Mysterious fairy circles killed by water

Water is life for all of Earth’s creatures, but for fairy circles, it’s death. New research finds that these strange, barren patches of soil—located predominantly in Namibia—accumulate and grow following dry years and shrink and disappear after rainy ones. Although an explanation for the circles’ existence continues to elude researchers, several teams hypothesize that intense competition among grasses for crucial resources like water and nutrients likely accounts for the patterns. Exploring that hunch, researchers analyzed a 10-year data set of high-resolution satellite imagery from the NamibRand Nature Reserve. Then, they built a mathematical model of the fairy circle ecosystem using field measurements, including soil type, vegetation, rainfall, and soil-water content. The model’s predictions correspond with satellite observations of fairy circle dynamics, and also indicate a causal relationship between rainfall and circle birth, growth, and death, the team reports online this month in the Proceedings of the National Academy of Sciences. Specifically, 1 to 2 years of especially wet or dry conditions triggers a size shift in circles, whereas 5 or more dry or wet years leads to circle births or deaths, respectively. Although the findings do not prove that competition between grasses for water causes the circles to form, the study does indicate that that essential liquid will likely be a crucial clue in solving the fairy circle mystery.