Growth response of spruce infected by Inonotus tomentosus in Alaska and interactions with spruce beetle

Abstract

Thirty-eight trees from Alaska's Kenai Peninsula and 39 from the interior near Fairbanks (Delta Junction) were sampled by detailed stem dissections to determine the impact of tomentosus root disease [Inonotus tomentosus (Fr.: Fr.) S. Teng] on growth and decay volume in spruce, with and without the influence of past spruce beetle activity in stands. Disease severity was assessed by the number of primary roots (out of four) infected and by the average proportion of root cross-section area colonized by stain and (or) decay. Butt rot volumes were positively related to disease severity at both locations, but only the Delta Junction trees showed a significant negative relationship between relative volume increment and disease severity. Substantial mortality of spruce, caused by the spruce beetle (Dendroctonus rufipennis (Kirby)), has occurred on the Kenai Peninsula since the late 1970s. Mortality of overstory spruce trees released surviving trees from competition, causing compensatory growth in healthy to moderately infected trees, which masked the effect of the root disease. We found that the magnitude of growth release was negatively related to disease severity and that the mean proportion of root cross-section with decay or stain was a better estimator of disease impact on tree growth.