D

  in all woods if environmen-

tal conditions are conducive to biotic or abiotic degradation

processes. Environmental factors, especially moisture levels, are

of paramount importance to the type and rate of decomposition. In ter-

restrial environments, a complex association of biological and chemical

processes may cause extensive biomass loss within a very short time.

A variety of biotic agents, including insects, fungi, and bacteria, work

together to decompose wood. If decay-limiting conditions are imposed

that exclude microorganisms and insects, wood can survive for exceedingly

long periods of time.

Old panel paintings are subject to deterioration. Many forms of

deterioration may affect painted wooden objects, depending on the envi-

ronments where the artworks have been found or stored. The extent of

damage is related to how well these objects have been protected from

moisture, insects, microorganisms, and extraneous compounds. This article

provides basic information about biological deterioration processes of

wood, as well as a guide to the microorganisms and insects that attack

wood, their mode of action, and the effect on chemical and physical prop-

erties ofwood.

Wood is composed ofcells that consist ofcellulose, lignin, and

hemicellulose. Mono- and disaccharides, aromatic compounds, inorganic

substances, and other compounds arealso present in varying amounts.

The chemical as well as anatomical nature of wood varies greatly among

tree species. Differences are seen in various cell types, amounts ofextrac-

tive material, wood densities, and so on (see Hoadley, “Chemical and

Physical Properties of Wood,” herein). Sapwood, the outermost part of

the tree’s wood, which contained living cells while growing, may have

high concentrations offree sugars, starch, amino acids, and proteins that

make it highly susceptible to attack by some fungi and insects. In contrast,

heartwood, the innermost region of the tree, often contains cells with

accumulated substances that resist degradation. The heartwood of some

trees—such as oak, walnut, cypress, redwood, and cedar—contains com-

pounds that provide some degree of natural durability. Most of these

compounds are phenols synthesized by parenchyma cells from carbohy-

drate precursors at the sapwood-heartwood transition zone (Hillis 1987;

Fengel and Wegener 1984). These substances may diffuse into cell walls

and fill cell lumina. Although some heartwood is very resistant to attack,

prolonged exposure to adverse environments or the presence of aggressive

55

Robert A. Blanchette

A Guide to Wood Deterioration Caused by

Microorganisms and Insects