Numbering in the millions, the so-called fairy circles are in the eastern interior of the coastal Namib Desert, stretching from southern Angola to northern South Africa. Ranging in size from about 12 feet to more than 100 feet, they are bare patches of soil ringed by tall grasses. The origins of the circles have long been debated by researchers.
"This study provides some 'fresh eyes' for looking at the existing debate, using new field methodologies and data for a less studied location," said Sujith Ravi, lead author of the study and assistant professor in the Department of Earth & Environmental Science (EES). "It's a major contribution to resolving the fairy circles enigma."
Ravi and another EES faculty member, Associate Professor Ilya Buynevich, worked with researchers from Indiana University-Purdue University and the National Museum of Namibia. Their paper, titled "Ecohydrological interactions within 'fairy circles' in the Namib Desert: Revisiting the self-organization hypothesis," is published in the Journal of Geophysical Research: Biogeosciences a peer-reviewed journal of the American Geophysical Union. The team's results provide support to the self-organization hypothesis of fairy circle formation.
Self-organization theory says that the circular vegetation pattern is created by plant competition for scarce water. It's believed that the bare patches percolate more rainfall and act as water reservoirs, which the grass along the edges of the circle can access.
A second major theory is that fairy circles are created and maintained by sand termites that clear vegetation in the area of their nests. By making the soil porous, it's believed, the termites establish permanent reservoirs of rainwater below the surface that sustain them and the surrounding plants.
The research team brought new equipment and research specialties for measuring infiltration rate, soil moisture, grass biometric, and sediment grain-size distribution from multiple circles and spaces between the circles.
Water infiltration flow rates were measured inside and outside the circles, with very fast infiltration rates recorded within the inner portion of the circles. The faster infiltration rates were facilitated by coarser particle size inside the circles. The team also found the grass along the circle edges were much larger compared to the grasses outside, while the root activity was more toward the inside of the circles. With help from Eugene Marais, a termite expert from the National Museum of Namibia, the research team conducted surveys to determine the presence or absence of termite species.