Factors influencing the distributions of two endangered lichens in Nova Scotia, Canada

Abstract

The lichens Erioderma pedicellatum (Hue) P.M. Jørg. and Erioderma mollissimum (G. Sampaio) Du Rietz are endangered species in Canada. Both species are obligate epiphytes found in forested wetlands near the Atlantic Coast. They are thought to be primarily threatened by logging and acid pollution, but the influence of these factors has not been examined at large-extents or relative to other habitat features. Critical habitat for protection has remained difficult to define beyond observed occurrences, because of the low accuracy of existing habitat models. To facilitate improved recovery planning and understanding of their ecology in the province of Nova Scotia, we created high-resolution distribution models for both species, incorporating elements of climate, forest composition, hydrology, acid pollution, and anthropogenic influence using the MaxEnt algorithm and a backwards stepwise selection process. The most important predictors were related to rainfall or an oceanic moderation of thermal optima. Depth to water table and the presence of suitable forest composition were also included, as was distance from roads for E. pedicellatum. The putative threats, acid pollution and silvicultural treatment, were not important and therefore excluded from models. Although both species have highly specific habitat requirements, E. pedicellatum appears to be more sensitive to human activities.