Physical Variables and Community Structure of the White Rocks Cliff System, Cumberland Gap National Historic Park

Walker, Gary; Ballinger, David; Matthes, Uta; Dobson, David

A vegetational survey of the White Rocks cliff system, located in the Cumberland Gap National Historical Park, was conducted from June to November of 2005, and May of 2006. Vascular plants, mosses, and lichens were surveyed on the cliff top, cliff face, and talus using 1m2 plots spaced evenly along 11 randomly located vertical transects. Physical characteristics including transect position on the cliff, slope, aspect, feature frequency and total feature area were measured for each plot. Biotic characteristics including vascular, bryophyte and lichen species percent cover per plot, and presence or absence of each species per microhabitat were recorded for each plot. Additionally, microhabitat type including ledges, cracks and pockets, and microhabitat size were recorded for each plot. Transect and plot locations with respective biotic and abiotic features were used to construct a GIS data base of the cliff system to assess the potential impacts of rock climbing. Biotic and abiotic factors were analyzed using multivariate statistics to determine physical factors which contribute to vegetational community structure of the cliff edge, cliff face and talus. Results indicate that slope, microfeature frequency, soil volume and aspect significantly impact vegetative community structure. The cliff face survey identified several rare and threatened plant species and several disjunct, glacial relict, and new habitat-type lichen species on the White Rocks cliff system. This assemblage is unique to the Cumberland Plateau, and perhaps, the Southern Appalachians, when compared to other cliff systems surveyed within this physiographic province. The boreal and arctic disjunct lichen species, one of which had not been previously reported from the Southern Appalachians, are further evidence that the Ridge and Valley physiographic region was very likely a migration corridor for biota during glacial advance and retreat. The unique assemblage of lichens and rare vascular plants found at this site warrant protection as this cliff system, as an escarpment for the Ridge and Valley, is serving as an interglacial refuge for these lichen species with more northerly main ranges. It is the recommendation of these investigators that the White Rocks cliff system be preserved from human impacts such as rock climbing and rappelling at the site and that the foot-traffic at the cliff edge be restricted. Further, given the unique nature of the biota found at the White Rocks site, other cliff systems and rock outcrops within the Cumberland Gap National Historical Park should likewise be protected until vegetational surveys at those sites can be conducted. It is likely that these other sites contain rare, restricted and disjuct species as well. This project was funded by the National Park Service in conjunction with the Southern Appalachian Cooperative Ecosystem Study Unit.

Physical Variables and Community Structure of the White Rocks Cliff System, Cumberland Gap National Historic Park

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