Namibia’s fairy circles offer insights on arid ecosystems

The mystery over what causes fairy circles to appear in the landscape of Namibia may at last be solved, with the findings from University of Göttingen researchers in Germany—on what may seem a whimsical topic—likely to add to the understanding of climate change in similar ecosystems.

The Namib Desert is home to millions of fairy circles, the gaps in grasslands that form circles a few meters wide for miles around. The desert circles are found between 80 and 140 kilometers inland from the Atlantic Ocean coast in the southwestern African nation.

But for nearly 50 years, the reason for the fairy circles has remained elusive to scientists trying to pinpoint their origin. There have been two main theories about what causes the fairy circles: either they’re the destructive work of termites that cause insect damage, or the plants are somehow organizing themselves in response to moisture and climate conditions.

It turns out to be the latter, according to the German scientists and the results of their work with the Gobabeb Namib Research Institute in Walvis Bay. The findings were published in December in the journal Perspectives in Plant Ecology, Evolution and Systematics.

The researchers closely monitored rainfall and soil moisture conditions across both the dry and rainy seasons from 2020 to 2022. They installed soil moisture sensors in and around the fairy circles and recorded moisture levels at 30-minute intervals for the entire time, checking to see how plant growth affected the levels.

“This enabled the researchers to record precisely how the growth of the new emerging grasses around the circles affected the soil water within and around the circles,” the university explained. “They investigated the differences in water infiltration between the inside and outside of circles at ten regions across the Namib.”

About 10 days after rainfall, grasses within the circles were already starting to die. After 20 days, the grasses were completely dead while the surrounding areas were green and alive. The root length showed the plants grew in search of water, with no evidence of termite feeding and no visible root damage for 50 to 60 days.

The soil-moisture measurements showed that the grasses around the circles strongly depleted the water within the circles, likely forcing the death of the grasses inside the circles as part of the self-organization of the plants.

What’s at work is that the grasses create soil moisture vacuums as they constantly transpire, losing water in the strong Namibian heat, says Dr. Stephan Getzin of the Department of Ecosystem Modelling at Göttingen. The water diffuses quickly across the sandy landscape in which the grass grows.

“By forming strongly patterned landscapes of evenly spaced fairy circles, the grasses act as ecosystem engineers and benefit directly from the water resource provided by the vegetation gaps,” explains Getzin. “In fact, we know related self-organized vegetation structures from various other harsh drylands in the world, and in all those cases the plants have no other chance to survive except by growing exactly in such geometrical formations.”

The scientists say the research findings may help in understanding these ecosystems, especially with regard to climate change that increases arid conditions.