When wolves were reintroduced to Yellowstone National Park in the United States after being absent nearly 70 years, the most remarkable “trophic cascade” occurred. What is a trophic cascade and how exactly do wolves change rivers? George Monbiot explains in this movie remix.

This explanation illustrates and provides understanding of how a small change in an ecosystem may actually start a chain reaction for restoration.

Submitted by: Joris de Vente, CSIC