Physical, mechanical, and drying properties associated with bacterial wetwood in red oaks

Physical, mechanical, and drying properties associated with bacterial wetwood in red oak trees in Mississippi and South Carolina were evaluated to identify possible predictors of bacterial wetwood, a major cause of value loss. The parameters tested were: moisture content (MC), specific gravity (SG), shrinkage, tension strength perpendicular to the wood grain, and travel time of stress waves both perpendicular and parallel to the grain. Drying properties were tested on both laboratory and commercial scales. Greater MC, abnormally high radial and tangential shrinkage, and lower tension strength perpendicular to the grain were characteristics of wetwood-affected trees in Mississippi and South Carolina. Lower SG and more drying defects, such as honeycombing and ring failure, were prevalent in severe wetwood trees but not in normal trees in Mississippi. However, the potential of these variables to be wetwood indicators depends on the severity of the wetwood and involves the destructive treatment of samples. MC appears to be the best indicator of the wetwood condition in living trees where increment cores can be utilized for measurement. Stress wave travel times are significantly different between wetwood and healthy wood if the wood is dried by accelerated schedules. Stress wave travel time may be the most practical method to identify wetwood in lumber in the mill.

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