Rock Gnome Lichen

Gymnoderma lineare

Description

Rock gnome lichen, Gymnoderma lineare, occurs in rather dense colonies of narrow straps or small scales, called squamules. The only similar lichens are the squamulose species of the genus Cladonia. Rock gnome lichen has terminal portions of the strap-like individual lobes that are blue-gray on the upper surface and generally shiny white on the lower surface; near the base they grade to black. In rock gnome lichen, the sparingly branched squamules are dark greenish mineral grey on the lower surface, becoming white to brownish toward the tips, tapering to the blackened base. The squamules are nearly parallel to the rock surface, but the tips curl away from the rock, approaching or reaching a perpendicular orientation to the rock surface. The fruiting bodies (apothecia) are borne at the tips of the squamules and are black. The apothecia are borne singly or in clusters, usually at the tips of the squamules but occasionally along the sides; these have been found from July through September. The apothecia are cylindrical in shape and radial in symmetry. The primary means of propagation of this lichen appears to be asexual, with colonies spreading by clones.

G. lineare is the only member of its genus occurring in North America; the other two species occur in the mountains of Japan and Eastern Asia, including the Himalayas.

Habitat

The rocks on which this lichen grows are of several types, including igneous, metamorphic, and metasedimentary rocks such as quartz diorite, garnet-rich biotite, muscovite and quartz schist, quartz phyllite, metagraywacke, metaconglomerate, and metarkoses containing feldspar and chlorite, amphibole, hornblende, and feldspar gneiss. The general area has warm and moderately wet summers, moderately cold and moderately dry winters, and a short freeze-free period. Annual rainfall at four occupied sites has ranged from 41 to 102 in (104.1 to 259.1 cm), with snowfall ranging from 4 to 101 in (10.1 to 256.5 cm). Average winter temperatures range from 5° to 48°F (-15° to 8.9°C), and average summer temperatures range from 49° to 73°F (9.4° to 22.8°C).

Rock gnome lichen is primarily limited to vertical rock faces where seepage water from forest soils above flows at very wet times. It appears that the species needs a moderate amount of light but that it cannot tolerate high-intensity solar radiation. It does well on moist, generally open, sites with northern exposures, but needs at least partial canopy coverage where the aspect is southern or western. It is almost always found growing with the moss Andreaea and/or Grimmia in these vertical intermittent seeps. This association makes it rather easy to search for, due to the distinctive reddish brown color of Andreaea that can be observed from a considerable distance. Most populations occur above 5,000 ft (1524 m) in elevation. Common associates of this species include the endangered Geum radiatum and Houstonia purpurea ssp. montana. The high-elevation coniferous forests adjacent to the rock outcrops and cliffs most often occupied by the species are dominated by red spruce (Picea rubens ) and a species of concern, Fraser fir (Abiesfraseri ), with northern hardwoods such as sugar maple (Acer saccharum ), yellow birch (Betula alleghaniensis ), mountain maple (A. spicata ), mountain ash (Sorbus americanus ), and beech (Fagus grandifolia ) mixed in.

Distribution

Rock gnome lichen is endemic to the southern Appalachian Mountains of North Carolina, South Carolina, Tennessee, and Georgia and occurs only in areas of high humidity, either at high elevations, where it is frequently bathed in fog, or in deep gorges at lower elevations. In Tennessee it is apparently restricted to the Great Smoky Mountains and Roan Mountain.

Only 35 populations of rock gnome lichen are currently known to exist. Five populations are known to have been extirpated. The remaining populations are in Mitchell (two populations), Jackson (five), Yancey (four), Swain (one), Transylvania (four), Buncombe (four), Avery (two), Ashe (two), Haywood (one), and Rutherford (one) Counties, North Carolina; Greenville County (one), South Carolina; Rabun County (one), Georgia; and Sevier (seven) and Carter (part of this one population is on the state line with Mitchell County, North Carolina) Counties, Tennessee.

Threats

Although some populations are declining and vanishing for reasons that are, in many cases, not clearly understood, there are several major threats to the remaining lichen populations. Five historically known populations of this species have been completely extirpated. The reasons for the disappearance of the species at most of these sites are undocumented; however, one is believed to have been destroyed by highway construction. Most of the formerly occupied sites are subjected to heavy recreational use by hikers, climbers, and sightseers. In addition, the coniferous forests, particularly those dominated by Fraser fir at the high-elevation sites, are being decimated by the balsam wooly adelgid, an exotic insect pest, and possibly by air pollution. Widespread mortality of mature fir due to the balsam wooly adelgid has resulted in locally drastic changes in microclimate, including desiccation and increased temperatures.

Numerous lichen species are known to be sensitive to air pollution. Documented declines of lichen species have been recorded in the forests of Europe and nearby large industrial cities around the world. Research indicates that rock gnome lichen colonies in the poorest health have a higher content of sulfur compounds than colonies which appeared to be healthy. Furthermore, the species appears to have specific environmental needs, such as a narrow pH range and sulfur deposits. Initial research indicates there is a high likelihood that current and previous air pollution levels, especially from sulfates, may be contributing to the decline of this species.

Only eight of the remaining 35 populations cover an area larger than 21.5 sq ft (2 sq m). Most are 10.8 sq ft (1 sq m) or less in size. It is unknown what constitutes a genetic individual in this species, and it is possible that each of these small colonies or patches consists of only a single clone. Over the past decade several of the currently extant populations have undergone significant declines, some within as little as one year. Although al but five of the remaining populations are in public ownership, many continue to be affected by collectors, recreational use, and environmental factors. Although no populations are known to have been lost as a result of logging operations, it is interesting to note that most of the remaining stream corridor populations occur in areas of old-growth forest.

Conservation and Recovery

In addition to the efforts taken to conserve habitat sites in the national forests, the U.S. Forest Service, the National Park Service, and the U. S. Fish and Wildlife Service have cooperatively funded investigations of the lichen's response to air pollution at different sites.

Contact

U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345
http://southeast.fws.gov/

References

U.S. Fish and Wildlife Service. 18 January 1995. "De-termination of Gymnoderma lineare (Rock Gnome Lichen) to be an Endangered Species." Federal Register 60 (11): 3557-3562.

U.S. Fish and Wildlife Service. 1997. "Recovery Plan for Rock Gnome Lichen (Gymnoderma lineare ) (Evans) Yoshimura and Sharp." Atlanta, Georgia. 30 pp.