Heavy browsing pressure by moose (Alces alces) can interfere with the objectives of ecosystem-based forest management

Abstract

Forest management can enhance the ecosystem services forests provide, but it can also alter the capacity of forests to provide those services in the future. Ecosystem-based management has been widely implemented to mitigate the deterioration of forest ecosystems by reducing dissimilarities between managed and natural forests. Ecosystem-based management objectives generally aim to maintain community composition, stand structure, ecosystem functions and services. Heavy browsing pressure by ungulates at densities unrepresentative of past abundance could interfere with these objectives by chronically and selectively browsing tree regeneration following logging.Using a browsing exclusion experiment, we investigated how the effects of different moose browsing pressures on tree regeneration could interfere with ecosystem management objectives in boreal forests of Quebec, Canada. Management objectives in this region include, among others, reaching targeted coniferous trees densities for commercial harvest, favouring the conservation of birches (Betula spp.) to maintain soil quality and conserving fruit-bearing trees due to their ecological significance for biodiversity. We used path analyses to differentiate direct and indirect effects of moose on seedling density and mixed models to investigate how browsing affected sapling recruitment and whether resulting densities are compatible with ecosystem management objectives.By directly reducing the overall sapling density, moose browsing indirectly increased seedlings densities of all deciduous species. This indirect effect increased with browsing pressure and favoured raspberry cover, which was positively or negatively linked to seedling density, depending on tree species. Moderate and heavier browsing pressures reduced coniferous sapling density below the ecosystem management target. Moose suppressed birch saplings so that the minimal target of 50 birches ha−1 was not met under heavier browsing pressure. Sapling density of fruit-bearing trees was low under all browsing pressures when compared to exclosures.Policy implicationsHeavy moose browsing is preventing the achievement of ecosystem management objectives in our study area. Positive indirect effects on seedling densities suggest that reducing moose density could allow released seedlings to replenish the sapling layer, but we discuss why this would not guarantee reaching ecosystem management objectives. To help forest managers evaluate and respond to challenges posed by high ungulate densities, we suggest incorporating browsing inventories in national forest surveys to monitor this chronic disturbance and modulate decisions for forest ecosystem management.