Impact of juvenile wood on hemlock timber drying characteristics

Large volumes of relatively small-diameter logs are currently harvested from sustainable sources such as the second-growth coastal forests of British Columbia. The percentage of juvenile wood in these trees is higher compared to limited old-growth wood supplies. Hence, this investigation evaluated the drying quality of green 115 mm square timbers from second-growth mixed coastal forests of hemlock baby-squares, under the influence of juvenile wood presence shown with a pith location at least on one of their end-surfaces, the tree harvesting season and drying target MC. Timber specimens were classified into four groups depending on the presence and location of the tree pith. They were dried in a laboratory conventional kiln in four drying runs to 15 percent and 20 percent target MCs, with that were cut either in the summer or fall season. The results revealed that specimens with the pith shown in the center exhibited high propensity for bow, twist and surface checks, due to variable shrinkage coupling of juvenile and mature wood areas. Specimens with the pith shown close to one of the sides in the cross section had a lower, but acceptable quality according to commercial grading rules, opposite to specimens with the centrally located pith.