Impacts of multi-species deer communities on boreal forests across ecological and management scales

Sammanfattning: During the past decades, the population density and distribution of deer (Cervidae) has increased across Europe. Particularly in Sweden, this led to an increased cooccurrence of several deer species in landscapes highly dominated by humans. In this novel setting, a deep understanding on the impacts of multi-species deer communities on boreal forests is needed across a variety of spatial and temporal scales. In this comprehensive thesis, I used national to local scale, observational and experimental data to investigate the drivers and effects of deer damage on economically important tree species in young forests by collating and linking diverse public and ecological datasets on multiple deer species. At the current wildlife management scale, which is centred on moose (Alces alces), I found that the whole deer community should be considered for regulating deer damage on Scots pine (Pinus sylvestris), especially in areas with high densities of the smaller deer species. Regulating only moose densities does not appear to control deer damage effectively. Forage availability, on the other hand, seems to affect damage levels on Scots pine across space and time and predicted deer damage equally or better than deer densities. This suggests a co-management between deer and forests. I also found that the spatial variation, influenced likely via landscape characteristics such as forage availability, seems to introduce a higher variation in damage levels than the temporal variation, influenced via e.g. climatic factors such as snow. At the plant community and individual plant scale, the whole plant-community should be considered to regulate deer damage. Associational effects and competition from neighbouring plant species might increase damage levels and limit conifer growth. Therefore, a full exclusion of deer might not promote conifer growth during the initial years of conifer regeneration. In conclusion, this thesis shows that the relationship between deer densities, forage availability, and deer damage in young forests requires a management approach beyond moose. Furthermore, it is highly scale-dependent and management actions should not be generalized across spatial and temporal scales.