EFFECTS OF PREVIOUS BROWSING ON THE SELECTION OF WILLOW STEMS BY ALASKAN MOOSE

Abstract

We tested whether regrowth from stems of willows (Salix glauca) browsed by Alaskan moose (Alces alces gigas) in the previous winter would affect selection for browse by moose in the following winter. We sampled willow in a power-line corridor near Fairbanks, Alaska, USA, during autumn 1995 and winter 1996. We collected current annual growth for 90 stems from 30 willows to establish relationships among stem length, stem diameter at the bud-scale scar, and dry mass. Strong curve-linear regressions were obtained between stem length and dry mass (R² = 0.91), and stem diameter and dry mass (R² = 0.90); stem length was linearly related to diameter (r² = 0.74). we randomly sampled an additional 30 willows to investigate levels of browsing by moose on leaders of new growth. Overall levels of browsing were high (70.4% ± 20.2% SD), but feeding on stems that were browsed previously was significantly (P < 0.001) higher (84.6% ± 16.0% SD). We estimated dry mass available to moose on willow stems not browsed in the previous or current winter (0.62 g ± 0.18 g SD), stems browsed in the previous winter but not the current one (0.87 g ± 0.48 g SD), and stems browsed during both winters (4.0 g ± 2.7 g SD); this pattern in biomass available to moose differed significantly (P < 0.001). We also estimated that moose removed 1.6 g (± 1.0 g SD) of current annual growth from each stem they browsed. This amount was greater than available on stems that were not browsed in winter 1995-1996, and may help explain selection of moose for regrowth from previously browsed stems. Consequently, moose would obtain more food for the same effort by feeding upon stems they had browsed previously. This outcome also may help explain why moose use traditional areas for feeding and other activities.