Mahoe

Alectryon macrococcus

Description

Mahoe (Alectryon macrococcus ) is a tree in the soapberry family (Sapindaceae) that reaches a height of 10-36 ft (3.0-10.9 m). A. macrococcus var. macrococcus and A. macrococcus var. auwahiensis are the two current varieties of this species. A. macrococcus has reddish-brown branches and its leaves are usually 8-22 in (20.3-55.9 cm) long. The leaves have five pairs of egg-shaped and slightly asymmetrical leaflets, each 4-11 in (10.1-28.0 cm) long by 1.6-4.7 in (4.1-11.9 cm) wide. The leaves are glossy and smooth above and have a conspicuous netted pattern of veins. The lower surfaces of mature leaves possess a dense covering of rust-colored hairs. The flowers may be either bisexual or male. The petalless flowers occur in branched clusters 12 in (30.5 cm) long. The single fruit is hard and spherical, enclosing a single glossy brown seed with a red aril.

The primary difference between A. macrococcus var. auwahiensis and A. macrococcus var. macrococcus is that the former variety has mature leaves that are glabrous. A. macrococcus is a relatively slow-growing, long-lived tree that grows in xeric to mesic sites and is adapted to periodic drought, although little else is known about its life history.

Habitat

This species typically grows on dry slopes or in gulches in north-facing, dry to mesic lowland forests at elevations of 1,200-3,500 ft (366-1,067 m). This habitat, characterized by dry summers and wet winters, was once widespread on leeward exposures of all the Hawaiian Islands, but is now almost completely eliminated. Associated native plants include Psychotria, Pisonia, Xylosma, Streblus, Hibiscus, Antidesma, Pleomele, Acacia, teralyxia, and Zanthoxlum. Associated alien plants include lantana, molasses grass, strawberry guava, and Christmasberry.

Distribution

A. macrococcus var. macrococcus occurs on Kauai, Oahu, Molokai, and West Maui. Six populations of this species occur on Kauai, where less than 100 plants grow on state-owned land in Waimea Canyon and in Na Pali Coast State Park. Most known individuals on Oahu are located at numerous sites in the Waianae Mountains, ranging as far north as Kaluakauila Gulch to as far south as the ridge above Lualualei; the species occurs much less often in the Koolau Mountains. The total number of individuals on Oahu is estimated to be about 400. The five extant occurrences on Molokai total only six plants. These are located on state and private land at Puu Kolekole jeep road, Kaunakakai Gulch, and Kamakou Preserve. Only a few plants occur on West Maui at three locations on private land located along the Honokowai ditch trail and in Laumupoko Valley.

This subspecies currently numbers about 500 individuals on city and county, state, federal, and private land; only two of the 27 populations have between 50-200 individuals, and most of the remaining locations number only one or two plants. Two populations of A. macrococcus var. maccrococcus on Oahu are on federal property, one at Schofield Barracks and the other at Lualualei Naval Reservation. Eight populations of this subspecies on Oahu occur on state land, three in areas leased to the federal government as part of Makua Military Reservation and five in a nearby state conservation district.

The var. auwahiensis occurs in the Auwahi and Kanaio districts on leeward East Maui. In 1910, J. F. Rock found about 40 trees in the rich forest of Auwahi on the south slopes of Haleakala. A single scattered population of about nine individuals of this subspecies now remains within a 72.5-acre (29-hectare) area on private land and state-owned (and privately leased) ranch land.

Threats

The major current threats to A. macrococcus are competition with alien plant species, the black twig borer, seed predation by alien rodents, trampling impacts by hoofed mammals, human-ignited fires, and risks associated with small population size.

The alien plants, molasses grass, kikuyu grass, and Christmasberry, pose threats to A. macrococcus reproduction because of competition with seedlings for light, space, and water. Christmasberry is now replacing the native vegetation of much of the southern Waianae Mountains. This plant threatens to occupy the range of all Oahu populations of A. macrococcus var. macrococcus. Most populations of this subspecies on Oahu and Molokai are immediately threatened by molasses grass. Kikuyu grass forms a thick mat that displaces reproduction of native plant species at Auwahi on East Maui. The West Maui individuals of A. macrococcus var. macrococcus are immediately threatened by competition with strawberry guava.

The black twig borer has been cited as an immediate threat to the extant populations of both recognized varieties of A. macrococcus. This pest burrows into the branches and introduces a pathogenic fungus that prunes the host severely, often killing branches or whole plants. The Waimea Canyon populations of A. macrococcus var. macrococcus, most populations on Oahu, and the single population of A. macrococcus var. auwahiensis all suffer severe defoliation and reduced vigor due to infestations of this alien insect. Most populations of this species probably sustain some damage from the borer.

