10.07.2017

Some fairy circles hail from John Constable’s times


Fairy circle in the vicinity of Namib Desert Lodge. (Sven-Eric Stender)

Professor Norbert Jürgens at a fairy circle in the vicinity of Namib Desert Lodge. (Sven-Eric Stender)

Aerial pictures of the same fairy circle plain at Featherlion Hill in the Marienfluss Valley in north-western Namibia, taken in 1956 and 2006 (below) respectively. (Land registry office Windhoek, Norbert Jürgens)

Aerial pictures of the same fairy circle plain at Featherlion Hill in the Marienfluss Valley in north-western Namibia, taken in 1956 (above) and 2006 respectively. (Land registry office Windhoek, Norbert Jürgens)

Queen and king of the sand termite Psammotermes allocerus. (Felicitas Gunter and Norbert Jürgens)

Death by competition: dying or dead fairy circle next to a circle that is alive. (Norbert Jürgens)

Years after the mystery of the bare circles in the grassy plains on the edge of the Namib has been lifted, biologists are still captivated. Not only can the circles grow as old as the hills but their creators now hold the world record in "ecosystem engineering". Much to the chagrin of beavers...

Fairy circles, the bare patches in the grassy plains on the eastern fringe of the Namib Desert, can reach an age of 200 years, or perhaps even up to 1,000 years – this is according to research conducted by biologist Professor Norbert Jürgens, based on projections and aerial photos taken of an area with barren circular patches in the Marienfluss Valley in north-western Namibia between 1956 and 2006. Some of today’s fairy circles may thus date back to the times of John Constable, the great romantic painter of landscapes.

The ‘maxium life expectancy’ of the circles should not be confused with the average age, however, which is probably much lower. New circles, formed in years of good rains, tend to disappear again in subsequent years of drought. And the age of a fairy circle doesn’t give any indication of the age of the sand termite colony that created it. A circle can be inhabited and maintained by successive colonies, says Professor Jürgens.

Even a thousand years, by the way, would not be a record for termite constructions. Organic material more than 2,200 years old was found in mounds in the Congo. And lime which is 4,000 years old formed in the heuweltjies (‘little hills’) in north-western South Africa. But scientists are not in agreement yet whether the heuweltjies are the work of termites. Some have the same doubts about the fairy circles in Namibia.  

Water storage for hard times

Meanwhile, however, the termite theory, published by Professor Jürgens in early 2013, has become the ‘generally accepted opinion’. It is based on data collected over the course of five years (in fact ten by now) at the Namib Desert Lodge of the Gondwana Collection 60 km north of Sesriem/Sossusvlei. The data consists of hourly soil moisture measurements at a depth of 10 to 90 cm inside and outside a fairy circle, meteorological information recorded by the weather station at the lodge and daily pictures taken by a camera trap of the condition of the grasses. 

The bottom line of the theory: the bare circular patches are caused and maintained by termites – the sand termite Psammotermes allocerus, to be more precise – so that rain water can percolate through the sandy soil and accumulate underground, at a depth of more than 50 cm, instead of being absorbed by grasses. Even during extended dry spells this storage system provides sufficient humidity in the termites’ tunnels and usually also for a ring of abundant grass, a ‘luxury belt’, around the circle. The grass outside the circle is used as a daily food source while the luxury belt serves as an emergency supply during exceptionally long periods of drought. This makes every fairy circle a perfect example of sustainable farming in arid areas, says Jürgens.

Drought the deadly foe number 1

A little more information has since been gleaned on the lifespan and demise of a circle. It all starts when winged termite queens and kings swarm out after the first downpour of a rainy season to settle and mate at a new spot. Initially the new colony of termites feeds on the roots of the existing grasses. A bare circular patch appears within five to six months, well ahead of the next rainy season. Now and then it may happen that a new queen takes over a ‘dead’ fairy circle. 

The circle becomes larger as the colony grows in years of good rains which provide sufficient water and food. If two colonies get too close to one another it usually spells death for the weaker one: its circle is absorbed by the stronger colony or disappears as it is reclaimed by grass. Hostile ants also pose a deadly threat. The major cause of death, however, is drought. After three to four dry years, when all the grass outside the circle and in the luxury belt has been eaten or the water storage system is depleted, the colony dies. This threat is the biggest in the beginning, before a new colony is able to store sufficient supplies. 

Doubts about the model theory

Some scientists are still doubtful about the termite theory even though it is based on a growing number of facts and also offers plausible explanations for specific parts of the circles’ phenomenons. So far the biggest question mark was raised by theorists who maintain that the pattern of bare patches in grassy plains is caused by competition among grasses. According to them, the competition results in circular patches without moisture and nutrients. Termites are excluded as a possible cause. 

But this purely abstract question mark ignores the fact that the soil everywhere within a fairy circle always contains more water than the soil outside the circle. Furtermore, scepticism emerged in the doubtful plant competition theorists’ own ranks in early 2017 because a new model showed that competition between termite colonies can indeed cause the known patterns of the fairy circles.                

Clinging to the fairytale 

In Namibia, too, some people stubbornly baulk at the termite theory, though with less motivation and with arguments which are less sound scientifically. In 2015, for example, a private nature reserve in the southern Namib arranged a fairy circle workshop. As many explanations as possible (termites, self-organisation, poisonous fumes, euphorbia) were presented as more or less equally worthwhile theories, apparently with the professed goal to prevent demystification of the bare circles.

The fairy circles at the same nature reserve are offered for ‘adoption’. Sponsors receive the GPS coordinates and are entered into a register. Perhaps there is a little concern about the reaction of potential sponsors when they realise that the godchild is not a myterious circle from a fairytale world but a profane termite mound in the sand of the Namib.  

In the world of science, however, the fairy circles, after their demystification, turn out to be another wonder of evolution – a unique adaptation to extreme aridity like lithops, the Welwitschia mirabilis or the plants of the genus Psammophora. The termites, according to Professor Jürgens, are the world champions of ecosystem engineering. The latter is the ability of organisms to redesign ecosystems to their advantage. Previously, the beaver held this distinction.

Sven-Eric Stender     


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