Mapping Eastern Spruce Budworm Cumulative Defoliation Severity from Landsat and SPOT

The eastern spruce budworm (Choristoneura fumiferana Clem.) is among the most damaging of forest insects in Canada’s boreal forest. In Eastern Canada, aerial observations have recently reported increasing outbreaks that are raising concerns to assess and monitor the location, area and potential impacts from this pest. In this study, field and remote sensing estimates of cumulative defoliation were compared for an outbreak in Baie-Comeau, Québec, to determine the extent that observed spectral response differences on remote sensing images were related to observations derived from the field. A method based on the relative difference in infrared simple ratio as a proxy for detecting differences in leaf area that was previously applied to aspen defoliation was adapted for this study. A post-defoliation Spot 4 multispectral image was registered and normalized to a pre-defoliation Landsat 5 image from which the relative difference in infrared simple ratio was empirically related to field-derived defoliation estimates. While both ocular and branch sample defoliation ratings were statistically correlated, branch sample estimates were more highly correlated to observed image values than ocular ratings. First iteration spruce budworm defoliation severity models were developed and applied to susceptible areas comprising dominant conifer and mixedwood land cover