Wood deterioration and decay
Nature
Wood in its natural state, whether living or felled, is subject to decay and deterioration which causes serious economic loss. High temperatures, exposure to salt water, and certain climatic conditions favour the development of harmful fungi and insects. All wood and wood products are subject to decay if the moisture content of the wood is at or above the fibre saturation point (approximately 30%), although for significant decay, temperatures in the range of 50 to 90 deg F, a supply of oxygen and a moisture content in excess of 90% are required. (Wood that is dry or immersed in water does not rot).
Mould and stem fungi, confined mainly to sapwoods, cause discoloration, increase the absorptiveness of the wood and reduce its strength. In the USA these fungi cause average annual losses of about US$ 10 million. Decay fungi reduce the specific gravity and the strength properties of wood. Brown-rot fungi attack the wood cellulose, and white-rot fungi attack both the lining and the cellulose.
Insects can damage the appearance of wood or seriously reduce its strength. Termites attack wood structures both above and below ground level. Bark, ambrosia and power-post beetles cause various kind of damage to wood. Carpenter ants damage partially rotted wood in buildings and poles. Various mollusc and crustacean groups, termed marine borers, damage pilings and boats.
Incidence
In the USA alone losses due to wood decay amount to approximately US$ 300 million annually, not including the cost of protective measures.
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(D) Detailed problems