Effects of moose (Alces alces) browsing on naturally regenerated deciduous trees and field layer in Swedish pine stands : a field study in northern Sweden

Sammanfattning

National and international forest biodiversity goals are not being met in Sweden, with 67% of productive forest area covered in even-aged monoculture coniferous forest stands. To diversify the forest management in order to increase, among other things, biodiversity in these stands, using natural deciduous regeneration can help in creating more mixed stands. Ungulate browsing can affect survival of this regeneration and possibly limit which trees forestry can select for. This thesis aimed to study the effects of ungulate browsing on the natural deciduous regeneration and field layer in young planted Scots pine (Pinus sylvestris) stands. This was done by comparing data from exclosure plots with unfenced plots, spanning a large part of the latitudinal range of Sweden. GLMM analyses showed that browsing affect the number of established (>2.5 m height) trees and the amount of deciduous forage biomass of the species silver birch Betula pendula, downy birch Betula pubescens, rowan Sorbus aucuparia, aspen Populus tremula and Salix spp. The abundance of RAS (i.e. rowan, aspen and Salix spp.) was low, even inside of the exclosures, which points out that regeneration of RAS is low even when browsers are excluded and thus other factors are also affecting abundance of RAS regeneration. The species composition as depicted by NMDS ordination and the Shannon diversity of different plots did not differ significantly, but did show patterns of more variation in species composition and diversity in the browsed plots. These results imply that management of browsed stands is less predictable than that of unbrowsed stands and thus delaying precommerical thinning could provide management with a clearer idea of which trees could be selected as main stems in the mixed stand. Further research efforts should focus on disentangling different factors affecting deciduous tree regeneration.