Surreal 'faerie circles' in Namibia dispel the mystery of their origins
The origin of the "faerie circles" in Namibia has puzzled scholars for nearly half a century. They are strange circles of sand, bare of grass, in places where there is plenty of grass. They form and disappear after years for no known reason.
Scientists have long attributed these reddish circles, most notable in the grasslands of Namibia and northwestern Australia, to either termites or plants that were somehow self-organizing.
Now, a group of scientists from the University of Göttingen in Germany has come up with new evidence to support the self-organization theory that previous studies have attempted to explain the nature of the mysterious "faerie circles" found in the Namib Desert, the world's oldest desert, along the coast of Namibia, southwest Africa and western Australia.
Based on two "exceptionally good" rainy seasons in the Namib desert, the scientists showed that grasses inside the "faerie circles" died immediately after the rains, but termite activity did not cause the bare patches to appear.
Continuous soil moisture measurements show that the weeds around the circles have strongly depleted the water inside the circles and, therefore, are likely to cause the death of the weeds inside the circles.
According to the findings, published in the journal Perspectives in Plant Ecology, Evolution and Systematics, grasses form these circles, between 2 and 10 meters wide, to make the most of the scarce rains.
Some 80-140 kilometers off the coast in Namib, there are millions of 'faerie circles', each a few meters wide, and together they form a distinctive pattern visible for miles around.
The scientists followed up the sporadic rain events in several regions of this desert, and examined the weeds, their roots and buds, and potential root damage caused by termites.
Termites, tiny insects that live in large colonies around the world, are often blamed for the death of grasses.
Scientists were very interested in investigating the dying conditions of weeds inside the “jinn circles” immediately after the rains, which led to new growth of weeds.
In addition, they installed soil moisture sensors in and around the circuits to record soil and water content at 30-minute intervals starting from the 2020 dry season until the end of the 2022 rainy season.
This enabled the scientists to accurately record how the growth of new emerging weeds around the circles affected soil water in and around the circles. They looked at differences in water seepage between the inside and outside of the circuits in ten regions across the Namib Desert.
The data shows that after about ten days of rain, the grasses already started dying inside the circles, while most of the inner areas of the circles had no grass germination at all. After twenty days of rain, the grasses inside the circles were completely dead and yellow while the surrounding grasses were vibrant and green.
When the team examined the weed roots inside the circles and compared them to the green weeds outside, they found that the roots inside the circles were as long or longer than those outside. This indicates that the weeds were struggling to grow roots in search of water. However, scientists found no evidence that termites feed on roots.
It was not until fifty to sixty days after the rains that root damage became more evident in the dead weeds.
“The sudden absence of grass in most areas within the circles cannot be explained by termite activity because there is no biomass for these insects to feed on,” explains Dr. Stefan Getzen, from the Department of Ecosystem Modeling at the University of Göttingen. But more importantly, we can show that the termites are not responsible, because the grass dies immediately after it rains without any sign of the creatures feeding on the roots.”
When the team analyzed data on soil moisture fluctuations, they found that the decline in soil water inside and outside the circles was very slow after the initial rains, when the grasses had not yet settled. However, when the surrounding weeds were established, the decline in soil water after rainfall was very rapid in all areas, even though there were almost no weeds within the circles to take up the water.
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