Mysterious fairy circles – research team sees causes of the phenomenon largely clarified

Worldwide inventory
Researchers believe the causes of fairy circles have largely been clarified

September 25, 2023, 9:20 p.m

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For decades, experts have been puzzling over the causes of fairy circles in Namibia and Australia. Now a research team is finding similar structures in other regions of the world and drawing conclusions about the cause of the phenomenon. A German expert has doubts – but he agrees on one point.

Fascinating and enigmatic: Scientists have been trying to understand the secret of fairy circles for decades. These circular, vegetation-free patches of four to eight meters in diameter, surrounded by grassland, are primarily known from Namibia, but have also been discovered in western Australia.

Since then, various theories have been circulating about the causes of the phenomenon, which only occurs in dry regions: According to this, termites or certain properties of the soil, vegetation and climate are said to be responsible.

Now a Spanish research team is presenting a global inventory of the phenomenon, which is apparently much more widespread than previously known. To do this, the team led by Emilio Guirado from the University of Alicante examined around 575,000 satellite images using artificial intelligence to specifically identify such structures without vegetation.

Fairy circle-like patterns in 15 countries

In total, the group discovered fairy circle-like patterns in 263 different areas in 15 countries on three continents, as reported in the “Proceedings” of the US National Academy of Sciences (“PNAS”). In addition to Namibia, these include several regions of Australia, as well as the Sahel and the western edge of the Sahara, the Horn of Africa as well as northern Saudi Arabia, Kazakhstan and Madagascar.

Fairy circles have fascinated science for decades and have sparked a lively discussion among researchers about the causes, the group emphasizes. However, there is still a lack of understanding as to what their occurrence depends on. In order to clarify this, the areas found were compared with regard to possible influencing factors such as climate, soil and vegetation.

Soils more important than termites

It is said that termites hardly play a role on a global level. Instead, the soils were more important: they contained little moisture (around 2 percent), but a lot of sand (52 to 80 percent) and little nitrogen (0.025 to 0.1 grams per kilogram) and had an alkaline pH value above 8.5 . In addition, seasonal precipitation – 100 to 300 millimeters per year -, little wind and no major slopes were typical for the areas. A model with these factors can predict fairy circle-like structures with around 80 percent accuracy, the group writes.

However, there are also areas where the phenomenon does not occur despite such circumstances, it is said. Examples of this are the Baja California peninsula on the northern Mexican Pacific coast, the northwest of Libya and the border region between India and Pakistan. Therefore, there could be other, as yet unknown factors that are involved in the creation of fairy circles.

“Study interesting – but it dilutes the term ‘fairy circles'”

“The colleagues’ study is interesting because it is the first worldwide search for fairy circle-related vegetation gap patterns using modern methods,” says desert ecologist Stephan Getzin from the University of Göttingen, who has been researching the phenomenon for several years. The study makes an important contribution to researching such gaps.

“But unfortunately the study waters down the term ‘fairy circles’ and ignores its definition.” Fairy circles are not just any regularly arranged gaps in vegetation, but rather they form very evenly ordered grids – for example in terms of the distances from one another. This special uniformity – called spatial periodicity in technical jargon – only exists in Namibia and western Australia, but not in the other regions mentioned in the study, emphasizes Getzin: “The study basically confirms that real fairy circles continue to exist only occur in the Namib Desert in southwest Africa and in a small area in western Australia.”

“Only correlation, no causation”

In addition, the study is only about statistical correlations, not causality, explains the researcher. “Environmental variables for predicting the patterns are important, but the example of fairy circles in particular shows that when examining these circles you always have to go into detail on the ground in order to separate mere correlation from causality of a gap pattern.”

Getzin explains the real fairy circles with the self-organization of certain plants when water is scarce. Like the expert at the end of 2022 wrote in the journal “Perspectives in Plant Ecology, Evolution and Systematics” using Namibia as an example, the edge grasses that often sprout particularly luxuriantly on the edge of the fairy circles create the vegetation gaps by removing moisture from the soil. Sandy soil contributes to this due to its special conductivity. By sucking in the moisture, water is withdrawn from the grasses in the fairy circle, so that they die. In his on-site studies, Getzin found no evidence of an influence from termites.

Agreement on one point: fairy circles are becoming more common

Getzin explains the round shape by saying that a circle has the smallest ratio of circumference to area. “By forming highly patterned landscapes of evenly spaced fairy circles, the grasses act as ecosystem engineers, benefiting directly from the water resource provided by the vegetation gaps.” However, the phenomenon is still not completely clear, says the researcher. “But there is no more plausible theory at the moment.”

Getzin agrees with the Spanish research group on one point: Given the strong involvement of climatic factors, they assume that fairy circles are likely to become more common in a warmer and drier world. The ecologist also believes this: “Fairy circles are an expression of the fact that there is not enough water for a continuous grass cover.”