Fairy rings created by the mushroom Agaricus urinascens dramatically transform Mediterranean grasslands. These fungal rings create zones of dead plants and altered soil conditions, killing vegetation and reducing plant species diversity by 40% at the fungal front. The fungi coat their mycelium with calcium oxalate crystals and create water-repellent soil conditions that essentially drown plants by preventing water absorption, ultimately favoring fast-growing grasses over diverse wildflower communities.