Blackfire is a kind of mushroom with black tops that look like clams that's very deadly to trees. When the mushrooms get into its roots, it would spread burning streaks on it, which will cause the tree to die. An older and stronger one can survive about a year before its fate.
The mushrooms could be killed off by using a potion made from a herb called Lyssop.
The Great Ga'Hoole Tree was once affected by Blackfire. A group of owls from the Ga'Hoolology Chaw went around the kingdom to gain information on the mushrooms and how to fight it. Aude the Snowy Owl, a tree healer, told of the cause and the cure. The Dark Sisters, a group of nest-maid blind snakes that specialize in potions, developed the potion made from Lyssop. Within two weeks, the streaks and the mushrooms disappeared from the tree.