INCIDENCE OF WETWOOD AND DECAY IN PRECOMMERCIALLY THINNED WESTERN HEMLOCK STANDS

The occurrence and pattern of stains in the base and lower stem of you ng-growth western hemlock (Tsuga heterophylla (Raf.) Sarg.) and its re lationship to root disease were studied at 16 sites in coastal Washing ton. Stands ranged in age from 17 to 35 years and were precommercially thinned 5-17 years previously. The most common stain was discolored w ood or wetwood, which is a type of heartwood in standing trees that ha s been internally infused with water. Wetwood occurred in more than 50 % of the 1215 trees examined, and within some stands it occurred in 80 % of the trees examined. The presence of wetwood did not indicate root disease or other decay. However, all wood decay infections were assoc iated with wetwood. Wetwood can be economically important because it i nterferes with drying and causes shake and warping in lumber. Incipien t decay stain was less common (<6% of the trees) and was caused predom inantly by the basidiomycete fungi Heterobasidion annosum (Fr.) Bref., Armillaria spp., and Perenniporia subacida (Pk.) Donk. Wetwood appear ance varied from bright pinkish, purplish, or pinkish brown to light b rown, depending on moisture and extractives content. Incipient decay s tain of H. annosum was distinguished from wetwood by its mostly brown, dark brown, or brownish black color. Heterobasidion annosum also has incipient decay stain that may be light brown to pinkish and closely r esembles wetwood. Experimental wounding of trees resulted in both wetw ood and incipient decay formation. Wetwood and incipient decay stain c an occur in the same bole section, so there is a potential for confusi ng them. Cultural isolation of fungi is the only sure way to distingui sh wetwood from incipient decay.