"Fairy circles" kill all newly-planted grasses, deepening their mystery

Namibia’s fairy circles have long captivated the imagination with their enigmatic presence in the dry grasslands on the Namib Desert’s fringe. These peculiar, circular, bald patches have puzzled scientists for decades, inspiring numerous theories about their formation.

A recent study by researchers from the University of Göttingen in Germany and Ben Gurion University in Israel delves deep into this mystery, challenging previously held beliefs and providing new insights into the phenomenon.

The study, published in the journal Perspectives in Plant Ecology, Evolution and Systematics, focuses on the lifecycle of freshly germinated grass within these circles and its struggle for survival.

Studying Namibia’s mysterious fairy circles

Contrary to the popular termite theory, the research reveals that these grass patches wither away due to a critical lack of water, not termite damage.

The top 10 to 12 centimeters of soil, described as a “death zone,” proves inhospitable for the young grass, which dies just 10 to 20 days following rainfall.

This research involved meticulous fieldwork, analyzing 500 individual grass plants across four Namib regions.

Through detailed measurements of root and leaf lengths, statistical analyses, and the comparison of photographic evidence, coupled with extensive soil moisture measurements during the 2023 and 2024 rainy seasons, the team uncovered startling findings.

Perennial grasses vs. new sprouts

The topsoil within fairy circles dries out significantly faster and remains drier compared to surrounding areas, creating an environment where freshly sprouted grass cannot thrive.

In sharp contrast, the study observed that perennial grass clumps around the fairy circles flourish, benefiting from deeper soil moisture levels. These clumps, with well-developed root systems extending 20 to 30 centimeters below the surface, exhibit a remarkable ability to quickly absorb water after rainfall.

“With their well-developed root system, these clumps of grass soak up the water particularly well. After the rain, they have a huge competitive advantage over the freshly germinated grasses in the fairy circle,” explains Dr. Stephan Getzin from Göttingen University’s Ecosystem Modelling Department.

“The new grass only loses a small amount of water via transpiration from its small leaves, resulting in insufficient ‘suction power’ to pull new water from deeper soil layers,” he continued.

Importance of soil moisture in fairy circles

The researchers also discovered that water’s physical conductivity is highest in the soil’s upper layers during the first 20 days after rain, favoring the established clumps of grass that primarily draw water from this zone.

“This is the cause of the death of the new grass in the fairy circle. Continuous soil moisture measurements over several years support this conclusion. This is because the soil water in the fairy circle only decreases noticeably quickly with the strengthening and regrowth of the surrounding grass after rain,” Gertzin explained further.

This phenomenon further exacerbates the difficulties faced by newly germinated grasses within the fairy circles, leading to their eventual death.

Continuous soil moisture tracking over several years has reinforced these findings, highlighting the role of fairy circles as crucial water reserves for the drought-stricken grasses of the Namib.

Disproving the popular termite theory

Interestingly, the study also challenges the sand termite theory, which suggests that termites feeding on the roots of new grass contribute to the formation of fairy circles. The researchers provide a compelling argument, backed by systematic data, debunking this theory.

They emphasize the lack of concrete evidence linking termite activity to the creation of these circles, critiquing the misinterpretation of cited research within the termite theory’s support base.

The fairy circles, according to Getzin and his colleague Dr. Hezi Yizhaq, represent a fascinating example of “swarm intelligence” or self-organization among plants, as they adapt to scarce resources in arid environments. This survival strategy, manifested in the circles’ round shape, maximizes soil water availability, showcasing nature’s ingenuity in the face of adversity.

One step closer to solving this Namibian mystery

In summary, this study has significantly advanced our understanding of Namibia’s fairy circles, though many questions still remain. The scientists debunked the long-held termite theory and highlighted the crucial role of water scarcity in their formation.

Through rigorous fieldwork and analysis, researchers have demonstrated that one significant cause of these enigmatic patterns results from the natural struggle for survival in harsh desert conditions, where perennial grasses outcompete newly germinated ones for limited water resources.

This intriguing research highlights the adaptive strategies of desert flora and underscores the complexity and beauty of natural ecosystems, revealing the intricate balance that sustains life in one of the planet’s most unforgiving landscapes.

The full study was published in the journal Perspectives in Plant Ecology, Evolution and Systematics.

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