The enigmatic fairy circles emerge in hundreds of arid areas of the planet

For decades they have intrigued ecologists and botanists: in several desert areas of Namibia, the little vegetation there is spreads out, creating circular patches on the ground, patches that, seen from the air, appear to be organized into hexagons. They are called fairy circles. A few years ago, very similar patterns were discovered in the Western Australian Desert, which added more intrigue to the matter. Now, Spanish researchers have complicated the mystery by discovering dozens and dozens of examples of this plant distribution. They all occur in arid areas where both water and nutrients are scarce. Circularity and hexagonal organization would be the optimal way that plants have found to survive.

In 1971, ecologist Ken Tinley observed along the coastal desert of the Namib (Namibia, Africa) large areas with circumferences of vegetation in which nothing grew inside. They must have reminded him of fairy rings or circles, an original circular distribution of several species of mushrooms from humid Europe, and he borrowed the name. Its formation would be due to the action of termites in sandy desert soils, according to many scientists who have studied these patterns. In 2017, Australian researchers discovered new fairy circles in its western desert. The authors of the work ruled out the action of termites and pointed to mechanisms of biological self-organization already anticipated by the mathematician Alan Turing. However, this same year and drawing on Aboriginal knowledge, other work has also linked Australian fairy circles to another species of termites. The debate continues and now some Spanish researchers are coming to fuel it even more: they have found many more fairy circles spread across the planet.

The scientific journal PNAS publishes this Monday a work by scientists from the Complutense Universities of Madrid, Almería and Alicante, in addition to the CSIC, who have created the first global atlas of fairy circles. To do so, they had to go high up, into space, so that an artificial intelligence (AI) system could analyze thousands and thousands of images captured from various satellites. They trained the system by showing it photographs of the circles in Namibia and Australia, to look for similar patterns. The AI ​​spent a month watching and watching. Afterwards, the image bank created by the AI ​​was reviewed by the authors of the work, ecologists and soil scientists who are experts in arid areas. Their result was not what they expected: They have found 265 places with fairy circles in 15 countries on three continents. In addition to expanding the known number of Namibian and Australian deserts, they have found similar formations in all the countries that border the Sahara to the south, from the territory of Western Sahara to the Horn of Africa. But they have also been detected in Madagascar, also on the African continent, in southern and western Asia and in large quantities in central Australia.

The composition shows new fairy circles in, starting at top right, Western Sahara, Mauritania, two from Niger, Sudan and the last one in Australia.Guirado et al.

“The ones we have seen have the same spatial distribution as those already known from Namibia and Australia,” says Emilio Guirado, from the Laboratory of Arid Zone Ecology and Global Change at the University of Alicante (UA) and first author of the study. In one of their most intriguing features, fairy circles form hexagons around each other, in an almost constant amount. The average of the known circles is 6.72 sides. In the new ones, it is almost identical, with 6.71 sides.

In a second part of the work, they crossed the results of this AI system with another artificial intelligence, dedicated in this case to the study of the environments and ecology of arid areas. The objective was to find out what factors facilitate the appearance of these patterns. Manuel Delgado Baquerizo, leader of the IRNAS-CSIC BioFunLab and co-author of this study, said it in a note: “Our study provides evidence that vegetation formations in fairy circles are much more common than previously thought, which “which has allowed us the first attempt to globally understand the factors that affect its distribution.”

Fairy circles appear, according to this work, in arid regions whose soil is mainly sandy. “The sand is very important. Where there is sand there can be fairy circles, but not in non-sandy areas,” explains Guirado. Other universal conditions that they have observed are the scarcity of water, especially the irregularity of the low rainfall, and the reduced presence of nutrients in the soil. “The vegetation makes its way in a different way than where there are no water problems,” concludes the UA researcher.

Regarding the role of termites, Guirado recalls that “they occur throughout the world, but their global importance is low.” He adds that they may have outstanding local importance in some cases, such as that of Namibia, “but there are other factors that are even more important,” he adds. It must be taken into account that this atlas is a photograph, a still image, “which looks at whether or not there are fairy circles, but does not show anything about their origin or formation,” the scientist concludes. So it cannot be ruled out that insects played a role at the time. For the authors of the work, it will be necessary to go down from the satellite to the ground to clear up the mystery.

Norbert Juergens is professor emeritus at the Institute of Plant Sciences and Microbiology at the University of Hamburg (Germany) and one of the leading experts on fairy circles. He has been studying those of Namibia for decades and is the first supporter of the engineering role of termites. From the Namib, he responds to Guirado’s work that, until the new patterns are closely studied, “it would be useful for scientific debate to limit the term fairy circle to those structures first described by Tinley in 1971″. After remembering that in all arid zones patterns are reproduced on the ground as a result of different processes, he wonders why “the methods applied by the authors found rounded and regularly spaced bare bald patches among the vegetation only in the Old World, not in America.” . And he adds: “If this is correct, it would be a strong indication of a central role for specific organisms such as, for example, termites, which evolved during evolution in Africa and Australia, but not in the Americas,” he adds.

“These regular patterns increase the productivity of the vegetation, maximizing the capture of resources”

Fernando Maestre, director of the Laboratory of Arid Zone Ecology and Global Change at the University of Alicante

Fernando Maestre, director of the Laboratory of Arid Zone Ecology and Global Change at the UA, acknowledges that they do not know why in the sandy deserts with low and irregular rainfall and scarcity of nutrients in America there are no these plant patterns. “We can only speculate. “It could be due to human action in the past, grazing, fires or changes in land use that reduced the vegetation cover.”

But what Master of the Fairy Circles highlights is its key role in these extreme environments. They have verified that in areas where there are fairy circles, the primary productivity of the vegetation is greater. “These regular patterns increase the productivity of the vegetation, maximizing the capture of resources at a local scale. Primary productivity is an index that can be compared with the greenness of the plants, with their lushness. These are not orchards, but they do maintain that cover of life all year round.

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