The Fairy Circles of Namibia

Some grasslands in Namibia are spotted with mysterious lifeless circles that appear, then disappear after a few decades. What are "fairy circles" and why do they form?

Writing in the journal PLoS One,Walter R. Tschinkel, the study’s author and a biologist at Florida State University, reports that the circles can last 24 to 75 years.
The circles, which range from about 6 to 30 feet in diameter, begin as bare spots on an otherwise continuous grass carpet; after a few years, taller grass starts to grow around the circle’s perimeter. [...]
So while the reasons for the circles are still unknown, Dr. Tschinkel says his study has raised several crucial questions: “Why are they regularly distributed, rather than random or clumped; why do they appear with the grass dying suddenly; why is there taller grass at the perimeter; and why is there a difference in diameters?”
Until then, he continued, “the mystery of the fairy circles, or at least what causes them, remains a mystery.”

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