Heart Rot of Black Spruce in Ontario. I. Stem Rot, Hidden Rot, and Management Considerations

Abstract

A total of 6553 black spruce (Piceamariana (Mill.) B.S.P.) trees of commercial size were sampled throughout the range of this species in Ontario. Four distinct types of rot occurred in the merchantable boles, accounting for 3% of the volume. In black spruce, rot develops much earlier and more extensively below stump height (particularly in roots) than it does above stump height. Trees growing on drier, generally upland sites were faster growing and shorter lived than those sampled on wetter, generally lowland sites. Site, based on moisture regime, and tree age were both significantly related to the incidence of heart rot within the merchantable bole. Trees on drier sites, and the faster growing trees on all sites, were more susceptible to stem rot. The growing use of measures to accelerate the growth rate of black spruce, such as fertilization or site improvement by drainage, may raise productivity but it is also liable to increase the incidence of root and stem rot markedly.