Regional-scale alteration of clear-cut forest regeneration caused by moose browsing

Forests are often managed for the timber resources they contain, but they also provide habitat for large and commonly increasing populations of cervids. Interactions between forest management and cervid browsing are thus of importance, but are rarely investigated except within isolated exclosure studies. In this study we use a regional network of exclosures in the forests of mid and south Norway, where large and recently peaked populations of moose Alces alces are present, to assess the impact of moose browsing on forests regenerating after clear-cutting. We found marked influences of moose browsing on tree (individual and population) regeneration following clear-cutting. For the highly selected birch and rowan, which dominate in early successional stages from clear-cuts, height growth of 1 m tall individuals was prevented when around 45% of shoots were browsed. By developing a regional-level relationship between moose density and browsing intensity, this was linked to a density of 3.0 moose km−2. Pine growth was prevented when 30% of shoots were browsed whilst spruce maintained growth when over 60% of shoots were browsed. Although coniferous species were less likely to be browsed, moose browsing caused apparent slowing of succession from coniferous to deciduous trees in the regenerating forests. The increase in height growth and decrease in density of the deciduous species in the exclusion treatment suggests that intra- and inter-specific competition from unbrowsed stems may cause self-thinning and drive a reduction in the density of deciduous species, and hence a shift in community composition towards a more coniferous state in the absence of moose. By taking a regional approach, this study has been able to link the growth response of trees to moose density, and highlights the key role of cervids in influencing regeneration of managed forests.

► Moose browsing was investigated using a network of cervid exclosure experiments.
► Rowan and birch sapling growth was prevented by moose densities of 3.0 km−2.
► Successional dynamics were changed by browsing moose within a rapid time frame.