Restoring Riparian Ecosystems with Large Predators the Yellowstone Experience
Large predators can help shape the structure and functioning of terrestrial ecosystems. While various studies in national parks scattered across the western United States and Canada have shown the loss of large predators (e.g., wolves, cougar) allowed native ungulates (e.g., elk, mule deer) to greatly alter the structure and functioning of ecosystems via increased herbivory, studies of trophic effects of reintroduced/recolonized large predators have been relatively rare, with Yellowstone National Park being a major exception. The reintroduction of wolves into Yellowstone National Park in 1995-97, after a 70 year absence, allowed for studies of trophic cascades of a restored large predator guild upon elk and woody species such as aspen, cottonwoods, willows, and berry-producing shrubs. Overall, these studies indicate that the reintroduction of wolves triggered a trophic cascade, in conjunction with bottom-up forces, with increasing recruitment (i.e., growth of woody plants into tall shrubs or trees) of browse species in riparian areas. This situation represent a fundamental change in plant community dynamics in comparison to previous decades of browsing suppression--when wolves were absent. Although wolf reintroduction has resulted in substantial initial effects to both plants and animals, the Yellowstone ecosystem still appears to be in the early stages of ecosystem recovery. In other areas of western North America where large carnivores have been previously extirpated or displaced, their recovery may be necessary for assisting in the ecological restoration of large herbivore altered ecosystems.