Moose impacts on forest regeneration

Published versionTwo interacting disturbances such as stand-level defoliation by spruce budworm (Choristoneura fumiferana) and subsequent herbivory by moose (Alces alces) may affect landscapes differently than if they occurred in isolation. We studied moose (A. a. andersoni) browsing on sites disturbed approximately 25 years ago by a severe spruce budworm outbreak in a region historically dominated by balsam fir (Abies balsamea) forest on northern Cape Breton Island, Nova Scotia, Canada. Our objectives were to 1) describe the impact of a large resident moose population on post-budworm regeneration of balsam fir and white birch (Betula papyrifera), and 2) to examine the interplay between moose abundance, site conditions, and variation in post-budworm forest regeneration. Fifty-eight ran­domly located sites were sampled for composition and structural characteristics, moose browse severity, moose pellet group density, and site conditions. We used univariate general linear modelling (GLM) and multivariate redundancy analysis (RDA) to examine relationships between moose abundance as indicated by pellet-groups, site conditions, and post-budworm regeneration. Approximately 65% of all balsam fir and white birch saplings tallied were severely browsed by moose, exhibiting stunted, abnormal growth forms. Both the GLM and the RDA indicated that moose abundance was the best predictor of variation in the density of post-budworm regeneration of balsam fir and white birch. Site conditions were less useful predictors of variation in regeneration. The relationship between moose abundance and regeneration of balsam fir and white birch was positive, suggesting that moose may be more abundant in areas where regeneration is denser. Sustained, severe browsing in areas regenerating after spruce budworm outbreak may significantly inhibit future forest development and alter the well documented spruce budworm-balsam fir cyclic successional system of northern Cape Breton Island