Restoration of Buck Creek Serpentine Barrens
Tusquitee Ranger District, Nantahala National Forest
A physiognomic patchwork of forest, dense grass patches and partially open woodland occurs across a serpentine site surrounding Buck Creek in Clay County, North Carolina on the Nantahala National Forest. The dominant rock types, serpentinized dunite and olivine, influence the striking vegetation present on this site. Soil depth is variable, ranging from zero to 60 cm, although rock outcrops represent between 5 and 10% of the local landscape. Soil characteristics reveal higher base saturation, cation exchange capacity, pH, and magnesium relative to surrounding sites in the Nantahala Mountains. The serpentine plant communities occupy both east and west-facing slopes extending over 300 acres from 3,400 feet elevation along Buck Creek to over 4,000 feet elevation atop Corundum Knob.
The hierarchical United States National Vegetation Classification of the southeastern United States classifies the community association type as a "Pitch Pine - White Oak/ Prairie Dropseed - Big Bluestem Woodland" or "Southern Blue Ridge Ultramafic Outcrop Barren". This community is believed to be unique to the Buck Creek area. Within the woodland, the forest canopy varies from 20-60% cover depending on the intensity and frequency of recent prescribed burns. The woodland is dominated in the tree canopy by older stunted white oak (Quercus alba) and smaller denser pitch pine (Pinus rigida) stems. Eastern hemlock (Tsuga canadensis), sassafras (Sassafras albidum), red maple (Acer rubrum), sourwood (Oxydendrum arboreum), and smooth serviceberry (Amelanchier laevis) occur within the canopy and subcanopy. Shrub cover is meager, typically occurring in clumps and providing no more than 10% cover. Diagnostic shrub species include swamp azalea (Rhododendron viscosum), ninebark (Physocarpus opulifolius), northern wild raisin (Viburnum cassinoides), mountain laurel (Kalmia latifolia), northern maleberry (Lyonia ligustrina var. ligustrina), deerberry (Vaccinium stamineum), and smooth high bush blueberry (V. corymbosum).
The grass dominance within the herb stratum is reminiscent of prairie vegetation and dominated by big bluestem (Andropogon gerardii), little bluestem (Schizachyrium scoparium var. scoparium), and prairie dropseed are the most important grasses. Characteristic forb species include small-leaved meadow rue (Thalictrum macrostylum), Indian paintbrush (Castilleja coccinea), Appalachian phlox (Phlox latifolia), cowbane (Oxypolis rigidior), Canadian burnet (Sanguisorba canadensis), gaywings (Polygala pauciflolia), ebony spleenwort (Asplenium platyneuron), grey goldenrod (Solidago nemoralis), wavy-leaved aster (Symphyotrichum undulatum), Rhiannon’s aster and Appalachian clasping aster (S. phlogifolium). Two of the striking forbs, currently characterized as Appalachian little brown jug (Hexastylis arifolia var. ruthii) and prairie ragwort (Packera plattensis) may represent new endemics if additional taxonomic work is completed (A.S. Weakley, University of North Carolina Herbarium curator, personal communication).
A striking contrast within the herb layer is the juxtaposition of both mesophytic and xerophytic species. It is not unusual to observe Canadian burnet and cowbane emerging from a grassy thicket of prairie dropseed and little bluestem. Mansberg noted a perched water table while surveying the site and suggested that there is a complex soil moisture gradient within the serpentine site (Mansberg and Wentworth 1984). Minerals predominant in ultramafic rocks chemically weather to clays, and the soils at Buck Creek have a substantial clay component, providing a perched water table and abundant seepage after rains, but drying to highly xeric conditions during droughts.
In addition to the presence of the unusual plant community (G1 rank), the presence of rare species adds to the conservation importance of the Buck Creek Serpentine Barren. Twenty-two state-listed rare plant species and four state-listed butterfly species occur within the site. Most of these species are primarily wide-ranging and globally secure (G4 or G5 rank), yet rare in NC; a few grasses are restricted to only this site within the state. Although serpentine is well known for its tendency to generate locally endemic species relatively few endemics have been described from the serpentine areas in eastern North America. Within the Buck Creek site, one endemic species, Rhiannon’s aster (Symphyotrichum rhiannon), was recently described in 2004.
In 1995, the U.S. Forest Service initiated active conservation management of the site, using prescribed fire as the primary tool. At the time, there was no evidence of a burn at the Buck Creek site for at least 50 years. The scattered patches of open grassland within the forested matrix indicated periodic fire to restore and maintain this unique community. The natural fire frequency for the community type was not known when burning was initiated in 1995. The North Carolina Vegetation Survey established eight permanent plots in the burn areas. These plots document current vegetation and provide a baseline to detect change. Forest Service personnel or a University of North Carolina student resampled selected plots in 1999 and 2007.
The initial burns were successful in stimulating flowering of previously sparsely flowering species, such as the rare grass, prairie dropseed (Sporobolus heterolepis). However, the burn intensity was insufficient to appreciably decrease woody vegetation and create large enough dispersed openings. In 2000, mechanical canopy thinning and shrub slashing was completed prior to additional burns. Three burning blocks, varying in size from 50 to 230 acres, were delineated across the potential restoration area to provide annually refugia sites for the diverse lepidopteron flora. Eight burns have been conducted across the three areas from 1995 to 2007. During that time, each of the burning blocks has burned once. One area has burned three times, while a portion of another area has burned four times in the last 13 years.
Woody species have been significantly reduced because of the burns (Marx 2007). The six rare grasses, prairie dropseed, slender wheatgrass (Elymus trachycaulus ssp. trachycaulus), tufted hairgrass (Deschampsia cespitosa ssp. glauca), drooping bluegrass (Poa saultensis), Porters reed grass (Calamagrostis porteri ssp. porteri), and spiked muhly (Muhlenbergia glomerata) are more evident across the more frequently burned areas. Both prairie dropseed and Porter’s reed grass have strikingly increased. A review of the initial plot data shows that all the rare dicot herbs prefer conditions that are more open. These conditions occur almost exclusively within plots with less than 50% tree cover and primarily in plots with less than 40% canopy cover. All are less abundant than the rare grasses; cover estimates in plots typically have not exceeded 2% cover. As a result, it is more difficult to detect change in abundance because of the active management. However, most have increased in abundance; some appear stable, while one, fringed gentian (Gentianopsis crinata), is less evident.
- North Carolina Vegetation Survey
Mansberg, L., and T.R. Wentworth. 1984. Vegetation and soils of a serpentine barren in western North Carolina. Bull. Torrey Bot. Club. 111:273-286
Marx, Elizabeth. 2007. Vegetation Dynamics of the Buck Creek Serpentine Barrens, Clay County, North Carolina. A thesis submitted to the faculty of the University of North Carolina at Chapel Hill in partial fulfillment of the requirements for the degree of Bachelor of Science in Biology with honors. Chapel Hill, North Carolina. 46 pp.