Interactions of Snowshoe Hare and Feltleaf Willow in Alaska

Evidence from experimental feeding trials and chemical analysis showed that, when severe winter browsing of adult—form Alaska feltleaf willow (Salix alaxensis) causes it to revert to juvenile—form stump sprouts, the twigs are unpalatable and of lower nutritional quality to the hares than are twigs of adult—form S. alaxensis plants. Further feeding choice trials demonstrated that the palatability of winter—dormant S. alaxensis to snowshoe hares is a function of the age of the sprout and its chemistry rather than the accessibility (height) or morphology of the twigs. The low nutritional quality of juvenile sprouts is partially caused by decreased dry matter and nitrogen digestibility, which may be related to increased lignin and phenolic content of the twigs. This browsing—induced resistance to future winter browsing by hares relaxes within 3 yr and within the height range of twigs normally available to snowshoe hares in winter. These results are compatible with hypothesis that the inducation and relaxation of resistance to browsing in the preferred winter food of snowshoe hares is a cause of the well—known 10—yr snowshoe hare cycle.