THE EFFECTS OF LARGE HERBIVORES ON SMALL MAMMAL COMMUNITIES, PLANTS AND ECOSYSTEM PROCESSES IN NORTHERN ARIZONA

Large herbivores are major drivers of community structure and function in many terrestrial systems. Through their direct effects on plants, large herbivores can influence the structure and complexity of habitats, the population abundance of animals that rely on those habitats, and the rates of ecosystem processes within those systems. These manifold impacts on systems are potentially magnifying, as removal of top predators and changes in land use have triggered large increases in large herbivore populations. Although increasing evidence suggests that large herbivores can critically shape the structure and function of the ecosystems they inhabit, few studies have detailed the direct and indirect effects of large herbivores on vegetation, animal populations, and ecosystem processes in the same system. Typically these varied impacts are studied in isolation and it is often unclear what the magnitude or sources of spatio-temporal variation in these effects might be. I used a large-scale replicated elk-exclusion experiment to determine the effects of elk on small mammal communities, plants, and ecosystem processes. I found that five years of elk exclusion led to noticeable changes in small mammal communities; some small mammals increased in the exclosure while others declined on controls. These changes were likely due to increasing habitat quality inside the fences and declining habitat quality outside. Elk browsing also decreased the recruitment of two dominant deciduous species and the quantity of litter of both of these species deposited on the forest floor during the peak in litterfall. Elk similarly reduced the cover of nitrogen fixing forb species, and the decomposition rates of both aspen and maple litter were more rapid inside the fences after 2 years of decomposition. These results indicate that elk are influencing the quantity and quality of litter inputs into this system as well as the decomposition environment. Finally, I found that mixtures of deciduous and evergreen litter influenced decomposition dynamics, the net mineralization of nitrogen, and plant growth. These results suggest that shifts in litter quantity and quality from browsing ungulates could have important indirect effects on plant growth. Overall, this work indicates that elk can have effects on multiple components of the community and ecosystem in only a short five year time period