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By Meagan Cantwell
The drylands of Namibia and Australia are well known for their fairy circles – barren rings that dot the grasslands and are believed to result from termites and water scarcity. But humid regions also have fairy circles. A new study reveals what motivates their formation in the salt marshes of eastern China.
In the coastal swamps near Shanghai, fairy circles are ephemeral – appearing for a few years before giving way to large expanses of deep-rooted grass. Grass circles often collide and have areas of open mud in the center.
Scientists hypothesized that the availability of nutrients could be the cause of their formation. To find out, they created a computer model that simulated the growth of fairy circles using two inputs: the slow build-up of sulfide, a toxic byproduct of bacterial growth, and the depletion of nutrients at the center of the rings. as they developed. To their delight, the model has recreated the nesting rings seen in the swamps (see video above). To verify their findings, the scientists then applied fertilizer to the dense outer edges of the rings and the sparsely vegetated centers; While the increase in nutrients did not make a difference to the well established outer rings of vegetation, it made the areas within the rings bloom.
Because grasses in the center take root first, they face increased competition for nutrients as successive plants grow around them. This makes them die first and leaves newer, more alive rings behind, scientists report this month in Scientific advances. Sometimes a bird’s eye is the best way to understand microscopic interactions on the ground.
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