PARENT SESSION
Contributed Oral Session 101: Mammalian Herbivory
Wednesday, August 10, 1:30 PM - 5:00 PM, Meeting Room 520 A, Level 5, Palais des congrès de Montréal
Interacting effects of water table and herbivory on willow in Yellowstone National Park.
Bilyeu, Danielle*,1, Hobbs, N. Thompson1, Cooper, David2, Singer, Francis1, 3, Wolf, Evan2, 1 Natural Resource Ecology Laboratory, Fort Collins, CO, USA2 Department of Forest, Rangeland, and Watershed Stewardship, Fort Collins, CO, 805233 Biological Resources Division, Fort Collins, CO, 80525
ABSTRACT- Over the past 100 years, the stature and extent of willow communities in the northern elk wintering range of Yellowstone National Park have declined. Potential causes for the decline include an increase in browsing by elk and lowered water table due to decreased beaver activity. We examined the influence of water table and herbivory on growth and height of three willow species (Salix geyeriana, S. bebbiana, and S. boothii) in Yellowstone using a factorial experiment with two treatments, water-table elevation and exclusion of large herbivores (n=4). Water table elevation increased growth in S. geyeriana, while exclusion of herbivores decreased it. This response may have been mediated by treatment effects on plant water balance, as late season midday shoot water potential also increased in water-elevated plots and decreased inside exclosures. Such a relationship between water potential and growth was not seen for S. bebbiana, a species more tolerant of dry conditions. For this species, there was a significant interaction between treatments such that increased growth occurred only in water-elevated and exclosed plots. Growth of S. boothii did not respond to water elevation or exclosures. Height responses of S. geyeriana and S. bebbiana were similar, with water elevation and exclosures each resulting in height gains of about 50 cm. For all species, after three years of treatment, height gains sufficient to confer protection from elk browsing occurred only in plots that were both water-elevated and exclosed. Establishment of such tall willow communities is a necessary precondition for re-establishment of beaver colonies. The potential for recovery of willow-beaver systems under different browsing pressure scenarios is explored given ambient water tables.
Key words: Salix, Yellowstone, riparian, herbivory