16.23 Taxon Summary: Pritchardia kaalae

Transcription

1 Taxon Summary: Pritchardia kaalae Photographer: Hawaii Natural Heritage Program Scientific name: Pritchardia kaalae Rock Hawaiian name: Loulu Family: recaceae (Palm family) Federal status: Listed endangered Description and biology: Pritchardia kaalae is a fan palm reaching up to 10 m (33 ft) tall (Lau pers. comm. 2000). It is a tree with a single erect trunk surmounted by a cluster of fronds. The species inflorescences are very long, nearly reaching the frond tips to often extending well beyond the fronds. The flowers are borne in one or more bunches on the inflorescence. The fruits of P. kaalae are globose, and measure about 2 cm (0.8 in) in diameter. Pritchardias usually, if not always, bear perfect (possessing male and female reproductive parts) flowers. Pritchardia kaalae is most likely self-compatible, as cultivated trees of other species of Pritchardia produce viable seeds even when far away from any other Pritchardias. Not much is known about the pollination of Hawaiian Pritchardias. However, with respect to palms in general, it had been traditionally believed that all are wind pollinated. Recent research, however, indicates otherwise. Uhl and Dransfield (1987) predict that "most palms will be shown to be insect pollinated, or that both wind and insects are involved." The large fruits of some Hawaiian Pritchardias have been cited as examples of gigantism in plants of Oceanic islands (Carlquist 1974). The fruits of P. kaalae, however, are much smaller than the larger-fruited Pritchardias, and appear to be small enough to have been consumed and dispersed by the larger of the now extinct flightless birds that occurred in Hawaii prior to human settlement.

2 Chapter Taxon Summary: Pritchardia kaalae The longevity of individuals of this species has not been documented, although they undoubtedly live for many decades. Known distribution: Pritchardia kaalae has been found only in the northern Waianae Mountains. The great majority of the trees are on either Ohikilolo Ridge or on the northern side of Kaala from East Makaleha Valley to Manuwai Gulch. The few known trees beyond the major concentrations are in the bottom of Makaha Valley and on the ridge between Waianae Kai and Schofield Barracks Military Reservation. The recorded range in elevation for this species is from m (1,500-3,100 ft). In some parts of Hawaii, the current distribution of Pritchardia is apparently at least partially determined or influenced by the planting of trees by native Hawaiians (Hodel 1980). This is especially evident in the Kona region of Hawaii Island where there are no sites where P. affinis can be considered truly wild. ll of the currently known older trees are in areas that were densely populated at the time of western contact. In the case of P. kaalae, however, there does not seem to be any evidence of native Hawaiian influences in the distribution of the species (Lau pers. comm. 2000). Population trends: The number of mature trees of this species has been slowly decreasing as the older trees die off with very few immature plants to take their place. Current status: The total number of individuals of P. kaalae is slightly more than 300 plants. little more than half of these are on Ohikilolo Ridge in the Makua action area. The current populations units are listed in Table and their sites are plotted on Map The sites of the population units proposed for management for stability are characterized in Table and threats to the plants at these sites are identified in Table Habitat: Pritchardia kaalae is found in the mesic zone on moderately steep slopes to very steep cliffs. Many of the trees in the lower elevations are in forests dominated by lama (Diospyros sandwicensis) and/or ohia (Metrosideros spp.). The highest trees are in the upper wetter zone of the mesic forest, which is often dominated by lehua ahihi (a species of ohia, Metrosideros tremuloides). The steeper, more open cliffs where this species grows are vegetated largely with shrubs, grasses and sedges, and small trees. Taxonomic background: Pritchardia is a genus restricted to the tropical Pacific islands and the Hawaiian Islands including about 25 species, about 20 of which are endemic to the Hawaiian Islands. The taxonomy of the Hawaiian species of Pritchardia are taxonomically difficult because characteristics used to distinguish the species appear to be highly plastic (Read and Hodel 1990). Pritchardia kaalae's extremely long inflorescences sets the species apart from all other Hawaiian Pritchardia species except one. The Waianae Mountains to the south of P. kaalae territory in the northern part of the mountain range are devoid of Pritchardias of any kind, with the exception of a Pritchardia colony south of Pohakea Pass in North Palawai Gulch. There are only two mature trees and one juvenile in the colony. These plants are the only members of what is considered to be an undescribed species

