Yggdrasil Is Mortal

In Norse cosmology, there is no more important entity than Yggdrasil. When it dies, the myths tell us, the whole world of the gods dies with it. Nearly every Norse text that mentions Yggdrasil emphasizes that the tree is not only sacred, it is mortal, and sorely in need of compassion and protection. Odin, in the Poetic Edda, says Yggdrasil "suffers agony / more than men know, a stag nibbles it above, but at its side it's decaying, and Niohoggr [a malicious serpent or dragon] rends it beneath". Elsewhere in the Eddas, we're told that countless dangerous serpents slither below Yggdrasil; a squirrel is constantly scurrying up and down its trunk, bringing news and Gullinkambi, one of the three roosters whose crowing will will signal Ragnarok (the Twilight of the Gods), nests in Yggdrasil's upper canopy like a sentry.

"The Ash Yggdrasil", illustration in Carla Wenckebach's A Christmas Book: Origin of the Christmas Tree, the Mistletoe, the Yule Log, & St. Nicholas (1898).