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Fairy circles are circular patches of land, barren of plants, though often encircled by a ring of stimulated growth of grass. They typically appear in the arid grasslands of the western part of Southern Africa. Fairy circles are particularly common in Namibia, but also occur in parts of Angola and South Africa.〔(BBC News - Enigma of Namibia's 'fairy circles' )〕 Fairy circles vary between in diameter. They typically occur in essentially monospecific grassy vegetation, especially in Namibia, where conditions are particularly arid. Associated grasses commonly are species in the genus ''Stipagrostis''. Like the causes of heuweltjies and Mima mounds, the origin and history of fairy circles have long been a puzzle and their investigation has proved challenging. One controversially favoured suggestion is that the activity of the sand termite ''Psammotermes allocerus'' is adapted to create locally favourable ecosystems that improve the supply of moisture and food.〔(African ‘fairy circles’ back in the mystery books after termite theory turned on its head )〕 As of 2014, Namibia's fairy circles are still considered "one of nature's greatest mysteries".〔 Daisy Carrington. ("Namibia's 'fairy circles': Nature's greatest mystery?" ). 2014. 〕 == Location == The circles occur in a band lying about inland, and extending southward from Angola for some 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.〔(【引用サイトリンク】 title=By building "fairy circles," termites engineer their own ecosystem )〕 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.〔 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.〔 Examples can be found at . 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Fairy circle (Africa)」の詳細全文を読む スポンサード リンク
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