EFFECTS OF BROWSING HISTORY BY ALASKAN MOOSE ON REGROWTH AND QUALITY OF FELTLEAF WILLOW

We studied effects of browsing history by Alaskan moose (Alces alces gigas) on regrowth and quality of feltleaf willow (Salix alaxensis) during late winter 2002 in interior Alaska, USA. We recorded extensive browsing on willows, with 55.6% of leaders on 43 plants browsed by moose and 3.9% browsed by snowshoe hares (Lepus americanus). Foraging moose removed, on average, 15.1 mm of current annual growth from willow twigs, which averaged 24.1 mm in length (62.3% removed). Twigs re-growing from 2-year-old stems that were browsed previously had larger diameters at their bud scale scar than those re-growing from stems that were not browsed in the previous year. Browsing history by moose, however, had no effect on nitrogen content, in vitro dry matter digestibility, or tannin content of willow twigs. Willows did not respond to browsing on individual twigs with an inducible defense system that involved tannins. Diameter at point of browsing (bite size) was larger on twigs that had been browsed previously than for twigs re-growing from second-year growth that had not been browsed. Moose did not exhibit an optimal bite size, but took larger-diameter bites from larger compared with smaller leaders of current annual growth. Forage selection by moose for previously browsed twigs likely relates to greater forage biomass on those twigs rather than to forage quality. We caution, however, that foraging behavior by moosecannot be understood fully without considering additional factors, including predation risk in relation to forage availability