Winter browsing in absence of an apical predator: Do high moose densities compromise tree regeneration?

Abstract

Over the last decades, the increasing intensity of timber harvesting and the changes in forestry practices have impacted the population dynamics of many wildlife species. Moose (Alces alces americana) densities have strongly increased, leading to an extensive pressure on vegetation but also to the growing popularity and socioeconomic benefits of sport hunting. On the south shore of the St. Lawrence River, eastern Québec (Canada), moose densities have been on a constant rise for 3 decades, reaching unprecedented levels due to the absence of its main predator (wolf Canis lupus), conservative sport hunting regulations (females protected 1 year out of 2) and increases in early seral forests induced by logging. Resource managers now need to find the balance between ensuring adequate regeneration of cutblocks and maintaining quality habitat to support the hunting industry, a task that requires identifying the level of use and damages on commercial tree species, and the variables related to such damages. We evaluated the effect of 4 common silvicultural treatments and time elapsed since treatment on proxies of resource use and suitability for moose in the mixed forest of the Bas-Saint-Laurent region. Besides silvicultural treatments, we evaluated the effect of various characteristics – at the stand and landscape scales – on the habitat use of moose and the damage they caused in 440 sampling plots. We found no difference in use and damage between all types of treatment, suggesting that local conditions vary between replicates of a given treatment. At the stand scale, variations of occurrence of browsed commercial and non-commercial stems and severe damages to commercial stems were strongly related to forage diversity, relative nitrogen availability and the proportion of alternative species that are browsed. At the landscape scale, the area occupied by naturally regenerating stands around our sample plots increased the occurrence of severe damages to commercial species. The variations in occurrence and in the number of moose feces were best explained by relative moose density and the proportion of browsed stems. Our results showed the importance of considering stands characteristics to provide quality habitat for moose. We recommend that managers avoid the aggregation of naturally regenerating stands, and prioritize high-density plantations without pre-commercial thinning or low-density plantations to reduce the probability of severe damage by moose. These approaches promote stand diversity, forage quality and availability, and favor quality habitat for moose while ensuring maximum timber yield from planted spruce, which is not targeted by moose browsing.