Are wolves saving Yellowstone’s aspen? A landscape-level test of a behaviorally mediated trophic cascade

Aspen stands across northern Yellowstone were sampled along a measured gradient of wolf predation risk, testing the specific prediction that aspen should recover where elk are most afraid to browse.

Studied in

Canis lupus, Cervus canadensis, Populus tremuloides

Sample size

aspen stands sampled across a gradient of wolf predation risk

Aspen were not recovering preferentially in high-risk areas. Browsing intensity did not track predation risk in the way the behaviourally mediated cascade predicts, and no landscape-wide aspen recovery was detected.

• Aspen only; willow and cottonwood show different and sometimes stronger responses.
• Predation risk is estimated from wolf use and terrain rather than measured directly on individual elk.
• A snapshot fifteen years in; slow vegetation responses could still be under way.

• Wolves

  Whether returning wolves reshaped Yellowstone’s vegetation and rivers is genuinely disputed

• Trophic cascades

  Removing a predator sometimes changes vegetation two links down the chain. It is demonstrated in small manipulable systems and much harder to establish in large ones — where it is asserted most often.