This weak branch union has failed, creating a highly hazardous situation. Decay Decaying trees can be prone to failure, but the presence of decay, by itself, does not indicate that the tree is hazardous. Evidence of fungal activity including mushrooms, conks, and brackets growing on root flares, stems, or branches are indicators of advanced decay. A tree usually decays from the inside out, eventually forming a cavity, but sound wood is also added to the outside of the tree as it grows. Trees with sound outer wood shells may be relatively safe, but this depends upon the ratio of sound to decayed wood, and other defects that might be present.
Advanced decay is associated with cracks, weak branch unions, or other defects.
A branch of sufficient size to cause injury is decayed. This seriously decayed tree should have been evaluated and removed before it failed. Cankers A canker is a localized area on the stem or branch of a tree, where the bark is sunken or missing. Cankers are caused by wounding or disease. A tree with a canker that encompasses more than half of the tree's circumference may be hazardous even if exposed wood appears sound.