Credit: Florida State University
Walter Tschinkel, a Florida State University professor of biological science, recently had a paper published in the prestigious journal PLoS One about so-called “fairy circles,” strangely grassless circular patches usually surrounded by a ring of taller grass on the Namibian landscape.
Newly forming fairy circles in a grass matrix: A. Note circle of grey, dying and collapsed grass in the upper panel, and B. its substantial disappearance in the lower panel. C. Excerpt from Fig. 10B showing aerial view of newly forming fairy circles.
Credit: PLoS One/ Photographs courtesy of Denis Hesemans of Namib Sky Balloon Safaris.
No one knows what causes the circles, which appear from southern Angola to northern South Africa. In Tschinkel’s paper, “Life Cycles of Mysterious Namibian Grassland ‘Fairy Circles’ Characterized,” he provides a description of the variations in size, density and other attributes of the circles. Tschinkel also found that the circles are not permanent.
The circles occur in a range of sizes from small to large. Tschinkel found that the smaller circles, about 2 meters wide, arise and vanish over an approximately 24-year cycle, and the larger ones, about 12 meters wide, arise and vanish in about 75 years. He came to his conclusions after reviewing four years of satellite images and extrapolating the circles’ lifespans from the data.
Tschinkel’s paper provides a more complete description of the variation in size, density and attributes of fairy circles in a range of soil types and situations. Circles are not permanent; their vegetative and physical attributes allow them to be arranged into a life history sequence in which circles appear (birth), develop (mature) and become revegetated (die). Occasionally, they also enlarge.
The appearance and disappearance of circles was confirmed from satellite images taken 4 years apart (2004, 2008). The frequency of births and deaths as a fraction of the total population of circles allowed the calculation of an approximate turnover rate, and from this, an estimate of circle lifespan. Lifespan appeared to vary with circle size, with small circles averaging about 24 years, and larger ones 43–75 years.
Jeffery Seay
Citation: Tschinkel WR (2012) The Life Cycle and Life Span of Namibian Fairy Circles. PLoS ONE 7(6): e38056. doi:10.1371/journal.pone.0038056
