Changes induced by elk browsing in the aboveground biomass production and distribution of willow (Salix monticola Bebb): their relationships with plant water, carbon, and nitrogen dynamics

Willows are dominant woody plants of many high-elevation riparian areas of the western USA, and constitute an important food resource for various ungu lates, which tend to concentrate in riparian areas. The response of willow to browsing was analyzed in the elk winter range of Rocky Mountain National Park, by considering the effect of elk browsing on Salix monticola Bebb, o ne of the most common willow species in this area. Unbrowsed and browsed tr eatments were established during the 1997 growing season (May to October), using eight long-term exclosures built in the fall of 1994. Plants in the b rowsed treatment were in the areas open to browsing, but they were protecte d from browsing by small exclosures during the experimental period. Winter browsing by elk induced the following measured responses in plant morpholog y and development: (I)higher shoot biomass production but similar leaf biom ass and leaf area per plant, (2) a lower number of and bigger shoots, (3) a lower number of and bigger leaves, and (4) flower inhibition. In addition, we infer that browsing induces (5) lower belowground allocation and (6) a more negative N balance but a higher soil N uptake. We conclude that elk br owsing negatively affects willow even though willow compensate for abovegro und biomass removal. Continuous browsing produces long-term changes in will ow morphology which constrain plant growth and development. High browsing u tilization, as occurred in this experiment, could therefore reduce the comp etitive ability and survivorship of willow, in particular under drier envir onmental conditions.