Foraging by moose on two species of birch when these occur in different proportions

The two tree-like birch species Betula pendula and B. pubescens are of medium preference to moose during winter in northern Sweden. Because these birches are abundant in many biotopes, they form a major part of the moose diet. The two birches are very similar in appearance and often occur in mixed stands. Twenty-one birch stands where B. pendula formed from 2 to 97% of the birches were investigated to determine how the relative composition of the stands affected browsing of the two species by moose. In stands composed of 60% or less of B. pendula , there was a preference for this species when regarding 1.5–3.0 m high birches, which carry the largest amount of available browse per tree. At higher proportions B. pendula was still preferred, but use was closer to availability. However, in all stands there were significantly more moose bites per tree of B. pendula than of B. pubescens . In four birch stands browsing on 1.0–1.5 m high birches was also investigated. For this height class there was still a preference for B. pendula , but the difference between the two species was less pronounced than for the 1.5–3.0 m height class.