Abstract
Gray wolves (Canis lupus) were reintroduced into Yellowstone National Park in 1995-96, thus completing the park's large predator guild. In the fall of 2010, approximately 15 years after wolf reintroduction, we sampled ten genera/species of berry-producing shrubs within 97 aspen (Populus tremuloides) stands in the park's northern ungulate winter range. Regression analysis indicated shrub heights for five of the ten genera/species were positively correlated with height of understory aspen; greater shrub richness was found in aspen stands with the tallest understory aspen. In addition, the proportion of shrubs with berries was positively correlated with shrub height for six of the ten genera/species. Results were consistent with the re-establishment of a tri-trophic cascade involving wolves, elk (Cervus elaphus), and palatable woody plants in northern Yellowstone. After multiple decades of browsing suppression by elk, it appears that aspen and at least some genera/species of berry-producing shrubs are in the early stages of recovery. If shrub recovery continues, improved food-web and habitat support could benefit a wide range of terrestrial wildlife species in northern Yellowstone.