If you visit the Namib desert after rainfall, you’ll see the sand spring to life – but not everywhere. In some places, patches known as fairy circles appear. Inside the circle, grass will be dead or dying, yet around the outside of the circle, grass will be lush and green. Why? Stephan Getzin and colleagues studied the circles to see if termites caused these dead zones or if something else was happening. Their results have been published in Perspectives in Plant Ecology, Evolution and Systematics.

As the name Namib desert suggests, rain is a relatively rare event in the region. However, botanists were able to exploit two good wet seasons to pounce on fairy circles as they happened. They installed soil-moisture sensors in and around the fairy circles to record the soil-water content at 30-minute intervals starting in the dry season of 2020 to the end of the rainy season of 2022.

They found that about ten days after rainfall, the grasses were already starting to die within the circles, while most of the interior area of the circles did not have grass germination at all. Twenty days after rainfall, the struggling grasses within the circles were completely dead and yellowish in colour, while the surrounding grasses were vital and green. When the researchers examined the roots of the grasses from within the circles and compared them to the green grasses on the outside, they found that the roots within the circles were as long as, or even longer than, those outside. This indicated that the grasses were putting effort into the growth of roots in search of water. However, the researchers found no evidence of termites feeding on roots.