Summary 1.We examined the effects of browsing by moose and snowshoe hares on vegetation structure, species composition, plant demography and element cycling in 25 riparian (willow) vegetation stands along the Tanana River, interior Alaska, across a 250-km gradient that represented a fivefold range in moose densities (0.2-1.0 km -2 ). 2. Browsing frequency was much greater in areas with high moose densities. The combined browsing pressure (% of annual browse production consumed by herbivores) of moose ( Alces alces ) and snowshoe hares ( Lepus americanus ) on forage species was over fivefold greater in the high moose density areas (33%) than the low moose density areas (6%), reflecting the fivefold difference in moose densities. 3. Above-ground biomass of preferred willow species was lower in high moose density areas, and the age structure of the vegetation was significantly skewed towards younger age classes. This shift in age structure was accompanied by higher proportion of dead to live ramets, indicating higher mortality under increased browsing pressure. Increasing browsing pressure favoured later-successional species ( Alnus tenuifolia and Populus balsamifera ) on the landscape, as shown by both a reduction in the number and size of willow stands in high-density areas. 4. High rates of fecal input resulted in a doubling of above-ground N input in high moose density areas. The rates of carbon and nitrogen input from willow communities to the soil as mediated by moose herbivory were approximately fivefold and eightfold greater in high moose density areas than in low moose density areas, respectively. 5. Synthesis . The effects of herbivory were manifested at several ecological hierarchies, including the individual, the community, and the landscape. Across these spatial scales herbivory appears to accelerate the ecosystem turnover of carbon and nitrogen by a combination of both plant-and animalbased processes.

Aim  We examined the interactive effects of mammalian herbivory and fluvial dynamics on vegetation dynamics and composition along the Tanana River in interior Alaska. Location  Model parameters were obtained from field studies along the Tanana River, Alaska between Fairbanks (64°50.50′ N, 147°43.30′ W) and Manley Hot Springs (65°0.0′ N, 150°36.0′ W). Methods  We used a spatially explicit model of landscape dynamics (ALFRESCO) to simulate vegetation changes on a 1‐year time‐step. The model was run for 250 years and was replicated 100 times. Results  Increases in herbivory decreased the proportion of early successional vegetation and increased the proportion of late successional vegetation on the simulated landscape. Erosion and accretion worked as antagonists to herbivory, increasing the amount of early successional vegetation and decreasing the amount of late successional vegetation. However, the interactive effects of herbivory and erosion/accretion were especially important in determining system response, particularly in early seral vegetation types. High erosion rates, when coupled with low herbivory, greatly increased the proportion of willow on the landscape. When coupled with high herbivory, however, they greatly increased the proportion of alder on the landscape. At low levels of herbivory, alder abundance peaked at intermediate levels of erosion/accretion. Main conclusions  Neither erosion/accretion nor herbivory produced consistent landscape patterns that could be predicted independently of the other. These findings underscore the importance of the interactive effects of biotic and abiotic disturbances in shaping large‐scale landscape vegetation patterns in boreal floodplain ecosystems – systems traditionally thought to be driven primarily by abiotic disturbance alone.

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