Open access publications in the SLU publication database

Abstract

Ungulates have traditionally been viewed as consumers of plants and prey for predators, but recent studies have revealed that they also can have a significant indirect impact on fundamental ecosystem processes and biodiversity. In my thesis, I focus on how moose (Alces alces) can affect the boreal forests ecosystem in Sweden. Because of its wide distribution and at present high population densities we can expect moose to be important. The outcome depends on moose density as well as habitat productivity, and we chose an experimental approach where we simulated browsing, defecation and urination of different moose population densities in exclosures situated along a forest productivity gradient. The simulation was based on a review of available literature. I found that moose can have a significant impact on the morphology and productivity of the main food plants in winter, Scots pine (Pinus sylvestris) and birch (Betula pubescens and B. pendula). The outcome was highly dependent on moose density. At “low” to “moderate” moose densities, small and non-significant effects were found, whereas the effects were large at higher moose densities. I concluded that both foraging efficiency and food availability can be affected at higher moose densities over extended time, and that food production may steadily decrease to a level where winter food is limiting. Habitat type also affected the results. At low productive sites both birch and pine had low productivity and thus compensatory ability to defoliation by moose. Birch and pine also seemed to respond differently to habitat productivity, and the explanation might have been that pines suffered from competition with deciduous trees at richer sites. The quantity and quality (species mix) of litter from the tree and shrub layers were affected by the level of simulated moose population density and habitat. Richer sites produced more high quality litter (i.e. lower proportion of conifer needles). The quantity decreased and the proportion of conifer needles increased with simulated moose density. Despite the high browsing pressure on Scots pine, the general outcome of moose at high population densities over extended time seems to be decreased quantity and quality of litter, and thus reduced nutrient cycling and habitat productivity in the long run. Decay rates of moose dung appeared to be rather low, suggesting that the fertilizing effect also was low. However, the dung disappeared fast at richer sites due to concealment by vegetation, and visibility was negatively correlated with litter production. The coprophilous community colonizing moose dung appeared to be species rich and poorly known, and the abundance and species richness are affected by interactions with other organisms as well as habitat type. In my thesis I show that moose can affect fundamental ecosystem processes and biodiversity in Swedish boreal forests, and act as an important ecosystem engineer. Productivity gradients are important to consider when studying effects on the ecosystem level. Based on my findings, I suggest that more studies should be done on other tree species, plants in the field and bottom layers, soil properties, microclimate, and organisms connected to faeces and urine.