The Short Version
Wolf reintroduction did produce some trophic-cascade effects in parts of Yellowstone, but describing it as a force that "fundamentally transformed" the park's ecosystem overstates the scientific evidence. Peer-reviewed research and the National Park Service itself acknowledge that the cascade is weaker, more spatially variable, and more confounded by other factors — including hydrology, climate, and human elk harvest — than popular accounts suggest. Key quantitative claims underpinning the "transformation" narrative have been challenged as methodologically flawed in recent studies.