Canadian Forest Service Publications

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Abstract

An analysis of forest tent caterpillar Malacosoma disstria defoliation records from Ontario and Quebec over the period 1938-2002 indicates that outbreaks recurperiodically and somewhat synchronously amongregions of the two provinces. Cluster analysis revealed that the most strongly periodic, large-scale, synchronized fluctuations occurred within three regions: northwestern Ontario, eastern Ontario/western Quebec and southeastern Quebec. Defoliation in the vast sur rounding hinterlands tended to beinfrequent andsporadic, loosely tracking defoliation in the core outbreak regions. One small cluster in northeastern Ontario stoodout asanomalous, asa result of an increasing trend in the durationof periodic defoliation episodes, marked by an unprecedented double-wave of defoliation that persisted from 1992 to 1999. This is the precise area where, in the early 2000s, trembling aspen Populus tremuloides stems were mapped as being in a state of decline of unprecedented severity and extent. Our results suggest forest tent caterpillar hasthe potential to cause significant impacts on forest health and, hence, carbon budgets in east-central Canada and that the forest tent caterpillar deserves moreattentionasa model system of forest insect disturbance ecology.