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Brief Summary

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Acacia koa, koa, is a large evergreen flowering tree in the Fabaceae (legume family) native to the Hawaiian Islands. Koa was prized by early Hawaiians for its exceptionally fine wood. It is the second most common tree species on the islands, and the most valuable native timber species. Its wood has a curly grain and striking coloration, and was traditionally used to build canoes, which were made of single, giant koa logs; the largest were war canoes that extended 21 m (70 ft). Koa wood was also used for surfboards, paddles, framing grasshouses, and making ukuleles. It is now used primarily for furniture, cabinet work, and face veneers. During its lifetime, A. koa undergoes a change from true leaves (consisting of compound leaves with 12 to 15 paired, bipinnate leaflets) to sickle-shaped phyllodes, leaves in which the leaflets are suppressed, and the leaf-stalks (petioles) become vertically flattened, generally oriented vertically to avoid intense sunlight. This change often occurs while plants are small, often less than 2 m (6 ft) tall. Phyllodes persist under moisture stress, transpiring about 20 percent as much as true leaves. Old trees usually bear only laurel green phyllodes, but true leaves sometimes appear on the trunk or lower branches, or after wounding. In contrast to many acacia species, A. koa is thornless. The tree may flower and fruit starting at 2 to 3 years of age. In some locations, it flowers year-round. The insect-pollinated, pale yellow flowers are arranged in axillary racemes with many hermaphroditic (bisexual) flowers. Individual flowers average 8.5 mm (0.3 in) in diameter, with one to three on a common peduncle, each with a single elongated style and an indefinite number of free stamens. The fruit is a legume or pod, slow to dehisce (split open), about 15 cm (6 in) long and 2.5 to 4 cm (1 to 1.5 in) wide. Pods contain about 12 dark brown to black seeds, which are hard and durable. Seeds may germinate after one or two years, or persist in the seed bank for 25 years or more. Koa grows best in high rainfall areas—those receiving 190 to 510 cm (75 to 200 in) annually. It is an important component of montane Hawaiian rain forests, where it grows in nearly pure stands or in mixtures with ohia (Metrosideros polymorpha), and is also associated with more than 80 species of trees, shrubs, vines, herbs, ferns, club mosses, grasses, and sedges. Koa forests provide habitat for numerous native forest birds, including three endangered species on the island of Hawaii: akiapolaau, Hemignathus munroi; akepa, Loxops coccineus; and Hawaiian creeper, Manucerthia mana. Koa forests were more extensive in the past than they are today. Land clearing, poor cutting practices, and destruction by animals, insects, and fire have all taken a toll. Koa is susceptible to numerous native insects, including the koa moth (Scotorythra paludicola), a lepidopterus defoliator that caused mortality of one third of a stand of koas on Maui in an 1841 outbreak; such severe outbreaks occur periodically. In addition, the introduced koa haole seed weevil (Araecerus levipennis) and other seed moth species may destroy 90 percent or more of any given seed crop in the pods. Koa also suffers damage and mortality from browsing by pastured or feral cattle, pigs, sheep, and goats. Craig D. Whitesell, modified by Jacqueline Courteau
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Whitesell, C. D. Acacia koa A. Gray, Koa. In Burns, Russell M., and Barbara H. Honkala, tech. coords. 1990. Silvics of North America: Vol. 2. Hardwoods. Agriculture Handbook 654. U.S. Department of Agriculture, Forest Service, Washington, DC.
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Physical Description

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Perennial, Trees, Woody throughout, Nodules present, Stems erect or ascending, Stems greater than 2 m tall, Stems solid, Stems or young twigs glabrous or sparsely glabrate, Leaves alternate, Leaves petiolate, Extrafloral nectary glands on petiole, Stipules inconspicuous, absent, or caducous, Stipules deciduous, Stipules free, Leaves simple, or appearing so, Leaf or leaflet margins entire, Leaflets 1, Leaves glabrous or nearly so, Leaves reduced to phyllodia, Inflorescences racemes, Inflorescence panicles, Inflorescences globose heads, capitate or subcapitate, Inflorescence axillary, Inflorescence terminal, Bracts very small, absent or caducous, Flowers actinomorphic or somewhat irregular, Calyx 5-lobed, Calyx glabrous, Petals united, valvate, Petals white, Stamens numerous, more than 10, Stamens completely free, separate, Stamens long exserted, Filaments glabrous, Style terete, Fruit a legume, Fruit unilocular, Fruit freely dehiscent, Fruit elongate, straight, Fruit oblong or ellipsoidal, Fruit coriaceous or becoming woody, Fruit exserted from calyx, Fruit compressed between seeds, Fruit glabrous or glabrate, Fruit 3-10 seeded, Seed with elliptical line or depression, pleurogram, Seeds ovoid to rounded in outline, Seed surface smooth, Seeds olive, brown, or black.
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Acacia koa

provided by wikipedia EN

Acacia koa, commonly known as koa,[3] is a species of flowering tree in the family Fabaceae. It is endemic to the Hawaiian Islands,[2] where it is the second most common tree.[4] The highest populations are on Hawaiʻi, Maui and Oʻahu.

