Wolves did not simply change a river

After wolves returned to Yellowstone, elk numbers and behaviour changed, and some streamside willows, aspens and cottonwoods recovered in some places. Wolves were part of that story. So were hunting outside the park, drought, snow, bears, cougars, bison, beavers and the physical character of each valley. Vegetation responses have been patchy rather than a single park-wide switch.

The famous claim that wolves “changed the rivers” compresses those linked effects into one heroic cause. Predators can initiate trophic cascades, but a cascade is not a magic chain with every link proven everywhere. Yellowstone is better read as a long natural experiment: reintroducing a top predator altered relationships, while water and plants answered through local histories of their own.