UBC Theses and Dissertations
Causes of dieback of Douglas-fir in the interior of B.C. Reich, Richard William
Frost damage to sapling size plantation Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco.] in the central interior of B.C. was identified as the major cause of dieback and canker through tree dissections. Prominent frost rings in the wood and frost damage to buds and shoots corresponded to the dates of dieback initiation and canker events throughout the history of the plantations. Frost rings and frost cankers were reproducible using an artificial freezing technique. Symptomatic frost-damaged buds and elongating shoots were described for Douglas-fir, white spruce [Picea glauca (Moench) Voss] and subalpine fir [Abies lasiocarpa (Hook.) Nutt.]. The effect of growing season frost was most noticeable on early flushing trees. Frost and dieback damage was most severe on concave and flat landforms, which are conducive to cold air pooling on nights with strong radiative cooling. Several pathogens isolated from recently killed stems were identified from fruiting bodies and culture. Leucocytospora kunzei (Sacc.) Urban was the pathogen most commonly isolated from the edge of expanding cankers and progressive dieback margins. Sclerophoma semenospora Funk was commonly found fruiting on dead stems and leaders killed by frost or by mechanical means. Cinara pseudotaxifoliae Wilson feeding caused latent cankers on one year old leaders of Douglas-fir, which are thought to be activated by frost. Boron levels of both healthy and severely affected trees were in the intermediate range, and were not considered to play an important role in frost or pathogen susceptibility for Douglas-fir in the interior.