10.5061/DRYAD.M63XSJ44W
Cushman, J. Hall
0000-0003-3210-4261
University of Nevada Reno
Reikowski, Elizabeth
University of Nevada Reno
Refsland, Tyler
Michigan State University
Ungulate herbivores as drivers of Aspen recruitment and understory
composition throughout arid Montane landscapes
Dryad
dataset
2022
FOS: Biological sciences
Nevada Department of Wildlife
https://ror.org/044bng944
2022-07-05T00:00:00Z
2022-07-05T00:00:00Z
en
50697 bytes
4
CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
Herbivory by wild and domestic ungulates can influence tree recruitment
and understory forest communities throughout the world. Herbivore-driven
declines in tree recruitment have been observed for quaking aspen (Populus
tremuloides), a foundation species whose health and management is
recognized as a critical priority throughout much of its range. Livestock
fencing is commonly used to promote aspen regeneration, but its
effectiveness is rarely assessed, especially across large spatial scales.
Using a livestock-reduction experiment, we evaluated the effects of
ungulate herbivory on aspen in the Great Basin and southern Cascades, an
expansive and environmentally heterogeneous region where aspen faces the
interacting threats of climate change, conifer encroachment, and
herbivory. We found that livestock fencing only reduced the intensity of
herbivore browsing on aspen when wild ungulate abundance was low, and did
not increase stem densities of aspen recruits. Contrary to expectations,
wild ungulate abundance was a strong driver of browsing intensity on
juvenile aspen within fenced, but not unfenced aspen stands, and when the
abundance of these herbivores was high, browsing intensity in fenced
stands exceeded that in unfenced stands. The density of aspen recruits
decreased with browsing intensity on juvenile aspen and with the density
of both adult aspen and conifers, suggesting that both herbivory and
intra- and interspecific competition are important drivers of recruitment.
Fire history was also an important driver of recruitment, with stands that
burned 10-20 years ago having the greatest density of aspen recruits.
Finally, in the stand understory, we found that livestock fencing
decreased forb cover, increased shrub species richness, and increased the
cover of exotic annual grasses, a group dominated by Bromus tectorum. This
latter finding suggests that livestock fencing may not be appropriate in
areas where controlling the spread of this invader is a priority. In sum,
our findings indicate that aspen recruitment is limited by browsing by
both wild and domestic ungulates, is mediated by competition with
neighboring trees and fire history, and will require management actions
beyond livestock fencing, as this approach does not control browsing by
wild ungulates.