WHAT WOOD DECAY IS - TIMBER AND LUMBER Authorities estimate that the equivalent of nearly eight billion board feet of timber is annually destroyed by decay in the United States. This consists chiefly of lumber used for building purposes in places where most likely to decay, together with railroad ties. posts, poles, and mine timbers.
The decay of timber is caused by minute organisms called bacteria and fungi. They feed upon wood, and change it as completely as the digestive processes change the material upon which the higher forms of life feed. Sapwood is the most liable to decay, because it contains much more food for bacteria and fungi than does heartwood. The conditions which permit the growth of decay-causing organisms in wood are requisite amounts of heat, air, and moisture. These conditions usually exist in the most favorable combination at or just below the surface of the ground; so it is at these points that timber rots most quickly. The entire absence of either heat, air, or moisture, makes decay impossible. Timber kept either absolutely dry or absolutely web lasts indefinitely, if not subject to wear. Sound timber found in the tombs of Egypt is an example of the former; and sound timber found in the Thames, dating from the Roman occupation of England, is an example of the latter.