Salvatore R. Curasi Arctic ecosystems are responding to unprecedented climate change with implications for the carbon cycle and feedbacks to global climate. The balance between carbon losses through increased soil respiration and carbon gains through changes in vegetation productivity will in part determine the strength of these feedbacks. Climate change is altering the productivity of arctic vegetation as well as the distribution of species within tundra ecosystems. However, gaps exist in our

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... nderstanding of arctic vegetation, including how shifts in species with different growth forms and intra-specific variation impact the climate response of these ecosystems. In this dissertation, I utilize field observations and models to explore these knowledge gaps via a detailed investigation of the foundation arctic sedge Eriophorum vaginatum L. in tundra ecosystems. I first broadly investigated the role of the foundation tussock forming sedge E. vaginatum in tundra ecosystems and find that tussocks are a large climatically vulnerable arctic carbon stock. I then investigate E. vaginatum's unique tussock growth form and find that tiller root production and the carbon balance of the