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Yellowstone National Park Report

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This study examines the relationship between wolf, elk, and aspen within the framework of trophic cascades inside and outside of the Gallatin elk winter range. The overall goal of this study is to determine if an association exists between aspen recruitment, and historic and current elk browsing activities as affected by the absence or presence of wolf predation. This study also examines if other factors (climate fluctuations, conifer invasion, ftre suppression) may have had a role in aspen decline. Through the examination of current and historic elk browsing levels, current and historic browsing effects on aspen recruitment are addressed. Potential historic browsing affects were assessed with tree rings, aspen age structures, historic documents, and an elk exclosure erected in 1945. Current browsing levels were assessed through plant architecture methods and elk pellet counts. Initial results indicate that a gap in aspen recruitment is present yet aspen have successfully recruited inside an elk exclosure located within the same elk winter range. The lack of recruitment outside the exclosure appears to be due to chronic elk herbivory, although other factors need further evaluation. Future results will elucidate if the recruitment gap occurred after wolf extirpation in the 1920's.