EFFECTS OF DEFOLIATION BY SPRUCE BUDWORM (CHORISTONEURA FUMIFERANA CLEM.) ON RADIAL GROWTH AT BREAST HEIGHT OF BALSAM FIR (ABIES BALSAMEA (L.) MILL.) AND WHITE SPRUCE (PICEA GLAUCA (MOENCH) VOSS.)

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Abstract
The relationship between spruce budworm defoliation and radial growth at breast height for balsam fir and white spruce trees of merchantable size was studied in various stands in northwestern Ontario. Defoliation was recorded yearly for these stands from the beginning of the infestation, and radial growth measurements were obtained from increment cores. The first year of radial growth suppression was calculated by comparing the growth of the affected species with that of jack pine and red pine trees by means of a growth-ratio technique. Apparent suppression in balsam fir and white spruce varied between stands, and, generally, occurred at the earliest in the second year and at the latest in the fourth year of severe defoliation. A wide ring at the base of the tree coinciding with the first year of suppression as reported by Craighead was non-existent.

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