Fairy Circles Mystery May Be Solved as Physicist Reveals Missing Link

The mystery of so-called fairy circles may have finally been solved—and it involves a "missing link."

This is the conclusion of an international team of researchers who studied the strange phenomena—hexagonal or round barren patches up to 39 feet across—that can be seen in the grasslands of Namibia and parts of Western Australia.

Exactly what causes these strange patterns has been an enduring mystery. In the myths of northern Namibia, the circles are attributed to the action of gods and spirits.

Scientists, meanwhile, have developed many theories, including that they emerge from the existing patterns of termite nests, as well as being caused by scale-dependent water-vegetation, a press release reported.

Now, scientists have come up with a new theory—these fairy circles may actually be a stress response.

In a new study, physics professor Ehud Meron of the Ben-Gurion University of the Negev in Israel reports that fairy circles could result when plants have a stress response to a lack of water.

"Understanding ecosystem response to drier climates is of utmost importance for maintaining ecosystem function and the services ecosystems provide to humans in the current era of climate change," Meron told Newsweek.

"Our study deepens this understanding by considering for the first time the combined effects of two response mechanisms of dryland ecosystems. Using the Namibian fairy circles as a case study and a novel mathematical model that captures the two response mechanisms, we resolve two outstanding fairy circle puzzles and thereby demonstrate the importance of considering the interplay between the two mechanisms. Importantly, besides solving these puzzles, we find that this interplay results in significantly higher resilience to water stress compared to the resilience that each mechanism alone provides."

The researchers believe that two important but previously overlooked processes could actually be working together to create the fairy circles.

These two processes are "phenotypic plasticity" at the level of a single plant and "spatial patterning" at the scale of a whole plant population.

Phenotypic plasticity refers to a plant's ability to change and adapt in response to environmental stresses.

Spatial patterning, meanwhile, is a term biologists use to describe the structure of plants or objects in a landscape.

These two mechanisms work in conjunction with each other when there is less water available.

When water is scarce, the top layers of soil dry out faster. Accordingly, individual plants tend to grow deeper roots, seeking out more moist layers of soil.

However, in the NamibRand Nature Reserve where the fairy circles are found, the deeper you go, the more compact the soil tends to become, meaning that water can't diffuse as far.

"This is where spatial patterning comes in. As the climate becomes drier, bare-soil gaps develop (the fairy circles) and form water reservoirs from which adjacent plants can draw water and survive," Meron said.

"When the climate becomes yet drier, phenotypic changes from shallow-rooted plants to deep-rooted plants take place. The deep-rooted plants can survive the dryer conditions because they benefit from a moister deep soil layer."

However, Meron said that the patterns they form are "short-ranged" because that soil layer is compacted with short-range soil-water diffusion.

"The outcome is a multi-scale fairy circle pattern consisting of large-scale gaps and small-scale spots in between the gaps as observed in the field.

"This is unlike the prediction of the classical theory that does not consider phenotypic plasticity. According to this theory, along the rainfall gradient gap patterns transform into stripe patterns, and stripe patterns into spot patterns, but the latter two patterns are not observed in Namibia."

Fairy circles, the team believes, may be just one of the many "stress relaxation pathways" used by plants when there is a lack of water—a trick that is becoming more common as climate change worsens.

The grasses' ability to do this also implies "a previously underestimated resilience of dryland ecosystems," the team argues in the study.

"Identifying these alternative pathways is essential for shifting fragile ecosystems on tracks to collapse to pathways of resilience," said Meron in a statement.

He added: "This study highlights the importance of considering more elements of ecosystem complexity when addressing how to evade tipping to dysfunctional ecosystem states as warmer and drier climates develop."

According to the study, drier conditions caused by climate change are severely affecting the health of ecosystems—as well as "the services they provide to humans."

"Understanding the response of ecosystems to drier climates may provide clues on how to improve their resilience," the team wrote in their study.

"Generally speaking, the next challenge is considering more elements of ecosystem complexity in the study of ecosystem response to water stress. In our current study, we added one element of complexity to the current theory of vegetation pattern formation—phenotypic plasticity," Meron said.

"Phenotypic plasticity is a plant-level mechanism to cope with water stress. For example, a plant can close its stomata to reduce water loss to the atmosphere or deepen its roots to reach moister soil layers (the case we considered in the current study). Spatial patterning is a population-level (many individuals of the same species) mechanism involving partial population mortality and the formation of bare soil patches that act as an additional water resource to adjacent vegetation, besides direct rainfall (plants have several means to draw water from their bare soil surroundings). But there are additional mechanisms operating at other levels of ecological organization besides the plant and population levels."

The full findings of the study were published in the journal PNAS.

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Update 12/13/23, 5:44 a.m. ET: This article has been updated to include additional information.

Update: This article has been updated to include additional comment from the author.

Correction 12/20/23, 07:10 a.m. ET: This article was updated to correct the explanation of how spatial patterning works, with new comments from Ehud Meron.