Terrestrial Gastropod Grazing on Macrolichens in a Northern Broadleaf-Conifer Forest

Herbivory by terrestrial gastropods, particularly Anion spp. (a slug), can alter epiphytic lichen communities; however, little is known about this interaction in forests of North America. We used 3 lines of evidence to explore this interaction: field grazing assessments on lichen thalli, a 10-y re-measure of gastropod abundance, and gastropod feeding trials in a montane forest at Hubbard Brook Experimental Forest (HBEF) in northern New Hampshire. Grazing damage by terrestrial gastropods was widespread, though few sites had severe grazing. Grazing damage was significantly higher on flatter terrain and on broadleaf trees. Slug densities were significantly lower in 2016 than in earlier surveys (1997-2006) on 4 of 6 plots. In feeding trials, 2 common lichens, Hypogymnia physodes and Platismatia glauca, were grazed more heavily by both native and non-native slugs than other lichen species. However, the Succineidae (amber) snails preferred Lobaria pulmonaria, a lichen that has been declining at HBEF in the last decade. Overall, lichen communities in the HBEF were moderately impacted by terrestrial gastropod grazing, but potential effects of the non-native slugs at higher elevations and impacts on lichen health of widespread. moderate grazing deserve further study.