Influence of Wetwood on Pulsed-Current Resistances in Lumber Before and During Kiln-Drying

Measurements of resistance to a pulsed electric current were lower in wetwood of aspen ( Populus tremuloides ) and white fir ( Abies concolor ) than in normal wood—i.e., sapwood and heartwood—both before and during kiln-drying. The physicochemical properties of wetwood associated with lower resistances are apparently due to invasion of the living tree by bacteria; these bacteria may concentrate excess amounts of ions as well as chemically altering the ion-binding nature of cellular surfaces in the wood. Wetwood also caused discrepancies in the estimation of fiber saturation points (FSP) from measurements of shrinkage and of pulsed-current resistances taken during kiln-drying. Fiber saturation point discrepancies between wetwood and normal wood indicate a need to develop electronic measuring devices in lumber charges, for computerized control of kiln-drying, that will compensate for wetwood.