Uhiuhi

Caesalpinia kavaiense

Description

Uhiuhi, or Caesalpinia kavaiense, is a medium-sized tree up to 35 ft (10 m) tall with rough, dark bark and a spreading crown. The leaves are twice compound, made up of one to five pinnae with four to eight pairs of leaflets. Each leaflet is about 1.5 in (3.8 cm) in length. The flowers are borne in terminal racemes and are pink to red in color. The pink seed pods are short and broad, winged on one side. These pink pods, the bright flowers, and bright green lacy foliage make this an attractive tree.

The wood is highly valued for its color, grain, and density. The heartwood is very dark brown, almost black, and close-grained. Among other uses, Hawaiians took advantage of the wood's high density to make fishing implements that sink rather than float.

Some isolated trees produce viable seed, showing that the species is capable of self-pollination, e.g. the single living wild tree on Kauai. Some wild trees and some cultivated trees regularly produce a good quantity of viable seeds. Seeds germinate in nature and can be germinated in nurseries. However, some isolated trees that flower apparently do not produce viable seed. The tree growing in the Botany Department Courtyard, University of Hawaii at Manoa, has been found to produce normal pollen, but has never set seed. It is not known what kinds of barriers to self-pollination, if any, may be responsible for this failure. The flower may be insect-pollinated. The broad, winged pod suggests that the seeds are dispersed by a combination of gravity and wind. Seeds may also be dispersed by ingestion by birds or introduced mammals.

Sprouts sometimes form at the base of the stump but no other vegetative reproduction is known. Attempts to root cuttings have been unsuccessful. Growth rates, age at reproductive maturity, and life span are almost entirely unknown. The extreme density of the wood suggests a slow growth rate in the adult stage.

Eight nursery grown seedlings less than one year old were planted in a Puuwaawaa exclosure in 1989. Two of these flowered and set fruit in 1991 and 1992. Seed collected appeared normal in every way. It was noted that many young pods blew off the trees before maturing. Herbarium specimens collected throughout the year have flowers, fruit and new leaves, indicating no marked seasonality. Growth and flower and leaf production may decline during drought periods.

Habitat

On Hawaii, the major habitat of C. kavaiense is the northwest and west slopes of Mount Hualalai in the District of North Kona. Historically, C. kavaiense has occurred at elevations between about 200 and 3,000 ft (61 and 914 m). The substrate is mostly rough a'a lava covered by a thin and discontinuous layer of organic soil. The steep slope and rugged volcanic features of the landscape impede passage on the ground.

The rainfall in this area is about 30-40 in (76-102 cm) a year, with no pronounced wet and dry seasons. Air temperature also fluctuates little during the year, with mean monthly temperatures varying between 58 and 64°F (14-18°C). The moderate rainfall and high insolation in combination with the shallow, excessively drained, soil provides a dry habitat where moisture is probably frequently limiting.

The Kaupulehu and Puuwaawaa habitat of C. kavaiense is lowland dry forest. The canopy of this open forest is 16-20 ft (4-6 m) high and is made up of a diversity of native tree species with native shrubs below, and includes several other rare plant species. Formerly, the ground between the woody plants was mostly bare. Today, the ground layer is filled with the alien lantana and, especially, fountain grass. Few native grasses are found.

The trees of C. kavaiense that persist at lower elevations in Kiholo may be within another lowland forest subtype, the Wiliwili forest. The habitat of the subpopulation of C. kavaiense in Kealakehe is described as open mixed shrubland on a'a lava.

All of these formerly diverse native tree and shrub communities have been heavily impacted by human activity, especially browsing by ungulates, alien plant invasions, and fire.

On Oahu, C. kavaiense occurs in the Waianae mountains of the Aulu Forest community of the lowland dry forest subtype. This is a drought-resistant community dominated by 50-ft (15-m) tall Sapindus trees with a sparse understory, including some other rare native plant species.

Distribution

C. kavaiense occurs or has occurred on dry leeward portions of five of the main Hawaiian Islands. The species was first discovered on Kauai around 1864. By 1888, collections had been made from Oahu and Maui as well as Kauai, and in 1909 C. kavaiense was discovered on Hawaii in North Kona. In 1992, a single tree was discovered on Lanai, the first record from that island. The relatively late discovery of this species on the various islands implies that it probably was never abundant in the past 200 years.

All occurrences of C. kavaiense on the Big Island of Hawaii are within the District of North Kona on the leeward (west and northwest) slope of Hualalai. The known range extends from the ahupuaa of Puuanahulu, in the north to Kealakehe in the south. It is probable that there are other living C. kavaiense at unknown locations.

