Na'ena'e

Dubautia herbstobatae

Description

Dubautia herbstobatae (Na'ena'e) is a small, spreading shrub of the aster family that grows 20 in (51 cm) high. The shiny, leathery leaves are alternate, narrowly elliptic, and 0.8-2.2 in (2-5.5 cm) long. Each flower cluster contains five to 15 flower heads that are composed of four to 20 yellowish-orange, tubular florets. The fruit is a dry seed, covered with silky hairs. It is possible that D. herbstobatae can not self-pollinate. Flowering usually occurs in May and June. Pollination is almost certainly achieved by insect activity, and fruit dispersal is probably quite localized. The species has also been known by the name Railliardia herbstobatae.

Habitat

D. herbstobatae occurs on rock outcrops of north-facing ridges in dry shrubland at an elevation of 1,900-3,000 ft (579.1-914.4 m). Associated plant species include ohia (Metrosideros polymorpha ) and kawelu (Eragrostis variabilis ).

Distribution

D. herbstobatae was discovered in 1971 in the northern Waianae Mountains in western Oahu. This species is now known to be extant in the northern Waianae Mountains at four locations on federal, state, and city/county lands, scattered over an area about 1 by 3 mi (1.5 by 5 km). The Makua-Keaau Ridge, Waianae Kai Ridge, Kamalleunu Ridge, and Keaau Valley occurrences had respective 1997 populations of about 500, four, one, and 20 plants. These 525 individuals constitute the only known examples of D. herbstobatae.

Threats

The main threats to D. herbstobatae, as for almost all rare species in the Waianae Mountains, are habitat degradation by feral pigs and goats, and competition from invasive, alien plant species. The species faces additional threats associated with low numbers and a limited distribution, such as fire and trampling by hikers.

Several invasive plant species threaten D. herb-stobatae. Christmasberry (Schinus terebinthifolia ), an aggressive tree introduced to Hawaii before 1911, forms dense thickets and may also release chemicals that inhibit the growth of other species. Koa hoale (Leucana leucocephala ), an alien tree that colonizes disturbed lowland areas, is also a threat. Molasses grass (Melinis minutiflora ), which ranges from the dry lowlands to the lower wet forests of the leeward ridges, grows in dense mats that smother native vegetation. It is also fire adapted and provides a fuel for spreading wildfires.

Fire is particularly a threat to D. herbstobatae 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.

The small, isolated population of this species leaves it especially vulnerable to extinction from an unpredictable human or natural event.

Conservation and Recovery

The army is constructing a fence along Ohikilolo Ridge and the eastern rim of Makua Valley to provide a barrier against goats and pigs. This fence should help to prevent further goat ingress into Makua from the neighboring Keaau Ranch.

To minimize damage from fires, the army has constructed firebreaks between weapons practice areas and the surrounding forest.

National Tropical Botanical Garden holds seeds of D. herbstobatae.

Contacts

Pacific Joint Venture
300 Ala Moana Boulevard, Room 3-122
P.O. Box 50167
Honolulu, Hawaii 96850-0056
(808) 541-2749

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

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.

Macdonald, G.A., A. T. Abbott, and F.L. Peterson.1982. Volcanoes in the Sea, 2d ed. University of Hawaii Press, Honolulu.

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

U.S. Fish and Wildlife Service. 13 May 1992. "Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for Six Plants from the Kokee Region, Island of Kauai, Hawaii." Federal Register 57 (93): 20580-20587.

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