Opuhe

Urera kaalae

Description

Urera kaalae (Opuhe) is a shrub or small tree of the nettle family that grows 10-23 ft (3-7 m) in height. On exposure to the air, the tree's sap turns greenish black. The branches are hollow, and the bark is pale brown. The heart-shaped leaves are pale green, thin and membranous, and 4-11 in (10-28 cm) long. The flowers are male or female and can grow on the same or on different trees. The sepals of male flower are fused into a somewhat globe-shaped structure, about 0.06 in (0.2 cm) long. U. kaalae, a fast-growing plant, has been observed flowering in the spring. It is difficult to predict when seeds will be produced; even when produced, seeds are often sterile. This may be an indication of pollinator limitation.

Habitat

U. kaalae typically grows at elevations between 980 and 2,700 ft (299 and 823 m) on slopes and in gulches in diverse mesic forest dominated by papala kepau. Associated species include alaa, poola, ieie, mamaki (Pipturus sp.), U. glabra, kopiko (Psychotria sp.), lama (Diospyros sandwicensis ), papala kepau (Charpentiera sp.), and olopua (Nestegis sandwicensis ).

Distribution

U. kaalae was known historically from Waianae Lika to Kupehau Gulch in the central to southern windward Waianae Mountains. This species now occurs only in North and South Ekahanui, Pualii, Napepeiauolelo, Halona, and Kalnaa gulches; North and South Palawai; Schofield Barracks Military Reservation; and Waianae Kai on Federal, state, city, county, and privately owned lands. The 10 known populations, sparsely distributed over an area of about 2.5 by 7 mi (4 by 11.3 km), contained approximately 44 individuals in 1997.

Threats

The main threats to U. kaalae are disturbance of its habitat by feral pigs and competition from alien plant species. Feral pigs, which are managed by the state as game animals, have been in the Waianae Mountains for about 150 years and have had a major effect on the native flora. Their rooting destroys plants and opens the habitat to invasive species. They also help spread these alien plants by carrying seed on their bodies and in their feces.

Several invasive alien plants are direct threats toU. kaalae. Christmasberry (Schinus terebinthifolia ) forms dense thickets and may also release chemicals that inhibit the growth of other species. Fire-tree (Myrcia faya ) was planted in the Waianae Mountains during a reforestation project. Besides forming a dense closed canopy that excludes other species, it produces its own nitrogen, enabling it to colonize areas to which native species have become adapted. Molasses grass (Melinis minutiflora ) grows in dense mats that smother native vegetation. Huehue haole is a vine that smothers the subcanopy of dryland habitats. Molasses grass and daisy fleabane grow in dense mats that smother native vegetation.

Fire is a threat to U. kaalae trees that lie near the U.S. Army's Makua Military Reservation and Schofield Barracks. Within a 14-month period from 1989 to 1990, 10 fires resulted from weapons practice on the reservation.

Conservation and Recovery

The Nature Conservancy of Hawaii outplanted three individuals in 1995 in a fenced exclosure near existing wild populations in Honouliuli Preserve. Only one plant had survived as of 1997; it appears to have moderate vigor and is being monitored regularly. The Nature Conservancy of Hawaii has also recently searched for populations in Kaluaa and South Ekahanui gulches to monitor and conduct threat management but was only able to find isolated individual plants. The Nature Conservancy of Hawaii constructed an exclosure at Palawai in 1998 that should help to protect individuals reported from this area. This species is also being successfully propagated at the National Tropical Botanical Garden and the Waimea Arboretum.

Contacts

Pacific Joint Venture
300 Ala Moana Blvd., Rm. 3-122
Honolulu, Hawaii 96850-0056
Telephone: (808) 541-2749
Fax: (808) 541-2756

U.S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N.E. 11th Avenue
Portland, Oregon 97232-4181
Telephone: (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.

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