Ecologists have been studying and debating the mystery of the Namib Desert’s “fairy circle” for over 50 years. These are circular, mostly barren, patches that stretch across 1,100 miles of the dry grasslands of Southern Africa.
They are not fairies, despite their whimsical names, which are similar to “fairy rings”, which refer to circular patterns of fungi that can be found in forested areas. There have been many theories, but only two have merited the most. One theory blames termites for the dry patches. The other considers the evolution of grasses. Although scientists have been arguing for decades about the cause, a new study may provide some evidence.
Stephan Getzin, an ecologist at the University of Gottingen, Germany, was the first to start his studies on fairy circles. He has published more papers about the circles and their origins than any other expert in the years that followed.
The fairy circles are distinguished by the presence of barren areas within them. However, the growth of grasses around these patches is also notable — it is believed that they have found a way of thriving in one of the driest places on the planet. Getzin and his colleagues had previously hypothesized that the plants within the outer rings of the circles had evolved to make the most of the limited water available in the desert.
For the past three years, Getzin has been spending time in Namibia monitoring the growth of grasses for more proof. Getzin and his team installed sensors to measure the soil’s moisture at 7.9 inches (20 cm) depth and monitor grass water uptake.
Getzin stated that in 2020, there was very little vegetation. In fact, in 2020, there was almost no grass vegetation within the fairy circle. “But, in 2021 and this year in 2022, we had a very strong rainfall season so we could track how the growth of new grasses was redistributing soil water.”
The data from these rain seasons were analyzed by Getzin’s team. They found that water within the circles was eroding quickly, even though they didn’t have any grass to use, while grasses outside were still as strong as ever. These well-established grasses, which had been established in the desert, created a vacuum around their roots, drawing any water towards them under the intense heat. The grasses within the circles, which try to grow right after the rain, couldn’t get enough water to survive.
Getzin stated that a circle is the most natural geometric form you could create for a plant in water deprivation. These circles could be squares or complex low-level structures. This would result in more grasses around the circumference. … A circle has a smaller area than one that grows in. These grasses are arranged in a circle to maximize water availability for each plant.
This is an example of ecohydrological feedback, according to the study. The barren circles are used as reservoirs to sustain grasses at their edges. However, this can be detrimental for grasses in middle. Getzin explained that this self-organization helps to mitigate the negative effects of increased aridity. It is also common in other drylands around the world.
Responding to the termite theory
The termite hypothesis suggested that fairy circles could be caused by sand termites, which can damage grassroots. This was well received by other scientists. A 2016 Australian study on similar fairy circles found no evidence of pests. Similar conclusions were reached by Getzin’s most recent research.
Getzin stated that there was an instance where it rained once and the grasses rose, but then the grasses within the fairy circles started dying after about eight to nine days. “We (excavated these grasses) carefully and examined the roots. None of them had root damage by termites, but they still died. These grasses are not affected by termites, as our results show.
Getzin and his colleagues also noticed that the roots of young plants in the circles were longer than the ones on the outside. Getzin believes this suggests that the grasses have created longer routes to seek water, further evidence of their competition in the water-scarce desert.
Although the results of the study are encouraging, Getzin and other scientists believe that there is more to be done. Getzin said that it was time to take on a new challenge.
Getzin stated that fairy circles found in Namibia and Australia are altering the soil’s moisture distribution, increasing survival chances and so allowing for a form of “swarm intelligence”. “Plants can make complex patterns and formations. I will continue to work towards this goal.”
Researchers have found another species of grass that forms large circular rings in the Namibian fairy circle. Getzin stated that although it is a different grass genus, it forms identical circular formations. This process will be studied during Namibia’s next rainy season in 2023.