Acacia koa

Acacia koa, commonly known as koa,<ref name=HIHP/> is a species of flowering tree in the family Fabaceae. It is endemic to the Hawaiian Islands,<ref name="GRIN"/> where it is the second most common tree.<ref name=TravisIdol>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The highest populations are on [[Hawaii (island)|HawaiTemplate:Okinai]], Maui and [[Oahu|OTemplate:Okinaahu]].

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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The Hawaiian Acacia koa is closely related to a common tree in Taiwan called Acacia confusa. The two species also share a very similar appearance.

Koa also means brave, bold, fearless, or warrior.<ref name=HIHP>Template:Cite book</ref>

Description

File:Acacia Koa trees.jpg

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 Template:Convert and a spread of Template:Convert.<ref name="TradTree">Template:Cite journal</ref> In deep volcanic ash, a koa tree can reach a height of Template:Convert, a circumference of Template:Convert, and a spread of Template:Convert.<ref>Template:Cite book</ref> It is one of the fastest-growing Hawaiian trees, capable of reaching Template:Convert in five years on a good site.<ref>Template:Cite book</ref>

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 Template:Convert long, Template:Convert wide phyllodes on an adult tree.<ref name="TradTree" />

Flowers

Flowers of the koa tree are pale-yellow spherical racemes with a diameter of Template:Convert.<ref name="RNGR">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Flowering may be seasonal or year round depending on the location.<ref name="TradTree" />

Fruit

Fruit production start occurring when a koa tree is between 5 and 30 years old. The fruit are legumes, also called pods, with a length of Template:Convert and a width of Template:Convert. Each pod contains an average of 12 seeds. The Template:Convert long, Template:Convert 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.<ref name="RNGR" />

Habitat

Koa is endemic to the islands of [[Hawaii (island)|HawaiTemplate:Okinai]], [[Molokai|MolokaTemplate:Okinai]], Maui, [[Lanai|LānaTemplate:Okinai]], [[Oahu|OTemplate:Okinaahu]], and [[Kauai|KauaTemplate:Okinai]], where it grows at elevations of Template:Convert. It requires Template:Convert of annual rainfall. Acidic to neutral soils (pH of 4–7.4)<ref name="TradTree" /> that are either an Inceptisol derived from volcanic ash or a well-drained histosol are preferred.<ref name="Silvics">Template:Silvics</ref> Its ability to fix nitrogen allows it to grow in very young volcanic soils.<ref name=TravisIdol /> Koa and Template:OkinaōhiTemplate:Okinaa lehua (Metrosideros polymorpha) dominate the canopy of Hawaiian mixed mesic forests.<ref name="Ziegler">Template:Cite book</ref> It is also common in wet forests.<ref name="Sohmer">Template:Cite book</ref>

Uses

File:Hawaiian Koa Micro Slab.jpg

A thinly sliced section of wide Hawaiian Koa lumber

The koa's trunk was used by ancient Hawaiians to build [[Waka (canoe)|waTemplate:Okinaa]] (dugout outrigger canoes)<ref>Template:Cite book</ref> and papa heTemplate:Okinae nalu (surfboards). Only paipo (bodyboards), kikoTemplate:Okinao, and alaia surfboards were made from koa, however; olo, the longest surfboards, were made from the lighter and more buoyant wiliwili (Erythrina sandwicensis).<ref>Template:Cite book</ref> The reddish wood is very similar in strength and weight to that of black walnut (Juglans nigra), with a specific gravity of 0.55,<ref name="RNGR" /> and is now sought for use in wood carving and furniture.<ref name="TradTree" /> Koa is also a tonewood,<ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref> often used in the construction of ukuleles,<ref>Template:Cite book</ref> acoustic guitars,<ref>Template:Cite book</ref> and Weissenborn-style Hawaiian steel guitars.<ref>Template:Cite encyclopedia</ref> B.C. Rich used koa on some of their electric guitars as well,<ref>Template:Cite book</ref> and still uses a koa-veneered topwood on certain models.<ref>Template:Cite journal</ref> 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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Taylor, Collings and Martin are few among the many other brands that use that tonewood for manufacturing acoustic guitars. <ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

File:Koa‛Umeke(Bowl)byMelBlair(1914–1995).jpg

‛Umeke Lū‛au Pākākā (Hawaiian: "low, broad feast bowl") hand-turned from Koa by master woodworker Mel Blair (1914–1995), owner of Blair’s at Waikiki (1945–1986).

