Viewed from the skies, the Namibian desert looks like the
surface of a wild and desolate planet. There are no obvious plants, and
thousands of tiny craters dot the red barren earth. But zoom in a little closer
and a different picture emerges: patches of green appear, along with the
occasional tree, and, eventually, perfect rings of tall, sometimes lush, grass
come into focus, each one enclosing a plate of bare-hollowed out earth.
These grass-ringed patches are the fairy circles of Namibia . For
centuries they’ve entranced the local bushmen, the Himba. One oral myth says
the circles are the footprints of the gods; another that a dragon living
beneath the earth’s crust breathes fiery bubbles which, when they hit the
surface, burn the vegetation into the near-perfect circles.
But the circles haven’t just confused the Himba. Despite
decades of investigation, and a multitude of theories, scientists still haven’t
come up with a definitive explanation for their existence. To this day, the
circles remain one of nature’s greatest mysteries.
A thousand unblinking eyes
Perhaps the fairy circles wouldn’t have been able to guard
their secrets so successfully if they hadn’t been so concentrated in a region
referred to as “The land God made in anger.” The circles occur in millions in a
band where the arid grasslands transition to desert, a 1,800km-long strip
extending southward from Angola
to the Northwestern Cape province of South Africa . Most of them,
however, flank the red sands of the Namib desert ,
a remote and harsh environment.
Scattered across the landscape, never overlapping, the
circles gaze silently up at the sun like a thousand unblinking eyes, oblivious
to the harshness of their surroundings. A tall ring of grass surrounds the
barren centres, which can measure between two and 20 metres in diameter. The
lush periphery of each dish stands at knee height, dwarfing the scrubby grasses
between the circles, seemingly standing guard to protect them from incoming
vegetation.
“There are a few key things that any science theory has to
explain about fairy circles,” says Michael Cramer, a plant physiologist at the
University of Cape Town, South Africa. “Why are they circular and barren and
why are they regularly spaced from each other?”
But since the 1970s, when researchers first started
investigating the phenomenon, no single theory has yet managed to do that. At
least not to the satisfaction of the scientific community.
But this failure is not for want of trying, or desire.
“There is a tremendous sense of excitement that there is
something really interesting going on and we want to know what that is,” says
Professor Don Cowan, director of the Centre for Microbial Ecology and Genomics
at the University of Pretoria, South Africa. “It is a desire to understand the
system. What is going there? What is happening?”
Fairies run rings around scientists
“They are really neat places, these little clean patches,”
says Walter Tschinkel, a biologist at Florida State
University Florida , first saw the fairy circles on a visit to the
NamibRand Nature Reserve in southwestern Namibia , he knew right away what
was causing them. "I looked at them and thought ‘this has to be termites,’”
Tschinkel says. “It is the sort of things termites do.”
Tschinkel dug for termites in one or two circles and
returned in 2007 to investigate, and hopefully prove, his hypothesis. “It took
us about three days to establish, without a doubt, that termites were
absolutely nothing to do with this,” Tschinkel says.
Tschinkel’s theory proved to be just one of the many to hit
the Namibian dust. Scientists have ruled out poisoning from toxic indigenous
plants, milk bushes that produce toxic latex, and also contamination from
radioactive materials. They have also rejected the idea that the ostriches
created the circles by bathing in the dust.
Some theories are still holding strong though, and Cowan
jokes that each scientist sees the solution in terms of their own particular
area of expertise: the insect biologists think the circles are created by ants
or termites, the plant physiologists think it’s grasses, and the chemists think
it’s gases. Cowan, a microbial ecologist, proves no exception.
“Once we saw them, we immediately thought, ‘it has got to be
microbial ecology,’” Cowan says, meaning, in layman’s terms, that means he
believes that microorganisms have been killing the plants inside the circle.
The fact that the circles are round, start off small and
grow large is entirely compatible with the presence of a pathogenic organism,
such as a fungus, Cowan says. Fungal strands, or mycelium, would spread outward
radially, infecting the roots of plants and causing them to die. Once the
fungus establishes itself in the circle it infects new grass seeds preventing
them from growing, creating the barren interior.
“It is just a hypothesis,” Cowan says. But it’s more compatible
with the evidence than many other theories, he adds.
It is like panning for gold. Once in a while you find a
little flake or a nugget and sometimes it is fool's gold.
Another theory is closer to the folklore; a team of chemists
from the University
of Pretoria
The scientists worked out this theory when they collected
soil samples from inside the fairy circles and planted seeds inside them. The
seeds didn’t last for long, and neither did seeds planted directly in the
centres themselves. The bare soil, the scientists concluded, provides the real
clues. Chemical analysis revealed that natural gas seeping to the surface could
be killing the plants. Once the gas finds an outlet it spreads radially outward
in a spherical shape destroying grasses in a near perfect circle.
However, yet another recent theory proposes that grasses competing
for water and nutrients - limited resources in the Namib
desert - create the circles, explaining why they never overlap.
When Cramer examined precipitation levels and seasonal temperatures, he found
that the occurrence of fairy circles appears to be restricted to particularly
arid zones right at the transition from grassland to desert regions.
