Degradation of Boreal Forests by Nonnative Herbivores in Newfoundland's National Parks: Recommendations for Ecosystem Restoration

Abstract

For land management agencies such as Parks Canada that are tasked with maintaining the ecological integrity of protected, natural landscapes, dealing with the impacts of non-indigenous species on forest succession is a serious management concern. In both Terra Nova and Gros Morne National Parks (island of Newfoundland, Canada), the cumulative impacts of non-native species are negatively affecting the capacity of a dominant conifer, balsam fir (Abies balsamea), to regenerate following canopy disturbance by forest insects. Early development of an understory fir layer is compromised by heavy predation on female cones by red squirrels (Tamiasciurus hudsonicus), and post-dispersal seed and seedling predation by non-native rodents and slugs. Taller saplings are then subjected to heavy browsing from non-native moose (Alces alces) so that recruitment to reproductive-aged trees is largely inhibited. An indirect effect of the long-term removal of understory fir is that seedbeds are shifting from optimal feathermoss types towards seedbeds dominated by competing grasses and non-native plants, thus reducing potential germination of balsam fir. We provide evidence that these changes to forest composition and structure are occurring at large spatial scales across both protected and non-protected landscapes. Finally, we offer management recommendations including sustained reductions of moose numbers and the supplemental planting of fir where understory densities are exceptionally low and seedbed degradation has occurred.