Latest Solution To The Fairy Circle Riddle Does Not Hold Water

8 Nov 2022

Mysterious: Fairy circles in the grassland on the eastern edge of the Namib Desert. Photo: Norbert Jürgens

"Secrets of Namibia's fairy circles demystified", headlines The Namibian. "Researchers solve mystery of fairy circles in Namibia", reports the Kronen-Zeitung in Austria. Even the New York Times suggests that one of the two leading theories can be ruled out.

But Google urges scepticism. Search results show: Since 2000, the mystery of the bald circles in the grasslands on the eastern edge of the Namib has been solved time and again. At first it was said to be grass-cutting termites. Then it was toxic residues in the soil. Then there was talk of gases.

In the meantime, only two hypotheses are still in the running. The sand termite Psammotermes allocerus, which creates a water reservoir and a food reserve. Or the Stipagrostis grasses, which form the bare patches by means of "self-organisation" and thus benefit from their moisture and nutrients.

"Solution" not new

The recent study (Plant water stress, not termite herbivory, causes Namibia's fairy circles) that triggered the headlines advocates the second hypothesis. The "solution" is therefore not new. Its authors, however, claim to provide new evidence and disprove the competing termite hypothesis.

Ecosystem modeller Stephan Getzin from the University of Göttingen examined circles at eleven spots for this purpose. At fairy circle "hotspots" in the Namib from a point near the border with Angola to Garub near Aus. In the rainy seasons of 2020, 2021 and 2022.

But the methodology alone casts doubt on the results. Most of the circles were apparently only visited briefly a few times. At five of the spots, the researchers dug up grass plants that had germinated after rainfall but then died. The roots, according to Getzin, showed no signs of termites feeding.

Photo evidence inapt

As evidence, he presents photos that mean nothing to experts like Hamburg biologist Norbert Jürgens: "You need microscope images to make qualified statements." Jürgens is a leading proponent of the termite theory.

Termites were also not to be found in the circles, Getzin said, adding: As recognised insect experts would have already stated. Like Walter Tschinkel from Florida State University. Or Eugene Marais from the National Museum of Namibia.

Tschinkel had extensive excavations carried out in the NamibRand Nature Reserve, but in his 2010 study he concentrated on the harvest termite Baucaliotermes hainesi. Five years later, he ruled out Psammotermes as the cause, after experiments in the field, for example with nutrients or foils. Jürgens comments: "It was only found that the interventions did not reveal any difference with regard to the existence of the fairy circles. Possible effects of the interventions on important factors or processes such as the soil water balance were not measured." According to Jürgens, Marais was asked about fairy circles that were actually inactive after several years of drought.

Study refutes own basic assumption

At ten sites, Getzin's team measured soil moisture after local rainfall. In the circles, at their edge and in the surrounding grassland, the so-called matrix. In the NamibRand Nature Reserve, a data logger collected readings for three years.

The result: rainwater does not seep away significantly faster inside the circles than outside. This, too, cannot explain the death of the young grasses, Getzin concludes. And the new measured values would confirm his hypothesis.

However, these measurements are not new either, says fairy circle researcher Jürgens. "They are consistent with the values I have been measuring in circles at various locations in the Namib since 2006." Data from 2006 to 2008 can be found in his study The Biological Underpinnings of Namib Desert Fairy Circles. Published in 2013 in Science magazine, which reviews articles particularly rigorously.

"My and Getzin's values consistently show that the soil in the circle is wetter than in the matrix," says Jürgens. "Since the plants in the circle wither before those in the matrix, lack of water cannot be the cause."

Grasses "suck circles dry"

Even the foundation of the self-organisation hypothesis is not convincing. The roots of the grasses develop suction forces, explains Getzin when asked by Gondwana News. In this way, moisture is sucked in, up to a distance of seven metres. If there is a lack of water and competing plants of the same species (in the case of the Namib: the grass Stipagrostis ciliata), bare patches then form. As it were, as a water and nutrient reservoir from which the surrounding plants benefit. Especially the grass plants at the edge. They are clearly larger and thus form a ring.

The hypothesis is also based on a model developed by the mathematician Alan Turing. With variables such as water shortage and competition among plants, patterns like those of the fairy circles in the grasslands of the Namib can be generated in computer simulations, and also their circular shape, with ring.

"Dying" circles not explained

But the claim that grasses in the ring and in the matrix suck the circle dry cannot be true. As Jürgens and renowned experts such as Kelly Vlieghe and Mike Picker stated in a joint reply to the self-organisation hypothesis in 2015. For then the young grasses in the circle would have to die from the edge inwards. Photos by Jürgens, however, prove the opposite. The dying takes place from the centre outwards.

