The Catalysis of Belowground Processes in Grazing Ecosystems

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A major challenge facing society is understanding the ecological processes contributing to atmospheric CO2 concentrations and how human land use practices influence atmospheric CO2 levels. Herbivores are known to strongly affect plant and soil carbon dynamics; but how grazers may determine the rate that carbon flows into and out of the soil remains unclear. In this study, the effects of grazing by elk and bison on carbon processes in Yellowstone National Park will be examined at three ecologically important time scales: (1) instantaneous rates of ecosystem CO2 exchange, (2) the rate that carbon flows through the plant - soil system during yrs 1-3 after carbon is assimilated by plants, and (3) 40-50 yr soil carbon storage. Yellowstone Park is one of the few remaining vestiges of a once widespread and stable grassland ecosystem that supported abundant migratory ungulates in prehistory, and thus can serve as a natural benchmark against which to compare grassland managed for livestock. With half of the earth's terrestrial surface area used as rangeland for large herbivores, the impact of ungulates on the global carbon cycle may be substantial. This research will contribute significantly to our understanding of factors that regulate carbon dynamics in grazed grassland.