Cliff-Face Ecology and Plant Population Genetics
 Gary L. Walker
Professor and Graduate Program Director
Ph.D., University of Tennessee at Knoxville
My research interests are in two areas of plant ecology. Most of my laboratory-based research has been in the area of plant population genetics. The population genetics of rare, restricted and disjunct plant species in the southern Appalachians has been a field of investigation that has interested me for many years. These studies began with the examination of a glacial relict tree species, Thuja occidentalis, northern white cedar, which is found on cliff-faces in its southern disjunct range. These boreal disjunct populations are associated with many other species of Canadian wildflowers and shrubs at relatively low elevations in the southern Appalachians. Allozyme analyses of northern white cedar populations have revealed levels of genetic variation higher in the disjunct range than those observed in the main range in the boreal forests of Canada. These high levels of variation seem to have been accumulated and preserved over long periods of time through the use of alternative breeding systems, asexual and sexual, in these small, cliff-face populations. My lab has also investigated graduate thesis projects involving the genetic architecture of several other plant species, including disjunct ferns, the subspecies of bald and pond cypress, and a number of animal species, such as saw-whet owls, southern Appalachian brook trout, scorpions and hell-benders. My field-based research has been in the area of plant ecology including a series of four grants from the National Park Service for the Blue Ridge Parkway. Most of these grants have had management implications including vegetational surveys of backcountry areas susceptible to Gypsy Moth invasion, the construction of a high elevations wetlands atlas using GIS techniques, a genetic survey of endemic brook trout, and comparisons of various treatments for achieving arrested succession in viewshed clearcuts. Most recently, my original studies with cliff-face plant populations have led to graduate projects concerning the cliff-face ecology of plant communities. A recent graduate student's project on cliff-face communities in the Linville Gorge Wilderness Area was featured in Science. He described the community-level differences in cliff-face plant communities, compared to those in adjacent rock outcrops, demonstrated changes in species composition from cliff-face top to cliff-face bottom, and characterized the changes in species composition on climbed vs unclimbed cliff faces. He also discovered a new species of lichen in the course of his study. I am presently in collaboration with a cliff-face ecology research group at the University of Guelph in Ontario, Canada. We recently published papers in Nature and Journal of Biogeography on the ancient trees, including northern white cedars, on cliff-faces. This work has revealed that some of these trees reach ages in excess of 1000 years and that cliff-face habitats may act as refugia for many different groups of organisms.
Selected Publications
Hong-tu, W., and Walker, G.L. (1992) Age structure and regeneration characteristics of Pinus densiflora Forest in the Su Cheng Reserve of the Yuntai Mountains in Jiangsu Province." Acta Phytoecologica Et Geobotanica Sinica 16(1):52-63.
Shull, L., and Walker, G. L. (1998) Evaluating genetic diversity of brook trout along the Blue Ridge Parkway in preparation for species reintroduction. U.S. Department of the Interior, National Park Service, Blue Ridge Parkway, Asheville, North Carolina.
Walker, Gary L. (1999) Groundtruthing for construction of a high elevation wetlands atlas for the blue ridge parkway. U. S. Department of the Interior, National Park Service, Technical Report.
Larson, D. W., Matthes, U., Gerrath, J.A., Gerrath, J.M., Nekola, J.C., Walker, G.L., Porembski, S., Charlton, A., and Larson, N.W.K. (1999) Ancient stunted trees on cliffs. Nature 398:32-33.
Larson, D.W., Matthes, U., Gerrath, J.A., Larson, N.W.K., Gerrath, J.M., Nekola, J.C., Walker, G.L., Porembski, S., and Charlton, A. (2000) Evidence for the widespread occurrence of ancient forests on cliffs. Journal of Biogeography 27: 319-331.
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