A study published in Journal of Ecology in 2013 showed that reintroduction of wolves in Wisconsin produced a positive trophic cascade for plant species. The results are consistent with hypothesized trophic effects on understorey plant communities triggered by a keystone predator recovering from regional extinction. In addition, authors identified the response variables and spatial scales appropriate for detecting such differences in plant species composition. This study represents the first published evidence of a trophic cascade triggered by wolf recovery in the Great Lakes region.
Read the study from the link above.