Incidence of tomentosus root disease relative to spruce density and slope position in south-central Alaska

Abstract

Inonotus tomentosus causes tomentosus root disease of spruce in boreal and sub-boreal forests of south-central Alaska. The relationship between the incidence of I. tomentosus and spruce diameter, density and basal area was examined on two different sites on the Kenai Peninsula. Sites were systematically surveyed using 50 m 2 plots and disease incidence was calculated as the percent of spruce trees infected with I. tomentosus. Transects from the top of slopes to the bottom were also established at the same sites and soil moisture probes were installed in the upper 15–20 cm at five equidistant points on each transect. The relationship between slope position, percent soil moisture content, soil pH and disease incidence was determined by ANOVA and regression analysis. The incidence of I. tomentosus in the plot survey ranged from 0 to 100% and spruce density (stems per hectare) and basal area had no relationship with disease incidence. Disease incidence was significantly and positively related to individual tree diameter and disease was most common on slopes compared to either bottom or top (flat) positions. Percent moisture content was greatest at bottom slope positions and at flat sites located beyond the crest of slopes. Disease incidence was negatively related to percent moisture content, but not related to pH. Slope position, or soil moisture content, may be used by forest managers to indicate areas more likely to have a higher incidence of root disease and can therefore reduce costs of disease surveys by enabling stratification of managed forest stands. Further, the results suggest that a higher planting density to compensate for losses to tomentosus root disease will not significantly increase disease incidence.