Science Snap (#29): African Fairy Circles

Originally posted on the EGU blog network

Fairy Cirlces
Mysterious Fairy Circles dotting the Namibian grasslands. Credit: Neurgens

If you’re wandering among the arid desert that stretches from Angola to South Africa, you may notice the ground pot-marked by millions of circular barren patches. These striking features are known as “Fairy circles”, and can grow up to 15 meters in diameter. Tall grasses often surround these circles, further accentuating these miniature crop circles. How these Fairy Circles form is hotly debated. Theories have to account for their non-random location, and a lifespan 30-60 years where they grow in size borefore grassland eventually invades them again.

Oral myths of the Himba people attribute the circles to gods and spirits and traditionally they are thought to have spiritual and magical powers. My favourite myth, however, is that these Fairy Circles are scars in the landscape where a dragon breathed out toxic gases.

Unfortunately, a scientific explanation likely exists. In 2013, Juergens published an article supporting a popular theory that sand termites are responsible. The paper states that sand termites form the circles by eating grassroots to expose the soil. Once exposed, the soil more easily absorbs, which ultimately helps maintain the grasslands in extremely dry conditions. However, the sand termite theory has been critiqued for assuming correlation with causation, as Juergens suspects that termites are responsible because they’re the only species consistently observed at the circles. Thus, sand termites were identified by a process of species elimination.

In contention to the termite theory, Cramer and Barger (2013) believe that Fairy Circles are a consequence of natural competition in grasses. They suggest that landscapes with a mixture of grasses form “self organizing” circles due to underground competition for water resources. Both hypotheses have aspects that remain inconclusive, thus no theory currently prevails. They currently struggle to explain why circles appear across a variety of regions, soil and vegetation types and furthermore, no one has ever observed termites gnaw out a circle. Perhaps there is still room for a supernatural cause after all.

Namibian Fairy Cirlces
Namibian Fairy Circles. © 2013 Cramer, Barger. Published under Creative Commons License

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