Namibia’s ‘fairy circles’ explained
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Cape Town - “The land God made in anger.” That’s what Namibia is often called because of its vast sweeps of rugged, deeply forbidding wilderness areas, although the expression is believed to derive from the local San inhabitants who were referring specifically to the treacherous Skeleton Coast of the Namib Desert.
Either way, God must have had a whimsical side too, because one of the most intriguing features of this vast and beautiful country is the appearance of thousands upon thousands of mysterious and evocatively named “fairy circles”.
These are rings of barren sand, between two and 20 metres in diameter, surrounded by a rim of often lush grass and other natural vegetation that flank the harsh desert in a 2 000km-long belt.
According to a folk tale of the Himba residents, the circles are caused by a dragon that lives beneath the earth’s crust whose fiery breath bubbles to the surface, burning the vegetation into near-perfect circles. Others have postulated that the phenomenon is caused by ants, termites, radioactive soil or toxins secreted by the Damara euphorbia, a poisonous endemic plant. And of course some superstitious people offer completely fanciful and implausible suggestions that don’t warrant repeating.
Now, the mystery of the creation of the fairy circles has been solved by biology professor Norbert Juergens of the University of Hamburg, who has discovered that the intriguing phenomenon is actually the result of sophisticated ecological engineering by the sand termite Psammotermes allocerus on an even bigger scale than the beaver, and that it also has substantial benefits for a wide range of other plants and animals.
His scientific exposé, “The Biological Underpinnings of Namib Desert Fairy Circles”, appeared in Friday’s edition of the prestigious journal Science.
Juergens is no stranger to southern Africa, having worked in the Richtersveld since 1980. He has made more than 40 field trips to the region and was closely involved in discussions that eventually led to the establishment of the Richtersveld National Park, and subsequently the Ai-Ais/Richtersveld Transfrontier Park.
“The first Fairy Circles I saw in my life are located in the valley of Numees in the Richtersveld,” he told Weekend Argus.
“Then, 20 years later and jointly with colleagues from UCT and Sanbi (SA National Biodiversity Institute) at Kirstenbosch, I started a project for the long-term observation of biodiversity, BIOTA Africa. (BIOTA is an acronym for Biodiversity Monitoring Transect Analysis.) In the framework of this project, I started to observe the formation of young fairy circles and I got more interested in general.”
In his paper, Juergens notes that previous observers suggested poisonous plants, carnivorous ants, termites and volatile organic compounds, among others, as the possible causes of the circles, but most of those hypotheses had been tested and rejected.
“Despite the many hypotheses, the origin and the ecosystem function of fairy circles are still a much-debated mystery.”
Juergens measured the water content of the circles, and looked at species lists to see what organisms were associated with them.
He found that water accumulated in the soil of the circles, and that only the sand termite – in large numbers – was found at all of them, even in the early stages of the circles’ development.
So he hypothesised that in young, newly forming fairy circles, the sand termites feed on the roots of grasses, and increased termite activity correlates with reduced grass growth in the fairy circle.
When he looked more closely, he discovered that the soil-living termites killed all grasses within the fairy circle by feeding on their roots.
Then, because of the lack of grasses, rainwater was not lost through transpiration (the evaporation of water from plants), but was instead stored below the surface of the sandy soil where it was shielded from evaporation.
In turn, this soil water supply allowed the termites to remain alive and active during the dry season, and also helped grasses growing at the margin of the fairy circle to thrive.
The termites fed steadily on these grasses, thereby gradually extending the circle.
The fairy circles strongly enhanced biodiversity by attracting many other organisms, including ants, bees, wasps, spiders, geckos, small mammals like aardvarks, bat-eared foxes, black-backed jackals and golden moles.
“Fairy circles can be regarded as an outstanding example of of allogenic ecosystem engineering (allogenic = modifying the environment by mechanically changing materials from one form to another) resulting in unique landscapes with increased biodiversity, driven by key resources such as permanently available water, perennial plant biomass, and perennial termite biomass,” Juergens concluded.
“The termites match the beaver with regard to intensity of environmental change, but they surpass it with regard to the spatial dimension of their impact.
“The sand termite turns wide desert regions of predominantly ephemeral life into landscapes dominated by species-rich perennial grassland, supporting uninterrupted perennial life even during dry seasons and drought years.” - Cape Argus