# Computer modeling solves ‘fairy circle’ mystery

This is pretty cool. For years circular barren patches of land, known as Fairy Circles and typically found in the grasslands of the western part of Southern Africa have remained a mystery, but thanks to computer modeling we may finally have an answer.

Cristian Fernandez-Oto at the Université libre de Bruxelles in Belgium, along with a couple of colleagues, used computer simulations to show that the circles are actually naturally occurring patters which start to appear when plants compete for water in arid conditions.

As MIT’s Technology Review points out, the model is actually fairly simple and based on the fact that a single plant’s root structure can cover a much larger area than the part of the plant that appears above the surface.

It then posits that there are two uniform states of vegetation: uniform grassland and the bare states. The Fairy Circles, they say, result from strong interaction between interfaces connecting the two states — a front if you will.

The model focuses on this interaction to show that when the barren region gets smaller, the plants along the front come closer together and their root systems begin to interact.

But, the root systems can only go so far and the plants can’t get closer than the root system allows. And, as the computer model shows, the most efficient way of packing plants around a barren patch is in the form of a circle.

The model also predicts that the more arid the region, the bigger the circles will be just as they are in the real world. Their diameters vary between two and 15 metres, with the most extreme ones found further North in the drier part of the region.

“Our analysis explain how a circular shape and fringes are formed, and how the aridity level influences the size of the fairy circles,” they say.

There you have it then. If you have an ancient mystery that needs solving, forget Sherlock or Hercule Poirot, all you need is a little sophisticated maths (okay probably a lot) and some advanced computer modeling.

Image: Thorsten Becker (via Wikimedia Commons)

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• Pieter

You did not mention anything about the ants that inhabit those ‘fairy circles’. Are those circles not made by the ant colonies? I don’t think this post is accurate at all. How much research goes into your articles?

• Stuart Thomas

Hi Pieter,

I assume you mean the termite theory? I am well aware of it but deliberately left it out because of the controversy it has invoked with scientists accusing each other of “confusing correlation with causation”.

The fact that the model used here, works so accurately using the variables it does, suggests that it is far more compelling.

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