For centuries, people have tried to explain the mysterious circles found in the Namib Desert (southwestern Africa). The locals call these areas of bare ground surrounded by rings of tall grass, "the footprints of God." Some believe that this is the mark of a fire-breathing dragon living underground.
Researchers also came into play and tried to explain the nature of the strange circles. Over the past 16 years, several candidates have been proposed as the culprit for the emergence of bare areas, for example, the reason for their appearance was the intense competition between termite colonies and even plants thirsty for water.
Now in more detail. Some scientists believe that termites living in the soil are responsible for arid areas. They make the soil porous by creating a permanent reservoir for rainwater 50 centimeters below the ground. It supports the life of insect colonies and the surrounding ecosystem. Due to this, in fact, vegetation appears in the places of existence of termites.
But there is also an alternative point of view. "Witch's circles" are created by plants competing for water. Other scientists think so. But both theories could not explain the whole nature of the appearance of such "patterns".
Now ecologists say both are correct. Both termites and plants can be implicated in the formation of circles due to lack of nutrition and moisture.
On the edge of the Namib Desert, where the mysterious rings are formed, there are arid sandy areas that receive less than 100 millimeters of rainfall per year. This amount of moisture seems to be sufficient to support the growth of some types of grasses, but it is not enough to create a continuous meadow.
(By the way, the same rings can be found in western Australia. But scientists still do not know the circumstances, as a result of which such circles appear.)
Theoretical biologist Corina Tarnita of Princeton University wanted to know how these patterns are formed on the ground, for example, the same phenomenon of "witch's rings" (fairy circles). To this end, she created mathematical models that predict what patterns will appear here or there (and what they will look like), taking into account various factors.
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She and fellow (and part-time husband) Princeton University ecologist Rob Pringle felt that "witch circles" could be a good way to test a model.
Scientists, along with other ecologists, have predicted for the first time how termites can transform the landscape, given the available vegetation. Through simulations, they found that colonies would appear and disappear over the decades (as would the observed "witch circles"), and that they could eventually self-organize. The result is a systematic cellular arrangement of insect colonies, that is, each colony will be surrounded by six others.
The specialists were also interested in the contribution of plants that they can make to the appearance of unusual rings. They turned to an already published paper suggesting that plants can also self-organize based on the moisture in the soil.
“There is simply not enough water to maintain full grass cover, which leads to such gaps in the pattern,” explains Stephan Getzin, an ecologist at the Helmholtz Center for Environmental Research. …
The researchers, combining the two models of explanation, came up with a mixed solution: termites can create large-scale patterns, while plants can create smaller patterns.
During the construction of their homes, insects change the flow of water in the soil, which leads to the appearance of desert areas surrounded by a ring of tall grass. But the models also predict that there will be systematic thickets of grass between the "witch circles" in such places. They will create a drawing within a drawing.
When researchers photographed such "witch circles" in Namibia, they found similar thickets of grass, indicating the correctness of the modeling conclusions. Other observers usually ignored such areas, Tarnita adds.
Many researchers agree with the findings of their colleagues. “To me, research has shown that large-scale patterns in Namibia can be explained by a combination of termites and plants,” says MG (Max) Rietkerk, an ecologist at the University of Utrecht in the Netherlands. He notes that this work will help explain the patterns found in other regions of the world.
True, there are those to whom the decision seemed not so obvious. “There is no doubt that the 'witch's circles' are the product of an ecosystem created by termites living in the soil,” says ecologist Norbert Jürgens of the University of Hamburg. In 2013, he was the first to suggest that termites are responsible for such patterns. And physicist Cristián Fernández-Oto of the Free University of Brussels, meanwhile, notes that the study "does not change his opinion that plants are the main ingredient."
The scientific world needs to conduct experiments to determine the exact cause, according to entomologist Walter Tschinkel of the University of Florida in the United States. He also studies mysterious "patterns", but through other studies. “We also need more knowledge about the biology of termites and the grasses present in these areas,” he says.
A study explaining the nature of the "witch's circles" was published in the scientific journal Nature.