Name

The name koa in the Hawaiian language ultimately comes from Proto-Austronesian *teRas meaning "core" or "ironwood"; many names referring to certain ironwood or heartwood species in Southeast Asia and Oceania such as Vitex parviflora (tugás in Cebuano), Eusideroxylon zwageri (togas in Tombonuwo), and Intsia bijuga (dort in Palauan) descend from this root.[5]

Koa also means brave, bold, fearless, or warrior.[3]

Description

Upper branches of a koa tree, showing the bark, sickle-shaped phyllodes, greenish rounded flower heads, and seedpods

Koa is a large tree, typically attaining a height of 15–25 m (49–82 ft) and a spread of 6–12 m (20–39 ft).[6] In deep volcanic ash, a koa tree can reach a height of 30 m (98 ft), a circumference of 6 m (20 ft), and a spread of 38 m (125 ft).[7] It is one of the fastest-growing Hawaiian trees, capable of reaching 6–9 m (20–30 ft) in five years on a good site.[8]

Leaves

Initially, bipinnately compound leaves with 12–24 pairs of leaflets grow on the koa plant, much like other members of the pea family. At about 6–9 months of age, however, thick sickle-shaped "leaves" that are not compound begin to grow. These are phyllodes, blades that develop as an expansion of the leaf petiole. The vertically flattened orientation of the phyllodes allows sunlight to pass to lower levels of the tree. True leaves are entirely replaced by 7–25 cm (2.8–9.8 in) long, 0.5–2.5 cm (0.20–0.98 in) wide phyllodes on an adult tree.[6]

Flowers

Flowers of the koa tree are pale-yellow spherical racemes with a diameter of 8–10 mm (0.31–0.39 in).[9] Flowering may be seasonal or year round depending on the location.[6]

Fruit

Fruit production occurs when a koa tree is between 5 and 30 years old. The fruit are legumes, also called pods, with a length of 7.5–15 cm (3.0–5.9 in) and a width of 1.5–2.5 cm (0.59–0.98 in). Each pod contains an average of 12 seeds. The 6–12 mm (0.24–0.47 in) long, 4–7 mm (0.16–0.28 in) wide seeds are flattened ellipsoids and range from dark brown to black in color. The pods are mature and ready for propagation after turning from green to brown or black. Seeds are covered with a hard seed coat, and this allows them to remain dormant for up to 25 years. Scarification is needed before A. koa seeds will germinate.[9]

Habitat

Koa is endemic to the islands of Hawaiʻi, Molokaʻi, Maui, Lānaʻi, Oʻahu, and Kauaʻi, where it grows at elevations of 100–2,300 m (330–7,550 ft). It requires 850–5,000 mm (33–197 in) of annual rainfall. Acidic to neutral soils (pH of 4–7.4)[6] that are either an Inceptisol derived from volcanic ash or a well-drained histosol are preferred.[10] Its ability to fix nitrogen allows it to grow in very young volcanic soils.[4] Koa and ʻōhiʻa lehua (Metrosideros polymorpha) dominate the canopy of mixed mesic forests.[11] It is also common in wet forests.[12]

Uses

The American Pop singer Taylor Swift with a Taylor acoustic guitar made of Acacia koa wood

The koa's trunk was used by ancient Hawaiians to build waʻa (dugout outrigger canoes)[13] and papa heʻe nalu (surfboards). Only paipo (bodyboards), kikoʻo, and alaia surfboards were made from koa, however; olo, the longest surfboards, were made from the lighter and more buoyant wiliwili (Erythrina sandwicensis).[14] The reddish wood is very similar in strength and weight to that of Black Walnut (Juglans nigra), with a specific gravity of 0.55,[9] and is sought for use in wood carving and furniture.[6] Koa is also a tonewood,[15] often used in the construction of ukuleles,[16] acoustic guitars,[17] and Weissenborn-style Hawaiian steel guitars.[18] B.C. Rich used koa on some of their electric guitars as well,[19] and still uses a koa-veneered topwood on certain models.[20] Fender made limited edition koa wood models of the Telecaster and the Stratocaster in 2006. Trey Anastasio, guitarist for the band Phish, primarily uses a koa hollowbody Languedoc guitar. Commercial silviculture of koa takes 20 to 25 years before a tree is of useful size.[21]

A thinly sliced section of wide Hawaiian Koa lumber.

