Diellia falcata

No Common Name

Description

Diellia falcata is a terrestrial fern that grows from an underground stem (rhizome) 0.4-2 in (1-5.1 cm) long. The fronds are 8-40 in (20.3-101.3 cm) tall and have dark brown to pale tan stalks. There are 12-45 undivided leaflets (pinnae) on each side of the stem axis. The lower leaflets are rounded; farther up the frond they become larger and are sickle-shaped or triangular. The fruitdots or sori, which are the fern's spore-bearing bodies, appear as short lines on the underside of the leaflet margins. D. falcata hybridizes with D. unisora. It has been observed with fronds bearing sori year round. This species has also been known as Schizoloma falcata, Lindsaea falcata, and D. erecta var. falcata.

Habitat

D. falcata is a terrestrial fern that typically grows in deep shade or open understory in dryland forest at an elevation of 1,280-2,700 ft (390.1-823 m). Associated plants include aulu, lama, and alaa.

Distribution

D. falcata had historical occurrences on Oahu from Maxfini Gulch to Palehua Iki that spanned almost the entire length of the Waianae Mountains and from Kaipapau Valley to Aiea Gulch in the Koolau Mountains. This species remains in the Waianae Mountains on federal, state, and private land at locations ranging from Manini Gulch to Puu Hapapa, Makua Valley, and Makaha-Waianai Kai Ridge. The 22 known populations, found within an area of about 2 by 11 mi (3.2 by 17.7 km), contained an estimated 5,540-6,540 individuals in 1997. Fourteen populations each number between 40 and 2,000 individuals; however, the eight populations at Nanakuli-Lualualei Ridge, Makaleha Valley, Puu Kumakalii, Mohiakea Gulch, Pualii Gulch, Puu Kaiwi, Palikea Gulch, and Ekahanui Gulch each number fewer than ten individuals. Recent field observations indicate that this plant may be more locally common than previous records suggest.

Threats

The major threats to D. falcata are habitat degradation by feral goats, pigs, and cattle; competition from the alien plants Christmas berry, huehue haole, Koster's curse, molasses grass, strawberry guava, and Blechnum occidentale; and fire. The two-spotted leafhopper is also a potential threat.

Fire is a threat to D. falcata populations near the U. S. Army's Makua Military Reservation and Schofield Barracks. Within a 14-month period from 1989 to 1990, ten fires resulted from weapons practice on the reservation. In order to minimize damage from fires, the army constructed firebreaks between the target areas and the surrounding forest.

Conservation and Recovery

The army adopted a fire management plan that includes realigning targets and establishing firebreaks at Makua Military Reservation, which may aid in protecting D. falcata from the threat of fire. Additionally, the army protected individuals in Kahanahaiki Gulch from pigs with a fenced enclosure.

Fencing and removal of feral pigs in the Pahole drainage was completed by the Division of Forestry and Wildlife in July 1997. Weeding of strawberry guava, Christmas berry, and Koster's curse continues into the twenty-first century in the surrounding areas. Individuals of this plant in the Palawai Gulch are protected from hoofed mammals by a fenced enclosure that the Nature Conservancy of Hawaii constructed in 1998.

Specific efforts should be made, wherever feasible, to immediately fence, weed, and otherwise protect the eight populations (cited in the Distribution section above) that have only a few remaining individuals. A commitment should be developed for long-term stewardship and conservation of these areas once they have been enclosed.

Contacts

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

U. S. Fish and Wildlife Service
300 Ala Moana Blvd., Rm. 6307
P.O. Box 50167
Honolulu, Hawaii 96850

References

Cuddihy, L. W., and C. P. Stone. 1990.Alteration of Native Hawaiian Vegetation: Effects of Humans, Their Activities and Introductions. Cooperative National Park Resources Study Unit, University of Hawaii Press, Honolulu.

Culliney, J. L. 1988. Islands in a Far Sea: Nature and Man in Hawaii. Sierra Club Books, San Francisco.

Stone, C. P., and J. M. Scott, eds. 1985. Hawaii's Terrestrial Ecosystems: Preservation and Management. Cooperative National Park Resources Study Unit, University of Hawaii Press, Honolulu.

Wagner, W. L., D. R. Herbst, and S. H. Sohmer. 1990. Manual of the Flowering Plants of Hawaii. University of Hawaii Press and Bishop Museum Press, Honolulu.