Scientists have been left puzzling over the origin of Namibia's mysterious fairy circles for nearly half a century - but they may have now conjured up the answer regarding the strange spirals in the ground.
About 80 to 140 kilometres from the coast, in the Namibia coastal desert, Southern Africa, there are millions of what have been described as "fairy circles".
They are circular gaps in the grassland - each ranging a few metres in width - and together form a distinctive pattern across the whole landscape, making it visible for miles around.
Previously, the reason for the phenomenon was put down to two main theories: either termites were responsible for nibbling away at the grass, or the plants themselves were somehow self-organising.
In fact, termites - tiny insects that live in large colonies around the world - were often blamed for the death of the grasses.
Now, researchers led by Göttingen University, Germany, have revealed the bizarre but real reason behind the occurrence.
The team of researchers have disclosed that plant water stress causes the circles in the ground to die and the grass around to thrive.
They went on to say that the study benefitted from two exceptionally good rainfall seasons in the Namibia Desert, which showed that the grasses within the fairy circles died immediately after rainfall - proving that termite activity did not cause the bare patches.
Instead, it has been revealed that the continuous soil-moisture measurements the scientists took during the dry season 2020 to the end of the rainy season 2022 demonstrate that the grasses around the circles strongly depleted the water within the circles.
Therefore, they likely induced the death of the grasses inside the circles, leaving it bare.
Dr Stephan Getzin, Department of Ecosystem Modelling at the University of Göttingen, explained: "The sudden absence of grass for most areas within the circles cannot be explained by the activity of termites because there was no biomass for these insects to feed on.
"But more importantly, we can show that the termites are not responsible because the grasses die immediately after rainfall without any sign of creatures feeding on the root."
During the investigation, researchers followed the sporadic rain events in several regions in the Namibia Desert and examined the grasses, their roots and shoots, and potential root damage induced by termites.
The circumstances of dying grasses within fairy circles were investigated straight after the rainfall, which triggered new growth around the grasses.
Additionally, scientists went on to install soil-moisture sensors in and around the spirals in order to record the soil content at 30-minute intervals during the dry to wet season this year.
What this enabled was for the researchers from the university to precisely record the growth of new emerging grasses and see how the circles were affected by the soil water.
After this, they also went on to investigate the differences in infiltration between the inside and outside of circles at ten regions across Namibia.
The data has gone on to show that about ten days after rainfall, the grasses were already starting to die within the circles - while most of the interior area of the circles did not have grass germination at all.
And then twenty days after rainfall, the struggling grasses within the circles were completely dead and yellowish in colour, while the surrounding grasses were vital and green.
When researchers went on to examine the roots of the grasses and compared them to the greener shrubs on the outside, they found that roots within the circles were as long as, or even longer than, those outside - indicating that the grasses were putting effort into the growth of roots in search of water.
What was surprising was that it was not until fifty to sixty days after the rainfall that root damage became more visible at the dead grasses.
And when boffins analysed the data on the soil-moisture fluctuations, they noticed that the decline in soil water around the circles was very slow after the first round of rainfall.
But, when grasses around the area were well established, the decline in soil water after rainfall was very fast in all areas - even though there there were no grasses to take in the water.
Dr Getzin went on to explain this, saying: "Under the strong heat in the Namib, the grasses are permanently transpiring and losing water.
"Hence, they create soil-moisture vacuums around their roots and water is drawn towards them.
"Our results strongly agree with those of researchers who have shown that water in soil diffuses quickly and horizontally in these sands even over distances greater than seven metres.
"By forming strongly patterned landscapes of evenly spaced fairy circles, the grasses act as ecosystem engineers and benefit directly from the water resource provided by the vegetation gaps."
The researcher continued: "In fact, we know related self-organised vegetation structures from various other harsh drylands in the world, and in all those cases the plants have no other chance to survive except by growing exactly in such geometrical formations."
The research has is important for understanding similar ecosystems, especially with regard to climate change.
This is because the self-organisation of plants buffers against negative effects induced by increasing aridification - which is the the process of a region becoming increasingly arid, or dry.
The findings of the study were published in Perspectives in Plant Ecology, Evolution and Systematics.
