THE INFLUENCE OF STAND COMPOSITION ON THE MORTALITY OF VARIOUS CONIFERS, CAUSED BY DEFOLIATION BY THE WESTERN HEMLOCK LOOPER ON VANCOUVER ISLAND, BRITISH COLUMBIA

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Abstract
Western hemlock looper outbreaks periodically occur in British Columbia. A guide for estimating losses that accrue from looper feeding has not been available in the past. This report describes the influence of various tree and stand characteristics on the mortality of forests damaged during the last looper out-break from 1944 to 1946.Tree death commenced one year following the collapse of the outbreak and continued for another three years. The cumulative mortality up to 1950 was taken as the total loss directly attributable to the insect damage. Tabular analyses of this mortality total with various factors showed that percentage defoliation and tree size were most consistently associated with tree death. Three major forest types were recognized. The basal area mortality of the types was related to the pre-outbreak basal area and to defoliation by multiple linear regression. These analyses arrived at parameters on which future damage surveys in similar forest types can be based.

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