When wolves aren't enough: revisiting trophic cascades in northern Wisconsin

Elimination of top predators has allowed large herbivores to flourish in many terrestrial ecosystems, transforming food webs and ecosystem functions. Restoration of large predator communities is hoped to reverse negative effects of this trophic downgrading, but evidence for such effects is elusive. Wolves were extirpated in northern Wisconsin but returned via natural dispersal in the 1970s. We use spatially explicit information about wolf range expansion and plant community data collected in the 1950s and again in the early 2000s to assess whether wolves initiated a trophic cascade. We evaluated the hypothesis that the return of wolves benefits native plant species by protecting them from excessive deer browse. Surprisingly, understory plant diversity, richness, and frequency decreased more in areas with longer wolf presence, providing no evidence that wolves have the ability to protect forest understory vegetation. Instead, the data suggest a bottom–up process: deer occupy areas where their preferred food plants are abundant, and wolves follow deer. Wolves do not appear to have the often anticipated ability to down‐regulate large deer populations or their browsing pressure to function as biodiversity guardians.