A study in Denali National Park, Alaska, studied bark stripping by moose (Alces alces) in order to determine the proportion of bark in their diet, what conditions induce bark stripping, and assess the combined impact of stem breakage and bark stripping in a quaking aspen (Populus tremuloides)-white spruce (Picea glauca) community. Bark comprised less than 4% of the diet of moose. Based on the proportion of foraging bouts in which bark stripping occurred, female moose ate bark more often than did males. Males rarely stripped bark in any season, but females ate bark in 23% of their foraging bouts. Seasonal differences in the use of bark by females were marginally significant with greatest use in the spring. Based on foraging bout observations and transect data, moose stripped bark most commonly in aspen-spruce forests. Females stripped bark in 75% of their foraging bouts in aspen-spruce communities but only 10% in other habitats. Moose preferentially stripped bark from larger stems. The amount of bark removed and the percentage of the trunk circumference girdled were positively associated with mortality of aspen and balsam poplar. Spruce was the most abundant component in the understory, and second only to aspen in the overstory. The most common successional pattern in interior Alaska is for aspen to be replaced by spruce. In Denali National Park this pattern is evident in the aspen-spruce forests, but pressure by moose may be increasing the rate at which replacement is occurring. Stem breakage and bark stripping by moose are acting in concert to reduce density of deciduous species in the understory and canopy and accelerate succession towards a spruce-dominated forest.
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