Background/Question/Methods Spatial synchrony of outbreaks of forest insects is important because of the role that synchrony plays in creating large outbreaks, and the role that outbreaks play in shaping forest landscapes. Although it has been shown that environmental factors influence the duration and severity of spruce budworm (Choristoneura fumiferana (Clem.)) outbreaks, the role of climate and forest composition in promoting outbreak synchrony had never been determined, and the scale at which the factors exert their influence was not known. The technique of principal coordinates of neighbor matrices (PCNM) was used to determine the spatial pattern of outbreak initiation in eastern Canada. Results/Conclusions About 87% of the variability in outbreak initiation was described by a collection of 100 significant principal coordinates. Four subsets of principal coordinates described the pattern at spatial scales from ~200–1200 km. The role of significant environmental factors at each spatial scale was estimated by a permutation test. Fourteen environmental variables (five climate and nine forest composition) were significant factors in the observed variability of outbreak initiation at one or more spatial scales.