Decay resistance owing to near-anaerobic conditions in black cottonwood wetwood

Abstract

Gases extracted from wetwood of unwounded black cottonwood (Populustrichocarpa Torrey and Gray) trunks near Vancouver, B.C., throughout 1974 contained less than 0.10% O2 for periods of 5 to 19 weeks during the summer, and an average of approximately 2.5% O2 in winter. CO2 ranged from an average of about 8.5% in summer to about 6% in winter. Decay tests using surface and completely sterilized cottonwood sapwood and wetwood blocks showed no significant weight loss (average 0.2%) after 10 weeks under near-anaerobic conditions (O2 at 0.08%), while parallel tests under aerobic conditions resulted in 42% average weight loss. Both test fungi (Polyporusdelectans Peck and Ganodermaapplanatum (Pers.) Pat.) survived 10 weeks under near-anaerobic conditions, but resumption of decay following this period was considerably delayed. It is suggested that in black cottonwood, wetwood is not necessarily a deleterious phenomenon but rather a condition that imparts considerable decay resistance to the inner wood of unwounded trees.