University of Pretoria scientists believe microorganisms such as bacteria, fungi or viruses in the soil could be the answer to fairy circles.
In the decade he has spent trying to unravel the mystery of the tens of thousands of “fairy circles” that dot Namibia’s arid landscape, Don Cowan has encountered numerous theories seeking to explain what causes them.
For the director of the Centre for Microbial Ecology and Genomics at the University of Pretoria, among the nicest of the indigenous folklore comes from the Nama, who believed the enigmatic circles were caused by dragons.
“Presumably these things [fairy circles] have existed in one form or another for thousands of years and the original Nama tribes would have seen them and been fascinated by them in their own way hence their belief, I understand, that they were caused by dragons, which I rather like.”
Fairy circles are bare patches surrounded by grass. Most are between 2m and 5m in diameter, occurring over thousands of square kilometres in Namibia and into southern Angola. While similar circles have been found in Australian deserts, Cowan said that doesn’t necessarily mean they have been caused in the same way.
On whether aliens could be behind them, Cowan laughed. “Somebody, probably anonymously, suggested somewhere in the literature that they were the result of UFOs. I have to say that if they are, there have been a lot of UFOs and I personally haven’t seen them [but] it would surprise me if the UFOs were really quite that specific and only found in remote areas. As a scientist, that doesn’t seem to be entirely sensible.”
Microorganisms could be the cause
The existence of the circles has intrigued and perplexed scientists for more than 50 years, but no one knows the actual cause. Current theories span toxic gases from deep in the soil, toxic chemicals from dead Euphorbia plants, sand termites or the effects of natural plant “self-organisation” processes over long periods. Each of these major theories is supported by a research group often purporting to have “discovered” the cause.
Cowan and his team have investigated the cause of fairy circles for more than 10 years and they have their own theory: that microorganisms could be the missing piece of the polka-dot puzzle.
They think that plants growing inside the circles could be dying as a result of phytopathogenesis — the presence of pathogenic microorganisms such as bacteria, fungi or viruses in the soil. Cowan said the growth of fairy circles is like a growing microbial culture, which is circular and spreads at the margins.
While several other theories can explain plant death, they struggle to explain the growth of the circle itself.
To test their theory, he and his team used the DNA that can be extracted from an environmental sample such as a gram of soil or water — and modern metagenomic methods — to investigate the bacterial and fungal diversity of soils inside the fairy circles, and compared them with soils outside circles.
“We found significant differences between these communities, but this is not causative proof,” he said. “Interestingly, some of the unique fungal species found only in the soils inside the fairy circles are known plant pathogens, though this is also not final proof that they cause the circles. We would need to isolate these fungi as cultures and prove that they are infecting and killing the plant species.”
Complex effects
Some proponents of the various major theories tend to ignore contrary evidence, he said. “For example, proponents of the Euphorbia theory seem to ignore the fact that fairy circles exist extensively in the gravel desert areas where Euphorbias do not grow and may never have grown.”
There are suggestions that the effect that causes fairy circles may be complex, with possible secondary effects. Plants germinating inside fairy circles, as they do after rain, die quickly and seem to be more susceptible to drought. This implies the causative agent is somehow related to root function.
Cowan believes there are perhaps multiple causes of localised plant death that generate the surreal phenomena. “Fairy circle structures might be caused by sand termites eating roots in one desert area, while residual toxins in the soil from dead Euphorbia plants might be the cause in another, and pathogenic fungi in a third.
“Once again, it’s part of the fascination, there are multiple causes of the same physical morphology.”
Unanswered questions
He spoke of an early study that suggested fairy circles have a lifespan of 40 years, although Cowan said he is not sure how much of that is real science or guesswork.
“Interestingly, no one seems to report ‘newborn’ or very small fairy circles. Certainly, I have never seen one.”
The circles seem to grow with the death of grass plants around the outer margin, which makes the circle larger. Plants around the edges of the circles grow taller and stronger than those on the outside, probably because they have less competition for nutrients and water, until they die as the circle expands.
“There are a lot of unanswered questions that don’t really fit anyone’s theory. Why don’t they [the fairy circles] overlap or run into one another? They can be beautifully spread and distributed, if you look at some of the online imagery.”
Fundamental science
Cowan’s research focuses on the microbiology of extreme environments, including hot (Namib) and cold (Antarctic) desert soils. His work on the microbial ecology of Antarctic desert soils spanned more than two decades.
“Going to a remote, beautiful, pristine part of the world as a scientist has another dimension beyond going as a tourist,” he said. “As a scientist, there’s another level of excitement and the excitement is trying to understand something about the system.”
He is a firm believer in the value of fundamental science and, in particular, trying to understand the world around us. “Much of what I do, including my work in the Namib desert and my work on fairy circles, is part of that philosophy, just trying to understand the world around us, make sense of it, and understand its fascination.”
Working on fairy circles falls right into that category, he said. “Why are they there, what causes them and how does my knowledge of my subject and my expertise contribute to that understanding?”
He finds it such an exciting project that he rather hopes that nobody ever finds the real answer. “It’s a lot more fun in this case to just to keep looking.”