Aleutian Shield Fern

views updated

Aleutian Shield Fern

Polystichum aleuticum

Status	Endangered
Listed	February 17, 1988
Family	Dryopteridaceae (Wood fern)
Description	Low-growing, tufted fern.
Habitat	Rock outcrops on treeless, alpine talus slopes.
Threats	Extremely limited numbers, grazing animals.
Range	Alaska

Description

Aleutian shield fern, Polystichum aleuticum, perhaps the rarest fern in North America, is a lowgrowing, tufted fern, only about 6 in (15 cm) tall. It sprouts from a stout, dark brown rhizome covered with brown scales and numerous chestnut-brown stubs of former frond bases. The fronds are featherlike (simple pinnate) with spiny-toothed segments (pinnae) and distinctive chestnut-brown stalks (stipes). It is readily distinguishable from all other ferns in the Aleutian Islands and has no close relatives in either North America or northern Asia.

Habitat

The surviving population of Aleutian shield fern grows on a north-facing rock outcrop at an elevation of 1,936 ft (590 m). The alpine talus slopes of the site are treeless and covered with hardy, lowgrowing herbs and prostrate shrubs.

Distribution

Aleutian shield fern was first collected in 1932 from Atka Island. The two documented populations in the Aleutian Islands provide insufficient information to project an historic range for the species. It is possible that the fern is a relict species that was more prominent thousands of years ago when the Aleutians formed a land bridge between Asia and North America.

Today, the Aleutian shield fern is known from Atka and Adak Islands, two islands of the Andreanof island group in the Aleutians. Surveys so far have failed to relocate the Atka population first described in 1932.

In 1975, botanist D. K. Smith discovered a population of 15 plants on Mt. Reed, Adak Island, about 100 mi (160 km) west of Atka. When Smith revisited the site in 1987, he found only seven plants. The 1992 Recovery Plan, from the U.S. Fish and Wildlife Service (FWS), noted population numbers of approximately 112 individuals, all on Adak Island. According to a 1989 survey, the majority of the plants (98) are within a 6,400 ft (600 m) area on the northeast arm of the mountain, with the remaining 14 plants growing in a 400 ft (40 m) area to the north.

Threats

Although the fern has long been extremely rare, grazing reindeer and caribou have taken a toll of plant life in the area and have probably cropped back the fern as well. The alpine habitat is also very unstable, suffering from wind erosion and soil movements caused by freezing and thawing. These ground events can kill plants by pushing roots out of the soil.

Conservation and Recovery

The Mt. Reed site on Adak Island lies partially within the Adak Naval Air Station and partially within the Alaska Maritime National Wildlife Refuge. The Navy has cooperated fully with the FWS's efforts to locate and conserve the plant. Atka Island is owned in part by the Atxam Native Corporation; another section is administered as a national wildlife refuge.

The listing proposal suggested several immediate steps to save the fern. These include surveying for additional plants, fencing as protection from grazing animals, and cultivating a nursery stock for reintroduction efforts. Botanists have distributed a drawing and description to Naval personnel and other interested parties to aid the search for additional plants. Recovery of the Aleutian shield fern will depend much on finding new and viable populations.

Propagation efforts are at last paying off. In 1990, researchers at the University of Alaska in Fairbanks were successfully produced the first sporophyte (i.e., the spore-producing phase of a plant) of the Aleutian shield fern. Two previous attempts to propagate the plant in vitro were unsuccessful.

The 1992 Recovery Plan noted that, pending additional information, downlisting could be considered only with the discovery of significant new populations. Other downlisting criteria include the maintenance of a greenhouse population of at least 1,000 mature sporophytes, and the storage of genetic material in a germplasm repository. The extant population must also be protected from disturbance by humans and introduced ungulate. To achieve the downlisting goal, the recovery plan recommends the population protection and habitat management; biological research of the species; and searches for additional populations.

Recovery efforts in the summer of 1995 involved the collection of fronds from wild populations for cultivation by the New York Botanical Garden and the Royal Botanical Garden (Kew) Gardens in Kew, England. Spores were also supplied to the Cincinnati Zoo Plant Conservation Program, where they will be deposited into a permanent germplasm repository.

Reclassification of the species to Threatened status may be appropriate if significant new wild populations are discovered, but it is unlikely that this rare endemic could be delisted in the foreseeable future.