Abstract

Topic: Moose and forestry

The effects of moose- and pine densities on browsing damages in Sweden

Oskar Franklin¹, Christer Kalén², Annika M. Felton³, Märtha Wallgren⁴

IIASA, International Institute for Applied Systems Analysis, Schlossplatz 1, 2361 Laxenburg, Austria, Austria
Skogsstyrelsen - Swedish Forest Agency, Bryggaregatan 19-21, 503 38 Borås, Sweden
Institutionen för sydsvensk skogsvetenskap, Box 190, 234 22 Lomma, Sweden
Skogforsk, Uppsala Science Park, SE-751 83 Uppsala, Sweden

Abstract
A current lively debate in Swedish moose management concerns the relationships between moose, pine, and browsing damage on pine. In 2024 it was reported that, although the moose population had declined in many places, the browsing damages did not decrease to the same extent. In moose management a view gained traction that the number of pine trees is more important than the number of moose for limiting browsing damage. Some scientific studies also support this view but not all of them, and so far, explanations of the reasons behind the results are largely lacking. The question we address is: Across the whole of Sweden, what does the data really tell us about the browsing damage and what are the roles of moose- and pine densities? We investigated the relationship between browsing damage and moose- and pine densities using 718 observations of browsing damage from the Moose Browsing Inventory (Äbin in Swedish) for all of Sweden’s moose management areas (MMAs) in 2015-2024, with spatially matched estimates of moose densities. We analysed the data using a model based on ecological mechanisms that statistically quantifies the individual effects of moose and pine density on browsing damages, accounting for regional differences between MMAs. The model explains 50 percent of the variation in browsing damage between the MMAs and between years. The fraction damaged pines increases with moose density and decreases with pine density. Contrary to many previous studies, moose density has a stronger effect than pine density on average. On average nationally, both effects are strongly significant, but locally the effects vary widely among different counties and MMAs and are often not statistically significant. Our interpretation is that differences in moose- and pine density are generally of great importance for browsing damage, but the magnitude of the effects varies between areas due to other influencing factors, such as other deer species, climate, site productivity, and other vegetation. These results can contribute to a more informed discussion about future moose and forest management.