Strange ‘fairy circles’ in the Namibian grasslands have baffled scientists for nearly 50 years, but a new study has shed more light on the puzzling phenomenon.
Millions of circular patches, each a few meters wide, are found in the coastal Namib desert region, about 80-140 km from the Atlantic coast.
Termites were thought to be responsible for the phenomenon.
But a new study, published in the journal Perspectives in plant ecology, evolution and systematics, suggests that the circles could be caused by the grasses themselves adapting to the very limited supply of water.
He evaluated sporadic rain events in numerous desert regions and analyzed grasses, their roots and shoots, as well as potential termite root damage to explain these patterns, and concluded that the “fairy circles” are caused by stress plant water.
Researchers, including some from the University of Göttingen in Germany, have found that grasses “self-organize” into geometric formation to share water to survive.
They installed soil moisture sensors in and around the fairy circles to record soil water content at 30-minute intervals, starting in the 2020 dry season and continuing through the end of the 2022 rainy season.
Scientists also investigated how newly emerging grasses around the circles affect soil water in and around the circles and evaluated differences in water infiltration between inside and outside the circles in 10 regions. of the Namib.
The results revealed that, about 10 days after the rain, the grasses were already starting to die within the circles while most of the area inside the circles had no grass germination at all.
About 20 days after the rain, the distressed grasses inside the circles were completely dead while the surrounding grasses were green.
The scientists then examined the roots of the herbs from inside the circles and compared them to the green herbs on the outside.
They found that the roots of the grasses inside the circles were as long as, or even longer, than those outside, indicating that the grasses were engaging in root growth in search of water.
However, they found no evidence of root-feeding termites, and it was only 50 to 60 days after the rain that root damage became more visible on the dead grasses.
“The sudden absence of grass for most of the areas within the circles cannot be explained by termite activity because there was no biomass for these insects to feed on,” explained Stephan Getzin, co-author of the study.
“But more importantly, we can show that termites aren’t responsible because the grasses die immediately after rain with no sign of creatures feeding on the root,” said Dr. Getzin.
The scientists also found that the decline of soil water in and out of the circles was very slow after the initial rainfall, when grasses had not yet been established.
But when the surrounding grasses were well established, the decline of soil water after rain was very rapid in all areas, even though there were almost no water-absorbing grasses within the circles.
“Under the strong heat of the Namib, the grasses are constantly perspiring and losing water. Then, they create soil moisture voids around their roots and water is drawn towards them,” Dr Getzin explained.
Scientists have said that the grasses act as “ecosystem engineers” and directly benefit from the water supply provided by the crevices of the vegetation.
“Indeed, we know of related self-organizing vegetation structures from various other rugged drylands around the world, and in all of these cases the plants have no other chance of survival than by growing exactly in such geometric formations,” said Dr. Getzin.