Sometimes the circle of life needs a little bit of fortune

THOSE ancient gods, the sun and moon, appear as circles in the sky, writes Richard Collins.

The fairy circles of Namibia, Africa. Picture: Hoberman Collection/UIG via Getty

Johannes Kepler was shocked to find that the planets moved elliptically; the orbits of celestial bodies must surely be circular. To think otherwise seemed blasphemous.

Ploughs and bulldozers didn’t desecrate our ringforts, at least until recently; raths were the abodes of fairies. These round earthworks date back to Iron Age and early Christian times. The great stone circles of Brodgar Avebury and Lough Gur are at least 4,000 years old. Were these sacred enclosures inspired by the mysterious fairy circles of grasslands and forests?

Rings found in other parts of the world have puzzled scientists. In Namibia, strange circles of bare brown earth dot an arid landscape like craters on the moon. Their origins, it’s said, are “one of nature’s greatest mysteries”. The patches become visible when about 2m in diameter and grow for up to two months. Some reach 20m, or more, before disappearing. Vegetation grows within Irish fairy rings but nothing survives inside the Namibian ones. Oddly, grass grows particularly vigorously just outside the rims of the circles, providing a feeding bonanza for the local herders’ cattle. How can plants thrive on one side of the divide, yet not grow at all on the other?

The bush-men say the rings are footprints of gods or that the poisonous breath of underground dragons kills the vegetation. Scientists, studying the rings since the 1920s, didn’t come up with a better explanation. The discovery of similar bare patches in the Australian outback three years ago, led to renewed interest in the Namibian rings. In an article just published in Nature, researchers from the Universities of Strathclyde and Princeton claim to have solved the riddle. The African fairy rings, it seems, have very different origins from Irish ones.

Our rings are the work of fungi, not fairies. Neither plant nor animal, fungi belong to a completely separate kingdom. These cleaners and recyclers produced thread-like structures which penetrate the soil, breaking down dead wood and roots. Spores, the seeds of fungi, are spread in various ways; mushrooms and puffballs being “fruiting-bodies”, seed-dispensers. A giant puff-ball, which you might find when walking in the country, is the world’s most prolific fungus. It can send 7,000,000,000 spores into the air.

A fairy ring, it’s thought, may grow from a single spore. Threads work progressively outwards, forming an expanding underground ring. If conditions become very dry, plant-roots weaken and the fungal threads attack them, causing withering in the grass above. Nutrients released in the process may stimulate growth around the ring’s perimeter.

Water shortage, it seems, also plays a role in forming the Namibian rings but no fungi are involved. Enter the termites, members of the cockroach order. These social insects live in colonies with castes of soldiers, infertile blind workers, fertile kings, and queens which are the world’s longest-living insects. Termites, found on every continent except Antarctica, are highly successful creatures.

Insect cities need water. To increase the supply, the sand-termites of Namibia destroy water-demanding vegetation above their colonies, creating the mysterious bare patches. But there’s a spin-off for plants; surplus water running off the exposed earth, helps grasses grow immediately outside the perimeter. If there were no termites in this dry arid environment, vegetation wouldn’t survive at all. Plants re-arrange their roots to cash in on water the termites make available. The overall result is a pock-marked honey-comb-like landscape. By reducing the numbers of competing plants and collecting what little moisture there is, the termites have enough water for themselves, with a surplus to help the local plants survive.

  • Corina Tarnita et al. A theoretical foundation for multi-scale regular vegetation patterns. Nature. January 2017.


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