By Meagan Cantwell
Dry areas of Namibia and Australia are known for their fairy circles – arid rings that dot on grasslands and are presumably the result of termites and water scarcity. But humid regions also have fairy circles. A new study reveals what drives their formation in the salt marshes of eastern China.
In swamp shores near Shanghai, fairy circles are short-lived – they appear a few years before they make way for wide expanses of well-rooted grass. The circles of grass often bump into each other and have open mud in the middle.
Scientists reckoned that the availability of nutrients could drive their formation. To find out, they created a computer model that simulated the growth of fairy circles using two inputs: the slow accumulation of sulfide, a toxic byproduct of bacterial growth and the depletion of nutrients in the middle of the rings as they expanded. To their delight, the model recreated the decorated rings seen by the swamps (see the video above). To verify their findings, the scientists applied fertilizer to the rings’ dense outer edges and sparsely vegetated centers; While the increase in nutrients made little difference to the well-established outer rings of vegetation, it allowed the areas within the rings to flourish.
Because the grasses in the middle first take root, they have more competition for nutrients as successive plants emerge around them. This led to them first dying and leaving newer living rings behind, the scientists reported this month Scientific progress. Sometimes a bird’s eye view is the best way to understand microscopic interactions on the ground.