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Termites behind desert 'fairy circles'

Fairy circles in the Marienfluss Valley, Kaokoveld, Namibia. Transition of desert margin grassland to Mopane savanna. Fairy circles seem to be gaps in the grassland.
[Image courtesy of N. Juergens]

A new study uncovers the origin of fairy circles, circular patches of perennial grasses with a barren center that grow in the desert on the southwest coast of Africa. The research appears in the March 29 2013 issue of the journal Science.

Fairy circles occur in regular patterns and can persist for decades, but the cause of these striking rings that dot the Namibian desert remains a mystery.

Now, scientist Norbert Juergens shows that a particular species of sand termite called Psammotermes are likely creating the circles. Studying a 2000 kilometer-long belt of desert from mid Angola to Northern South Africa, the author noticed that whenever he found fairy circles, Psammotermes termites were also found within the bare patch of the circle and in the surrounding vegetation.

The author determined that Psammotermes is the only organism constantly found in the earliest life stages of fairy circles. In young fairy circles, Psammotermes feeds on the roots of grasses. More termite activity is correlated with reduced grass growth in the fairy circle.

Taking a closer look, Juergens discovered that the soil-living termites kill all grasses within the fairy circle by feeding on their roots. Because of the lack of grasses, rain water is not lost by transpiration (the evaporation of water from plants), but is instead stored in the depths of sandy soil, where it is sheltered against evaporation.

The soil water supply allows the termites to remain alive and active during the dry season, and helps grass plants growing at the margin of the fairy circle to survive and grow. The findings are an example of ecosystem engineering by termites, whose fairy circles are able to short-lived deserts into permanent grasslands.