Go west into more arid regions and the circles disappear, go
east into the wetter mountains and they vanish. “So it is a very narrow band in
Namibia
where the conditions are just right,” Cramer says.
In these regions, where both rainfall and nutrient levels
are low, grasses have to compete for resources. Hardier grasses suck up all the
water and nutrients leaving the neighbouring vegetation to die. The gap between
vegetation gets larger until eventually water and nutrients pool and collect in
the centre like an oasis. Then, larger grasses grow around the pool, sucking
out the water and creating a fairy circle.
Tschinkel believes that this theory accounts for all the
characteristics of fairy circles, but since his first visit he has been busy
testing out theories. He’s added zinc to the fairy circles and replaced the
soil with other fertile soil only to find the same results as the Pretoria chemists: nothing
grows in the circles.
If there were an award for the time spent examining fairy
circles, the prize would surely go to Norbert Jürgens, an ecologist at the University of Hamburg
in Germany .
By 2013, Jürgens had completed 40 field trips and sampled about 1200 fairy
circles, testing the soil and noting the vegetation and organisms present.
Jürgens found only one organism lay within the circle
boundaries, in nearly all the circles. And it was the type of animal originally
suspected by Tschinkel; a termite, specifically the sand termite Psammotermes
allocerus.
“So the answer to the criminal question: Who did it?”
Jürgens says. “There was only one suspect at each crime site. That was the sand
termite.”
The soil-living termites feed on the roots of plants killing
them, and then, because no vegetation sucks up the rainwater, water pools below
the sandy soil, Jürgens says. This soil water supply allowed the termites to
survive during the dry season and also helped the grasses on the periphery of
the circle to thrive.
Jürgens published his findings and theory in the prestigious
journal Science in 2013 and the ensuing media fanfare dubbed the mystery as
“solved.”
But other scientists aren’t so sure. “It is the classic
mistake of confusing correlation with causation,” Tschinkel says. “There was a
high correlation of sand termites in fairy circles but that is not evidence
that they are causal.”
The termite theory cannot explain many of the traits of
fairy circles, Tschinkel says, including that the circles have a perimeter of
tall grass and reside only on sandy soils in a certain range of rainfall.
Other researchers question the theory on different grounds,
many unable to find termites consistently in the circles. "The termites
are just not there," Cramer says.
The circles compete with one another and space themselves
apart from the circles around them.
Among the skeptics is Stephan Getzin, an ecologist from the
Helmholtz Centre for Environmental Research, in Leipzig , Germany
“We’ve had analysis of the soil in labs and we’ve had people
digging in the soil but neither has solved the mystery so far,” Getzin says.
“Field studies seem unable to solve the problem at this moment.”
And the approach that Getzin took cast a whole new
perspective on the puzzle.
Fairies dancing in formation
Scientists had looked underground for gas and dug in the
soil for termites and microbes but Getzin wanted a bird’s eye view of the
challenge. For that he looked at multiple Near InfraRed orthophotos - aerial
images that provide an exact geometrical perspective, similar to a map.
In these images Getzin closely inspected not the circles
themselves, but the way they lay across the landscape. And he stumbled across a
hitherto unknown feature of fairy circles: they dance in formation.
Are scientists any closer to solving the enigma?
Instead of being simply scattered like a collection of
dropped coins, the circles lie regularly spaced from one another. Moreover,
this patterning remains the same across the landscape.
“It’s a very consistent regular pattern,” Getzin says, “and
it is very homogenous at large spatial scales.”
This regular spacing isn’t so unusual in nature. In other
regions of Africa , tiger bush - alternating
bands of shrubs and bare earth - run parallel to the contour lines of
hillsides, in a marked striped pattern. In Australia , burette-like clumps of
spinifex grass dot the desert - like fatter, less elegant cousins of fairy
circles.
They almost function like an organism
Both these phenomena are caused by arid conditions. When
water and nutrients are scarce, plants compete and “organise” themselves
sufficiently far from other plants in an arrangement that best conserves
resources.
Drawing from these examples, Getzin proposes a similar
mechanism lies behind the shape and regularity of the fairy circles. It’s an
answer that agrees with Cramer’s competing grass theory.
“The circles compete with one another and space themselves
apart from the circles around them,” Cramer says. “They almost function like an
organism.”
Creating these patterns over such large scales requires very
consistent conditions - like those in the Namib desert ,
Cramer says. “The park I work in is a sand plain of about 25km across and I
think you'd be hard pressed to find any variation across that at all,” Cramer
says. “Nutritionally, hydrologically, topologically it is very uniform. “
The finding also calls into question other theories. “Based
on all the knowledge that is currently existing those patterns cannot be caused
by social insects or gas leakage,” Getzin says.
So is this finally the end of the mystery?
Getzin is cautious. “What we have done is reopened the whole
discussion because we can say with confidence that the termite hypothesis is
very unlikely,” he says.
Getzin plans to get funding to have an unmanned aerial
vehicle (UAV) fly over the circles in the NamibRand reserve every month.
Swooping low, the UAV could record the landscape in greater detail than
previously possible.
Such a perspective could reveal other, previously unknown
secrets of the circles.
“I’m sure this is not the end of the story,” Getzin says.
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