In Hawaiʻi, the ‛umeke ‛ (Hawaiian: “wooden bowl”) has been a highly-perfected art form and considered a prized possession for well over a thousand years. They were expertly handcrafted using rare and exotic hardwoods like Kou, Milo, and Koa. Prior to 1819, ‛umekes were considered sacred and strictly reserved for ‛Ali‛i (Hawaiian: “Royalty”), and under penalty of death for a commoner to possess one. Today, ‛umekes are highly collectible and have become known as a universal symbol of generosity and welcome.<ref>American Woodturner --- Journal of the American Association of Woodturners volume 32, issue 5 – October, 2017, Feature Article, pgs. 45–51 “‘UMEKE LA‘AU: A RICH HAWAIIAN TRADITION”, Sharon Doughtie shares a well-researched account of the historical uses and nuances of Hawaiian bowls, or ‘umeke la‘au. </ref>

Relation to other species

File:Acacia koaia3.jpg

KoaiTemplate:Okinaa 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.<ref>Template:Cite journal</ref> Genetic sequence analysis results announced in 2014 confirmed this close relationship; the estimated time of divergence is about 1.4 million years ago.<ref name = "Marris2014">Template:Cite journal</ref><ref name = "Le Roux2014">Template:Cite journal</ref> A. heterophylla sequences nest within those of the more diverse A. koa, making the latter paraphyletic.<ref name = "Le Roux2014" /> 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.<ref name = "Le Roux2014" /> Both species have very similar ecological niches, which differ from that of A. melanoxylon.<ref name = "Le Roux2014" />

A closely related species, koaiTemplate:Okinaa or koaiTemplate:Okinae (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.<ref name="TradTree" /> KoaiTemplate:Okinaa has been much more heavily impacted by cattle and is now rare, but can be seen on ranch land in North Kohala.Template:Citation needed

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.<ref name="TradTree" /> 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.<ref name="Silvics"/> Experiments at the Hakalau Forest National Wildlife Refuge have shown that Template:OkinaōhiTemplate:Okinaa lehua (Metrosideros polymorpha) survives best in pasture when planted under koa. This is because koa trees reduce radiative cooling, preventing frost damage to Template:OkinaōhiTemplate:Okinaa lehua seedlings.<ref>Template:Cite journal</ref>

Ecology

Koa is the preferred host plant for the caterpillars of the green Hawaiian blue (Udara blackburni), which eat the flowers and fruits.<ref name="Scott">Template:Cite book</ref> Adults drink nectar from the flowers. Koa sap is eaten by the adult Kamehameha butterfly (Vanessa tameamea).<ref>Template:Cite book</ref> The koa bug (Coleotichus blackburniae) uses its rostrum to suck the contents out of koa seeds.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Koa is vulnerable to infection by koa wilt.

Gallery

• Starr 070205 4082 acacia koa2.jpg
• Starr 060325-6745 Acacia koa.jpg
• Starr 041127-1178 Acacia koa.jpg
• Starr 051122-5287 Acacia koa.jpg
• Starr 060312-6710 Acacia koa.jpg
• Starr 041214-1500 Acacia koa.jpg
• Starr 040220-0316 Acacia koa.jpg
• Starr 040723-0533 Acacia koa.jpg
• Starr 030405-0136 Acacia koa.jpg
• Starr 041113-0733 Acacia koa.jpg
• Starr 051211-5686 Acacia koa.jpg
• Starr 030405-0092 Acacia koa.jpg
• Acacia koa with phyllode between the branch and the compound leaves.JPG

  Acacia koa with phyllode between the branch and the compound leaves

External links

• Template:Commons category-inline
• Template:Wikispecies-inline
• Photos of Acacia koa at Hawaiian Ecosystems at Risk Project (HEAR)
• UCLA botanical garden and home
• Historic photos and descriptions of Acacia koa