In this study, the natural progression of decay is being monitored in 2.4-m (8-ft) lengths of dimension lumber. The 2.4-m lengths are supported without restraint in a horizontal plane approximately 0.75 m above ground in a partially shaded field plot in southern Mississippi. The lumber is 100% sapwood. Prior to installation in the field, each piece was planed to exactly 38 by 89 mm² (1.5 by 3.5 in²) when conditioned to 10% moisture content. Members were then sorted according to modulus of elasticity (MOE) into groups with equivalent mean and range. Sets were removed at intervals and the distribution of decay was nondestructively monitored by measuring speed-of-sound transmission through the width of each member. Analysis of the patterns of decay within the members permits design of optimum configuration of above-ground test units. Some key points of consideration were the large variation in amount of naturally occurring decay within a similar population of test units, density-dependent differences in rates of decay development, and overlapping members and end effects. Preliminary results indicate that decay does not become universally established simultaneously along the length of the members. Decay is detected first at the ends and with continued exposure, it progresses to locations more distant from the ends. Presumably, this reflects some contribution of wetting of the exposed end grain to early onset of wood decay.

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