Trees occur as widely scattered small clusters or individuals, or in one of two small subpopulations. The best known of the two subpopulations, contained about 48 trees in 1989 in a kipuka, which is a remnant area of older land surrounded by a recent lava flow, of the Kaupulehu flow. It was estimated that 19 trees were on the state-owned portion of the kipuka. Twenty-one trees were estimated to survive on the privately owned portion of the kipuka. The majority of this kipuka was burned in a wildfire in May, 1993, and 80% of the C. kavaiense trees growing there were killed.

The second sizeable subpopulation of 21 mature C. kavaiense was discovered in 1989 in the ahupuaa of Kealakehe in North Kona. in Puuwaawaa. All or most of the trees are growing on land owned by the state of Hawaii.

Approximately 10 C. kavaiense trees are known between Kealakehe and the boundary kipuka. A single tree was recorded in 1981 and two trees were observed in the ahupuaa of Puukala in 1986. A cluster of four trees survives in Kaupulehu near the Kaupulehu lava flow, and another single tree occurs in Kaupulehu. Approximately 11 other trees have recently been observed northeast of the kipuka.

North Kona, at 2,000 ft (609 m) elevation between Huehue and Puuwaawaa, is the location of the largest extant population of C. kavaiense. In the last two decades, C. kavaiense has been found at more North Kona locations than at any previous time. However, C. kavaiense has never been found growing naturally in any other district on Hawaii.

On Maui, no trees have been located since 1946 where it was observed in the dry fore hills of West Maui. On Oahu, the populations in the Waianae Mountains in Makaleha Valley and at Puupane survive but the third population at Makua Valley has not been seen since 1931. The Koolau Mountain population is extinct.

On Oahu, a total of 11 living mature trees are known from three locations in the Waianae mountains. A few other trees may exist elsewhere at inaccessible sites in the Waianae Mountains.

Two mature trees are in the Waianae Kai Forest Reserve, but no seedlings or saplings are reported at this site. Two mature trees survive at Puupane. Five mature trees and five seedlings were reported at this site in 1981. This site in Kaimu-hole Gulch is within the Mount Kaala Natural Area Reserve.

The largest remaining population in the Waianae mountains is in Makaleha Valley. Eight mature trees and three saplings were confirmed in 1992 and four adults and three saplings were seen there in 1993.

On Kauai, one living C. kavaiense tree in the Koaie Valley near Waimea Canyon was reported in 1982, but it has since fallen and died. However, viable seeds may still be in the soil.

Another fallen but still living tree was discovered in 1987 in the Poomau Branch of Waimea Canyon. This tree and a sapling and seedling reported nearby have since died. A mature, fruiting tree and several young individuals were observed in 1988 on nearby privately owned land. Currently, access to this area is not allowed, but the owner has an ongoing native plant conservation program, and seed from this individual is stored in the National Tropical Botanical Garden collection.

On Lanai, in 1990, a single mature, fruiting C. kavaiense tree was found in Kaoha ahupuaa on windward Lanai. The tree is on the edge of Puhielelu Ridge; this tree appears to be naturally established even though no others are known from this island.

Threats

The alien black coffee twig borer attacks and may kill C. kavaiense. Its attacks on outplanted seedlings in North Kona have been observed but no deaths have been attributed to them. Damage may be far more serious on Oahu. Based on observations over a 20-year period, the marked decline of this previously widespread species on Oahu was attributed to a combination of the twig borer and drought. Ants farming aphids are one of the biggest threat to the survival of outplanted C. kavaiense seedlings in North Kona.

Predation of seeds by introduced rats, mice and unspecified game birds and invertebrates is well known. Rats eat the seeds while they are still on the tree. The large, hard, bean-like seeds of C. kavaiense have been found in rat burrows.

The North Kona area has experienced drought conditions for several years, and if this species reproduces only in widely spaced times of favorable climatic conditions, the prolonged drought could be a factor in its recent decline. It is also possible that the drought conditions have exacerbated the insect infestation problems because dry vegetation is more susceptible to such invasion.

Because of past habitat destruction, current C. kavaiense populations on Oahu are now limited to steep, inaccessible terrain which is subject to frequent rock slides which damage the trees. Feral goats in these areas add to the landslide problem by dislodging rock and soil, and by browsing on stabilizing ground cover.

Conservation and Recovery

Federal listing of this species as endangered triggered listing by the state of Hawaii, resulting in significant benefits. The state's endangered species law has more stringent prohibitions on taking or damaging these species in their natural habitat and places these species in the state's threatened and endangered plant management program. Under this program, the state has made use of federal funds for fencing, fire control, weed removal and outplanting.

