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  • Frits Westra
    Mysterious fairy circles defy explanations http://www.newscientist.com/news/news.jsp?id=ns99994833 19:00 31 March 04 Exclusive from New Scientist Print
    Message 1 of 1 , Apr 1, 2004
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      Mysterious 'fairy circles' defy explanations

      http://www.newscientist.com/news/news.jsp?id=ns99994833

      19:00 31 March 04

      Exclusive from New Scientist Print Edition.

      The three main theories to explain the origins of the mysterious "fairy
      circles" of Namibia have just been dismissed, following an in-depth study
      by South African researchers.

      "They still remain a mystery," says Gretel van Rooyen, a botanist at the
      University of Pretoria, who headed the team conducting the study.

      Fairy circles are discs of completely bare sandy soil anything from two to
      10 metres in diameter. Found exclusively along the western coastal fringes
      of the Namib desert in southern Africa, they are easy to spot because they
      are barren in the middle yet have unusually lush perimeters of tall
      grasses, which stand out from the otherwise sparse vegetation of the
      desert.

      From the time researchers began to take an interest in how they were
      formed in the early 1970s, three major explanations emerged: termites,
      radioactive soil and toxic debris left in the soil by Euphorbia damarana,
      the poisonous milkbush plant.

      The radioactive soil theory was easily dismissed after van Rooyen sent
      samples to the South African Bureau of Standards to be tested for
      radioactivity and they were all found to be negative. "That would have
      been the perfect explanation," she says. "But they found no traces."

      Dead or alive

      To check out the poisonous plant idea, van Rooyen's team located some
      milkbushes in the desert - living and dead - and took samples of soil from
      underneath. They tried to grow desert plants on it in the lab and found
      that the grass species Lolium multiflorum flourished in the soil, showing
      there was no toxic debris to account for the barren patches.

      That left just one proposed explanation - that termites mop up all the
      seeds on the fairy circles leaving nothing that will grow. "It's the one
      most people believe," says van Rooyen.

      But when her team dug for termites, or their nests, they found nothing.
      "We dug trenches up to two metres deep, but found no signs or remains,"
      she says.

      So where do the circles come from? The researchers have shown that grasses
      withered on samples of soil taken from the fairy circles themselves, but
      did better than expected when grown on earth from the lush perimeter,
      proving that there really does seem to be something different about the
      two areas of soil.

      Van Rooyen is now following up the possibility that toxic elements are
      somehow deposited in the circles. "But even if we find them, how they came
      to be there is the next problem." For the moment, she admits, "we're left
      with the fairies."

      Journal reference: Journal of Arid Environments (vol 57, p 467)

      Andy Coghlan

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