Until recently, fairy circles — those strange, barren patches of earth that arrange themselves in a honeycomb-like pattern — had been documented only in southwestern Africa. In a paper Monday, scientists have confirmed the first example of this phenomenon in Australia, adding fuel to the hypothesis that competition for scarce water causes these mysterious patterns.
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The first fairy circles documented in Australia
When Stephan Getzin, an ecologist at the Helmholtz Center for Environmental Research in Leipzig, Germany, opened the email, his heart began to flutter. Attached was an aerial image of fairy circles, just as he had seen in countless photos before. But those images were always taken along long strips of arid grassland stretching from southern Angola to northern South Africa.
These fairy circles — which looked nearly identical — came from Australia, not Africa.
“I was really astonished,” Dr. Getzin said. “I couldn’t believe what I was seeing.”
The emailed photo came from Bronwyn Bell, who does environmental restoration work in Perth. She had read about Dr. Getzin’s research in Namibia and made a connection to the odd formations in her home state, Western Australia.
Until that point, Australian circles were completely unknown to science. “Not even the Australians were aware of their jewel,” Dr. Getzin said.
Scientists have been interested in fairy circles since the 1970s, but have not been able to agree on what causes the patterns to form. Researchers generally fall into two groups — team termite and team water competition — but there are other hypotheses as well, including one involving noxious gasses.
Dr. Getzin, like others on team water competition, explains the circles through pattern-formation theory, a model for understanding the way nature organizes itself. The theory was first developed not by biologists, but by the mathematician Alan Turing. In the 1990s, ecologists and physicists realized it could be tweaked to explain some vegetation patterns as well. In harsh habitats where plants compete for nutrients and water, the new theory predicts that, as weaker plants die and stronger ones grow larger, vegetation will self-organize into patterns ranging from gaps to spots to labyrinths.
“Such phenomena are explained with lots of theory and formulas and math, which ecologists can make use of,” Dr. Getzin said.
The difference between African and Australian circles
In the case of African fairy circles, the bare patches act as troughs, storing moisture from rare rainfalls for several months, lasting into the dry season. Tall grasses on the edge of the circles tap into the water with their roots and also suck it up with the help of water diffusion through the sandy soil.
Although similar in appearance, Australian fairy circles turn out to behave differently, Dr. Getzin and his colleagues have found. The soil where they form is loamy, not sandy as in Africa, they say. And rather than form a water trough, Aussie circles feature a very hard surface of dry, nearly impenetrable clay, which can reach up to a scalding 167 degrees during the day. Despite the differences, though, they believe the fairy circles’ function remains the same. When the researchers poured water into the circles in a simple irrigation experiment, it flowed to the edges, reaching the bushy grass that grew there.
“The gaps function as a source of extra water, like in Namibia,” Dr. Getzin says. “The mechanism of water transport is different, but the function of the fairy circles is the same.”
To test their self-organization theory, the researchers also ran a spatial pattern analysis of aerial imagery of the area and created computer simulations of environmental interactions. They found that the Australian fairy circles, like African ones, formed distinct hexagonal patterns, like a giant honeycomb. They also discovered labyrinth and spot patterns nearby, adding further evidence that plants in the area are engaged in cutthroat competition for water.
Accounting for termites
Dr. Getzin and his colleagues also paid special attention to the insect fauna in the area — knowing that that subject would be under extreme scrutiny by a group of competing researchers. In 2013, Norbert Jürgens, an ecologist at the University of Hamburg, published a paper in Science pointing to termites as the culprits behind fairy circles. Others, however, counteredthat the mere presence of termites did not prove the insects actually caused the circles to form.
In Australia, Dr. Getzin and his colleagues recorded all signs of termite and ant activity, such as mounds and foraging holes. They used GPS to map each nest and then compared their locations with those of the fairy circles, but they said that there was no evidence of correlation. Using electron microscopy, they also found that the circles’ hard center crusts were a result of natural weather processes, not insects.
Divisions among fairy circle scientists
Dr. Jürgens, however, has not been dissuaded. The discovery of so-called fairy circles in Australia is interesting, he said, but given the differences with the Namibian fairy circles, he asked whether we could really call them fairy circles, technically speaking. Referring to them as “something like ‘clay circles’ would be helpful,” he said.
Fairy circles or not, though, the Australian formations could also be the work of termites, he said. Dr. Getzin and his colleagues found that the Australian circles contain more clay and fine silt than the surrounding landscape, for example, and those “clay islands” could be a result of nests built over time by social insects, Dr. Jürgens said.
What would be considered fairy proof?
Others, however, were more charitable in their evaluations of the new work. The new research “moves us closer toward a unifying theory of fairy circle formation,” said Nichole Barger, an ecosystem ecologist at the University of Colorado, Boulder.
It could be that more fairy circles are yet to be discovered in arid environments around the world, she said.
According to Walter Tschinkel, an entomologist at Florida State University, the findings strengthen the claim that the circles are a result of self-organization by plants. He cautioned, though, that to be more certain, scientists would need to control environmental factors — water and termites, for example — to see which produce the predicted outcome. For now, though, limited budgets and logistical challenges have prevented such massive undertakings in the field.