any of several types of fungal decay of tree heartwood. often beginning with infected wounds in the living portions of wood tissue. Also called heart rot.
heartwood rot (Wikipedia)
In trees, heart rot is a fungal disease that causes the decay of wood at the center of the trunk and branches. Fungi enter the tree through wounds in the bark and decay the heartwood. The diseased heartwood softens, making trees structurally weaker and prone to breakage. Heart rot is a major factor in the economics of logging and the natural growth dynamic of many older forests. Heart rot is prevalent throughout the world affecting all hardwood trees and can be very difficult to prevent. A good indication of heart rot is the presence of mushrooms or fungus conks on the tree.
The bracket fungus Fistulina hepatica is one of many that cause heart rot.