The Sensitivity of Young White Spruce to Spruce Budworm Defoliation

Abstract Relationships between defoliation and volume growth were determined for 68 young white spruce trees in a 20-year-old plantation defoliated over a 2-year period by the spruce budworm. In the first year of defoliation, intensities ranging from 7 to 89% of the current foliage did not influence volume growth significantly. Two consecutive years of defoliation, averaging over the 2-year period from 0-33, 34-66, and 67-100% of the current foliage, reduced average volume growth by about 6, 11, and 27%, respectively. White spruce is much less sensitive to defoliation than balsam fir. This is partly due to white spruce's ability to compensate for even moderate defoliation intensities by a prolific shoot production. North. J. Appl. For. 8(4):168-171.