Influence of tree composition upon epiphytic macrolichens and bryophytes in old forests of Acadia National Park, Maine

Abstract

To better understand associations between epiphytes and old forests, lichens and bryophytes that grow on tree bark were quantified in relatively undisturbed stands of Acadia National Park (ACAD). Four plots were dominated by hardwoods and eight by spruce. To obtain data from upper boles, we climbed four maple trees per plot (eight plots) and four spruce trees per plot (four of the eight plots). We found 85 macrolichen species and 62 bryophyte taxa (60 species, two varieties). Eight macrolichens are newly documented from ACAD. At the state-level, Acadia NP plots were notably species-rich including 15 species not found in 50 other plots in Maine surveyed using the USDA FS Forest Inventory and Analysis Program (FIA) lichen protocol. At the plot-level, the epiphyte flora of spruce-dominated plots differed significantly from that of hardwood-dominated plots, although species richness was comparable. At the tree-level, the epiphyte flora of maple trees was significantly influenced by tree composition within the surrounding stand. Mixed composition of tree species in the stand correlated with higher epiphyte diversity. Cyanolichens were more likely to occur on large hardwood trees in hardwood-dominated plots. Fruticose lichen occurrence was influenced by interactions between tree size, plot and tree species. Using comprehensive tree tally searches in combination with climbing of four maples per plot, we found that we missed an average of 15% of the macrolichen flora in the search area using only the two-hour timed survey required by the FIA protocol. This study serves as an important baseline for detecting future changes in the epiphyte flora of ACAD and further highlights the importance of mature mixed stands to epiphyte conservation in northern forests of eastern North America.