In two corners of the world, a massive swath of land has long held a natural formation that has continued to stump scientists since their initial discovery in the 1970s. Known as fairy circles, “extremely ordered” round patches of bare soil appear to have been strategically placed in the grasslands of southwestern Africa and northwestern Australia. These landscape-scale vegetation patterns look like polka dots from above – but how did they form and why are they there?
Attempting to solve the mystery, a team of multidisciplinary scientists think they may have found an answer in Australia. Though separated by more than 10,000 kilometers (6,200 miles) from their much larger Namibian cousins, Australia’s fairy rings measure, on average, about 4 meters (13 feet) across. First discovered in 2014, theories explaining their origin ranged from poisonous Euphorbia plants and rising gases to ants and termites, infestation, and plant competition for water.
Their theory: a relatively simple one.
Writing in the journal Ecosphere, the researchers analyzed soil compaction and texture within 48 circles, the surrounding vegetation, and in nearby large areas of bare soil. They found that when compared to soil with grass cover, fairy circles had nearly three times more clay and lacked the kind of sediment that would be in its place if termites were the cause. Instead, they surmise that the strange circle patterns are created by weather processes like rainfall events, particle dispersion, surface heat, and evaporation, among other things, that inhibit plants from growing.
"The vegetation gaps caused by harvester termites are only about half the size of the fairy circles and much less ordered," explained study author Stephan Getzin in a statement. "And in most cases, we didn’t even find any hard subterranean termitaria that elsewhere in Australia prevent the growth of grasses."
The team then mapped three plots with a drone and compared their images against aerial photos of typical vegetation gaps created by two different species of termites. These differ from the unique differences found between circles, further proving that termites are likely not the culprit.
"Overall, our study shows that termite constructions can occur in the area of the fairy circles, but the partial local correlation between termites and fairy circles has no causal relationship," said Getzin. "So no destructive mechanisms, such as those from termites, are necessary for the formation of the distinct fairy circle patterns; hydrological plant-soil interactions alone are sufficient.”
The team is currently conducting a pilot study in Namibia using Google Earth to see how these fairy circles are formed. Here, they found huge circles measuring more than 20 meters (65 feet) across, as well as ovals that stretch like chains for more than 30 meters (98 feet).