3 Chapter Taxon Summary: Pritchardia kaalae most closely related to P. martii, the sole species of Pritchardia in the Koolau Mountains (Gemmill 1996). Outplanting considerations: Outplantings of P. kaalae should not be established in the southern Waianae Mountains since P. kaalae's recorded range is limited to the northern Waianae Mountains, and since there is a second extremely rare undescribed species of Pritchardia in the southern Waianaes. n outplanting line was drawn through the central portion of the mountain range limiting potential reintroduction sites to areas north of the line. Threats: Recent studies of fossil pollen and charcoal deposits on Oahu indicate that when the Polynesians first settled in Hawaii Pritchardia constituted a major element of the vegetation of the lowlands of Oahu, including the island s dry leeward lowlands adjoining the Waianae Mountains. The arrival of the Pacific rat (Rattus exulans) on Oahu via the canoes of early Polynesian voyagers appears to have brought about a collapse of these Pritchardia populations due to fruit predation by the rats (thens pers. comm. 2000). The Pritchardias growing in this largely vanished lowland vegetation have not been identified, but it is quite possible that P. kaalae formerly extended into the lowlands and was included in the lowland Pritchardia populations decimated by the rats. In any case, it can be surmised that the advent of the Pacific rat diminished P. kaalae s range and numbers to some extent. Western contact brought about the introduction of additional species of rats to Hawaii that potentially feed on Pritchardia fruits. The rate of recruitment in P. kaalae populations continues to be negatively affected due to fruit predation by rats, as evidenced by significant increases in recruitment rates when rats are controlled in P. kaalae groves (Rohrer pers. comm. 2000). Other major threats to P. kaalae include feral pigs and goats, which degrade the plants habitat and harm them through feeding on the plants, trampling them, or uprooting them. lien plants also threaten the species by altering its habitat and competing with it for sunlight, moisture, nutrients, and growing space. The non-hawaiian P. thurstonii and P. pacifica are commonly grown as ornamentals in Hawaii. It is not known if they pose a threat to the genetic integrity of the Hawaiian Pritchardias through hybridization. Hawaiian Pritchardias from islands other than Oahu are also occasionally planted as ornamentals on Oahu. In contrast, the Oahu species have almost never been utilized for this purpose (Lau pers. comm. 2000). The potential for genetic contamination of the native Pritchardias of Oahu by the planted Hawaiian Pritchardias from other islands remains to be investigated. Collection of Pritchardia fruits by commercial palm growers or their collectors has been a problem with some of the rarer Hawaiian Pritchardias. For instance, an immature plant of the extremely rare P. viscosa is known to have been illegally collected from the wild (Perlman pers. comm. 2000), and harvesting of fallen fruits has become evident at the only remaining grove of P. schattaueri (Perry pers. comm. 2000). It is not known to what level palm collectors are affecting P. kaalae. The most worrisome of any potential threat to the Hawaiian Pritchardias is lethal yellowing, a palm disease that is slowly making its way through the tropical and subtropical zones of the

4 Chapter Taxon Summary: Pritchardia kaalae world. It is most well known for its devastating effects on coconut trees, but Hawaiian Pritchardias planted in Florida as ornamentals have also proven to be extremely susceptible to the disease. The disease is fatal; there is currently no cure for it once a susceptible individual is infected with the disease. Lethal yellowing is caused by a mycoplasma-like-organism (Murakami 1999). The organism is transmitted by a sap-sucking plant hopper, Myndus crudus. Symptoms include the yellowing of the palm's fronds prior to its death. The disease is particularly frustrating because infected plants have an incubation period of from six months to two years before symptoms appear. The disease originated in islands in the Caribbean Sea, and is now known from many Caribbean islands, Florida and Texas in the United States of merica, Central merica, West frica, and Tanzania in East frica. The insect transmitter of the disease has not yet been found in Hawaii, so Hawaii is safe from this disease for now (Murakami 1999). Table Current Population Units of Pritchardia kaalae. The numbers of individuals include mature and immature plants, and do not include seedlings. Population units proposed for management are shaded. Island Population Unit Name Total Number of Individuals No Management Proposed Oahu: Makaha Makaleha to Manawai Ohikilolo Waianae Kai Management Proposed

5 Chapter Taxon Summary: Pritchardia kaalae Table Site Characteristics for Population Units of Pritchardia kaalae Proposed for Management for Stability. Population Unit: Site Characteristics: Habitat Quality Terrain ccessibility Existing Fence Makaleha to Manawai High-Medium Moderate to Vertical Low to High None Ohikilolo High- Medium Moderate to Vertical Low to Medium Large Table Threats to Population Units of Pritchardia kaalae Proposed for Management for Stability. Population Unit: Makaleha to Manawai Threats: Pigs Goats Weeds Rats Black Twig Borer Low to High High High Unknown B Slugs and Snails Unknown Ohikilolo Low Low High High N/ Unknown N/ Other rthropods Unknown Unknown Fire Ignition Fire Fuels Erosion Human Disturbance Low Medium High Low to Medium Very high Medium High Low

6 Chapter Taxon Summary: Pritchardia kaalae