The Effects of Overstory Shading on White Pine Weevil Damage to Interior White Spruce

A retrospective study was conducted in 1993 which quantified the effects of overstory shading on both spruce weevil, Pissodes strobi (Peck) damage, and leader growth on interior white spruce, Picea g/auca (Moench) Voss x engelmannii (Parry ex Englem.). The study was undertaken in the Prince George and Cariboo Forest Regions of British Columbia where the weevil is causing extensive damage to plantations of interior white spruce. Shading on the spruce trees was measured by calculating the Light Interception Index (Delong 1991) and percent overstory cover on individual white spruce trees at the center of a 2.52 m radius plot. Current weevil attacks decreased significantly with increasing overstory cover. Shading also decreased leader growth. These results indicate that he optimum level of overstory removal may be a compromise between volume loss due to overstory competition and volume gain due to decreased weevil attacks.