The effects of overstory shading on white pine weevil damage to white spruce and its effects on spruce growth rates

Abstract

A retrospective study was conducted in 1993 that quantified the effects of overstory shading on both spruce weevil (Pissodesstrobi (Peck)) and leader growth on white spruce (Piceaglauca (Moench) Voss × Piceaengelmannii Parry ex Engelm.). The study was undertaken in the interior 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 cover on individual white spruce trees at the centre of a 2.52 m radius plot. Current weevil attacks decreased significantly with increasing overstory cover, and the rate of decrease was greater in heavily versus lightly attacked stands. Shading also decreased leader growth. These results indicate that the optimum level of overstory removal may be a compromise between volume loss due to overstory competition and volume gain due to decreased weevil attacks.