The mystery of Namibia’s fairy circles is mysterious: plants are self-organizing

Scientists have puzzled over the origin of Namibia’s fairy circles for nearly half a century. This boils down to two main theories: either termites were responsible, or plants were somehow self-organizing. Now, researchers from the University of Göttingen, benefiting from two exceptionally good rainfall seasons in the Namib Desert, show that the grasses in the elm circle die soon after the rain, but termite activity did not cause the bare patches.

Instead, continuous soil-moisture measurements show that the grasses around the circle have strongly reduced the water within the circle, and this may have resulted in the death of the grasses inside the circle. Results are published Plant Ecology, Evolution and Systematic Perspectives.

There are millions about 80-140 km off the coast of the Namib fairy circle— Circular gaps in the grassland, each a few meters wide, together form a distinct pattern across the landscape and visible for miles around. The researchers followed sporadic rainfall events in several areas of this desert and examined potential root damage induced by grasses, their roots and shoots, and termites.

Termites, tiny insects that live in large colonies around the world, are often blamed for grass dieback. The researchers took great care to investigate the circumstances in which the grass died within the fairy circle rainfall, which triggers new growth of grass. Additionally, they installed soil-moisture sensors in and around the pari circle to record soil-water content at 30-minute intervals from the 2020 dry season to the end of the 2022 monsoon season.

This enables researchers to accurately record how new grass growth around the circle affects soil water in and around the circle. They investigated differences in water infiltration between inside and outside circles in ten regions across the Namib.

The data showed that about ten days after the rainfall, the grasses had already started to die within the circle while most of the inner area of ​​the circle had no grass germination. Twenty days after the rain, the struggling grasses within the circle were completely dead and yellow while the surrounding grasses were vital and green.

When the researchers examined the grass roots from inside the circle and compared them to the green grass outside, they found that the roots inside the circle were as long or longer than the grass outside. This indicates that grasses are making efforts to grow roots in search of water. However, the researchers found no evidence of termite feeding on the roots. Fifty to sixty days after rainfall, root damage becomes more visible in dead grasses.

Dr. Stefan Getzin, from the Department of Ecosystem Modeling at the University of Göttingen, explained that “the sudden absence of the grass Most of the area within the circle could not be explained by termite activity because there was no biomass for these insects to feed on. But more importantly, we can show that termites are not responsible because the grasses die soon after the rain without any signs of animal feeding on the roots.”

When the researchers analyzed data on soil-moisture fluctuations, they found that soil water loss inside and outside the circle was very slow after the initial rainfall, when the grass was not yet established. However, when surrounding grasses were well established, declines occurred Ground water All areas were very quick after the rains, although there was almost no grass in the circle to absorb the water.

Getzin explained that “under the intense heat of the Namib, the grasses are permanently transpiring and losing water. Therefore, they create soil-moisture voids around their roots and water is drawn towards them. Our results strongly agree with researchers who have shown that even at distances of more than seven meters this Soil water diffuses rapidly and horizontally in sand.”

Getzin adds that “forming strongly patterned landscapes of evenly spaced fairy circles, grasses act as ecosystem engineers and benefit directly from the water resources provided by vegetation gaps. Indeed, we know related self-organized vegetation structures from various other harsh arid lands. On Earth, And in all these cases the plant has no chance of survival except by growing in just such a geometrical formation.”

This research has implications for understanding similar ecosystems, particularly in the context of climate change, as plant self-organization buffers against the negative effects induced by increased desiccation.