Another discrepancy: there are series of photos of growing circles. Strong grasses in the ring die, despite supposedly superior suction power and advantageous location. Weaker grasses further out, on the other hand, grow stronger. Gondwana News asked Getzin how, no answer.

fairy circle Marienfluss valley Namib desert Gondwana Namibia
"Dead" fairy circle: Younger grasses on the former bare area, surrounded by older grasses of the still visible ring.  Photo: Norbert Jürgens

And "dying" circles? In which young grasses grow again? Next to the strong grasses in the ring, which, according to Getzin, play a decisive role in keeping the circle bare? This question also remains unanswered.

Permanent ecosystems created by termites?

The termite theory, on the other hand, seems solidly based. Jürgens measured the moisture at four soil depths. With automatic sensors. Inside and outside a total of 14 fairy circles. At nine sites, one in Angola, five in Namibia and three in South Africa. Since 2006. He found sand termites and had them determined: Psammotermes allocerus.

His theory in a nutshell: The termites create the bare circle by eating the roots of the grasses. In this way, rainwater seeps away without being absorbed by grasses. Underground, it lasts for years - even in drought. The so-called luxury belt of tall grasses at the edge of the circle serves as a food reserve.

"These tiny termites manage to turn precipitation of only 50 millimetres a year into a permanently habitable ecosystem," Jürgens put it succinctly at the time. If the colony grows, the circle enlarges. If it dies, the circle is covered by grasses again. The pattern of fairy circles in the grasslands would then (also) result from competition between the colonies, which was also discussed in research in 2017 (see study by Robert Pringle and Corina Tarnita).

Termites detected in 1,700 fairy circles

The question remains why many researchers have not found termites in fairy circles. "Psammotermes is actually a small, inconspicuous termite," Jürgens explains. "Their colonies inhabit several small underground nests. Nevertheless, it is possible to systematically track them and their tunnels in years of normal rain, as joint publications with entomologists have shown. We have a publication coming out soon describing how to find Psammotermes quickly." According to the biologist, he now has data on more than 1,700 fairy circles. In all of them, he says, the sand termites or their structures have been detected.

An impressive number of cases. But is it enough evidence? In addition to the occurrence of Psammotermes in circles, doesn't it also have to be proven that it actually causes them? Jürgens nods: "We will soon present even better evidence of root consumption than already in my 2013 study. By the way, in a laboratory experiment Kelly Vlieghe proved years ago that sand termites eat living grasses." With her 2014 publication, she refuted statements to the contrary by insect expert Tschinkel.

Why the global canard?

The layperson wonders why Getzin and the three co-authors speak of a conclusion of the scientific debate in their study. And why a Google search gives the impression that the self-organisation hypothesis is an equally, if not the predominant, opinion of fairy circle research.

Which leads back to the media headlines. A canard. Worldwide. And not for the first time. How can this happen?

Lack of control within science. Scientific publishers have studies checked by experts before they publish them. The publication by Getzin and his three co-authors appeared in the journal "Perspectives in Plant Ecology, Evolution and Systematics" on ScienceDirect. Apparently, their review criteria are not strict or there was no expert in the relevant disciplines among the reviewers.

Public relations of scientific institutions. Immediately after the publication of the study, prepared press releases were sent out in German and English.

Time pressure in the media. Especially in daily newspapers, no journalist can do long research. The article on Wikipedia, for example, gives an overview of the topic, but does not help to verify the current information.

Complex issue. Even if journalists ask other fairy circle experts, they can hardly form their own picture, as they lack the scientific background to do so. Then the only option is to let experts have their say. Like in a report by the New York Times.

Thanks to Gondwana and Norbert Jürgens

The problems of the media mentioned above also apply to Gondwana News. The time invested in this article was enormous. It could not have been done without Gondwana Collection Namibia's special interest in fairy circle research. Great thanks also go to Norbert Jürgens, who took the time despite a busy schedule. In detailed emails and online conversations lasting several hours, he provided essential information and explained contexts.

Jürgens had discovered winged queens and kings of the sand termite Psammotermes allocerus for the first time in February 2008 in the presence of the author of this report in the Gondwana Namib Park near the Namib Desert Lodge. Just before swarming after a good rain. In their burrow, which was under the ring of the circle. Co-discoverer was the renowned Namibian ecologist Joh Henschel, at that time director of the Gobabeb Namib Research Institute.

Fairy Circle Namib Desert Lodge Gondwana Namib Park Namibia
One of the many fairy circles in the grassland near Namib Desert Lodge in Gondwana Namib Park on the eastern edge of the Namib. In three of the circles in the park Norbert Jürgens has been measuring the soil moisture with automatic sensors since 2006. Photo: Sven-Eric Stender

Sven-Eric Stender

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