Effect of Northwestern Ontario Forest Ecosystem Classification treatment units on the infection levels of Armillaria in black spruce plantations

Abstract

Eight 5- to 15-year-old black spruce (Picectmariana (Mill.) BSP) plantations from each of the Northwestern Ontario Forest Ecosystem Classification treatment units B, C, D, E, and F were sampled for Armillaria root rot. All the plantations sampled were infected by Armillaria, with an infection rate ranging from slightly less than 1% to 32%. Some differences were observed among Northwestern Ontario Forest Ecosystem Classification treatment units but these differences were not statistically significant (p < 0.05). Plantations in treatment unit F had the highest average infection level (16.93%), while those in treatment unit B had the lowest (7.24%). Plantations in treatment unit F had significantly higher cumulative mortality levels than did those in treatment unit B (p < 0.05). The average ratio of infected healthy trees to infected dead trees was 3.28:1 across all treatment units. The total number and total basal area of all stumps and of all infected stumps were similar across the treatment units. Variations did exist in the ratio of conifer to hardwood stumps and reflected the differences in the species composition of the original stands. Infection levels based on trembling aspen (Populustremuloides Michx.) trap logs were not found to be a good indicator of percent infection in the trees. The use of colour and relative shoot growth was only moderately effective in identifying trees infected by Armillaria.