Strange barren spots destroy the vast Namib Desert, which stretches from southern Angola to northern South Africa. They are known as “fairy circles”, and for a natural phenomenon with such an odd name, scientific debates about their origin have been heated.
Michael Cramer, an ecological physiologist at the University of Cape Town who has studied fairy circles, said: “The back and forth between opposing camps is often no less than vitriolic.
Even though decades of research, no consensus exists about the origin of the mysterious formations. Theories have included poisonous gases, toxic bushes, and bacteria or fungi that kill plants. Two of these explanations – the circles are created by termites, or they are the result of plants competing for limited water – have dominated the scientific debate.
“Each publication has been hailed as finally solving the ‘mystery’ of the fairy circle in the mass media,” Dr Cramer said in an email, calling such reporting a approach is “not the norm for science”.
A rigorous study published in October won’t end this fight, but it does seem to give water-related hypothesis a clear lead on termite theory.
“Plants are forced to create these circles to redistribute water to maximize their chances of survival,” said Stephan Getzin, an ecologist at the University of Göttingen in Germany and an author of the study. “We call it ecosystem engineering.”
The Namib Desert is one of the driest places in the world, typically receiving only a few inches of rain per year. Researchers first proposed in 2004 that plants, in the competition for water in this extreme ecosystem, can organize themselves into fairy circles – an idea originally adapted from pattern formation theory developed by mathematician Alan Turing.
Over the past decade, Dr. Getzin and others have published more than a dozen papers supporting the hypothesis, known as plant water stress.
For their latest study, Dr. Getzin and his colleagues spent three years examining fairy circles at 10 study sites across 620 miles of desert. “In one of those years, 2020 was a drought, while 2021 and 2022 were exceptionally rainy — a lucky break that allowed researchers to compare different conditions,” said Dr. Getzin said.
They used soil moisture sensors to collect continuous readings every 30 minutes of water content in the sand in and around the fairy circle. They also examined hundreds of grass shoots and roots excavated at different time intervals from within the circles and surrounding areas.
After rain, the researchers found that the grass sprouted both inside and outside the fairy circle, but within 20 days almost all the young shoots inside the circle had died. They also found that the top eight inches of soil in the fairy circle quickly dried out, which they hypothesized happens when the plants around the fairy circle actively draw water toward them.
Plants are constantly evaporating – or losing water – through their leaves. Meanwhile, their roots take in water. In Namibia’s sandy soil, this creates a vacuum effect that transfers water from within the fairy circles toward the roots at the edge of the circle and beyond. “It’s similar to you opening a window in winter and the warm air immediately moves out,” says Dr. Getzin.
The new paper also addresses the termite hypothesis, which has been championed by Norbert Jürgens, an ecologist at the University of Hamburg in Germany. He reported in 2013 that the fairy circles were in fact created by sand termites damage grass roots.
In the new paper, Dr. Getzin and his colleagues note that termites have clearly disappeared from their study sites, and they found no sign of root damage from dead grass. rain.
“We can say the reason is not termites, because there are no termites,” says Dr. Getzin. “The reason is drought.”
Dr. Jürgens declined a request for comment.
Walter Tschinkel, an entomologist at Florida State University who was not involved in the study but has published papers supporting the water stress hypothesis, said the new findings provide “more nails in the water.” sarcophagus”.
“The support for the hydrodynamic explanation is currently very strong, and the support for termite causation is very weak,” said Dr. Tschinkel.
Yvette Naudé, an analytical chemist at the University of Pretoria in South Africa who was not involved in the study, agrees that this new study seems to confirm that, “contrary to popular belief, the activity of the relationship does not cause fairy circles”.
But she doesn’t consider the mystery to be solved. “Many questions remain unanswered,” she said.
Supporters of the water stress hypothesis still need to contend with other explanations, says Dr. Naude. She continues to suspect, based on previous studies, that something in the composition of fairy circle soil is inhibiting plant growth.
Marion Meyer, a plant scientist at the University of Pretoria, says that while the new study is “concluding” that termites are not a factor, the fairy circles may be the result of another species of plant, Euphorbia. According to research published by Dr. Meyer, it produces a toxic, milky sap that kills grass where it used to grow, causing fairy circles to form.
Dr. Getzin disagrees with these interpretations, pointing to the study that he says mutilated explain soil content and The Euphorbia hypothesis.
One of the reasons the various fairy-circle theories exist, says Dr. Cramer, is the cause of “a long-standing ecological pattern that cannot be reproduced in the laboratory.” is extremely difficult.” Finally, to put a stop to the debate, he called for “several manipulative experiments to test ideas in the field.”
But someone other than Dr. Getzin would have to conduct such challenging experiments, because he had decided to give up studying fairy circles.
“After more than 20 years, I consider this chapter closed,” he said.
He plans to shift his focus to investigation.”plant ring, ” Another strange natural event in the Namib Desert. The plant rings look similar to fairy circles but are a different phenomenon – and so far, they’ve escaped the attention of other scientists, says Dr Getzin.
