Availability and quality of herbivore winter browse in relation to tree height and snow depth

The vertical distribution of biomass, nutrients, and concentrations of secondary defence compounds in the current annual growth of the main winter forage trees (birch and willows) of herbivores was studied in the mountain range of northern Scandinavia. In addition, forage availability in relation to snow accumulation was studied throughout winter. The quantity and quality of forage improved with the height of the trees, i.e. biomass and nitrogen concentrations increased, and fibre decreased. The concentration of defensive compounds increased with height for willow, but decreased for birch. Shoots of willow were of better quality than of birch. The negative effect of the higher levels of total defensive compounds in birch may to some extent be balanced by their higher nutrient content and total forage biomass as compared with that of willow, however willow had more available biomass within the heights browsed by herbivores. Although snow accumulation had significant effects on forage availability, the effects within the entire height range browsed by herbivores were small.