Scientists unravel the mystery of the mysterious circles of Namibia

(ORDO NEWS) — Scholars have puzzled over the origin of Namibian fairy circles for almost half a century. It all boiled down to two main theories: either the termites were to blame, or the plants somehow organized themselves.

Now researchers at the University of Göttingen, who have capitalized on two exceptionally good rainy seasons in the Namib Desert, show that the grasses in fairy circles died immediately after the rain, but termite activity did not cause the famous bare spots, also known as fairy circles.

Instead, continuous measurements of soil moisture indicate that the grasses around the circles greatly deplete the water inside the circles and thereby likely cause the grasses inside the circles to die. The results were published in the journal 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 pastures, each several meters wide, together forming a characteristic pattern throughout the landscape and visible for miles around.

The researchers monitored sporadic rainfall in several regions of this desert and studied grasses, their roots and shoots, and potential root damage caused by termites.

Termites, tiny insects that live in large colonies around the world, are often blamed for the death of grasses. Researchers have taken a very close look at the circumstances of the death of grasses in fairy circles immediately after the rain that caused the new growth of grasses.

In addition, they installed soil moisture sensors in and around the fairy circles to record soil moisture content at 30-minute intervals from the 2020 dry season to the 2022 rainy season.

This allowed the researchers to accurately record how the growth of newly emerging grasses around the circles affected the soil water in and around the circles. They investigated differences in water infiltration between inner and outer circles in ten Namib regions.

The data show that about ten days after the rain, the grasses inside the circles had already begun to die, while most of the inside of the circles did not grow grass at all. Twenty days after the rain, the struggling grass inside the circles was completely dead and yellowish in color, while the surrounding grasses were alive and green.

When the researchers examined the grass roots inside the circles and compared them to the green grasses outside, they found that the roots inside the circles were as long or even longer than the roots outside.

This indicated that the grasses were making an effort to grow roots in search of water. However, the researchers found no evidence that termites feed on roots. It wasn’t until fifty or sixty days after the rain that the damage to the roots of the dead grass became more visible.

Dr. Stefan Götzin from the Department of Ecosystem Modeling at the University of Göttingen explains that “the sudden absence of grass in most areas inside the circles cannot be explained by termite activity because these insects had no biomass to feed on.

But more importantly, we can show that termites are not to blame because the grass dies immediately after the rain without any sign that the creatures are feeding on the roots.”

When the researchers analyzed data on fluctuations in soil moisture, they found that the decline in soil moisture levels inside and outside the circles was very slow after the initial rains, when the grasses had not yet taken root.

However, when the surrounding grasses were well established, the decline in soil moisture after rain was very rapid in all areas, even though there was almost no grass in the circles to absorb water.

Getzin explains that “in the intense heat in the Namibe, the grasses are constantly evaporating and losing water. Consequently, they create a soil-moist vacuum around their roots, and water is attracted to them.

Our results are in complete agreement with those of researchers who have shown that water in the soil diffuses rapidly and horizontally into these sands even over a distance of more than seven meters.”

He added that “By shaping highly patterned landscapes from evenly spaced fairy circles, grasses act as ecosystem engineers and directly benefit from the water resources provided by vegetation gaps.

In fact, we know related self-organizing patterns of vegetation from various other harsh drylands. in the world, and in all these cases, plants have no other chance to survive than to grow in precisely such geometric formations.

This study has implications for understanding such ecosystems, especially in relation to climate change, as plant self-organization protects against the negative effects caused by increased aridity.

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