Spatiotemporal patterns of large-scale defoliation caused by the spruce budworm in Ontario since 1941

Survey records of spruce budworm (Choristneura fumiferana Clem.) defoliation in Ontario, taken annually since 1941, were analysed using geographic information systems (GIS), spatial statistics, and time-series methods. Cumulative frequency maps indicated that the 41 x 10(6) ha of Ontario that had been defoliated in at least one year since 1941 could be sprit into three zones of frequent defoliation separated by two approximately 100 km wide, longitudinally oriented corridors of lower frequency. Analysis of annual records of the total area defoliated showed that the fluctuations in this time series are the result of a basic oscillation of approximately 36 years, which is modified by secondary fluctuations and occasionally by sharp drops. The secondary fluctuations are at least partially due to asynchrony in otherwise remarkably similar long-wave oscillations in the eastern (25.5 x 10(6) ha) and western (9.6 x 10(6) ha) zones of frequent defoliation. Analysis of this asynchrony showed that outbreaks in the eastern zone occurred 5 or 6 years before outbreaks in the central (6.6 x 10(6) ha) and western zones, which were synchronous. These observations contradict previous reports of the large-scale spread of outbreaks from west to east.