PS 17-164 - Impacts of SBW on seedling during an outbreak: Does harvesting method matter?

Background/Question/Methods

Spruce budworm (Choristoneura fumiferana (Clem)) is the main defoliator in the boreal forest of North America, and its outbreaks have major ecological and economic consequences and represent a challenge for forest management. Numerous studies have addressed the effects of this defoliator on mature trees, whereas the effects of spruce budworm on regeneration remain elusive. Furthermore, intensive exploitation practices during the last decades have left a large area of the Canadian boreal forest in an early development stage. In this context, it becomes vital to understand those factors affecting the severity of spruce budworm‐related defoliation on regeneration. Here, we determine the defoliation severity of black spruce and balsam fir seedlings in both mature pure black spruce and black spruce–balsam fir stands subjected to two different silvicultural treatments (clear‐cutting and partial cutting). To do it, an experimental design located in the North Short region was established in 20 study sites. For each black spruce and balsam fir seedling, cumulative defoliation, height and location were recorded.

Results/Conclusions

Our study demonstrated that defoliation intensity varied between stand types, silvicultural treatments, species, and height classes. Black spruce seedlings experienced 3X more defoliation under clearcutting than under partial cutting, while balsam fir seedlings were 2X more affected under clearcutting. Seedlings within mature mixed stand dominated were 2x more affected than those within pure black spruce stand. The level of defoliation also increased with seedling height.

This study will help silvicultural strategies adapt to the effects of natural disturbance regimes. As the intensity and severity of defoliator outbreaks are expected to increase under climate change, these results will help guide forest management strategies to select harvesting methods that will limit the effects of defoliation on conifer regeneration.