From Mike Walker
The photo reminds me very much of salt scalds in Tasmania. Here the groundwater comes up through cracks in some rocks in very dry areas and produces perfectly symmetrical rings of luxuriant growth on the perimeter of circles. The fact that the Namib desert fairy rings occur in sandy soil along the coastal fringes could mean they are caused by sea water bubbling up from ancient palaeochannels.
The water in the Tasmanian rings evaporates in the centre, concentrating the salt and leaving it bare. The rings are about the same size as the ones you describe.
Spalford, Tasmania, Australia
