Fairy circle (Africa)

The Feenkreis (german fairy circle ) is a phenomenon that could be observed especially in dry grasslands in southern Africa, for example, in Namibia. It is devoid of vegetation roughly circular bald patches surrounded by grassy areas, which are surrounded by a ring of strong growing grass. The emergence of these circuits is studied scientifically for decades.

Formation

All fairy circles contain subterranean termites transitions. Radar investigations lead to the conclusion that there are among the circles moister soil layers.

On 29 March 2013, the journal Science published together with the Gondwana Collection Namibia in a scientifically from many quarters occupied originating cause. Consequently, frees the ' Sandtermite ' Psammotermes allocerus the sandy soil of annual grasses, so that the seeping rainwater is not absorbed by the grasses and evaporates through the leaves, but remains in the deeper soil layers. In areas with an average of 100 mm of rain per year, are located in the sandy soil under the circles always more than 5 percent by volume of water - even after years of drought. These values ​​received by the biologist Norbert Jürgens as part of a long-term study in fairy circles on the grounds of the Namib Desert Lodge south of Solitaire. The water cylinder is in the corridors of the termites for a relative humidity of 98 % required for the insect to survive. Jürgens examined not only the vegetation-free zones, but also the grass belt on the edge of fairy circles, which he called because of their luxuriant growth " Luxury belt".

Further development hypotheses

In addition to the Sandtermite Psammotermes allocerus also other insects, including termites and ants be held responsible for the rise of fairy circles. A similar phenomenon is available in the North American prairies. In Idaho, however, ants were made ​​as the cause identified.

One hypothesis is that the bare interior of the circles go back to the business of harvesting termites Hodotermes mossambicus, which erode the grass in the environment of their nest. The diameter of the fairy circles varies from a few tens of centimeters up to a size of 12 meters.

The termites of the species Baucaliotermes hainsei are suspected to cause the circles.

The investigation of the phenomenon is complicated by the hidden life of termites, whose construction can be several meters below the earth's surface. For grass harvest, the harvest termites move only by night from their construction or when acute food shortage forces the insects to leave their nest. They are often prey to the Erdwolfs ( Proteles cristatus), a company specializing in termite hyena and other predators, such as the Wüstengoldmull.

However, recent studies in Africa could also be a chemical origin hypothesis. Scientists at the Department of Botany, University of Pretoria, South Africa, have been studied in selected fairy circles, the gas composition of the soil with analytical methods. Accordingly seemed gases and liquids of geological origin in the development of fairy circles to play a role. Using a portable gas analyzer was several times the amount of carbon monoxide (CO ), carbon dioxide (CO2 ), oxygen ( O2), hydrogen sulfide (H2S ) and nitrogen dioxide ( NO2 ) was determined. CO allows to draw conclusions on the presence of natural gas. Natural gas proves to be not as poisonous plants, but as an important stress factor for the vegetation: hydrocarbons increase the activity of oxidizing as well as sulfur -reducing bacteria, which reduce the oxygen content in the soil. This will affect the pH of the soil, and thus the availability of minerals, which are necessary for plant growth.