Document: DES-3-42-20

Impact of the last spruce budworm outbreak in Quebec and Ontario in relation to the balsam fir relative proportion in a stand.

DESJARDINS, O.* ¹, H.MORIN ^1,2 and Y.BERGERON ¹

Université du Québec à Montréal, Montréal, Québec, Canada, H3C 3P8 ¹
Université du Québec à Chicoutimi, Chicoutimi, Québec, Canada, G7H 2B1 ²

Abstract:
The boreal forest region of Canada, main source for pulp production, is an important source for the economy. Since the beginning of the post-glacial period, this region has been regulated by important perturbations. Fire and, more recently, major logging operations have maintained a forest mosaic of different age-classes and species. Spruce budworm outbreaks (Choristoneura fumiferana Clem.), in the southernmost part of the boreal forest are the second most important perturbation after fire. To have a better understanding of this last player in the dynamic of the boreal forest, the present study focuses on the behaviour of the last outbreak in the black spruce-mosses zone of western and central Quebec and eastern Ontario. It is thought that the relative proportion of balsam fir has increased in the last century in eastern Canada due to longer fire cycle, clear-cutting, fire control and insect spraying operation. This study will assess whether there is an effect of the balsam fir-black spruce ratio, at a stand level, on the impact of the spruce budworm on those two host species. Ten plots have been sampled; seven from two regions of Quebec and three from Ontario. Disks from the trees (over 600) were analysed. The maximum and mean growth reduction, the duration, the beginning and the end of the last outbreak were the principal variables analysed. While there were no evident trends of a variation of the duration, we found a significant growth reduction (58-100% maximum growth reduction, 26-53% mean growth reduction) in relation to the increase of balsam fir proportion in a stand.

Keywords: Spruce budworm outbreak; perturbation; boreal forest; black spruce; balsam fir

This abstract is being presented at: 3:30 PM in session:
HERBIVORE EFFECTS ON PLANTS