Fairy circle

from Wikipedia, the free encyclopedia
Fairy circles in the Marien River Valley in Namibia, with the Hartmann Mountains in the background
Fairy circles in the Marien river valley in Namibia
Single fairy circle in the Marien river valley in Namibia
Fairy circles from the air in the Namib-Naukluft-Park (2017)World icon

The fairy circle is a phenomenon that can be observed primarily in dry grasslands in southern Africa , for example in Namibia . These are roughly circular bald spots without vegetation in the middle of grassy areas, which are surrounded by a ring of sturdy grass. The origin of these circles has been scientifically investigated for decades.

In 2015, a team of researchers from the Helmholtz Center for Environmental Research Leipzig (UFZ) discovered and examined fairy circles in Australia .

Origin hypotheses

Animal activities (termites)

The fairy circles examined in Namibia contain underground termite tunnels . Radar surveys suggested that there are layers of wetter soil beneath the circles.

On March 29, 2013, a possible cause was published in the journal Science together with the Namibian Gondwana Collection . As a result, the sand termite ( Psammotermes allocerus ) frees the sandy soil from annual grasses so that the seeping rainwater is not absorbed by the grasses and evaporated through the leaves, but remains in the deeper soil layers. In areas with an average of 100 mm of rain per year, there is always more than 5 percent by volume of water in the sandy soil under the circles - even after years of drought. The biologist Norbert Jürgens received these values as part of a long-term study in fairy circles on the grounds of the Namib Desert Lodge south of Solitaire . The water reservoir ensures a relative humidity of 98% in the tunnels of the termites , which the insect needs to survive. Jürgens examined not only the vegetation-free zones, but also the grass belts on the edge of the fairy circles, which he called "luxury belts" because of their lush growth.

In addition to the sand termite, other insects , namely termite and ant species, are also held responsible for the formation of the fairy circles. There is a similar phenomenon in the prairies of North America. In Idaho , ants have been found to be responsible.

One hypothesis is that the bare interior of the circles goes back to the activity of the harvest termites ( Hodotermes mossambicus ), which eat the grass in the vicinity of their nest. The diameter of the fairy circles varies from a few decimeters to a size of 12 meters.

The termites of the species Baucaliotermes hainsei are also suspected of causing the circles.

The investigation of the phenomenon is made difficult by the hidden way of life of the termites, the structure of which can be several meters below the surface of the earth. For the grass harvest, the harvest determinants only leave their burrow at night or when an acute lack of food forces the insects to leave their nest. They are often prey of the aardwolf ( Proteles cristatus ), a type of hyena that specializes in termites , and other predators such as the golden mole rat .

According to the biologist and ant researcher Walter Tschinkel, however, there are no indications of the action of the insects in the soil. The nutrient situation in the circles does not differ either.

Geological conditions

More recent studies in Africa, however, also allow a chemical origin hypothesis. Scientists from the Department of Botany at the University of Pretoria have used analytical methods to study the gas composition of the soil in selected fairy circles. Accordingly, gases and liquids of geological origin seemed to play a role in the formation of the fairy circles. The contents of carbon monoxide (CO), carbon dioxide (CO 2 ), oxygen (O 2 ), hydrogen sulfide (H 2 S) and nitrogen dioxide (NO 2 ) were determined several times with a portable gas analyzer . CO allows conclusions to be drawn about the presence of natural gas . Although natural gas is not a poison to plants, it is an important stress factor for vegetation: Hydrocarbons increase the activity of oxidizing and sulfur-reducing bacteria, for example, which reduce the oxygen content in the soil. This affects the pH of the soil and thus the availability of minerals that are necessary for plant growth.

self-organisation

According to researchers at the UFZ, the remarkably homogeneous distribution of the circles over large distances speaks in favor of natural self-organization . The large-area distribution pattern is said to have been replicated using a computer simulation . The effect is therefore based on competition for resources. In the areas with a better water supply, there is a significantly reduced distribution density.

The self-organization theory is supported by the discovery of further fairy circles in Northwest Australia. These are 10,000 km away from Namibia and have no termite activity. Occurrence in distant, differing ecosystems suggests a universal principle of pattern formation. The cause is a biomass-water feedback that creates a circular arrangement. This also means that these patterns are more widespread than assumed and have only remained mostly unobserved by humans.

