May 21, 2014
Self-Organization Most Likely Cause Of Namibian Fairy Circles: Study
Lawrence LeBlond for redOrbit.com - Your Universe Online
A new study of mysterious bare “fairy circles” of ground dotting the landscape in the Namibian grasslands have been determined to not be the work of sand termites as had been previously suggested, but rather self-organization.Scientists have been researching these crop circle-style, bare patches of ground for decades trying to come up with a reasonable explanation for why these formations occur. Research published last March suggested that sand termites eat up all the grass in a circular pattern to make water traps. When it rains, these patches of ground will hold any water that falls within their plot. Since there is no plant contact within the circle to evaporate the water, it becomes a sustainable source for the termites as well as keeping the grasses that line the pockets alive.
The evidence by University of Hamburg researcher Norbert Juergens seemed pretty clear cut. But it wasn’t the only theory out there. In fact several theories, some more crazy than others, seemed to arise for how these fairy circles came to be: Were they work of giant underground creatures? Did radioactivity create the formations? Is a rash of deadly plants killing off their rivals to blame? Is toxic gas being released from the ground?
According to the new research, published in the scientific journal Ecography, none of these theories explain how and why these fairy circles exist.
A team of researchers led by Dr Stephan Getzin, of Helmholtz Centre for Environmental Research (UFZ) in Leipzig, Germany has tested different prevailing theories as to their respective plausibility. For the first time they carried out a detailed analysis of the spatial distribution of these fairy circles, discovering a remarkably regular and spatially comprehensive homogenous distribution pattern. This work may be best explained by way of reference to local resource-competition for water among the plants and vegetation of the Namibian grasslands.
The arid grasslands of southwest Africa are freckled with these barren circular patches, some of which only measure a few meters (6-7 feet) in diameter and some that measure as much as 20 meters (65 feet) in diameter; as well most do have a pronounced and lush peripheral growth of grass. It is mysterious details like these that have drawn scientists to them, trying to determine the reasoning behind their puzzling formations,
“Although scientists have been trying to answer this question for decades their mystery remains as yet unresolved”, stated Dr Getzin – because until now, nobody has been able to actually observe, in situ, the genesis of a fairy circle.
THREE PREVAILING THEORIES
Working with colleagues from Germany, Italy and Israel, Dr Getzin has investigated the three most prevailing theories – sand termites, hydrocarbon release from underground and self-regulating grass growth – to determine which is the most likely correct scenario for the fairy circle production.
“We have adopted an entirely novel approach in this research”, said Dr Getzin, who has been studying fairy circles for more than 15 years.
Dr Getzin added that this study is based on the review and evaluation of aerial images, covering representative regions with fairy circle occurrences throughout northwest Namibia. Using the images as a guide, the team determined for the first time the exact spatial location and distribution patterns of these barren patches of earth within the surrounding landscape.
Even within this newly explained theory there are questions. Are the circles arranged and positioned only by chance – like coins dropped on the ground and then scattering all over the place? Are there signs or distinguishable patterns of clustering in certain locations? Do these patches need to maintain a minimum distance from their neighboring patches?
The team acknowledges that these questions cannot be answered through naked-eye observations. But through statistical methodology, they can illustrate the respective distribution patterns at different levels of scale. According to this methodology, the fairy circles are distributed in a surprisingly regular and homogenous way, even across large spatial areas.
“The occurrence of such patterning in nature is rather unusual,” says Dr Getzin. “There must be particularly strong regulating forces at work.”
Dr Getzin maintains that this new research discredits the generally popular theory of sand termites creating these patches.
In the 2013 study, it seemed pretty clear that the termite species Psammotermes allocerus was the most likely suspect for the creation of the fairy circles – albeit primarily based on the argument that the occurrence of this particular species has been commonly found in all fairy circles investigated at the time. Dr Getzin explained that no one has so far observed these creatures actually creating these holes in the Namibian grasslands.
“There is, up to now, not one single piece of evidence demonstrating that social insects are capable of creating homogenously distributed structures, on such a large scale,” maintained Dr Getzin.
The team also do not see underground emission of abiotic gases as a likely scenario for the evenly dispersed and homogenous spatial distribution seen in these fairy circles.
So, the team is left with only one other theory, and one that remains as a probable cause: local resource-competition among the plants and vegetation of the Namibian grassland region. For its own part, this theory could very well account for the regular, homogenously scattered circles.
As an example, the team noted that in a young-growth forest plants will grow and develop at comparatively close range, vegetation will thin out and regress, over the years, in a self-organizing process. Each mature tree needs sufficient space and nutrition for its development and will therefore be able to survive only at an appropriate distance from its neighbor. The fairy circles in the Namibian grasslands seem to be following a very similar self-organizing process to ensure survival.
Using a computer model, Dr Getzin and colleagues have simulated belowground competition for water and the resulting spatial vegetation distribution patterns. The model indeed showed very similar patterns to the images of the Namibian fairy circles. And in the course of all statistical review and analysis performed, the characteristics of both simulated and real fairy circles turned out to be remarkably congruent and closely identical.
The imaging, modeling and statistical analysis all tied together represents compelling evidence for the research team that the fairy circles may be the result of spatially self-organizing grass growth.
“We consider this at present being the most convincing explanation,” concluded Dr Getzin.