Small shrubs with large importance? Smaller deer may increase the moose-forestry conflict through feeding competition over Vaccinium shrubs in the field layer

Robert Spitzer,Eric Coissac,Annika Felton,Christian Fohringer,Laura Juvany,Marietjie Landman,Navinder J Singh,Pierre Taberlet,Fredrik Widemo,Joris P.G.M Cromsigt

doi:10.1016/j.foreco.2020.118768

Abstract

The moose (Alces alces) is a dominant large mammalian herbivore in the world’s boreal zones. Moose exert significant browsing impacts on forest vegetation and are therefore often at the centre of wildlife-forestry conflicts. Consequently, understanding the drivers of their foraging behaviour is crucial for mitigating such conflicts. Management of moose in large parts of its range currently largely ignores the fact that moose foraging is influenced by increasing populations of sympatric deer species. In such multispecies systems, resource partitioning may be driven by foraging height and bite size. Feeding competition with smaller species might replace larger species from the field layer and drive them towards higher foraging strata offering larger bites. This bite size hypothesis has been well documented for African ungulate communities. Based on a large diet DNA metabarcoding dataset we suggest that feeding competition from three smaller deer species (red deer Cervus elaphus, fallow deer Dama dama, and roe deer Capreolus capreolus) over Vaccinium shrubs in the forest field layer might drive moose towards increasing consumption of Scots pine (Pinus sylvestris) in Sweden. We found that in areas of high deer density, moose diets consistently contained less Vaccinium and higher proportions of pine over three spring periods. Utilization of these food items by the smaller deer species was either unaffected by deer density or, for Vaccinium showed the opposite pattern to moose, i.e., increases of proportions in the diet of roe and red deer with increasing deer density. Availability of pine and Vaccinium, measured as proportion of available bites, did not explain the observed patterns. Our results suggest that managing key food items like Vaccinium and the populations of smaller deer may play an important role in controlling browsing impacts of moose on pine.

Highlights

The moose (Alces alces) is a dominant large mammalian herbivore across the world’s boreal zone and a major driver of the functioning of boreal forests (Pastor et al, 1988)
The proportion of pine in moose diet increased with increasing deer density whereas the proportion of Vac cinium decreased
Variation in the availability of these forage items did not explain any of these trends, it is important to remember that we measured availability of these two food resources as proportions of available bites and did not quantify the absolute size or mass of these bites

Summary

Introduction

The moose (Alces alces) is a dominant large mammalian herbivore across the world’s boreal zone and a major driver of the functioning of boreal forests (Pastor et al, 1988). Moose are the central player in human-wildlife interactions in these areas, being a highly valued game species across North America and Eurasia and a concern for forestry due to their impacts on commercially exploited tree species (Horne and Petajisto, 2003, Ezebilo et al, 2012, Herfindal et al, 2015, Timmermann and Arthur, 2017). Given the large potential diet overlap among these deer species (Spitzer et al, 2020), we expect the smaller deer to strongly influence moose resource use and, the impacts of moose on forests and forestry. We investigate these largely unexplored relations, using Swedish moose and multispecies ungulate communities as our model system (Linnell et al, 2020)

Methods

Results

Conclusion