ADVANCES IN THE UNDERSTANDING OF HEMLOCK BROWNSTAIN

Lumber (hem-fir) cut from western hemlock (Tsuga heterophylla (Raf.) Sarg.) and amabilis fir (Abies amabilis (Dougl.) Forbes) trees represent about 60 % of Canada's west coastal production of wood. Hem-fir is exported to many overseas destinations where the lumber is highly regarded for its white or light appearance and fine grain. However, a series of complex brown/black discolorations, periodically cause loss in value. In this study hemlock brownstain is described microscopically in discoloured hem-fir lumber. Brownstain was most often observed in parenchyma cells and less often in tracheids. Microorganisms were frequently found in discoloured specimens and an association between fungi and bacteria and brownstain was indicated. For the first time catechin and/or epicatechin were histochemically demonstrated in brown deposits present in western hemlock and amabilis fir but also in western hemlock free of brownstain. Three Ophiostoma piceae strains and a mixed bacterial culture were demonstrated to produce in vitro brownstain in liquid culture and in western hemlock wood.