Presentation: Plant water stress, not termite herbivory, causes Namibia’s fairy circles by Dr Getzin

The fairy circles of Namibia have been called one of nature’s greatest mysteries. These circular grassland gaps form along the Namib below 150mm mean annual precipitation, where moisture is overall too low to sustain a continuous layer with uniform vegetation.
Dr Stephan Getzin studied the fairy circles for the first time in the Kaokoveld in the year 2000 when the resulting publication established the term “fairy circles” in the scientific literature. Since then, he has closely followed research developments on the subject. In 2012, he began a detailed analysis of the spatial patterns of the fairy circles and thereby tested the plausibility of various hypotheses about the circles' origin. Since 2015, Dr Getzin has visited the Namib Desert every year, covering all the hotspot regions where fairy circles occur. Especially during the rainy seasons from 2020 to 2022, he visited the fairy circles in several regions of the Namib immediately after the rains. In his talk, he gave an overview of his past research on testing the “abiotic gas”, the “Euphorbia” or the “social insect” hypotheses, and he presented the major findings of his recent fieldwork, which was just published in October 2022.
This new research from the past three years demonstrates that the grasses in the fairy circles died quickly after rainfall within as little as one to three weeks. His novel data show that the roots of the dead grasses within the fairy circles were even significantly longer than the roots of the vital grasses outside of the circles, which refutes termite herbivory as a causal process because consumption of biomass can only lead to shorter but not to longer roots. In contrast, such plant investment of biomass into long roots is indicative of strong water stress because the grasses tried to reach deeper soil layers which retain more water. Dr Getzin’s photos from the regions Garub, NamibRand, Naukluft Park, and Brandberg also clearly show that the roots of the dead grasses within fairy circles had no signs of damage induced by termites. The reason for the quick death of these grasses was desiccation and lack of water. His continuous soil-moisture recordings in and around fairy circles reveal that the vital matrix grasses outside of the circles strongly pulled the underground water from the interior of the fairy circles. The large and competitively superior grasses around the circles thereby actively engineer the vegetation gaps and benefit from these additional water reservoirs via long-distance diffusion of soil water.
In his presentation, Dr Getzin not only showed that the Stipagrostis grasses form fairy circles via plant self-organization. He also showed so-far unknown plant rings of the Namib, where annual Schmidtia grasses and annual Limeum forbs engineer similar but smaller circles, in order to exclusively utilize the soil water from the interior of these rings. In agreement with many related dryland ecosystems worldwide, where such emergent vegetation patterns occur, the circularity and strong symmetrical distribution of biomass is the most logic and efficient geometric plant pattern to cope with permanent water stress. However, this does not take away the “magic” of Namibia’s fairy circles, as many aspects of plant communication are so far unknown. In times of climate change and prolonged droughts, researchers are increasingly interested in studying the ability of plants to self-organize and redistribute scarce resources. In this endeavour, the fairy circles are a shining example and may inspire further research on this topic in the future.
This presentation was held on 9 February 2023 at the Namibia Scientific Society.
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