The habitat within Puuwaawaa ahupuaa is owned by the state of Hawaii. It is zoned as agricultural land and managed under the jurisdiction of the Division of Land Management of the Department of Land and Natural Resources. Most of the best habitat for this species is within the Puuwaawaa Ranch which is leased to a private operator. The best forest habitat within this lease was proposed as a State Natural Area Reserve prior to the fires of 1986, 1988 and 1993. Most of the state land below the Mamalahoa Highway where the majority of C. kavaiense are found (Puuwaawaa makai lands) has been withdrawn from the ranching lease. This land will probably be managed in the future as a State Game Management Area. A new county landfill is also proposed for the Puuwaawaa makai lands. The management goals include reduction of the threats of fire and damage by mammalian herbivores, habitat improvement to encourage natural regeneration, and outplanting nursery-raised trees.

The management strategy is centered on fenced exclosures. The exclosures are designed to be large enough to permit expansion of the subpopulation by natural regeneration and outplanting. Fire breaks and fire roads outside the exclosures have been cleared to protect and give access to the ex-closures. The fences protect the trees from browsing by domestic cattle and feral ungulates. Within the exclosures, fountain grass is periodically removed to reduce the fuel near the endangered trees. Fountain grass removal also increases the probability of natural regeneration and seedling establishment by reducing the competition for water and light. Some trapping of rats has been carried out to reduce seed predation.

Wild and cultivated trees produce viable seed which can be readily germinated. Seeds are occasionally collected by and grown in Hilo nursery. Seedlings have been planted into the fenced exclosures. Seedling establishment is aided by some watering and weed removal. C. kavaiense seedlings do well but have been attacked by boring beetles. All attacked seedlings and saplings have survived. Seed collections, plantings, and survivorship are not documented. Limited resources and personnel prevent the frequent monitoring and tending of outplanted seedlings.

The colony of 21 or more mature C. kavaiense recently found in Kealakehe is on land owned by the Department of Land and Natural Resources. This parcel is the proposed site of a housing development sponsored by the Housing Finance and Development Corporation, a State agency. A mitigation plan to protect C. kavaiense concentrates on protective actions during the construction phase and calls for a master plan to manage C. kavaiense and other natural resources on the site following the construction phase. The proposal specifies protective fencing, fire prevention and other activities.

The habitat within Kaupulehu ahupuaa is owned by the Kamehameha Schools/Bernice Pauahi Bishop Estate. The land below the Mamalahoa Highway is leased to PIA Sports Properties, Inc. Most of the area is undeveloped and unused. PIA has taken some steps to protect and manage the endangered species on the leased lands. PIA Sports Properties, Inc., has established a fenced exclosure of 2,500 square feet to protect one C. kavaiense tree. The Kaupulehu land above the Mamalahoa Highway is leased to Hualalai Ranch which practices commercial ranching and other agricultural pursuits.

A jeep road through the Kaupulehu side of the boundary kipuka is maintained to provide access and to serve as a firebreak within the habitat. Since 1986, a private landowner has managed a 100-acre (40-hectare) preserve on his land for the conservation of native plant species. After clearing of the dominant non-native vegetation from this area, the native vegetation began to recover and individuals of several extremely rare species, including C. kavaiense, were able to grow from long dormant seeds which remained in the soil. In the late 1980s, a mature C. kavaiense individual was observed as well as several seedlings and saplings which were thriving in the preserve thanks to the landowner's efforts. Any individuals of this species which have survived because of the landowner's hard work and dedication are probably the last on Kauai.

C. kavaiense grows on Oahu and Kauai on State-owned forest reserves zoned conservation districts. The tree at Puupane, Oahu, is within the Mount Kaala Natural Area Reserve. No specific management programs are carried out for the trees on any of these islands. None of these trees are protected by exclosure fences.

National Tropical Botanical Gardens (NTBG) on Kauai maintains a seed bank for C. kavaiense and is growing seedlings in a nursery. NTBG has entered into a cooperative agreement with and has a permit to collect seeds and propagate endangered species. NTGB participates with the Center for Plant Conservation, St. Louis, Missouri, and maintains C. kavaiense as part of the national collection of endangered plants. NTBG made multiple seed collections of C. kavaiense in 1990, 1991 and 1993 from Hawaii, Kauai, and Oahu and some seed is in storage at NTBG. Currently, they also have a small number of seedlings in the nursery and a few dozen have been planted on their grounds.

Contact

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

References

U. S. Fish and Wildlife Service. 1986. "Determination of Endangered Status for Mezoneuron kavaiense." Federal Register 51: 24672-24675.

U. S. Fish and Wildlife Service. June 1994. "Recovery Plan for Caesalpinia kavaiense and Kokia drynarioides." U. S. Fish and Wildlife Service, Portland. 92 pp.