The fairy circles of Kaokoland (North-West Namibia) origin, distribution, and characteristics

Abstract

Embedded in species-poor grasslands, fairy circles are circular or sub-circular patches devoid of any vegetation. Characteristically, the circumference of each circle shows a band of more densely packed taller tussocks within a shorter, more sparse grassland matrix. The average diameter of the circles is between 5-8 m. Restricted to sites showing deep sandy deposits, in Namibia, fairy circles occur in a broken belt in the pro-Namib from southern Angola to the Orange River (Republic of South Africa). The distribution of fairy circles is significantly limited to areas with an average of 50-100 mm of annual precipitation. Based on remote sensing methods and expeditions, a map of the distribution area of fairy circles in Kaokoland (NW Namibia) was drawn up. The map indicates that fairy circles are more widely spread over the western parts of Kaokoland than previously reported. The two different active biological hypotheses of the fairy circles' origin comprise 1. the allelopathic interaction between Euphorbia damarana and the contemporary herbaceous vegetation (Theron 1979) and 2. the involvement of harvester termites (Moll 1994). Both hypotheses are discussed and a model about the origin and dynamic of fairy circles is presented. This model includes the foraging behaviour of the harvester termite Hodotermes mossambicus which is the prime causal factor in forming the fairy circles of Kaokoland.