Cliffs support lichen communities unique from nearby forests

Abstract

Cliffs support rare, endemic, and glacial relict vegetation that may differ from vegetation in surrounding forests. Yet, cliffs are difficult to sample, and rock-dwelling lichens can be challenging to identify; therefore, cliff lichens are often excluded from biodiversity studies. This omission creates fundamental gaps in our understanding of cliff lichens that lead to underestimation of overall community diversity. This study addresses one such gap by asking a basic question: do lichen communities on cliffs differ from rock-dwelling lichen communities in forests? To answer this question, we compared lichen communities from three cliffs in the Linville Gorge (North Carolina, USA; 369 m² of cliff face surveyed) to rock and soil-dwelling lichen communities in forested plots across the same region (Southern Appalachian Mountains, USA, Alabama to North Carolina; 198 1-hectare forested plots). Forest plots were further divided into three groups based on elevation, proximity to Linville Gorge cliffs, and location within the state of North Carolina. A total of 225 rock or soil-dwelling lichen species were found in forest plots throughout the study area, while 104 species were found on cliffs. Two rare cliff-specialist species, Canoparmelia alabamensis, and Chrysothrix susquehannensis, were locally abundant on the studied cliffs but absent from surrounding forests. Our results show that cliffs support 20% of regional rock-dwelling lichen diversity, and that these cliff communities are distinct from those in forests. The high diversity, occurrence of unique species, and presence of rare lichens on cliffs indicate that cliff lichens should be included in biodiversity inventories and stewardship plans. To support this inclusion, we provide the first checklist for the lichens of Linville Gorge. Checklists like this one, including both cliff and non-cliff lichens, provide data on regional diversity and rarity that inform lichen conservation and rock climbing management.