Influences of elk on upland aspen, riparian willow, and associated landbirds in and near Jackson Hole, Wyoming.

Authors(s): S. Anderson and E. Anderson

Publication:

Publisher:

Publication Date: 0000-00-00

Type: final report

Location: Cheyenne Wyoming

Abstract: Aspen (Populus tremuloides Michx.) and riparian willow (Salix spp.) communities support high levels of diversity, yet are failing to regenerate throughout much of the Rocky Mountain region. We evaluated changes in landbird distributions associated with habitat alteration by supplementally fed elk (Cervus elaphus nelsoni) in and near Jackson Hole, Wyoming. For aspen, we first defined elk use within each aspen stand (n = 30) using nine measures quantified in the field (e.g. browse rates). Analyses were conducted across all stands and between objectively defined groups of lower and higher elk use stands. Across all stands, there was a negative relationship between elk use and understory volume of vegetation, and positive relationships between understory volume and bird abundances within understory nesting and foraging guilds. Aspen recruitment to overstory and densities of non-sapling aspen trees (DBH >5 cm) were lower in stands of greater elk use, explaining why bird abundances within overstory nesting and foraging guilds were also lower in these stands. Abundances of most cavity nesting species were greater in stands of higher elk use, probably because of higher rates of aspen decay and mortality following bark damage by elk. Across all willow stands (n = 11), the proportion of annual willow segments browsed was negatively related to multiple willow structural measures (willow volume, shrub height, and shrub diameter) that were positively associated with the abundances of several willow-dependent bird species. Sage-grassland bird species were generally more abundant in stands close to elk feeding stations, a probable effect of elk-induced conversion of willow to sage-grassland habitat. Critically, long durations of elevated elk use ultimately reduce landscape diversity of birds by eliminating aspen and willow structure. For instance, rates of aspen stand area loss quantified from dead and down trees were greater in stands of higher elk use. We suggest elk use was more important to variation in aspen recruitment, willow structure, and landbird distributions than multiple alternative influences.

Keywords: habitat, animal, mammal, ungulate, Cervidae, Cervus elaphus, Cervus elaphus nelsoni, elk, wapiti, grazing, food , feeding, winter food supplementation, bird, Aves, ornithology, Jackson Hole, Teton County, National Elk Refuge