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Ungulate Herbivory as a Chronic Disturbance Agent on Western Landscapes
Marty Vavra, USDA Forest Service, Pacific Northwest Research Station, La Grande, OR
In the western United States, foraging by wild ungulates has not been recognized as an ecological force as evidenced by the lack of its mention in land management plans. Ungulate herbivory has the potential to influence nutrient cycling, net primary production, and act as a chronic disturbance agent, thereby influencing ecosystem patterns and processes. Ungulates can alter forest successional pathways and disturbance regimes as validated in recent research conducted in northeastern Oregon. Identifying how ungulate herbivory influences composition and structure of forest understories following disturbance is critical to successful forest management. Potential impacts to biodiversity have not been addressed. Additionally, herbivory-induced changes in the understory may affect productivity of native ungulate herds and the degree of interspecific competition among ungulates. The issue of scale is very important when considering management and planning of successional dynamics for habitats that cross land ownerships. Unfortunately, private landowners, state government agencies, and federal agencies each manage landscapes at different temporal and spatial scales. These scales of management may or may not align with the scales at which interactions between herbivores and plants play out. Conflicting management actions may be counterproductive to the management of ungulates. Timber harvest or the lack thereof, human disturbance (road density, off-road recreation), and livestock grazing may positively or negatively impact animal distributions across landscapes. The overarching challenge facing managers is to develop information systems through which multi-species management can be planned so as to demonstrably contribute to long-term ecosystem sustainability.