Trophic Cascades and Historic Aspen Recruitment in the Gallatin Elk Winter Range of Southwest Montana

The extirpation of the gray wolf (Canis lupus) by 1930 in Yellowstone National Park (YNP) provided us with an opportunity to study historic aspen (Populus tremuloides ) recruitment with and without a top carnivore predator present. Herbivory, climate trends, fire records, and current conifer invasion were also examined within the context of aspen recruitment. We obtained tree cores and diameter at breast height measurements to create an aspen age-diameter relationship which we used to approximate aspen origination dates. One elk (Cervus elaphus) exclosure, erected in 1945 within the same elk winter range, was compared to the rest of the winter range. Consistent recruitment inside the exclosure began in the 1940s and has continued into the present. Outside of the exclosure, aspen recruitment began decreasing in the 1930s and ceased in the 1950s. Within the scope of the study, we found little correlative evidence between aspen decline and climate trends, conifer invasion, or fire suppression. The results are suggestive of a trophic cascade between aspen recruitment, and historical elk browsing activities as affected by the absence or presence of wolf predation.

Aspen Recruitment and Stand Structure in the Gallatin Elk Winter Range of Southwest Montana

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.