Fairy circle (arid grass formation)
Fairy circles are circular patches of land barren of plants, varying between 2 and 12 metres (7 and 39 ft) in diameter, often encircled by a ring of stimulated growth of grass.
[4] The circles have been recognised and informally remarked on for many years, first being mentioned in technical literature in the 1920s[5] and intermittently thereafter[6] with the intensity of study increasing during the final quarter of the 20th century.
[2][8] Examples can be found at 24°57′S 15°56′E / 24.95°S 15.93°E / -24.95; 15.93 (Namibia) and 23°27′S 119°51′E / 23.45°S 119.85°E / -23.45; 119.85 (Western Australia) Fairy circles typically occur in essentially monospecific grassy vegetation, where conditions are particularly arid.
[14] Like heuweltjies in South Africa and Mima mounds in the U.S., the cause of fairy circles has long been a puzzle and the investigation has proved challenging.
[15] In 2004, University of Pretoria botanist Gretel van Rooyen rejected proposals of termite activity, radioactive soil, and of plant toxins.
All rings have been found to contain termite casts, and radar investigations suggest that a moist layer of soil is situated beneath the fairy circles.
Juergens found evidence that the sand termite, Psammotermes allocerus, generates a local ecosystem that profits from and promotes the creation of the fairy circle.
[5][6] Later in 2013, Michael Cramer and Nichole Barger suggested that the circles were the consequence of vegetation patterns that arose naturally from competition between grasses.
The patches are maintained because they form a reservoir of nutrients for the taller grasses at the periphery and possibly because of the activity of termites, as in the theory above.
According to Walter Tschinkel, this theory accounts for all the characteristics of fairy circles, including the presence of tall grass species.
[20] Other recent work has considered interacting combinations of both animal- and vegetation-induced patterning effects as a potential unifying theoretical explanation for the fairy circle phenomenon.
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.
[31] In the oral myths of the Himba people of the Kunene Region of northern Namibia, these barren patches are said to have been caused by the gods, spirits and/or natural divinities.
[3] Of specific beliefs, the Himba people note that their original ancestor, Mukuru, was responsible for the creation of the fairy circles, or that they were the footprints of gods.
[17] Another myth put forth, promoted by some tour guides in Namibia, is that the circles are formed by a dragon in the earth and that its poisonous breath kills the vegetation.
