Risk assessment and conservation strategies for rare lichen species and communities threatened by sea-level rise in the Mid-Atlantic Coastal Plain

Abstract

The Mid-Atlantic Coastal Plain (MACP) is an ecoregion with high biodiversity that is under imminent threat from sea level rise and habitat loss. Previous studies have shown i) the area to be high in lichen biodiversity, including endemic species, ii) the most lichen species-rich sites are the most imperiled by sea-level rise, and iii) common, widespread lichens have lost significant suitable habitat and are projected to lose more due to sea-level rise. Despite this, the spatial distributions of rare species and the compositional dynamics of lichen communities has not previously been examined. Here, we evaluate the community composition of 599 lichen species in 215 sites across the MACP. We tested whether community similarity is correlated with spatial proximity or environmental conditions. We found that sites with similar environmental characteristics had similar species composition, after controlling for geographic distance. Inland swamps had the highest per-site average number of unique species (1.3) and the two coastal ecosystems, maritime forests and pocosin (a unique form of peatland vegetation), each had an average of nearly one unique species per site. Across the entire MACP, 42% of species were found at five or fewer sites and these were mostly at sites under high risk of being affected by sea level rise. While habitats and species throughout the MACP have been projected to be negatively affected by sea level rise, our results suggest that rare lichens face particularly acute threats. Lack of suitable habitat inland at higher elevations may necessitate intensive mitigation, including facilitated transplants of both lichens and their host trees.