Carnivorous ants, poisonous plants, meteor showers, and underground gas vents have all been considered as possible culprits of “fairy circles” — bare patches of soil bordered by a ring of taller grasses and found dotting the desert grasslands of Namibia in southern Africa.
But time and time again, these various theories have been thrown out due to lack of evidence.
Now, scientist Norbert Juergens believes he has unlocked the mystery behind these circular gaps in vegetation that persist for decades before suddenly disappearing: termites.
See fairy circles in the wild >
Juergens has detailed his findings in a study published Thursday, March 28, in the journal Science.
The termite theory is actually not new. Florida State University biologist Walter Tschinkel thought the circles were formed by harvester termites, but could find no evidence of their nests. Last year, Tschinkel published a study in the journal PLoS One that detailed the life cycle of fairy circles, but their cause remained a mystery.
Juergens shows in the new study that the bare patches are likely formed by a particular species of sand termite called Psammotermes.
Among the species of termites, only the sand termite was found at all fairy circle hotspots that Juergens investigated. It made no difference if the fairy circles were young or old.
The theory goes that termites eat the roots of vegetation, resulting in barren circular patches. At the outer edge of the circle, taller grasses grow because of extra water in the soil from the empty areas — these are called perennial belts.
The lack of grass at the centre, Juergens hypothesizes, means that rain water is not lost through evaporation from plants. At the same time, water rapidly sinks into a deeper soil layer because of the absence of vegetation.
This extra soil water helps perennial, or long-living, grass plants grow on the border of the barren patches, which in turn, helps the termites survive in a hostile environment.
Juergens also found that fairy circles, because of their unique environment, attract ants, bees, wasps, small animals, and other plants. The termites also serve as food for desert animals like geckos, aardvarks, foxes, and jackals.
“Fairy circles can be regarded as an outstanding example of allogenic ecosystem engineering resulting in unique landscapes with increased biodiversity, driven by key resources such as permanently available water, perennial plant biomass, and perennial termite biomass,” Juergens writes.
Here are some examples of fairy circles in the wild.
In a normal dry year, only the perennial (long-living) grass plants of the fully developed fairy circles provide food and energy for herbivores.
Here's one of the fairy circles in Namib Desert Lodge, Namibia, during a dry year. Nearly all the grass in the landscape has been consumed or destroyed by sand storms. Only the perennial belts of fairy circles still provide plant biomass for herbivores.
The desert grasses that form a ring around the bare patches, can grow up to three-feet tall in a good year.
The average lifetime of a fairy circle is 24 years, but they can survive for up to 75 years before disappearing.
Although researchers recently determined the life cycle of fairy circles, the reason they form remained a mystery.
Now, researchers Norbert Juergens shows that termites, called Psammotermes, are likely creating the circles.
Since there are no grasses to evaporate rain water, the sandy soil underneath is able to retain water.
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