Namib Desert]

In drainage areas, for example, the researchers noticed oval fairy circles more than 98 feet (30 m) on the other side. In extremely dry places, they found very irregularly distributed circles. They also noted some “mega circles” more than 65 feet (20 m) in diameter. That study was just a pilot study, the researchers wrote, but it highlights questions about the plant and the soil dynamics outside of the eye-catching, very often fairy-circle patterns.

Getzin and his colleagues claim to have fairy circles, regions, a very homogenous soil, only one or two plant species, particularly growth and a just-right balance of rain and evaporation. These requirements may explain why the fairy circles are seen in only two deserts on Earth.

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Originally published on Live Science.

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