The ash, Fraxinus excelsior, is a tall, tough, straight-grained tree, and in Norse cosmology it is the frame of the cosmos itself: Yggdrasil, the world-tree that binds the nine worlds, is named an ash in the Prose Edda, its roots and branches holding heaven, earth and the underworld together, with a well of wisdom beneath it and Odin hanging on it to win the runes. The same tradition makes the ash the origin of humanity, the first man, Askr, whose name simply means ash, was made from a piece of ash-wood found on the shore by the gods, as the first woman Embla was made from another tree.
European ash populations now face a genuine modern crisis: ash dieback, a fungal disease caused by Hymenoscyphus fraxineus and first identified spreading through Europe in the early 1990s before reaching Britain around 2012, has killed a large proportion of the continent's ash trees and is expected to kill the great majority of those remaining, a disaster on a scale that threatens to remove the very tree that stood, in Norse cosmology, at the centre of the world. Conservationists now watch for a small proportion of naturally resistant trees in the hope of eventually breeding a disease-tolerant ash back into the landscape.