Trends in the frequency, extent, and severity of spruce budworm outbreaks in eastern Canada

The history of spruce budworm (Choristoneurafumiferana (Clem.)) outbreaks for the past 200 to 300 years, for nine regions in eastern Canada, indicates that outbreaks have occurred more frequently in the 20th century than previously. Regionally, 21 outbreaks took place in the past 80 years compared with 9 in the preceding 100 years. Earlier infestations were restricted to specific regions, but in the 20th century they have coalesced and increased in size, the outbreaks of 1910, 1940, and 1970 having covered 10, 25, and 55 million ha respectively. Reasons for the increase in frequency, extent, and severity of outbreaks appear mostly attributable to changes caused by man, in the forest ecosystem. Clear-cutting of pulpwood stands, fire protection, and use of pesticides against budworm favor fir–spruce stands, rendering the forest more prone to budworm attack. The manner and degree to which each of these practices has altered forest composition is discussed. In the future, most of these practices are expected to continue and their effects could intensify, especially in regions of recent application. Other practices, including large-scale planting of white spruce, could further increase the susceptibility of forest stands. Forest management, aimed at reducing the occurrence of extensive fir–spruce stands, has been advocated as a long-term solution to the budworm problem. The implementation of this measure at a time when man's actions result in the proliferation of fir presents a most serious challenge to forest managers.