(ORDO NEWS) — In the Namib Desert, in a remote stretch of the Namib Desert, grasses grow that survive on scarce rainfall.
The growth of so much grass in such harsh conditions is impressive, but at the same time, it is mysterious.
The pastures are dotted with millions of strange circles, each devoid of grass or other vegetation, which together form an eerie polka-dot pattern – “fairy circles” throughout the landscape.
Located 80 to 140 kilometers (50 to 87 miles) inland from the coast of Namibia, this area of circular pasture rips is visible for miles around, the study authors note, and shows “an extraordinary degree of spatial order.”
A typical circle of fairies is 2 to 10 meters across and is separated from the rest by up to 10 meters.
Scholars have made steady progress in demystifying Namibian fairy circles, with the leading theories falling into two main camps.
According to one theory, the circles are caused by termites feeding on roots, and according to another, grasses self-organize to maximize water availability.
Research has supported each of the theories, and some studies have shown that both termites and self-organization may be behind fairy circles.
But that explanation became more complicated after similar circles were found in Australia in 2016, but with no clear connection to termites.
Recent research points more confidently to self-organization, in which grasses form fairy circles to make the most of scarce rainfall, but the possibility of termites cannot be ruled out.
In 2020, a study led by Stefan Getzin from the Department of Ecosystem Modeling at the University of Göttingen in Germany further supported the water scarcity scenario that Getzin and colleagues called an example of the Turing model.
In their latest study, Getzin and a team of scientists returned to Namibia, hoping to find even stronger evidence by examining fairy circles in 10 regions of the Namib Desert.
Rainfall in this area is rare and irregular. Grasses sometimes appear in fairy circles immediately after rain, but they tend to die soon after, the researchers note, while the grass survives between circles.
Getzin and colleagues tracked sporadic rainfall in 10 regions, studying grasses, their roots and shoots, and possible termite damage to roots.
They studied dying grass after rain and installed soil moisture sensors in and around fairy circles to record data at half-hour intervals from the 2020 dry season to the end of the 2022 rainy season.
According to the results of the study, ten days after the rain, there was very little new grass inside the fairy circles, and what had sprouted was already dying. 20 days after the rain, all the grass inside the circles was dead, while the surrounding grass was “green and soft”.
The roots of dead grass inside the circles were as long, if not longer, than the roots outside the circles, suggesting that the plants invested heavily in root growth in search of water. The researchers found no evidence that termites fed on roots, they report.
“The sudden absence of grass in most areas within the circles cannot be explained by termite activity because there was no biomass for these insects to feed on,” says Getsin.
“But more importantly, we can show that termites are not to blame, because the grasses die immediately after the rain, with no sign of creatures feeding on the roots.”
Soil sensors showed a slow decrease in soil moisture inside and outside the circles after the first rain, when the grasses had not yet taken root.
However, as soon as the surrounding grasses got stronger, the moisture of the soil quickly disappeared everywhere – including inside the fairy circles, despite the lack of grass there that could absorb water.
“During the intense heat in the Namibe, grasses are constantly evaporating and losing water. So they create a vacuum of soil moisture around their roots, and water is attracted to them,” says Getzin.
“Our results are in complete agreement with the data of the researchers, who showed that the water in the soil spreads quickly and horizontally in these sands even over distances of more than seven meters.”
This is an incredible example of “eco-hydrological feedback,” the researchers write, where barren circles essentially become bodies of water that help support the grasses around the edges.
This research could have implications elsewhere as well, Getzin notes, as such self-organization appears to be protecting plants from increasing aridity, a problem already exacerbated in some places by climate change.
“By forming patterned landscapes of evenly spaced circles, grasses act as ecosystem engineers and directly benefit from the water resources provided by vegetation gaps,” Getzin says.
“In fact, we know similar self-organized patterns of vegetation from various other harsh arid regions of the world, and in all these cases, plants have no other chance to survive than to grow in precisely such geometric formations.”
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