THE EFFECTS OF OVERSTORY SHADING ON WHITE-PINE WEEVIL DAMAGE TO WHITESPRUCE AND ITS EFFECTS ON SPRUCE GROWTH-RATES

A retrospective study was conducted in 1993 that quantified the effect s of overstory shading on both spruce weevil (Pissodes strobi (Peck)) and leader growth on white spruce (Picea glauca (Moench) Voss x Picea engelmannii Parry ex Engelm.). The study was undertaken in the interio r of British Columbia, where the weevil is causing extensive damage to plantations of white spruce. Shading on the spruce trees was measured by calculating the light interception index and percent overstory cov er on individual white spruce trees at the centre of a 2.52 m radius p lot. Current weevil attacks decreased significantly with increasing ov erstory cover, and the rate of decrease was greater in heavily versus lightly attacked stands. Shading also decreased leader growth. These r esults indicate that the optimum level of overstory removal may be a c ompromise between volume loss due to overstory competition and volume gain due to decreased weevil attacks.