Influence of the Forest Tent Caterpillar Upon the Aspen Forests of Minnesota

Abstract

Outbreaks of Malacosoma disstria Hb. occur at intervals of about ten years in deciduous forests in northern Minnesota, have been of increasing intensity and duration and are expected to cause serious losses in the future by defoliating quaking aspen (Populus tremuloides]. During the outbreak of 1948-54, severe defoliation did not kill P. tremuloides or result in increased loss due to attack by Saperda calcarata Say or fungi of the genus Hypoxylon. and the increase in the radial growth of balsam fir [A bies balsamea] growing beneath the trees was less than a third of the decrease in radial growth of the aspen. Defoliation of aspen may favour regeneration of pine, where seedlings occur, but this is probably short-lived, and the main effect of M. disstria on timber values is the reduction in aspen growth. The extent of this under various conditions is discussed and related to the possible value of control by aeroplane spraying, and it is concluded that though this is not economic at present, it may become so if the value of aspen timber rises.