Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

The chronology of eastern spruce budworm Choristoneura fumiferana was determined for 200 yr using dendroecological methods. Growth patterns of two budworm host species, balsam fir Abies balsamea and white spruce Picea glauca were compared with white cedar Thuja occidentalis, a nonhost species, and with maps of defoliation surveys. Growth reductions associated with insect defolation situated three outbreak periods in this century between 1970-1987, between 1930-1950, and between 1919-1929. A fourth outbreak period may have occurred between 1810-1832. The outbreaks in this region were less severe than those that have occurred further south of the insect's northern limit of dispersion, but they did have a major impact on the dynamics of balsam fir populations in the region, as revealed by a massive invasion of fir between 1915-1940, and a marked growth release between 1940-1950. Dry periods, reflected in the growth curve of cedar, were associated with recorded outbreak periods.