Mammalian Herbivory, Ecosystem Engineering, and Ecological Cascades in Alaskan Boreal Forests

The mammalian herbivores of the taiga forests include members of the largest (moose) and smallest (microtines) vertebrates that inhabit North American terrestrial biomes. Their abundance in a particular area fluctuates dramatically due to seasonal use of particular habitats (moose) and external factors that influence demographic processes (microtines). The low visibility of herbivores to the casual observer might suggest that these animals have minimal influence on the structure and the function of boreal forests. On the contrary, seedling herbivory by voles, leaf stripping by moose, or wholesale logging of mature trees by beaver can profoundly change forest structure and functioning. These plant-herbivore interactions have cascading effects on the physical, chemical, and biological components of the boreal ecosystem that shape the magnitude and direction of many physicochemical and biological processes. These processes, in turn, control the vertical and horizontal interactions of the biological community at large. Herbivores act as ecosystem engineers (Jones et al. 1994) in that they reshape the physical characteristics of the habitat, modify the resource array and population ecology of sympatric species, and influence the flux of energy and nutrients through soils and vegetation. Additionally, many herbivores are central to a variety of human activities. Both consumptive and nonconsumptive use of wildlife represents a pervasive aspect of life in the North. In this chapter, we examine the interactions of mammalian herbivores with their environment, with an emphasis on moose, and attempt to delineate the biotic and abiotic conditions under which herbivores influence the phenotypic expression of vegetation. We also examine the role of herbivores, and of wildlife in general, in the context of human perceptions and interactions with their environment. Human-environment interactions are both direct and indirect and pertain to a variety of social expressions. The relationship between humans and wildlife has economic, cultural, and psychological dimensions, which underscore the importance of these animals in a broader social, as well as ecological, context. Northern ecosystems such as the boreal forest are characterized by extreme seasonality and pronounced change in resource availability between summer and winter. Not surprisingly, these conditions are reflected in the population dynamics of the animals that inhabit these environments, particularly in smaller-bodied herbivores.