The biologist Stephan Getzin had already been able to identify concise patterns through aerial photographs and satellite data; For the explanation of the origin and development of the fairy circles, however, the models of the Israeli physicist Ehud Meron, one of the most famous scientists of self-organization, and his working group at Ben-Gurion University were required . In Namibia the fairy circles are 12 to 14 meters apart; the soil is porous and coarse sand, where rainwater can penetrate quickly. In Australia, on the other hand, the fairy circles with diameters of 5 to 6 meters are smaller, so that nothing can be found under the surface of the ground. The characteristic of this self-organized vegetation pattern is the species poverty in the dry grasslands. There are only one or two types of grass that benefit from the rainfall that seeps into the upper ground surfaces. The different feedbacks from biomass and precipitation and thus the mutual influence of grass development and rainwater use lead to the formation of patterns in the fairy circles.

Long-term satellite observations showed that the fairy circles are subject to a life cycle of formation and decay, depending on the size, this is between 24 and 75 years.

See also

literature

Movie

  • Namibia - The secret of the fairy circles. Documentary, Austria, 2011, 45 min., Script and director: Barbara Fally-Puskás, production: Magic Touch Films, ORF , series: Universum (TV series) , first broadcast: September 22, 2011 on ORF2 , summary .

Web links

Wiktionary: fairy circle  - explanations of meanings, word origins, synonyms, translations
Commons : Fairy circles  - collection of images, videos and audio files

Individual evidence

  1. ↑ a b Stephan Getzin, Hezi Yizhaq, Bronwyn Bell, Todd E. Erickson, Anthony C. Postle: Discovery of fairy circles in Australia supports self-organization theory . In: Proceedings of the National Academy of Sciences . March 14, 2016, ISSN  0027-8424 , p. 201522130 , doi : 10.1073 / pnas.1522130113 , PMID 26976567 ( pnas.org [accessed March 16, 2016]).
  2. ↑ Wanja Njuguna: Fairy rings - enigmatic features of Namibia (English) . In: The Namibian , November 27, 2012. Archived from the original on February 21, 2013. 
  3. ↑ Secret of the fairy circles revealed. ( Memento of May 4, 2013 in the Internet Archive ) In: Gondwana Collection. March 29, 2013, accessed March 30, 2013.
  4. ^ Norbert Juergens: The Biological Underpinnings of Namib Desert Fairy Circles. In: Science Magazine . March 29, 2013.
  5. ↑ Barbara Fally-Puskás: Secret of the fairy circles. (No longer available online.) Arte , archived from the original on December 7, 2013 ; accessed on December 3, 2013 (The broadcast follows the laborious research of Prof. Norbert Jürgens' thesis that sand termites and, to a certain extent, ants lead to the formation of fairy circles and how they contribute through the vegetation belt around them at the end of the ten-month Dry season to allow the animals to survive.). Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. @1@ 2Template: Webachiv / IABot / www.arte.tv
  6. ↑ Biological Science Faculty Member Dr. Walter R. Tschinkel. Florida State University , accessed October 5, 2014 .
  7. ^ A b Walter R. Tschinkel: The Life Cycle and Life Span of Namibian Fairy Circles . In: PLoS ONE . tape 7 , no. 6 , June 27, 2012, p. e38056 , doi : 10.1371 / journal.pone.0038056 ( online [accessed January 19, 2015]).
  8. ↑ Guido Deussing: Thermal desorption GC / MS unravels natural phenomena in the Namib desert. In: Laborpraxis , No. 7/8, August 17, 2011, accessed on December 19, 2018.
  9. ↑ Fairy circles apparently not created by termites after all. Phys.org, May 20, 2014, accessed December 19, 2018 .
  10. ↑ Axel Bojanowski : Discovery in Australia. Researchers explain fairy circle puzzles. Der Spiegel, March 14, 2016, accessed December 19, 2018 .
  11. ↑ a b Martin Schäfer: The mystery of the fairy circles. In: giessener-allgemeine.de . December 5, 2019, accessed April 4, 2020 .