Fairy circle (Africa)

Fairy circles are circular patches of land barren of plants, varying between 2 and 15 metres (7 and 49 ft) in diameter, often encircled by a ring of stimulated growth of grass. Until 2014, the phenomenon was only known to occur in the arid grasslands of the Namib desert in western parts of Southern Africa, being particularly common in Namibia. In that year, ecologists were alerted to similar rings of vegetation outside of Africa, in a part of the Pilbara in Western Australia.

Fairy circles typically occur in essentially monospecific grassy vegetation, where conditions are particularly arid. Associated grasses commonly are species in the genus Stipagrostis. Studies show that these circles pass through a life cycle of some 30 to 60 years. They become noticeable at a diameter of about 2 metres, achieving a peak diameter of perhaps 12 metres, after which they mature and "die" as they undergo invasion, mainly by grasses.

Like the heuweltjies and Mima mounds, the cause of fairy circles has long been a puzzle and the investigation has proved challenging. One favoured theory is that the distinct vegetation patterns are a population-level consequence of competition for scarce water, as the plants "organise" themselves to maximise access to scarce resources. The circular barren patches capture water which then flows to the outer edges of the ring. More water available increases biomass and roots which leads to the soil becoming looser. The less dense soil allows more water to penetrate and feed the vegetation, creating a feedback loop supporting the plants at the edge of the circle.

In Africa, the circles occur in a band lying about 100 miles (160 km) inland, and extending southward from Angola for some 1,500 miles (2,400 km) down to the Northwestern Cape province of South Africa. It is largely a remote and inhospitable region, much of it over a hundred miles from the nearest village. The circles have been recognised and informally remarked on for many years, first being mentioned in technical literature in the 1920s and intermittently thereafter with the intensity of study increasing during the final quarter of the 20th century.

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