In Namibia, at the boundaries between grassland and desert, a strange phenomenon has puzzled people for centuries. Mysterious circles of barren land form in the middle of rich, thick grasses. Dubbed "fairy circles," their formation has been attributed to everything from termites to poison gas. Now, a group of scientists has a new theory.
Photo by Vernon Swanepoel
Environmental researcher Stephan Getzin and his team have been studying the formation of fairy circles for 15 years. They've considered the possibility that these circles are caused by termites eating plant roots, leaving strangely geometric, plant-free regions behind. They could also have been caused by toxic gas, emitted slowly from hydrocarbon deposits, that kill off any plants that try to take root where the gas is released.
Finally, the researchers hit upon another possibility. What if this was just a matter of resource competition among the plants themselves? Some grasses might be sucking up all the water, leaving other regions dry and arid. This idea seemed to make sense, because fairy circles form in regions where grasslands are giving way to desert, meaning that water supplies are limited.
Getzin and his team created a computer model of what might happen to grasses growing in areas with limited water, and found that one likely outcome would be patchy patterns of growth that create very regular patterns — something like fairy circles.
According to a release about the team's work, published today in Ecogeography:
This study is based on the review and evaluation of aerial images, covering representative regions with fairy circle occurrences throughout northwest Namibia. With the aid of these images scientists have analysed for the first time the exact spatial location and distribution of these barren patches within the surrounding landscape ...
Fairy circles are distributed surprisingly regularly and homogenously, even across large spatial areas. "The occurrence of such patterning in nature is rather unusual," says Stephan Getzin. "There must be particularly strong regulating forces at work".
What remains as a probable cause is local resource-competition among plants and vegetation – which incidentally seems quite capable of creating homogeneously scattered circles. [In] a young-growth forest plants will grow and develop at comparatively close range, [but] vegetation will thin out and regress, over the years, in a self-organising process. Each mature tree, after all, needs sufficient space and nutrition for its development and will therefore be able to survive only at an appropriate distance to its neighbour. A similar process of resource-competition may consequently also be the real cause for a self-organising formation of the mysterious fairy circle patterns.
If the researchers turn out to be right, what we're seeing is the strange beauty of a transitional ecosystem. Tiny patches of desert, leeched of water by surrounding plants, are emerging out of the grassland.
Read the full scientific study in Ecogeography