Dead circles in the desert
They range from southern Angola through Namibia to southern Africa, an area 2,400 km long and 160 km wide in the middle of the desert. they are dead circles surrounded by grass with a diameter of 2-12 meters. They form, grow and disappear in cycles of 30-60 years.
Radioactive soils, gases coming from underground, toxic proteins deposited by poisonous plants... scientists have studied several hypotheses in recent years in search of the origin of these circles. But it's not clear yet. in March 2013, researcher Norbert Juergens of the University of Hamburg gave the strongest explanation in a paper published in the journal Science. According to him, termites are likely to be the culprit. In almost all the circles studied by Juergens, termites of the species Psammotermes allocerus were found. These termites feed on the roots of the plants and, for Juergens, this is what causes the circles. In addition, during the disappearance of the plants, the rainwater in the bald areas is not lost by perspiration through the plants and remains under the sand. Thanks to this water the termites live and the herbs around the circle grow. Thus, the circles are considered by Juergens to be excellent termite engineering works.
However, not everyone agrees with Juergens, who seems to have confused correlation and causality. And there are others who believe that the cause is another: Another recent study published in the journal PLOS ONE shows with a computer simulation that competition between plants could be the cause of the appearance and disappearance of these strange circles.
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