The disenchantment of the fairy circles – Wissenschaft.de

There are many theories about the formation of fairy circles (here in the NamibRand nature reserve in the Namib Desert, Namibia). When it is dry, no grass grows between the circles. (Image: Stephan Getzin)

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There are many theories about the formation of fairy circles (here in the NamibRand nature reserve in the Namib Desert, Namibia). When it is dry, no grass grows between the circles. (Image: Stephan Getzin)

What creates the mystical “fairy circles” in dry areas? A German researcher is on the trail of the riddle.

The circular spots in the desert floor look like they have been drawn by magic. With the uniformity of a honeycomb pattern, such “fairy circles” decorate parts of the Namib in southern Africa and areas of the Australian outback. Satellite images show that there are several million of them. “They usually consist of 20 to 30 individual plants and usually have a diameter of four to eight meters,” explains Stephan Getzin from the Ecosystem Modeling Department at the University of Göttingen, who and his team want to unravel the secret of the fairy circles.

Fairy circles have always fascinated mankind. In 2000, Getzin and a colleague established the international scientific term “Fairy Circles”. Most recently, the Göttingen researcher worked on the world’s first sharp scientific definition of the term. “The problem is that the term fairy circle has been used in a very inflationary way for some time. But not everything that is green and grows in a circle can be considered a fairy circle, ”emphasizes Getzin. “For a long time I only knew real fairy circles from the Namib Desert, where they are formed by annual stipagrostis grasses. In 2014, however, I was contacted by an Australian ecologist who had found very similar formations in the outback in Northwest Australia. ”Getzin traveled to Australia and discovered that the formations there are real fairy circles. Unlike in the Namib, they are formed by perennial Triodia grasses and only reach a maximum diameter of seven meters. Otherwise, however, they have the same characteristics as those in the Namib, including the extraordinary spatial order.

Water competition as a possible explanation

How are the fairy circles created? Numerous ecologists, geologists and even physicists and mathematicians worked on the answer. Getzin has also been trying to solve this fascinating riddle of nature for two decades. The ecologist believes that there is “no absolute certainty yet” about the actual reasons for the formation of the circles. But he sees himself and his team on a hot track: “Our so-called self-organization theory says that circular growth formations offer the up to 30 grass shores that make up a fairy circle the best conditions for survival in this dry environment,” explains the scientist. “When it is dry, those grass cliffs that are positioned directly on the bare inner circle have the best access to water. Casually one could say: The marginal grasses make common cause by forming a stable circle that is in competitive equilibrium. ”They divide the water collected in the middle among themselves. In the middle, grass only germinates briefly when it is in abundance, as Getzin observed on site: “What we can already say is that grasses in the center of fairy circles, which sprout tentatively after some rain, begin to die off shortly after it has rained, but neither their roots are eaten by termites, nor are their roots shorter than those of the vital grasses at the edge of the circles. “

Getzin sees efficient eco-engineering in self-organization: “Without this remarkable ability of the grasses in the Namib and the Australian outback, the areas would probably be completely devastated and silted up.” However, the term “self-organization” is somewhat misleading: no plant gives anything voluntarily here to do a service to those of their own kind. Rather, some plants have better chances of survival than others due to their more favorable location.

As plausible as Getzin’s self-organization theory may be, testing it is hard work. Especially since critics complain that there must be fairy circles in other climatically similar zones of the earth, not just in the Namib and the Australian outback. But Getzin is working diligently to support his hypothesis: “We have now been following the precipitation in the Namib for over a year to investigate its effect on the fairy circles,” reveals the researcher. “We have to learn to better understand the water cycle in the vicinity of the circles. At the beginning of 2022 we will have the third rainy season behind us in the Namib. Until then, we hope to be able to say exactly how and why fairy circles are formed. At least we want to be very close to the solution. “

This abridged article is from the December 2021 issue of bild der Wissenschaft. Read more about fairy circles and how the Göttingen research team is studying them in the full article.

Reference-www.wissenschaft.de

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