In the Namib Desert of southern Africa, strange circles dot the landscape as regularly as polka-dots on a dress. The bare spots are ringed by lush grass. These structures are known as fairy circles. The fairy circles repeat for miles – and how they came to be is hotly debated. Scientists are divided regarding their origin: animal or vegetable?
“What’s the role of animals? Do they play a crucial role, or is this just plants self-organizing?” said Dr. Robert Pringle of Princeton, who recently visited Utah State University to speak about predicting large scale-vegetation patterns.
One camp is adamant that the fairy circles arose through interactions between plants. Plants benefit from being very near a neighbor because their neighbor shades the ground, preventing water evaporation from the soil. But more distant neighbors are competition for water, creating barren patches. The barren patches captures water, which flows to the edges, creating a feedback loop that supports plants on the edge.
Other researchers believe fairy circles formed around termite mounds. Termite mounds have more nutrients and water than the surrounding soil. However, termites will remove plants growing on top of the mound, causing the plants to be most successful at the edges of the mound.
“Termite mounds are often also very evenly spaced because termites fight with each other, and that leads to gaps between termite colonies,” said Dr. Pringle.
New research by Dr. Pringle and his colleague Dr. Corina Tarnita indicate it may be both. Dr. Tarnita created a mathematical model in which termites and plants interact. The simulated termites created evenly spaced bare patches. Under arid conditions, the simulated plants created vegetation rings around the mounds. The model with the interactions created very similar patterns to fairy circles – and predicted a previously unexplained vegetation pattern in between fairy circles.
However, not everyone is satisfied. Critics of Tarnita and Pringle’s model say it needs to be field-tested. The recent discovery of fairy circles in Australia – where termites are rare – also casts doubt on their theory. It looks like the debate over the fairy circles’ provenance will likely continue for many more years.