Circle game: plants build fairy circles? Brad Howe, Heliwest Group

Deep in the Australian outback, circular, grass-ringed patches of earth stretch for several hundred square kilometres across the red, ancient soil. This is the first time these “fairy circles” have been spotted outside the Namibian desert, where their formation has evaded explanation for decades. The new discovery could help resolve the long-standing mystery of how they form.

“It shows that the fairy circles of Namibia do not exist on their own,” says Stephan Getzin, an ecologist at the Helmholtz Center for Environmental Research in Leipzig, Germany.

Getzin and his team visited the site 15 kilometres south-east of Newman, Australia, to measure the circles and analyse the conditions on the ground after an environmentalist working for an iron ore mine nearby sent them an aerial shot of the formations.


“From the bird’s-eye perspective the pattern becomes clear, and you see the regular features indicative of the fairy circles,” Getzin says.

The team’s investigations found clues to the circles’ origins, a mystery that has defied explanation for decades (see video above).

In Namibia, local legends have explained the circles as the footsteps of the gods, burn marks from the breath of underground dragons, or even landing spots for UFOs.

The most popular scientific theory is that ants or termites nibble on the roots of grasses, so the plants die back in a circle from the site of an insect nest.

More recently, however, another theory has emerged that says the circles arise when the plants compete for water and nutrients and “organise” themselves to maximise access to scarce resources. The latest theory suggests such circles should be discovered in other arid regions of the world, too.

The Australian rings back up this self-organisation hypothesis. Getzin’s team found few ant or termite nests within, or near, the circles and no correlation between rings and locations of the nests that did exist.

But they did find that the hard soil crust within the circles was almost impermeable to rainfall – all the water pouring into this area flowed towards the periphery, where the thirsty plants await. “That gave us clear hints that the gaps serve as a source of water for the vegetation,” Getzin says.

More water around the circle edges means more biomass and roots, which leads to the soil becoming looser. The less dense soil allows more water to penetrate and feed the vegetation, creating a feedback loop supporting the plants at the edge of the circle.

The exact mechanism for how the circles arise is different in Namibia. There, the circles actually soak up more water and act as underground reservoirs for plants growing around the edges (see graphic, below).

The dominant grasses of the Triodia genus found in direct vicinity to the fairy circles in Australia also form other typical drought patterns such as stripes, labyrinths or spot patterns with individual plants surrounded by bare earth.

This provides strong evidence that the fairy circles also arise due to competition for water, Getzin says, though he doesn’t claim to have solved the origin of the circles.

“You should never claim to put an end to the mystery,” he says. “We’ve just made one significant step forward in solving the problem.”

“It’s pretty good evidence for the self-organising theory,” says Michael Cramer, a biologist at the University of Cape Town in South Africa. “There is still a long way to go to make it conclusive, but I think the evidence is mounting.”

Journal reference: PNAS, DOI: 10.1073/pnas.1522130113

Read more: What is making mysterious fairy circles appear in the desert?