Recolonization of wolves in Sweden - does it affect moose browsing damage on Scots Pine?

Abstract

The recent recolonization by wolves (Canis lupus) of Sweden has provided a unique opportunity to study their importance within terrestrial ecosystems, in particular to investigate the impact that recolonizing large predators may have on ecosystems with strong anthropogenic influence. I used data from the Swedish Forest Agency to investigate the presence and abundance of moose (Alces alces), as well as presence and intensity of browsing by moose on Scots pine in relation to wolf occurrence in Sweden. Data from the Swedish wolf-monitoring system was used to study the effect of wolf presence/absence and time since wolf territory establishment on moose presence and abundance and on moose browsing presence and intensity. The probability of moose presence was higher inside wolf territories compared to outside, whereas moose abundance was not significantly affected by wolf presence. There was no effect of time since wolf territory establishment on moose presence and abundance. The probability of browsing presence was not affected by wolf presence, whereas browsing intensity was higher within wolf territories than outside. Time since wolf territory establishment was positively correlated to the probability of moose browsing, but had no effect on browsing intensity. It might be possible that wolves in Scandinavia actively decide to establish a territory in areas with a higher probability of prey encounter, i.e. moose presence, and such pattern could also explain the higher browsing intensity found within wolf territories compared to outside. This study highlights that the return of large apex predators to landscapes with strong anthropogenic influence may not result in the same top-down effects described in many studies located in national parks in North America.

Popular Abstract

Are wolves affecting moose in Sweden?

The return of large predators has the potential to affect the behaviour, presence and abundance of animals, and possibly plants, in their surrounding. The goal of this thesis was to test whether the return of wolves in Sweden has affected the presence and intensity of moose browsing damage on Scots pine in young forest stands. Current studies are usually located in national parks, where there is little or no human activities. The recolonization of Scandinavia by wolves has provided a unique opportunity to study the importance of large predators within ecosystems outside of national parks and with human influence. Humans exploit the landscape through many activities, like hunting and forestry. Moose represents the main prey species of wolves during both winter and summer in Scandinavia, therefore the probability of moose presence is predicted to be higher outside of wolf territories. Scots pine represents quantitatively the most important food source for moose during winter in Sweden, despite being less preferred to aspen, willows and rowan. The probability of moose browsing presence and the intensity of browsing on Scots pine is therefore expected to be higher outside of wolf territories.

The study was conducted between 2003 and 2016 in the counties of Dalarna, Gävleborg, Värmland, Västmanland, Västra Götaland, and Örebro. During the study period the wolf population increased from 22 to 54 family groups and territorial pairs. I obtained data from the Swedish National Forest Inventory, which records moose presence and activity through pellet counts and browsing damage within forest plots scattered all over Sweden. Wolf presence was obtained using data available from the national wolf monitoring system conducted annually. Each forest plot was classified as being either inside or outside a wolf territory.

Results
The probability of moose presence was higher inside a wolf territory compared to outside, contrary to expectations. Furthermore, moose browsing intensity was also higher inside wolf territories. The higher probability of moose presence within wolf territories observed in this study might be the combination of two factors: 1) wolves select for areas with higher moose density to establish a territory, and 2) once they have established a territory, hunters within that area reduce the harvest of moose to compensate for the moose killed by wolves, resulting in an overall higher probability of moose presence. A higher browsing intensity by moose inside wolf territories would then be expected, which was also observed in this study. These findings seem to suggest that wolves may not be affecting moose, and browsing on Scots pine, as reported in previous studies. Further research is needed to better investigate the interactions between predators and prey in ecosystems where humans actively exploit the landscape.

Master’s Degree Project in Biology 60 credits 2018
Department of Biology, Lund University
Advisor: Åke Lindström
Department of Biology, Lund University

• author: Ausilio, Giorgia
• supervisor: Camilla Wikenros
• organization: Degree Projects in Biology
• course: BION03 20172
• year: 2018
• type: H2 - Master's Degree (Two Years)
• subject: Biology and Life Sciences
• language: English
• id: 8958439
• date added to LUP: 2018-09-11 11:51:03
• date last changed: 2018-09-11 11:51:03