Christian Boekweg, Brigham Young University
Plant and Wildlife Sciences
It has been shown that the population densities of deer and elk in the Rocky Mountains are at an unprecedented high. The heavy browsing of said species (ungulates) on regenerating aspen suckers can be devastating, leading to homogenously aged aspen stands that now have reduced resilience to drought, fire or logging disturbance, and an increased susceptibility to pathogens. Lastly, the extensive, highly selective herbivory of the aspen suckers may cause a shift in forest composition away from the aspen tree to an increase in other, less palatable species. We selected 186 sites across the 3 national forests of Central and Southern Utah, and characterized stand composition using the point quarter method. Stands were defined by successional stages from early to late; aspen, mixed or conifer. We then used pellet counts to estimate animal density and evaluated the effect of animal density and stand type on the regeneration success of aspen suckers. The key result of our study is that high ungulate density is highly correlated with reduced sucker heights (p<0.001). This indicates that high ungulate density impedes aspen regeneration by preventing aspen from recruiting into the overstory. Our study suggests that closer monitoring of the long term effects of herbivory on aspen development and regeneration is necessary to ensure vigorous aspen forests.