Biological degradation of wood.

Wood is decomposed by a variety of biological agents, including fungi, bacteria, and insects. Fungi colonize wood and degrade cell wall components to form brown, soft, or white rot. Brown-rot fungi, which degrade primarily the polysaccharide components of wood, leave a lignin framework. White-rot fungi may degrade all cell wall components. The rate and extent of lignin, cellulose, and hemicellulose removal varies among species of white-rot fungi. Soft-rot fungi erode the secondary wall or form discrete cavities within the cell wall. Each type of decay has many forms and can be classified by microscopic and ultrastructural characteristics. Bacteria can attack wood directly to cause various patterns of deterioration such as erosion, cavitation, and tunneling. Bacteria may have a synergistic or antagonistic effect on other microorganisms that inhabit wood. This article reviews the morphological and chemical changes that occur in wood after degradation by different microorganisms and provides information that will help identify the types of deterioration found in wood of historic value.