Abstract
Sequential color slides of a Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) tree were taken over several years to record the progression of crown defoliation by Douglas-fir tussock moth (Orgyiapseudotsugata McDunnough) and foliage recovery. The slides were digitized using a microdensitometer and analysed with a GEMS-300 image analysis system in an effort to detect changes in the amount of crown foliage. Digital images were successfully registered (overlaid) to standardize comparisons of the tree-crown profile in the various photographs. Image analysis algorithms developed for airborne or satellite multispectral scanner data were used to detect changes in crown profiles. The decrease in the amount of defoliation over time after the initial severe insect attack, estimated by a variable threshold technique, was similar to ocular ground-based estimates by well-trained observers. The supervised maximum-likelihood classification technique was found not suitable in this study.
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