Study
Trophic cascades in Yellowstone: The first 15 years after wolf reintroduction
Ripple, William J.; Beschta, Robert L.
Biological Conservation, 2012
A synthesis of measurements taken across Yellowstone National Park since the 1995 wolf reintroduction: elk numbers and distribution, willow and aspen and cottonwood growth, beaver colonies, and stream channel condition.
- Studied in
- Canis lupus, Cervus canadensis, Populus tremuloides
- Sample size
- fifteen years of vegetation, elk and wolf data
Elk numbers fell and their use of riparian areas changed after wolves returned, and woody browse species recovered in many locations, with associated increases in beaver activity and changes to stream banks.
What it means
The authors' reading, and ours. Where they differ, that difference is the point.
How the authors put it
Wolf reintroduction initiated a trophic cascade that propagated through elk to vegetation and on to stream systems.
How NatureHQ reads it
This is the paper behind "wolves changed the rivers", and the honest position is that it documents a real and important set of changes while not establishing that wolves caused all of them. Yellowstone in the same period also had a severe drought, a growing bison herd, returning grizzlies, and a substantial human elk hunt outside the park. The cascade is a plausible and partly supported reading of a system with several things happening at once, and the strength of the popular version is not the strength of the evidence.
- Observational and correlational; no control landscape without wolves exists.
- Confounded by drought, bison increase, bear predation on elk calves and human harvest.
- Recovery of woody vegetation is patchy, and several later studies find it much weaker than reported here.
What this study is used for on NatureHQ
One study can inform several subjects. Here is everywhere this one is cited.
Published by: Elsevier journalsPublished in an Elsevier journal.
doi.org/10.1016/j.biocon.2011.11.005
This reference was resolved automatically against Crossref on 2026-08-11.
NatureHQ summarises research in its own words and does not reproduce published text. Reviewed 2026-08-09.