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. Biological cause Heart rot is caused by fungi entering the trunk of the tree through wounds in the bark. These wounds are areas of the tree where bare wood is exposed and usually, a result of improper pruning, fire damage, dead branches, insects, or even animal damage. The fungal spores enter the exposed wounds, germinate within the wood tissues, and slowly ingest the heartwood. The infection is a very slow process and can take from months to years, depending on conditions and tree health. An average fungus will advance in the heartwood by 6–8 centimeters per year, and extensive development in the wood tissue is needed before mushrooms or conks are produced. Impact Heart rot fungi have both a huge economic and environmental impact. The fungi only target the nonliving wood tissue of the heartwood and do not affect the living sapwood. Initially, infected heartwood is discolored but not structurally compromised. As the fungi grow they decay more wood and the tissue becomes increasingly soft and weak. The tree can still grow around the decayed heartwood because the live wood tissue is not affected. The growth around decayed areas of heartwood creates structural weaknesses in the tree. Trees with extensive decay are more susceptible to broken branches and trunks. Logging Heart rot causes huge profit loss in the logging industry every year due to damaged and decayed timber. It is estimated that about one third of annual timber (20 billion board feet) harvest is lost due to some form of rot. Trees wounded from machinery or other falling trees are more susceptible to heart rot. It results in trees that cannot be sold due to substantial decay and introducing ideal rot conditions into younger forests that would normally not be as susceptible. Environmental Heart rot and other tree