Lo'ulu

Pritchardia aylmer-robinsonii

Description

Pritchardia aylmer-robinsonii, a fan-leaved tree of the palm family (Arecaceae), reaches 23-50 ft (7-15 m) in height and has a trunk approximately 8-12 in (20-30 cm) in diameter. The upper and lower leaf surfaces are green and hairless, and leaf segments are rather thin and drooping. The lower surfaces of the petiole and the leaf ribs are covered with dense, tan wool. The branched, hairless flower clusters are located among the leaves and are no longer than the petioles. Each flower is comprised of a cup-shaped and three-lobed calyx, three petals, six stamens, and a three-lobed stigma. The spherical, hard, and black fruit is 0.7-0.8 in (1.8-2.0 cm) in diameter. This species is distinguished from others of the genus by the thin leaf texture and drooping leaf segments; the tan woolly hairs on the underside of the petiole and the leaf blade base; the stout, hairless flower clusters that do not extend beyond the fan-shaped leaves; and the smaller spherical fruit.

Harold St. John, on one of his botanical collecting trips to Niihau in 1947, discovered a new species of the only genus of palms native to the Hawaiian Islands. He named it P. aylmer-robinsonii in honor of Aylmer F. Robinson, a member of the family that owns the island, and a person who provided St. John with much information regarding the island's plants.

Habitat

This species, originally a component of the coastal dry forest, now occurs only in a rugged and steep area where it receives some protection from grazing animals. The substrate in the seepage area is rocky talus. Prosopis pallida (kiawe), an introduced tree, is one of the palm's few associated plant species. Other native plants that have been found in the area include Brighamia insignis ('olulu), Cyperus trachysanthos (pu'uka'a), Lipochaeta lobata var. lobata (nehe), and Lobelia niihauensis.

Distribution

P. aylmer-robinsonii is endemic to the Hawaiian island of Niihau. This species was historically found at three sites in the eastern and central portions of Niihau. Trees were found on Kaali Cliff and in Mokouia and Haao Valleys at elevations between 230-890 ft (70-270 m). The most recent observations indicate only two naturally occurring plants in one population still on Kaali Cliff. Approximately 200 immature individuals have been cultivated on Niihau and Kauai.

Threats

Modification and destruction of habitat by introduced animals—formerly goats, currently cattle, pigs, and sheep—is the major threat facing P. aylmer-robinsonii. They have decreased available habitat and directly damaged trees, seedlings, and seeds. All feral goats were removed from Niihau in about 1910, but they had already caused considerable damage to the dry and mesic forests. Sheep were also introduced to Niihau, where they damaged and continue to damage the native vegetation and substrate. Pigs now cause damage to the substrate and plants on Niihau, and they eat the seeds of P. aylmer-robinsonii.

Niihau is used as a cattle and sheep ranch with animals ranging in many areas of the island; predation is therefore a probable threat. The current occurrence of plants only in a rocky area inaccessible to hoofed mammals indicates the effect that browsing mammals have had in restricting the distribution of P. aylmer-robinsonii. Although approximately 200 immature individuals have been cultivated on Niihau and Kauai, this species is still threatened with extinction from naturally occurring events and reduced reproductive vigor due to the small number of reproductive plants existing in a very narrow distribution. Because palms take many years to mature, it is not known whether the immature plants now in cultivation are capable of reproducing and sustaining a viable population. A single human-caused or natural environmental disturbance could destroy both the only two naturally occurring individuals and a significant portion of the cultivated plants on Niihau and Kauai.

Other threats are rats and the lack of regulatory protection. Roof and black rats, which occur on Niihau, have been reported to damage the fruit of other species of Pritchardia, thus posing a potential threat to P. aylmer-robinsonii. The known natural habitat of this species is located exclusively on privately owned land. There is currently no existing regulatory mechanism or other authority to prevent further decline of this species on private land, although federal listing automatically triggers listing under Hawaii state law, which prohibits taking of endangered plants in the state and encourages conservation by state agencies.

Conservation and Recovery

The Hawaii Department of Land and Natural Resources is mandated to initiate changes in conservation district boundaries to include "the habitat of rare native species of flora and fauna within the conservation district." The entire island of Niihau is currently within the Agricultural District.

Contact

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

Reference

U.S. Fish and Wildlife Service. 7 August 1998. "Endangered and Threatened Wildlife and Plants; Determination of Endangered Status for the Hawaiian Plant Pritchardia aylmer-robinsonii (wahane)." Federal Register 61(153): 41020-41024.