Asplenium fragile var. insulare

No Common Name

Description

Asplenium fragile var. insulare is a fern of the spleenwort family (Aspleniaceae) with a short suberect stem. The leaf stalks are 2-6 in (5-15 cm) long. The main axis of the frond is dull gray or brown, with two greenish ridges. The long and narrow fronds are thin-textured, bright green, 9-16 in (23-41 cm) long, 0.8 in (2 cm) wide above the middle, and pinnate with 20-30 pinnae or leaflets on each side. The pinnae are rhomboidal, 0.3 in (7 mm) wide, and notched into two to five blunt lobes on the side towards the tip of the frond. The sori (spore-producing bodies) are close to the main vein of the pinna, with one to two on the lower side and two to four on the upper side. The Hawaiian fern species most similar to A. fragile var. insulare is A. macraei. The two can be distinguished by a number of characteristics, including the size and shape of the pinnae and the number of sori per pinna.

The Hawaiian plants now referred to as A. fragile var. insulare were considered by William Hille-brand in 1888 to be conspecific with A. fragile from Central and South America. The Hawaiian plants were subsequently treated as a distinct endemic species, A. rhomboideum. However, that species is now considered native to the New World and not present in Hawaii. The name A. fragile var. insulare was published in 1947, as the Hawaiian plants were considered distinct at the varietal level from the extra-Hawaiian plants. Reproductive cycles, longevity, specific environmental requirements, and limiting factors are unknown.

Habitat

This fern is found on the island of Hawaii in Metrosideros (ohia) dry montane forest, Dodonaea (aalii) dry montane shrubland, Myoporum/Sophora (naio/mamane) dry montane forest, Ohia/Acacia (koa) forest as well as subalpine dry forest and shrubland. A. fragile var. insulare grows almost exclusively in lava tubes, pits, deep cracks, and lava tree molds, with at least a moderate soil or ash accumulation, associated with mosses and liverworts. This fern has been found growing infrequently on the interface between younger lava flows and much older pahoehoe lava or ash deposits. The population recently found on Maui is growing in montane wet 'ohi'a forest in a rocky gulch with other species of ferns. Although this plant is found in habitats with three different moisture regimes, the micro-habitat for A. fragile var. insulare is fairly consistent. The fern generally occurs in areas that are moist and dark; its relatively specialized habitat requirements may account for its apparently patchy distribution.

Distribution

A. fragile var. insulare was known historically from East Maui, where it was recorded from the north slope of Haleakala and Kanahau Hill. On the island of Hawaii, this fern was found historically below Kalaieha, Laumaia, Keanakolu, and Umikoa on Mauna Kea; Puuwaawaa on Hualalai; west of Keawewai, above Kipuka Ahiu on Mauna Loa; and near Hilo.

This species has eight extant populations on the island of Hawaii at elevations between 5,250 and 7,800 ft (1,600 and 2,400 m); a ninth occurrence was recently reported from East Maui, in Hanawi Natural Area Reserve. The current populations on Hawaii are located at Puu Huluhulu, Pohakuloa Training Area (nine subpopulations), Kulani Correctional Facility, Keauhou, the Mauna Loa Strip Road in Hawaii Volcanoes National Park, Kapapala Forest Reserve, Kau Forest Reserve, and the summit area of Hualalai. The largest population of this fern occurs at Pohakuloa Training Area; the latest monitoring in 1995 put total numbers at about 200 plants, a slight reduction in numbers from 1992. The nine known populations on Federal, state, and private land totaled approximately 278 plants in 1995.

Threats

The primary threats to A. fragile var. insulare are feral sheep and goats. Large numbers of feral goats are present on the island of Hawaii within Pohakuloa Training Area in the saddle between Mauna Loa and Mauna Kea, where they threaten this fern through both direct browsing on the plants and habitat degradation. Predation by feral goats and sheep has been reported for A. fragile var. insulare at Pohakuloa Training Area. Because no colonies have been decimated by the animals, it appears that goats do not seek out this fern. However, further predation may occur if their preferred forage is not available. Predation by feral goats is a potential threat to the other two sizable known populations of this fern at Keauhou and Kulani because goats can feed on the ferns at the entrance to lava tubes. At the Hawaii Volcanoes National Park fences are being used to protect the Mauna Loa strip population from eradication by the feral goats.

At least one population at Pohakuloa Training Area is threatened by military operations and fires resulting from these operations; construction needed for military activities could also affect populations at this installation. Another threat to A. fragile var. insulare at Pohakuloa Training Area is the alien plant fountain grass.

Populations of A. fragile var. insulare are threatened by the bulldozing of jeep roads and filling in of lava tubes. Also of concern is the small number of existing individuals, a situation that makes stochastic extinction through natural events a very real possibility. Even random fluctuations in numbers of individuals or a small increase in plant mortality could extirpate this species.

Conservation and Recovery

The Army has prepared a Preliminary Endangered Species Management Plan for Pohakuloa Training Area. The Army is also presently consulting with the U.S. Fish and Wildlife Service (FWS) under section 7 of the Endangered Species Act, and negotiations are underway to control threats and promote the recovery of endangered species at Pohakuloa Training Area. The FWS has a cooperative agreement for the management of Kilauea and Kulani forests with Kamehameha Schools/Bishop Estate, Hawaii Department of Land and Natural Resources, Hawaii Department of Public Safety/Corrections Division, and the National Park Service. One portion of Kulani Forest with a population ofA. fragile var. insulare has been fenced and the ungulates removed.

The most important recovery action for this fern is to protect high elevation lava tubes, a process that will need to include removal of hoofed mammals. The areas that are most important for protection include Pohakuloa Training Area, Keahou and Kulani Forests and portions of Kapapaia and Kan Forest Reserves. A portion of Kapapaia and Kan Forest Reserves important for protection of A. fragile var. insulare and other native plants has been proposed but not yet officially recommended as a potential Natural Area Reserve (Waihaka Natural Area Reserve). The establishment of such a preserve at Waihaka and protection for A. fragile var. insulare habitat are much-needed recovery actions for this species.

The Army should implement actions proposed in their Preliminary Endangered Species Management Plan for Pohakuloa Training Area. These actions include controlling feral animals, minimizing the impact of training activities, monitoring of known populations, and controlling fires and fountain grass.

Surveys to locate and map additional populations are also important to the recovery of this fern. For example, many areas at Pohakuloa Training Area have not been surveyed for biological resources, so the current level of survey coverage should be considered incomplete. A. fragile var. insulare has a very scattered distribution, and surveys will help determine the best areas for habitat protection. Optimal survey areas can be determined by considering the age of the substrate and the vegetation type.

Contact

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Building
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
http://pacific.fws.gov/

Reference

U. S. Fish and Wildlife Service. 10 April 1998. "Recovery Plan for Four Species of Hawaiian Ferns."U. S. Fish and Wildlife Service. Portland, Oregon.