Fairy circles are mysterious barren patches of land that are surrounded by healthy vegetation. The circles are common in many parts of the world but particularly in the arid grasslands of southern Africa where they range in size from 2 metres to 10 metres across (see picture above).
Plant biologists know these circles are stable having watched them over periods of decades. So these structures are clearly no accident. Indeed, exactly why fairy circles appear is something of a mystery. In particular, nobody has been able to explain why the patches are circular and not some other shape.
That changes today thanks to the work of Cristian Fernandez-Oto at the Université libre de Bruxelles in Belgium and a few pals who have used computer simulations to show that fairy circles are emergent patterns that occur naturally when plants compete for water in arid conditions.
Their model is relatively straight forward. It is based on the fact that a single plant can generate a root system below ground that is many times larger than the structure above the surface. The size of these roots determines how close together the plants can grow.
Next they assume that the land can exist in two stable states: either it is uniformly covered in vegetation or uniformly devoid of vegetation.
The interesting behaviour occurs when both states exist at the same time. In that case, there must be a “front” that connects the barren and fertile regions.
Fernandez-Oto and co specifically focus on the behaviour of this front in their model. They show that when a barren region shrinks, the plants along the front get closer together and their root systems begin to interact.
Via Sakis Koukouvis, Dr. Stefan Gruenwald