High densities of white-tailed deer throughout eastern North America have been implicated in changing forest community structure and composition. We hypothesized that the recovery of an apex predator, the gray wolf (Canis lupus), in a region affected by deer overabundance could reduce browsing impacts on vegetation via a trophic cascade. We tested this hypothesis by surveying an herbaceous forest understory species sensitive to deer browsing (Polygonatum pubescens) in areas of northern Wisconsin where wolves have re-colonized over the past 20 years. We used a natural experimental framework, surveying populations in areas that lack wolves (nonwolf, n = 3 sites), areas where wolves have been established for 3-5 years (3 sites), and areas where wolves have been established for 9-11 years (3 sites). Each site consisted of five 10m x 10m plots. We compared these populations to plants growing in deer exclosures continuously maintained for 15 years. The number of leaves per plant and percent flowering was recorded for 1,579 plants.

Results/Conclusions

The average size (number of leaves per plant) of individual plants increased 6% between nonwolf and 3-5 year wolf areas, and 14% between 3-5 and 9-11 year wolf areas. Plants in the deer exclosures were 66% larger than plants in the 9-11 year wolf areas. An analysis of Gini coefficients revealed that there were no shifts in population size structure inequity in response to wolf recolonization. The proportion of flowering plants was two times greater in 9-11 year wolf areas than nonwolf areas. Our results indicate that individual Polygonatum pubescens plants are larger and more likely to flower in areas with wolves, however, there appears to be a time lag between wolf recolonization and plant performance. This study provides evidence of a wolf-initiated, species-specific trophic cascade.