Pathology of conifer seed and seedlings on natural and disturbed forest floor seedbeds in the Engelmann spruce-subalpine fir zone of the interior of British Columbia
Creators: name: Zhong, Jian Wen
Publisher: name: University of British Columbia
Year: 2009

description: Natural regeneration in spruce-dominated stands is seldom satisfactory in British Columbia. The present study was undertaken to identify pathogenic fungi residing in seedbeds in the ESSF and able to infect seed and seedlings of Engelmann spruce (Picea engelmannii Parry ex Engelm.) and subalpine fir (Abies lasiocarpa (Hook.) Nutt.), and to estimate the frequency of infection of naturally shed seed and seedling by such fungi in various natural and disturbed seedbeds. This was determined by examining viability of conifer seed over-wintered on various natural and disturbed forest floor seedbeds in natural stands, isolating and determining any potential pathogenic fungi from ungerminated seed. A paralleled experiment was conducted in partially cut and clear-cut stands to evaluate the effect of silvicultural practices on the impact of such pathogenic fungi in the ESSF. The study was conducted at the Sicamous Creek research forest in the ESSFwc2 subzone. Seedbed treatments in natural stands consisted of i) undisturbed moss type forest floors; ii) undisturbed litter type forest floor; iii) and iv) removal of litter layer from i) and ii); v) removal of the whole forest floor; vi) mixing mineral soil with surface and organic layers; and vii) moss covered rotten wood. In disturbed stands, only two seedbeds (i and v above) were employed. In addition, a study of conifer seedling emergence, and first-year survival and a survey of pathogenic soil-borne fungi were conducted on these seedbeds in natural and disturbed stands. Engelmann spruce and subalpine fir seed over-wintered on natural forest floor seedbeds showed very poor seed survival. This was attributed to the presence of some pathogenic fungi in surface and organic layers which invaded and killed seed before snow melt. Average germination was 13% for Engelmann spruce and 12% for subalpine fir. Two major pathogenic fungi, an as yet unidentified black mold fungus and Rhizoctonia were responsible for the poor germination. Regression analysis showed that there was a significant linear relationship between frequency of the two pathogens and the viability of seed overwintered on various seedbeds. Another pathogenic pathogen, Caloscypha fulgens (Persoon) Boudier was also present on the undisturbed forest floor seedbeds in the ESSF and caused severe loss of Engelmann spruce seed under laboratory conditions. These pathogenic fungi reside mainly in litter and organic layers (L+F+H) of the forest floor. Exposure of mineral soil by removing surface and organic layers or scalping forest floor seedbeds was the best way to reduce the population of these pathogens and improved both Engelmann spruce and subalpine fir seed germination. Average germination on MIN was 57.3% for Engelmann spruce and 41.8% for subalpine fir, respectively. Removing only the litter layer significantly improves Engelmann spruce but not subalpine fir seed germination. Low seed viability and high frequency of pathogenic fungi also occurred on untreated forest floor seedbed in partially cut and clear-cut stands. Seedbed preparation such as the scalping forest floor is needed to reduce frequency of pathogens and to improve seed germination.