Spreading Avens

Geum radiatum

Description

Spreading avens is a perennial in the rose family that grows to a height of 8-20 in (20.3-50.8 cm). It has a basal rosette of leaves that arise from a horizontal rhizome. The leaves have a large terminal lobe and small laterals. From June through September it produces a cluster of bright yellow, five-petaled, radial flowers. From August through October it produces hemispheric fruits composed of hairy seeds. This species is distinguished from other species of southeastern Geum by its large, yellow flowers and leaf shape.

Habitat

Spreading avens grows in pioneer perennial herb communities at high-elevation rocky sites, with aspects ranging from west-southwest through north-northeast, where it is exposed to direct sunlight for at least part of the day. Populations occur at altitudes ranging from 4,500 to 6,100 ft (1,372-1,859 m). Occupied sites at higher elevations are surrounded by spruce-fir or by northern hardwoods containing scattered spruce. The Ashe County, North Carolina, sites are surrounded by high-elevation red oak forest. Other sites are surrounded by heath and/or grassy balds, with some adjacent to balds above and northern hardwood forest below.

The soils on which spreading avens grows are generally shallow and acidic, uniform, dark brown, coarse-loamy, and without distinct horizons. The soil usually collects in the cracks and crevices of the underlying rock, where it varies in depth from 0.8-14.2 in (2-36 cm).

Annual rainfall at four occupied sites has ranged from 41-102 in (104.1-259.1 cm), with snowfall ranging from 4-101 in (10.1-256.5 cm). Average winter temperatures range from 5 to 48°F (-15 to 8.9°C), and average summer temperatures range from 48 to 73°F (8.9 to 22.8°C).

The terrain of the occupied sites is generally uniform and moderately to well drained. Soils are intermittently saturated by rain, melting snow, high-elevation fogs, and downslope drainage. Consistent moisture may be one of the most important habitat requirements of this species.

Associated species include sand myrtle, minnie-bush, Catawba rhododendron, asters, sedges, goldenrod, alumroot, mountain saxifrage, and various grasses. On some sites it occurs along with Heller's blazing star, which is listed as threatened. It also sometimes occurs with Roan Mountain bluet, which is listed as Endangered. Surrounding coniferous forest is dominated by red spruce and Fraser fir, a candidate for federal listing.

Distribution

The species was described in 1803 from specimens collected in North Carolina. Sixteen populations have been reported in North Carolina and Tennessee, five of which no longer exist.

Eleven populations of spreading avens survive, mostly in North Carolina. Three are located in Ashe County, North Carolina, and one each is found in Avery, Buncombe, Transylvania, Watauga, and Yancey Counties, North Carolina, and Sevier County, Tennessee. The other two populations are on the Mitchell County, North Carolina/Carter County, Tennessee, line and the Avery/Watauga County line in North Carolina.

Four of these populations are on federal land managed by the Forest Service and Park Service, and one is on North Carolina state park land. The remaining six populations are on privately owned land.

Most populations consist of a small number of plants in a very limited area. Seven of the remaining sites consist of fewer than 50 plants, with three of these having fewer than 10 plants. One site on Forest Service land supports 73% of the known species population.

Threats

The main threats to spreading avens are habitat disturbance by hikers and recreational and residential development. Five of the remaining populations are on public land that is heavily used by hikers, rock climbers, and sightseers. Of the six privately owned sites, one has been developed as a commercial recreational facility and another is currently being developed as a ski resort. The area where the other four privately owned sites are located is being rapidly developed as a tourist center. The construction of recreational facilities such as roads, trails, parking lots, and buildings has probably destroyed local populations and, if the presence of spreading avens is not taken into account in planning, will no doubt destroy more.

Spreading avens faces additional long-term threats from natural processes. As an early successional plant, it is susceptible to invasion by shrubs and trees, which could shade out remaining populations. In addition, the surrounding high elevation forest is suffering a drastic decline caused by air pollution and the invasion of an exotic insect, the balsam woolly aphid. The loss of these forests might allow the habitat to become too arid to support healthy, reproducing spreading avens populations.

In recent years, dramatic declines have occurred in spruce-fir forests adjacent to spreading avens habitat. This is due, at least in part, to airborne pollution and an exotic insect, the balsam woolly adelgid. Impacts of the forest decline on this rare herb cannot be accurately assessed at this time. Even though the species is a mid-successional pioneer requiring exposure to full sunlight, the complete removal of the canopy at these high-elevation sites may result in excessive desiccation of the moist habitat occupied by the species. This theory would seem to be supported by the fact that fruiting stems have often been observed to wither before seed can be set in populations on naturally drier sites. However, this phenomenon has been observed at shaded sites as well. Another possibility for the premature senescence of fruiting stems is inferior or unviable embryos, due to high proportion of self-fertilization, or disease of a fungal or viral origin. This latter possibility has potentially serious implications for transplantation efforts between populations. In addition, at sites where all the mature trees are now dead, aggressive invading species such as Rubus spp. are starting to dominate sites where they were not formerly present, choking out other vegetation. The rhizomes of spreading avens are believed to be capable of surviving for decades, but continued failure in seed production or clonal spread poses a definite threat to long-term survival and recovery of the species. Although Geum radiatum has been found to be resistant to ozone in experimental treatments, the direct effects of acid precipitation on this species are unknown. As stated above, existing conditions at most of the occupied sites may be indicative of low genetic variability within populations, which makes it more important to maintain as much habitat and as many of the remaining colonies as possible.

At several sites, significant declines have been noted in the past decade, in the absence of overt habitat changes. Possible explanations include inbreeding depression, desiccation due to successive drought years in the mid-1980s, or disease. Systematic research is needed to illuminate the problems and their remedies. Since many sites on public land have been severely damaged by visitors, they may provide distorted views of the habitat requirements for spreading avens. High priority should be given to the protection and study of the few remaining pristine sites.

Conservation and Recovery

In North Carolina, where several of the remaining 11 populations survive, the State Natural Heritage Program, the Nature Conservancy, and the U.S. Fish and Wildlife Service are working with landowners to ensure the protection and management of spreading avens sites. The Nature Conservancy, which owns part of one site in North Carolina, is monitoring and protecting that population by limiting the number of visitors. The U.S. Forest Service is attempting to protect populations in the Pisgah and Cherokee National Forests by avoiding occupied sites when constructing new recreational facilities and by erecting barriers to minimize trampling on heavily used sites. Although several techniques have been tried, this latter problem is a difficult one to effectively control without compromising the aesthetics of some of the more scenic public recreation areas on the forests.

Restoration efforts are underway at two severely diminished populations on National Park Service lands in the Great Smoky Mountains National Park in Tennessee and the Craggy Mountains on the Blue Ridge Parkway in North Carolina. Preliminary genetic analyses and initial transplanting experiments look promising.

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

Massey, J., P. Whitson, and T. Atkinson. 1980. "Endangered and Threatened Plant Survey of Twelve Species in the Eastern Part of Region Four." U.S. Fish and Wildlife Service.

U.S. Fish and Wildlife Service. 28 April 1993. "Spreading Avens Recovery Plan." U.S. Fish and Wildlife Service, Atlanta, 32 pp.