The secret of Namibia's 'fairy circles' may be explained at last

Using computer models, ecologists think they have finally hit upon the reason for the strange polka dot patches scattered across the Namib desert.

The marks on the ground in the Namib desert resemble a vast sheet of polka dots, or to the less romantic observer, perhaps a bad case of chickenpox.

In local myths, the bare, red circles fringed with grass are footprints of the gods, or patches of land once poisoned by the breath of a subterranean dragon. But even among scientists, who strive for more convincing theories, the curious, repetitive patterns have proved hard to explain.

Since “fairy circles” became the focus of scientific study, researchers have proposed a host of ways by which the bare discs of soil may form. One idea points the finger at underground termites that engineer the landscape above their heads. Another proposal claims the patterns, which can grow to 25 metres wide, arise from natural competition between desert grasses.

In the latest effort to nail the answer, ecologists at Princeton University turned to computer models. To start with, they ran simulations to mimic the impact on desert grasses of termites building colonies underground. Sand termites in the Namib desert eat the roots of low-lying vegetation, meaning more moisture for them, and dead patches on the ground above. In the simulations, the dead zones were confined to patches created when neighbouring colonies of a similar size came up against one another, and settled on a border between their territories.

The “fairy circles” of the Namib desert, which can grown to 25 metres wide. Photograph: Jen Guyton
“The termites start with their own mound and go out and forage,” said Corina Tarnita at Princeton. “If they find a smaller colony, they simply kill it and expand their own territory. But if they run into a colony that is about the same size, they cannot do that, and end up with a boundary where there’s permanent conflict, but not a full-blown war.”

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Source: The Guardian