Trunk Decays
From Bugwoodwiki
USDA Forest Service. 1979. A guide to common insects and diseases of forest trees in the northeastern United States. Northeast. Area State Priv. For., For. Insect and Disease Management., Broomall, PA. p. 123, illus.
All tree species are susceptible to attack by decay fungi. Spores of these fungi are released constantly into the air from reproductive structures (conks) present on already infected and decayed trees. When the humidity and air temperature are suitable, the fungi can enter the tree through such openings as dead branches or branch stubs, fire or insect injuries, and mechanical wounds caused by loggers or recreationists.
After a tree is wounded, the time required for the wood to discolor and decay varies considerably. The presence of a conk usually indicates that tissue deterioration is quite advanced. The percentage of the tree affected varies with the fungus species and, of course, with the time the fungus has had to act. Trees resist fungal invasion by "walling off" an infection. Barriers or "walls" are formed, or already exist, on all sides of an injury. The barriers above and below the wound are the weakest. Therefore, the tree decays up and down more rapidly than to either side or toward the inside or outside of the tree. The strongest barrier forms toward the outside of the tree as the entire cambium reacts to the injury. This barrier confines decay to "old" wood, that is, the wood formed before injury. Unless the tree is wounded again, or unless the fungus itself can re-wound the tree and bypass this barrier (as the "canker rot" fungus Inonotus obliquus readily does), the wood formed in the years after injury is sound. Because of the resistance of the strongest "wall," a tree's trunk may be a tube of sound wood with the center of the tree completely decayed.
Recent botanical discoveries have led to reclassification of many of the rot fungi, and therefore, the names have been changed. In this publication the old names are in parentheses following the new ones. Most of the decay fungi discussed cause significant timber loss or degrade.
