Ungulate herbivores as drivers of aspen recruitment and understory composition throughout arid montane landscapes

Herbivory by wild and domestic ungulates can influence tree recruitment understory forest communities throughout the world. Herbivore-driven declines in have been observed for quaking aspen (Populus tremuloides), a foundation species whose health management is recognized as critical priority much of its range. Livestock fencing commonly used to promote regeneration, but effectiveness rarely assessed, especially across large spatial scales. Using livestock-reduction experiment, we evaluated effects ungulate herbivory on Great Basin southern Cascades, an expansive environmentally heterogeneous region where faces interacting threats climate change, conifer encroachment, herbivory. We found that livestock only reduced intensity herbivore browsing when abundance was low did not increase stem densities recruits. Contrary expectations, strong driver juvenile within fenced, unfenced, stands, these herbivores high, fenced stands exceeded unfenced stands. The density recruits decreased with both adult conifers, suggesting intra- interspecific competition are important drivers recruitment. Fire history also recruitment, burned 10–20 years ago having greatest Finally, stand understory, forb cover, increased shrub richness, cover exotic annual grasses, group dominated Bromus tectorum. This latter finding suggests may be appropriate areas controlling spread this invader priority. In sum, our findings indicate limited ungulates, mediated neighboring trees fire history, will require actions beyond fencing, approach does control ungulates.