The effect of stump removal and tree admixture on butt decay incidence, damage and wood density in western redcedar

Abstract

Western redcedar (WRC) trees of 48–49 years in age grown in monoculture and in admixtures with birch, Douglas-fir and pine in the interior of British Columbia were sampled for wood density and the presence and level of damage from butt decay initiated by Armillaria ostoyae in stumped and unstumped plots. Stump removal reduced butt decay incidence in WRC from 18% to 2% and damage from 3.5% of the diameter at base to 0.3% compared to when stumps remained. External lesions on tree bases caused by Armillaria root disease increased the probability of WRC stems having butt decay by 1.25 times for an average-sized lesion. The incidence of butt decay and the level of internal damage to WRC in sampled plots was not related to admixture, tree size or site index. Stump removal controlled the inoculum of Armillaria root disease, thereby reducing incidence and size of WRC basal lesions that probably act as infection courts for other fungi causing butt decay. WRC trees grown in monoculture or with birch had the highest wood densities of all planting mixes tested. Wood density in WRC was lowest at the outer edges of individual WRC trees, in larger trees, and in plots where stumps had not been removed. The lower density WRC wood is thought to occur by overtopping from fast-growing species in admixture and depletion of soil moisture affecting latewood formation. This is a first report of stump removal affecting butt decay and admixture affecting wood density in WRC.