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Mystery of the "Fairy circles" may finally be solved

“Fairy circles” are a fascinating natural phenomenon found in the Namib Desert and some other arid regions in southern Africa, such as parts of South Africa and Angola. They are circular patches of barren soil surrounded by a ring of lush grass or vegetation

The barren patches can range from a few feet to as much as 65 feet (20 meters) in diameter. From above, you can view them best, where their intricate patterns become more apparent.

The name originates from local folklore, which suggests that these circles are the footprints of the gods or fairies who dance in the desert. However, the true scientific explanation for their formation has been a subject of research and debate for over a decade. 

Several ecosystem modelers have argued that the circles are caused by self-regulation of the grasses. However, a team of scientists led by the University of Hamburg has recently found evidence that the circles in fact emerge from termite activity.

Different theories about fairy circles

A prominent theory explaining the circles was put forward by researchers from the University of Göttingen. They argued that the grass plants’ self-organization causes the bare patches. These plants draw water unevenly to themselves with their roots and through extensive diffusion in the sandy soils. This leads to the death of grasses in the bare patches. 

According to this theory, the grasses surrounding these patches cause the evidence of desiccation found beneath the fairy circles at a depth of about 20 centimeters through fast horizontal water sucking.

However, as early as 2013, the University of Hamburg botanist Norbert Jürgens proposed a different theory. He argued that activity of subterranean sand termites of the genus Psammotermes is causing the bare patches.

By eliminating the plants in the sandy soils, they enable long-lasting storage of water after infrequent rainfall. In the current study, Jürgens and his colleagues have proven the presence of sand termites on over 1,700 fairy circles in Namibia, Angola, and South Africa.

Self-regulation theory ruled out

“Of even greater significance is that the analysis of my colleague Gröngröft and the measurements of the hydrological properties of the desert sand carried out in the laboratory invalidate the crucial foundations of the assumption of self-regulation,” Jürgens explained. 

“The water conductivity of the coarse-grained sand of the fairy circles, in which the termites live, is indeed very high when a lot of water is present during a heavy rain event, which can then quickly seep away in the large pores.”

“However, the situation is completely different when the sand has released the easily movable water into the depths and has dried out to less than about eight percent of the soil volume. Then water is only stored at the points of contact between the sand grains. At this point, a continuous film of water is missing and the soil’s ability to conduct water drops to very low levels. This means that at the levels of moisture found below fairy circles (≤5 percent by volume), very little liquid water transport can take place over short distances.”

According to the experts, the horizontal water transports over meters in just a few days assumed by the representatives of the self-regulation theory are physically impossible. 

“The soil moisture measurements on the fairy circles and the soil hydraulic properties of the sand found in the laboratory thus rule out the self-regulation hypothesis as an explanation for the fairy circles. The cause for the formation of the fairy circles is thus clear. It is the sand termites that secure a considerable survival advantage through soil moisture storage,” Jürgens concluded.

More about fairy circles 

Fairy circles are a fascinating natural phenomenon. They exist primarily in the arid grasslands of the African continent, specifically in the Namib Desert. This area spans between Namibia and Angola’s southern parts, even reaching into South Africa’s northern Cape.

A significant amount of scientific interest and local lore surrounds these peculiar patches of barren land amidst otherwise verdant grassland expanses.

Physical characteristics and distribution

These unique patterns, often described as “bald spots,” range from 2 to 15 meters in diameter. Each circle encompasses a barren, compacted patch of soil encircled by a ring of tall, lush grass. They tend to occur in regions experiencing mean annual precipitation of 100-150mm, which primarily consist of grasslands.

The distribution of these fairy circles exhibits a remarkable degree of regularity, often appearing in vast hexagonal or honeycomb formations. This intriguing spatial arrangement is an example of natural self-organization, a process observed in numerous other natural phenomena.

Formation hypotheses

Despite extensive research, the exact cause behind the formation of fairy circles remains a subject of ongoing debate among scientists. Two primary hypotheses exist: the termite hypothesis and the self-organization hypothesis.

Fairy circles formed by termites

This theory posits that termites, especially the species Psammotermes allocerus, engineer these circles. Termites consume plant roots, leading to the death of the vegetation and subsequent formation of barren patches. The ring of enhanced grass growth surrounding the circle is a result of termites’ subterranean activities, which increase soil nutrients and water availability.

Fairy circles are self-organized

This hypothesis suggests that fairy circles are the outcome of competition for scarce water resources among grass plants in these arid environments. The theory suggests that the dying off of vegetation at the circle’s center helps promote the growth of the peripheral grass by reducing water competition.

Both hypotheses offer compelling arguments. The current scientific consensus is that a combination of biotic and abiotic factors likely contributes to fairy circle formation.

Ecological significance of fairy circles

Fairy circles play a crucial role in the ecology of arid grasslands, serving as miniature oases. During periods of drought, the circles trap water.

This nourishes the surrounding vegetation and creates a habitat for various small organisms. This functionality underlines their ecological importance, contributing to biodiversity in these regions.

Cultural significance

Fairy circles hold considerable cultural significance among local communities. These formations associate with various myths and folklore.

Some believe that these are footprints of gods, while others perceive them as the result of dragon’s breath. These cultural narratives add to the mystique of fairy circles and have a role in local tourism.

In summary, the mystery of fairy circles in Africa continues to inspire scientific research and cultural fascination. Understanding these unique natural phenomena provides essential insights into ecological dynamics and self-organization processes in nature.

As we uncover more about the fairy circles, we illuminate not only the intricacies of African grasslands but also broader themes of resilience and adaptation in ecology.

The study is published in the journal Perspectives in Plant Ecology, Evolution, and Systematics.


By Andrei Ionescu, Staff Writer

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