Moose Herbivory and Carbon Turnover of Early Successional Stands in Interior Alaska

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In the taiga of interior Alaska, early successional stands are dominated by deciduous species. These species represent the main forage base for many mammalian herbivores. In a long-term study employing large, permanent exclosures, we measured the impact of winter browsing by moose and snowshoe hares on carbon flux in riparian willow/alder communities. We found that browsing-induced changes in leaf litter chemistry increased the rate of litter decomposition both in the laboratory and under field conditions, and increased the pool of mineralizable carbon in litter. The aboveground input of higher-quality litter-carbon following browsing may explain the increased respiration potentials of soils sampled outside the exclosures. Moreover, winter browsing tends to reduce the production of fine roots and appears to decrease fine root longevity. Thus, the net effect of moose browsing on aboveground and belowground processes in these early successional stands is to accelerate carbon turnover. These results demonstrate that the effects of mammalian herbivory on element cycling in taiga is a two-stage process, involving intraspecific as well as interspecific responses at different time scales. Winter browsing by moose offer one example of how mammalian herbivory modify ecosystem-level processes that govern major functions in these ecosystems.