Researchers from Ben-Gurion University of the Negev in Israel and the University of Göttingen in Germany have shown that enigmatic witch circles form when soil becomes thirsty. The findings appear in a study published in the Proceedings of the National Academy of Sciences (PNAS).
Witch rings, sometimes called elven rings or fairy rings, are circular patterns created by certain fungi. They can span from a few tens of centimeters to several meters across. In folklore, these rings are often linked to nocturnal dances of elves or forest spirits. Legends also tie them to the sites of witches rituals and sabbaths.
For years, scientists debated what triggers the creation of these rings. Some explanations blamed termite activity that clears out roots, allowing mushrooms to spread. Others proposed that the rings arise from fungi regulating their growth in response to limited water, effectively fencing off moisture from nearby plants.
The researchers observed that witch circles tend to be more frequent in dry regions where soil nitrogen is scarce. Under such conditions, the fungi extend their network deeper and wider along roots, hindering neighboring plants from accessing the remaining moisture and nutrients.
To test ideas about their origin, the team developed a predictive model that simulates when and where witch circles are likely to appear. The model’s outcomes supported the drought-defense explanation, showing that water scarcity drives the formation of these fungal rings.
Earlier investigators had already noted a practical link between fungal activity and urban tree health. In modern urban ecosystems, understanding how soil moisture and nutrient limitations influence fungal growth helps explain why some trees show vigor changes in drought periods and how soil management can bolster urban greenspace resilience.