INFLUENCE OF FEEDING BY ZEIRAPHERA-CANADENSIS, THE SPRUCE BUD MOTH, ON STEM-WOOD GROWTH OF YOUNG WHITE SPRUCE

The influence of feeding by larvae of Zeiraphera canadensis Mut. & Free., the spruce bud moth, on stem-wood growth of young white spruce, Picea glauca (Moench) Voss, was assessed in a 10-year-old plantation in northern New Brunswick, Canada. Herbivory caused immediate, large reductions in height increment, but volume increment was not influenced until after 2 or 3 consecutive years of heavy damage (i.e. 60% or more of shoots damaged yearly). Short-term tolerance to tissue loss. in terms of stem-wood production, was a result of prolific epicormic shoot production following damage. Significant height growth reductions coupled with continued large radial growth increments by heavily damaged trees during the first few years of attack by Z. canadensis caused distinctive stem growth patterns evident in oblique sequence. Heavily damaged trees tended to be faster growing prior to attack suggesting that assessments of growth losses based upon comparisons of high and low damage categories were underestimates. The apparent tolerance of white spruce to tissue loss coupled with the rapid decline of Z. canadensis populations associated with canopy closure suggests white spruce may recover quickly from damage as plantations develop. However, assessments of long-term impacts will require comparisons between mature, damaged and undamaged trees with similar growth rates during the years prior to attack.