The Sustainability of Grazing Ecosystems

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ABSTRACT Proposal #9726569 (Frank and Groffman) Title: THE SUSTAINABILITY OF GRAZING ECOSYSTEMS Institution: SYRACUSE UNIVERSITY This research examines the question of whether large herbivores actually contribute to the sustainability of grasslands that they occupy, through their effects on soil carbon (C) and nitrogen (N) processes. The prevalent view that herbivores decrease belowground productivity is not supported by results from Yellowstone National Park, where grazers appear to increase belowground production, particularly the input of labile soil C. The hypothesis to be tested is that the promotion of labile C input by grazers is fundamental to acceleration of nutrient cycling in Yellowstone and may be critical in sustaining the energy and nutrient dynamics of Yellowstone and other grazed ecosystems. This work addresses three questions in Yellowstone: (1) How do grazers affect soil C input? (2) How do grazers influence soil C-N linkages? (3) What effects do the plant growth and allocation traits that are selected for in grazed grassland have on sustaining soil processes? Answers to these questions are important because abundant large herbivores and grasslands have coexisted for millennia, yet our current view of the effects of these animals on grassland processes suggest inherent instabilities of grazing ecosystems. Because 50% or more of the Earth's land surface is grazed by large herbivores, increasing our knowledge of how herbivores influence ecosystem C accumulation and N cycling should significantly improve our understanding of terrestrial effects on global C and N cycles.