Background/Question/Methods Nova Scotia’s forested wetlands host rare and at-risk epiphytic lichens that are threatened by clearcut logging and grazing by non-native gastropods. We investigated how lichens, native and non-native slugs and their interaction respond to clearcut edge influence at local and landscape scales. We also aimed to estimate the relative contribution of native and non-native slugs to the grazing pressure on lichens. We surveyed lichen and slug communities and estimated grazing pressure on lichens in 13 mixed-wood forested wetland sites adjacent to recent clearcuts (2-5 yrs. old) across Nova Scotia. In each study site, we set up a transect with seven 5 × 50 m plots (0, 20, 40, 60, 80, 100, and 150 m) from the clearcut edge to the forest interior. In each plot, we set up one pitfall trap on the ground and three trees were selected for lichen surveys. Distance from the clearcut edge and landscape clearcut cover were respectively used to estimate clearcut edge influence at local and landscape scales. Linear mixed models were used to estimate the effect of explanatory variables on lichens, slugs and grazing pressure.
Results/Conclusions We recorded 44 lichen species and nine slug species - six non-native Arion species and three native species. The three non-native species (A. subfuscus, A. fuscus, A. hortensis) encompassed 91% of total individuals collected. Lichen species richness and cover decreased with increasing abundance of non-native slugs and landscape clearcut cover, respectively. The abundance of non-native slugs increased with increasing clearcut edge proximity, while the abundance of native slugs and grazing pressure on lichens did not respond to any of the explanatory variables. Our findings suggest that clearcut edge influence negatively affects lichen communities by benefiting lichenivorous non-native species at local scale as well as by habitat loss at the landscape scale. Although lichen species richness declined with increasing abundance of non-native slugs, grazing pressure did not respond to any of the explanatory variables suggesting that slugs are not the main grazers in the study system. Moreover, despite the absence of effect of non-native slugs and clearcut edge influence on native slugs, we highlight that the studied wetlands support impoverished slug communities heavily dominated by three non-native species. Such information will aid forest managers and conservationists in defining buffer zones to reduce the impact of clearcut edge influence on biodiversity.