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The 'koa' (''Acacia koa''; Family Fabaceae) is a large tree endemic to the Hawaiian Islands, primarily Hawaii, Maui and Oahu.

Contents

Description

Uses

Relation to other species

Conservation

Gallery

References

External links

Description

The koa tree is somewhat unusual in that the leaves produced early in the growth of the plant are compound leaves typical of the pea family. However, the adult koa has thick sickle-shaped "leaves" that are not compound. 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.
It is one of the fastest-growing Hawaiian trees, capable of reaching over 20 feet in five years, but still requires 50 years or more to reach the size required by most users, making farming of koa difficult.

Uses

Its trunk was used by the ancient Hawaiians to build dugout canoes. The reddish wood is highly prized for use in wood carving, musical instruments, and furniture. Koa is also a tonewood, often used in the construction of the ukulele and the weissenborn-style Hawaiian steel guitar.

Relation to other species

The relationships of koa are not clear. Among other Pacific Islands of volcanic (non-continental) origin, only Vanuatu has native ''Acacia'' species. ''Acacia heterophylla'', from distant Réunion, is very similar and has been suggested to be the closest relative of koa, but this is far from certain.
A closely related species, koaia or koaie (''Acacia koaia''), is found in dry areas. It is most easily distinguished by having the seeds 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 has a different structure, and is harder than koa. Koaia 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 canoes, there are few koa remaining which are both large and straight enough to do so today. 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. Experiments at the Hakalau National Wildlife Refuge have shown that ōhia lehua, the dominant tree in most Hawaiian forests, survives best in pasture when planted under koa. The seeds of koa are hard and dry, and capable of surviving dormant for decades. It is often possible to bring begin reforestation in a pasture by running a bulldozer or other heavy equipment over the ground, as this scarifies the seeds in the soil and causes germination of large numbers of koa.

Gallery

References

★ Wilkinson, Kim M., and Craig R. Elevitch. ''Growing Koa: A Hawaiian Legacy Tree''. Permanent Agriculture Resources (PAR), Holualoa, 2003. ISBN 0-9702544-2-3.

External links

★ Photos of Acacia koa at Hawaiian Ecosystems at Risk Project (HEAR)

★ UCLA botanical garden and home

★ Historic photos and descriptions of Acacia koa