Hawaiian Red-flowered Geranium

Geranium arboreum

Description

The Hawaiian red-flowered geranium (Geranium arboreum ) is a many-branched, spreading wood shrub 6-12 ft (1.8-3.7 m) tall. The leaves are thin, bright green, broad and rounded at the base, tapering toward the end, and 1-1.5 in (2.5-3.8 cm) long. Each leaf has five to nine main veins, and has edges notched with tooth-like projections. The flower petals are red, about 1-1.5 in (2.5-3.8 cm) long; the upper three petals are erect, the lower two reflexed, causing the flower to appear curved. Due to the flower shape, this species is the only one in the genus that appears to be adapted to bird pollination.

Native honeycreepers appear to be a major pollination vector. Hawaiian red-flowered geraniums from the southwest area of Haleakala in the Kula Forest Reserve produce seeds that are larger and fuller than seeds from the northwest extension of its distribution. Native honeycreepers are reasonably abundant at both sites. It is possible that the larger numbers and clumped distribution of the southwest rift populations facilitate inter-plant visits by native birds and higher outcrossing frequency.

Habitat

The Hawaiian red-flowered geranium grows in steep, narrow canyons on the north and west outer slopes of Haleakala between 5,000-7,000 ft (1,524-2133.6 m) in elevation in an area that is roughly 9 mi (14.5 km) in length and 0.15 mi (0.24 km) in width. The environment of these gulches—damp, shaded part of the day, and protected—contrasts with the generally drier climate of the surrounding area. The moist habitat apparently is due to fog drip and run-off. The plants appear to obtain a significant amount of their water requirements by combing moisture out of their drifting fog. Vegetation in the ravines is often quite dense, consisting of mostly medium-sized woody shrubs, introduced grasses and weeds, and mixed ferns. The Hawaiian red-flowered geranium occurs in small isolated populations in the gulches and is a minor component of the vegetation. The habitat of the nearby and surrounding areas is subalpine dry forest or mesic scrub land; a few individuals grow near areas that have been converted to agricultural uses such as pasture land or experimental tree plots.

Distribution

The original range and abundance of the species is unknown; however, late 19th and early 20th century collections indicate that it once grew on the southern slopes of Haleakala, and that its distribution on the northern slopes extended beyond its presently known range.

There were 300 known individuals in 1992, found chiefly in the Polipoli Springs and Hosmer Grove-Puu Nianiau areas on the western and northwestern slopes of Haleakala on East Maui. About 250 plants occur on state-owned land within the Xula Forest Reserve, and the remaining plants are mostly in Haleakala National Park, The Nature Conservancy's Waikamoni Preserve, and on Haleakala, Kaonoula, or Erehwon ranches.

Threats

The greatest immediate threats to this species are habitat disturbance by feral pigs and competition from naturalized exotic vegetation, chiefly grasses and trees. Soil disturbance caused by trampling of cattle and rooting of pigs destroy plants and facilitate the encroachment of competing species. Lesser threats include browsing by cattle, fires, and seasonal pollen from exotic pine trees in the Polipoli springs area that can completely cover the stigmas of the geranium and thus preclude any fertilization by its own species. The small number of individual plants increases the potential for extinction from stochastic events, and the limited gene pool may depress reproductive vigor.

Rabbits almost became established on East Maui within Haleakala National Park in 1990 as a result of release of pet rabbits by a careless pet owner. Rapid response by Park management to the problem is apparently all that prevented a catastrophe. The site where the incipient rabbit population existed was adjacent to habitat of G. arboreum. It is almost certain that similar incidents will occur in the future. If rabbits were to establish, they would pose a severe threat to the survival of this species.

Conservation and Recovery

A very small proportion of the extant individuals of G. arboreum occurs within Haleakala National Park. Although the National Park Service does provide active management protection to sensitive resources, the small percentage of habitat of G. arboreum within the park limits the potential benefits of park management for this species.

Many sites on northwestern and southwestern Haleakala Volcano still have appreciable numbers of G. arboreum on which to center exclosure locations. On leeward Haleakala, this species is apparently extirpated and should be re-established through seed from the nearest extant populations on the southwest rift. Owners of sites appropriate for exclosures are the state of Hawaii (Kula Forest Reserve), Haleakala Ranch, Haleakala National Park, and The Nature Conservancy of Hawaii (Waikamoi Preserve).

Although this species was not being propagated in 1997, it is being grown as an ornamental by a number of individuals. Varying degrees of success have been reported with efforts at raising plants from wild-collected seed.

The inherent vigor, possibly genetic, of these seeds seems to have a direct correlation with the success of the seedlings. A cutting of G. arboreum has been successfully rooted on at least one occasion.

Contact

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

Reference

U.S. Fish and Wildlife Service. 13 May 1992 "Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for Geranium Arboreum (Hawaiian Red-Flowered Geranium)." Federal Register 57(93):20589-20592.