Western red cedar extractives associated with durability in ground contact

Western red cedar (WRC) is well known for its natural durability. However, the roles of all the extractives that may be associated with this durability are not fully understood. The literature primarily credits the thujaplicins, with a lesser role for the lignans; however, previous work has identified highly durable material with low thujaplicin content. To elucidate the relative importance of various extractives, the decay resistance of WRC stakes at four test sites was compared with data on the content of specific extractives to determine whether there was any detectable association. The concentration of plicatic acid, a lignan, was associated with the decay resistance of WRC lumber in ground contact. An unidentified, unquantified compound (B) appeared to be similarly associated with decay resistance. The thujaplicins were only weakly associated with the decay resistance of WRC in ground contact.