Relation to other species

Koaiʻa seedpod, showing the end-to-end arrangement of seeds.

Among other Pacific Islands of volcanic (non-continental) origin, only Vanuatu has native Acacia species. A. heterophylla, from distant Réunion, is very similar and has been suggested to be the closest relative of koa.[22] Genetic sequence analysis results announced in 2014 confirmed this close relationship; the estimated time of divergence is about 1.4 million years ago.[23][24] A. heterophylla sequences nest within those of the more diverse A. koa, making the latter paraphyletic.[24] Both species are thought to be descended from an ancestral species in Australia, presumably their sister species, Acacia melanoxylon. Dispersals most likely occurred via seed-carrying by birds such as petrels.[24] Both species have very similar ecological niches, which differ from that of A. melanoxylon.[24]

A closely related species, koaiʻa or koaiʻe (A. koaia), is found in dry areas. It is most easily distinguished by having smaller seeds that are arranged end-to-end in the pod, rather than side by side. The phyllodes are also usually straighter, though this character is variable in both species. The wood is denser, harder, and more finely grained than koa wood.[6] Koaiʻa has been much more heavily impacted by cattle and is now rare, but can be seen on ranch land in North Kohala.

Conservation

The koa population has suffered from grazing and logging. Many wet forest areas, where the largest koa grow, have been logged out, and it now comes largely from dead or dying trees or farms on private lands. Although formerly used for outrigger canoes, there are few koa remaining which are both large and straight enough to do so today.[6] In areas where cattle are present, koa regeneration is almost completely suppressed. However, if the cattle are removed, koa are among the few native Hawaiian plants able to germinate in grassland, and can be instrumental in restoring native forest. It is often possible to begin reforestation in a pasture by disk harrowing the soil, as this scarifies seeds in the soil and encourages large numbers of koa to germinate.[10] Experiments at the Hakalau Forest National Wildlife Refuge have shown that ʻōhiʻa lehua (Metrosideros polymorpha) survives best in pasture when planted under koa. This is because koa trees reduce radiative cooling, preventing frost damage to ʻōhiʻa lehua seedlings.[25]

Ecology

Koa is the preferred host plant for the caterpillars of the green Hawaiian blue (Udara blackburni), which eat the flowers and fruits.[26] Adults drink nectar from the flowers. Koa sap is eaten by the adult Kamehameha butterfly (Vanessa tameamea).[27] The koa bug (Coleotichus blackburniae) uses its rostrum to suck the contents out of koa seeds.[28] Koa is vulnerable to infection by koa wilt.

