SYMP 5 - Has Wolf Reintroduction to Yellowstone Provided Evidence for a Trophic Cascade?

Tuesday, August 8, 2017: 8:00 AM-11:30 AM
Portland Blrm 252, Oregon Convention Center
Dan MacNulty, Utah State University
Douglas W. Smith, National Park Service
Mark Hebblewhite, University of Montana
The ability of large predators to frighten and kill other animals is increasingly characterized as an ecosystem service critical to conserving biodiversity and ecosystem function. The pathway describing these effects is known as a ‘trophic cascade’, and a classic example that has captivated more minds than perhaps any other is wolf reintroduction to Yellowstone National Park. The textbook story is that wolves frightened and (or) killed enough elk to allow various woody deciduous plants (e.g., willow, aspen, cottonwood, and others) to recover from decades of unchecked herbivory. Less widely known is that the community of researchers that has been measuring the interactions between wolves, elk, and woody plants is divided about whether their data backup the textbook story. Although there is no argument that the removal of wolves from Yellowstone in the 1920s provided strong evidence of a trophic cascade, there is vigorous debate on ecosystem responses to wolf restoration. Some research indicates widespread vegetative recovery of woody deciduous plants primarily due to reduced elk browsing, while other work indicates recovery is limited because changes in the physical environment and disturbance regime that occurred after wolf removal have stabilized the system such that wolf restoration has not caused it to return to conditions that prevailed before wolves were extirpated. The debate has recently attracted attention in the popular media. The purpose of this symposium is to gather the principal researchers on trophic research in Yellowstone and fully discuss the evidence from studies by different groups, strive to reach consensus, and plot a way forward with new questions. Understanding of terrestrial food webs and community structure has lagged behind marine and aquatic systems, so this is a rare opportunity to advance understanding in a seminal terrestrial system. This symposium will offer an opportunity for researchers to present their views of the scientific evidence with a follow-up discussion. Important questions to be addressed will be explanations for changes in ungulate abundance and distribution, spatial heterogeneity in plant responses to trophic effects, the importance of elk relative to other large herbivores in shaping plant community dynamics, and the relative strength of top-down vs. bottom-up forces regulating elk and plant responses.
8:30 AM
 Carnivore recovery and Yellowstone's 'unnatural' history
Douglas W. Smith, National Park Service; Daniel R. MacNulty, Utah State; Daniel R Stahler, National Park Service; Matthew C. Metz, Yellowstone Center for Resources
9:00 AM
 Understanding the predatory effects of wolves in northern Yellowstone National Park
Dan MacNulty, Utah State University; Douglas W. Smith, National Park Service; Daniel R. Stahler, National Park Service; Michel T. Kohl, Utah State University; Matthew C. Metz, University of Montana; Aimee G. Tallian, Utah State University; Sarah R. Hoy, Michigan Technological University; Lacy M. Smith, Utah State University
9:30 AM
9:40 AM
 Understanding controls on state-transition of riparian willow ecosystems on Yellowstone's northern range
David J. Cooper, Colorado State University; N. Thompson Hobbs, Colorado State University
10:10 AM
 Recovering riparian vegetation in Yellowstone after wolf reintroduction: The first two decades
Robert Beschta, Oregon State University; Luke E. Painter, Oregon State University; William J. Ripple, Oregon State University
10:40 AM
 Synthesis and future directions
Rolf O. Peterson, Michigan Technological University
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