CHRONOLOGY OF SPRUCE BUDWORM OUTBREAKS NEAR LAKE DUPARQUET, ABITIBI REGION, QUEBEC

The chronology of eastern spruce budworm (Choristoneura fumiferana (Clem.)) outbreaks in the vicinity of Lake Duparquet in the Abitibi region, Quebec, was determined for a period of 200 years using dendroecological methods. Growth patterns of two budworm host species, balsam fir (Abies balsamea (L.) Mill.) and white spruce (Picea glauca (Moench) Voss). were compared with white cedar (Thuja occidentalis L.), a nonhost species, and with maps of defoliation surveys. The method permitted precise dating of past outbreaks prior to the last two decades, where cartographic information is either imprecise or nonexistent. Growth reductions associated with insect defoliation situate three outbreak periods in this century between 1970 and 1987, between 1930 and 1950, and between 1919 and 1929. A fourth outbreak period may have occurred in the 19th century between 1810 and 1832. The outbreaks in this region were less severe than those that have occurred further south of the insect's northern limit of dispersion. Nevertheless, 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 and 1940, and a marked growth release between 1940 and 1950. Dry periods, reflected in the growth curve of cedar, were associated with recorded outbreak periods.