Species-Area Relationships of Cliff System Vegetational Communities in Cumberland Gap National Historic Park

Harkey, Justin; Walker, Gary

Within the last three decades, cliff ecosystems have received increasing attention from ecologists. They are composed of distinct plant and lichen communities due to their unique physical conditions and reduced anthropogenic disturbance. Recent developments in cliff-face ecology focus mainly on the patterns and processes that determine plant community structure on cliffs. As recreational activities continue to pose a threat, understanding this ecosystem for preservation and management purposes has become a priority. A vegetational survey of vascular plants, bryophytes, and lichens was conducted on eleven discrete cliff systems in Cumberland Gap National Historical Park (CUGA) during the summer of 2011 and 2012. Slope, aspect, and percent cover was measured along 25 individual transects among the cliff systems. A systematic protocol was used to sample each site, recording data from a 1 m2 plot, at three meter increments. Species-area curves were constructed using PC-ORD and JMP. Multiresponse Permutation Procedures (MRPP) and Non-metric Multidimensional Scaling (NMS) were used to determine differences in community and diversity aspects. A total of 231 species were collected and identified, including 111 vascular plants, 37 bryophytes, and 83 lichens. Non-nested and nested species-area curves indicate that the sampling protocol was efficient at capturing diversity, and that larger cliff systems had higher levels of diversity. The steep slope of a generated log-transformed species-area curve, and the relatively low diversity compared to southern Appalachian forests, supports the hypothesis that cliff systems are similar to insular habitats. Multivariate analyses revealed that vascular plant, bryophyte, and lichen communities varied extensively across transects and cliff systems, largely unrelated to slope, aspect, or area. Based on these observations, it is imperative that each cliff site, and possibly each transect, be carefully surveyed before permitting recreational climbing. Several listed species were found during this survey, and all were established on smaller cliff systems. If the Park were most concerned with the protection of threatened, endangered, or disjunct species, it would be wise to preserve several small cliff systems, as opposed to a larger, more speciose cliff system.