Gallery

References

  1. ^ Contu, S. 2012. Acacia koa. The IUCN Red List of Threatened Species 2012: e.T19891713A19999145. https://dx.doi.org/10.2305/IUCN.UK.2012.RLTS.T19891713A19999145.en. Downloaded 8 May 2017.
  2. ^ a b "Acacia koa". Germplasm Resources Information Network (GRIN). Agricultural Research Service (ARS), United States Department of Agriculture (USDA). Retrieved 2010-05-03.
  3. ^ a b Kepler, Angela Kay (1998). Hawaiian Heritage Plants. University of Hawaii Press. p. 106. ISBN 978-0-8248-1994-1.
  4. ^ a b Idol, Travis (2008-04-16). "Environmental Controls Over Acacia koa Productivity". Travis Idol's Research Page. University of Hawaiʻi at Mānoa. Retrieved 2009-01-31.
  5. ^ Blust, Robert; Trussel, Stephen (2010). "*teRas: heartwood of a tree, hard, durable core of wood; ironwood tree". Austronesian Comparative Dictionary. Max Planck Institute for Evolutionary Anthropology. Retrieved 27 December 2022.{{cite web}}: CS1 maint: url-status (link)
  6. ^ a b c d e f g Elevitch, Craig R.; Kim M. Wilkinson; J. B. Friday; C. Baron Porter (April 2006). "Acacia koa (koa) and Acacia koaia (koaiʻa)" (PDF). The Traditional Tree Initiative. {{cite journal}}: Cite journal requires |journal= (help)
  7. ^ Welsbacher, Anne (2003). Life in a Rain Forest. Twenty-First Century Books. p. 30. ISBN 978-0-8225-4685-6.
  8. ^ Wilkinson, Kim M.; Craig R. Elevitch (2003). Growing Koa: A Hawaiian Legacy Tree. Hōlualoa, Hawai'i: Permanent Agriculture Resources. p. 13. ISBN 978-0-9702544-2-9.
  9. ^ a b c Allen, James A. (2003-01-01). "Acacia koa A. Gray" (PDF). Tropical Tree Seed Manual. Reforestation, Nurseries & Genetics Resources. Retrieved 2009-02-23.
  10. ^ a b Whitesell, Craig D (1990). "Acacia koa". In Burns, Russell M.; Honkala, Barbara H. (eds.). Hardwoods. Silvics of North America. Washington, D.C.: United States Forest Service (USFS), United States Department of Agriculture (USDA). Vol. 2. Archived from the original on 20 January 2009. Retrieved 2009-02-17 – via Southern Research Station.
  11. ^ Ziegler, Alan C. (2002). Hawaiian Natural History, Ecology, and Evolution. University of Hawaii Press. pp. 175–176. ISBN 978-0-8248-2190-6.
  12. ^ Sohmer, S. H.; R. Gustafson (1987). Plants and Flowers of Hawaiʻi. University of Hawaii Press. pp. 45–52. ISBN 978-0-8248-1096-2.
  13. ^ Bryan, William Alanson (1915). Natural History of Hawaii, Being an Account of the Hawaiian People, the Geology and Geography of the Islands, and the Native and Introduced Plants and Animals of the Group. Hawaiian Gazette Co, Ltd. p. 339. ISBN 978-1-4446-7820-8.
  14. ^ Marcus, Ben; Juliana Morais; Jeff Divine; Gary Linden (2007). The Surfboard: Art, Style, Stoke. MBI Publishing Company. pp. 17–19. ISBN 978-0-7603-2753-1.
  15. ^ Beberman, Norman L. "Koa: Beautiful Looking, Beautiful Sounding Tonewood". GuitarNation.com. Archived from the original on 7 February 2009. Retrieved 2009-02-23.
  16. ^ Gernot Rödder (2002). Total Ukulele: D-Tuning Method for Beginners. Mel Bay Publications. p. 93. ISBN 978-3-8024-0446-7.
  17. ^ Gerken, Teja (2000). Acoustic Guitar Owner's Manual: The Complete Guide. String Letter Publishing. p. 10. ISBN 978-1-890490-21-8.
  18. ^ Sheperd, John (2003). "Guitars". Continuum Encyclopedia of Popular Music of the World. Vol. II: Performance and Production. Continuum International Publishing Group. p. 283. ISBN 978-0-8264-6322-7.
  19. ^ Achard, Ken (1989). The History and Development of the American Guitar. Bold Strummer Ltd. p. 163. ISBN 978-0-933224-18-6.
  20. ^ Kirkland, Eric (December 2006). "Rich and Famous". Guitar World: 154.
  21. ^ "Silviculture: Diversification of Rural Economy". Leeward Haleakalā Watershed Restoration Partnership. Retrieved 2009-02-01.
  22. ^ Whitesell, Craig D (1964). "Silvical Characteristics of Koa (Acacia koa Gray)" (PDF). United States Forestry Service. {{cite journal}}: Cite journal requires |journal= (help)
  23. ^ Marris, E. (2014-06-19). "Tree hitched a ride to island". Nature. 510 (7505): 320–321. Bibcode:2014Natur.510..320M. doi:10.1038/510320a. PMID 24943937.
  24. ^ a b c d Le Roux, J. J.; Strasberg, D.; Rouget, M.; Morden, C. W.; Koordom, M.; Richardson, D. M. (2014-06-18). "Relatedness defies biogeography: The tale of two island endemics (Acacia heterophyllaandA. Koa)". New Phytologist. 204 (1): 230–242. doi:10.1111/nph.12900. PMID 24942529.
  25. ^ Friday, J. B.; Darrell A. Herbert (April 2006). "Metrosideros polymorpha ('ōhi'a lehua)" (PDF). The Traditional Tree Initiative: 21. {{cite journal}}: Cite journal requires |journal= (help)
  26. ^ Scott, James A. (1992). The Butterflies of North America: A Natural History and Field Guide. Stanford University Press. p. 399. ISBN 978-0-8047-2013-7.
  27. ^ Scott, Susan (1991). Plants and Animals of Hawaii. Bess Press. p. 78. ISBN 978-0-935848-93-9.
  28. ^ "Koa Bug Investigation" (PDF). Uhh.hawaii.edu. Retrieved 15 March 2022.

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Acacia koa: Brief Summary

provided by wikipedia EN

Acacia koa, commonly known as koa, is a species of flowering tree in the family Fabaceae. It is endemic to the Hawaiian Islands, where it is the second most common tree. The highest populations are on Hawaiʻi, Maui and Oʻahu.

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