Several fungal diseases, sometimes called heart or sap rots, cause the wood in the center of trunks and limbs to decay. Almost all species of woody plants are subject to trunk and limb decay, although older, weaker trees are most susceptible. Decay fungi destroy the tree’s internal supportive or structural components—its cellulose and hemicellulose and sometimes its lignin. Wood decay makes trees hazardous, because trunks and limbs become unable to support their own weight and can fall, especially when stressed by wind, heavy rain, or other conditions.
Wood decay usually is a disease of old, large trees. It is very difficult to manage, but a number of factors can reduce the risk of serious damage. Properly prune young trees to promote good structure and avoid the need to remove large limbs from older trees, which creates large wounds.