SPRUCE BUDWORM OUTBREAKS IN THE LOWER ST. LAWRENCE AND GASPE REGIONS

Abstract

Evidence of past spruce budworm outbreaks in the lower St. Lawrence and Gaspé regions was obtained through radial-growth studies of balsam fir and white spruce. Outbreaks of this insect were known to have taken place in the Lower St. Lawrence in 1878 and 1912; this was confirmed by the present investigations. However, the data indicate that the 1912 infestation was of greater severity and duration than previously supposed. Forests in the Gaspé were thought to have escaped these past outbreaks. Although no trace was found of the 1878 infestation in the Gaspé, the present study clearly shows that the infestation of 1912 covered close to 9,000 square miles in this region.The recent outbreak of 1950 which affected both regions was generally more severe than that of 1912, especially in the Gaspé. Changes in forest composition appear to be responsible for this situation. Balsam fir, the preferred host of the spruce budworm comprised 46 per cent by volume of the Gaspé forests 30 years ago, but this has since increased to 80 per cent as a result of the destruction of large quantities of white spruce and birch through the respective action of the European spruce sawfly and the birch dieback. The history of past spruce budworm outbreaks indicates that conditions for the development and maintenance of such outbreaks are less favourable in the Gaspé than in the Lower St. Lawrence. This situation appears to be the result of the prevailing cool, moist climate of the Gaspé.