Modelled on the 1995 reintroduction of grey wolves to Yellowstone National Park — one of the best-documented natural experiments in ecology. With no apex predator, elk grazed river banks year-round without fear, stripping willow and cottonwood shoots before they could mature.
- Direct effect — a small wolf pack culls only a modest number of elk; the population dip alone can't explain what follows.
- Landscape of fear — wolves patrol the open river corridor, the easiest place to run down prey. Elk learn to avoid it, browsing forest edges instead, even where they're never actually caught.
- Vegetation release — freed from constant browsing, riparian willow and cottonwood regrow taller each season.
- Bank stabilisation — deeper root systems bind the soil, cutting erosion; over years this narrows and steadies the channel — a real, surveyed outcome at Yellowstone.
Watch the vegetation-cover bar lag behind the wolf population — recovery takes simulated seasons, not instantly, exactly as in the real cascade.