Past predation on fruits and flowers by black rats and, less commonly, house mice has been documented for both varieties of A. macrococcus; rodent predation continues to be a substantial threat for both subspecies. Seed predation by black rats has inhibited reproduction of A. macrococcus for many years. Virtually all Alectryon seeds lying beneath the canopies of trees in Auwahi and Kanaio districts on Maui are destroyed by black rats.

Herbivory, trampling, and soil erosion caused by goats are immediate threats to A. macrococcus var. macrococcus. Goats have contributed largely to the substantial decline of all four populations of this plant in Waimea Canyon on Kauai. Goats on state lands in this area are managed for recreational hunting. In the Waianae Mountains of Oahu, encroaching urbanization and hunting pressure tend to restrict goats to the drier upper slopes, where A. macrococcus occurs. Over half of the Oahu populations of A. macrococcus var. macrococcus are affected by increasing numbers of goats in scattered locations along the Waianae Mountains, especially in Maknaa and Nakaleha. All five localities of A. macrococcus var. macrococcus on Molokai are restricted to a 4.7-sq mi (12.2-sq km) area that is immediately threatened by goats.

Both varieties of A. macrococcus have sustained losses of individual plants and habitat as the result of feral pig activity; present throughout the Waianae Mountains of Oahu in low numbers, feral pigs pose a significant threat to the scattered populations of A. macrococcus var. macrococcus. Herbivory, trampling, and habitat degradation by cattle also threaten the species, particularly A. macrococcus var. auwahiensis. The sole remaining habitat for this variety is on a cattle ranch consisting of private and state-leased lands. Although all individuals of A. macrococcus var. auwahiensis are protected from hoofed mammals with small woven-wire exclosures, these must be rigorously maintained. Cattle trample seedlings and damage mature plants by browsing.

Fire is a threat to some populations of A. macrococcus var. macrococcus. Unintentionally ignited fires have resulted from ordnance training practices in Makua Military Reservation on Oahu. Although most fires have been contained within 0.02 acres (0.008 hectares), a single 300-acre (120-hectare) fire in July 1989 spread upslope and came to within 0.2 mi (.3 km) of a population of A. macrococcus var. macrococcus, also threatening seven other populations in the area. Fires are also a potential threat to the Waimea Canyon population on Kauai and, to a lesser degree, the West and East Maui populations.

Due to the very small remaining number of individuals of A. macrococcus var. auwahiensis and their limited distribution, a single natural or human-caused environmental disturbance could easily be catastrophic. Gene pool limitations may depress reproductive vigor and adaptability for both these subspecies given their mixed population sizes and scattered distributions.

Another possible threat to both varieties is seed predation by insects, probably the endemic microlepidopteran, and loss of pollinators.

Conservation and Recovery

Makua Military Reservation and Schofield Barracks are controlled by the U.S. Army, and portions of their ranges are used by soldiers for ordnance training. The A. macrococcus var. macrococcus plants on this land are not located inside impact or buffer zones; therefore, they are not directly affected by military activities. The army has constructed firebreaks around the plants on the Makua Military Reservation to minimize damage from unintentional fires that occasionally result from stray bullets.

To protect the population of A. macrococcus var. macrococcus at Naval Magazine Lualualei, the U.S. Navy is working to control alien plants in areas where individuals of this variety are located. The navy also allows recreational hunting on their lands to control the feral pig population.

Small woven wire enclosures have been constructed at Auwahi on East Maui by a private conservation group, the Native Hawaiian Plant Society, with cooperation from Ulupalakua Ranch, to protect endangered and threatened plants from ungulates. A single A. macrococcus var. auwahiensis individual is protected within one of these enclosures. A. macrococcus var. auwahiensis has been propagated by the Hawaii Division of Forestry and Wildlife at its Maui baseyard near Kahului and at the Waimea Arboretum and Botanic Garden on Oahu. A. macrococcus var. macrococcus has been propagated at the Honolulu Botanic Garden and at Lyon Arboretum on Oahu. The National Tropical Botanic Garden has seed stored from a cultivated specimen of A. macrococcus var. macrococcus and has successfully propagated both varieties.

Contacts

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

Senior Resident Agent Office
U.S. Fish and Wildlife Service
300 Ala Moana Boulevard, Room 7-235
P.O. Box 50223
Honolulu, Hawaii 96850-5000
Telephone: (808) 541-2681
Fax: (808) 541-3062

Reference

U.S. Fish and Wildlife Service. 15 May 1992. "Endangered and Threatened Wildlife and Plants; Determination of Endangered or Threatened Status for 15 Plants from the Island of Maui, Hawaii." Federal Register 57 (95): 20772-20787.