Jan Bartek – AncientPages.com – Scientists have puzzled over the origin of Namibia’s fairy circles for nearly half a century. It boiled down to two main theories: either termites were responsible, or plants were somehow self-organizing. Now, researchers from the University of Göttingen, benefitting from two exceptionally good rainfall seasons in the Namib Desert, show that the grᴀsses within the fairy circles died immediately after rainfall, but termite activity did not cause the bare patches.
Researchers investigated grᴀss death within the fairy circles in several regions of the Namib. The roots of the yellowish ᴅᴇᴀᴅ grᴀsses from within the fairy circles are as long and as undamaged as the roots of the vital green grᴀsses outside of the circles. There was no sign of termite activity. Credit: Dr Stephan Getzin
Instead, continuous soil-moisture measurements demonstrate that the grᴀsses around the circles strongly depleted the water within the circles and thereby likely induced the death of the grᴀsses inside the circles. The results were published in Perspectives in Plant Ecology, Evolution and Systematics.
About 80-140 kilometers from the coast in the Namib, there are millions of fairy circles—circular gaps in the grᴀssland, each a few meters wide, together forming a distinctive pattern across the whole landscape and visible for miles around. The researchers followed the sporadic rain events in several regions in this desert and examined the grᴀsses, their roots and shoots, and potential root damage induced by termites.
Fairy circles in Namibia’s Marienfluss valley. Credit: Thorsten Becker – CC BY-SA 2.0 de
Termites, tiny insects that live in large colonies around the world, have often been blamed for the death of the grᴀsses. The researchers took great care to investigate the circumstances of dying grᴀsses within fairy circles right from straight after the rainfall, which triggered the new growth of the grᴀsses. Additionally, they installed soil-moisture sensors in and around the fairy circles to record the soil-water content at 30-minute intervals starting in the dry season 2020 to the end of the rainy season 2022.
This enabled the researchers to record precisely how the growth of the new emerging grᴀsses around the circles affected the soil water within and around the circles. They investigated the differences in water infiltration between the inside and outside of circles at ten regions across the Namib.
The data show that about ten days after rainfall, the grᴀsses were already starting to die within the circles while most of the interior area of the circles did not have grᴀss germination at all. Twenty days after rainfall, the struggling grᴀsses within the circles were completely ᴅᴇᴀᴅ and yellowish in color while the surrounding grᴀsses were vital and green.
When the researchers examined the roots of the grᴀsses from within the circles and compared them to the green grᴀsses on the outside, they found that the roots within the circles were as long as, or even longer than, those outside. This indicated that the grᴀsses were putting effort into the growth of roots in search of water. However, the researchers found no evidence for termites feeding on roots. It was not until fifty to sixty days after the rainfall that root damage became more visible at the ᴅᴇᴀᴅ grᴀsses.
Credit: University of Göttingen
Dr. Stephan Getzin, Department of Ecosystem Modeling at the University of Göttingen, explains that “the sudden absence of grᴀss for most areas within the circles cannot be explained by the activity of termites because there was no biomᴀss for these insects to feed on. But more importantly, we can show that the termites are not responsible because the grᴀsses die immediately after rainfall without any sign of creatures feeding on the root.”
When the researchers analyzed the data on soil-moisture fluctuations, they found that the decline in soil water inside and outside of the circles was very slow after initial rainfall, when grᴀsses were not yet established. However, when the surrounding grᴀsses were well established, the decline in soil water after rainfall was very fast in all areas, even though there were almost no grᴀsses within the circles to take the water.
Getzin explains that “under the strong heat in the Namib, the grᴀsses 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 meters.”
This research has implications for understanding similar ecosystems, especially with regard to climate change, because the self-organization of plants buffers against negative effects induced by increasing aridification.
The study was published in Perspectives in Plant Ecology, Evolution and Systematics
Written by Jan Bartek – AncientPages.com Staff Writer
