Effect of the latitude of seed origin on moose (Alces alces) browsing on silver birch (Betula pendula)

Moose is a major cause of damage in young plantations of silver birch (Betula pendula Roth) in Finland, as they break stems and browse twigs and leaves. Damage by moose was measured in a provenance trial of silver birch situated at Loppi, southern Finland. The trial includes stand seed origins from Finland, Sweden, Estonia, Scotland and Russia, ranging in latitudes from 53° to 67°. The trial was established on a typical, southern Finnish moist upland clear-cut area that had been protected against moose by fencing. After the break-down of the fence, at the age of 5–11 years, the trial was frequently visited by moose. The effects of browsing were measured in early spring 2001, when the trees were 11 years old. The average proportion of trees browsed by moose varied between 6 and 86% among the seed origins. Browsing by moose decreased with increasing latitude of seed origin and sapling height. Seed origins transferred from more southern latitudes (southern Estonia, southern Sweden, Scotland, Russia) had a higher proportion of browsed trees than the more northern native ones. A similar pattern was also seen in the proportion of trees with stem breakage and the proportion of repeatedly browsed trees. Latitude of seed origin and sapling height covariate had a significant effect on moose browsing. The moose browsed more branches per browsed tree of southern origins, whereas sapling height had no significant effect. It is suggested that the variation in moose browsing among the seed origins was related to differences in their annual physiological rhythm, i.e. timing of growth cessation, leaf discoloration and abscission, and related changes in digestibility and palatability. It was concluded that importing birch regeneration material to Finland from more southern latitudes should be avoided because of the risk of browsing damage.