Koa
From Wikipedia, the free encyclopedia
- For other uses, see KOA.
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 A young Koa tree showing compound leaves and phyllodes
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| Acacia koa A.Gray |
The koa (Acacia koa; Family Fabaceae) is a large tree endemic to the Hawaiian Islands, primarily Hawaii and Maui. Its trunk was used by the ancient Hawaiians to build dugout canoes.
The 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 at all 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.
The relationships of koa are not clear. Among other Pacific Islands of volcanic (non-continental) origin, only Vanuatu has native Acacia species. It has been suggested that A. heterophylla, from Réunion, is the closest relative of koa, but this is far from certain.
The koa population has suffered from grazing and logging. The reddish wood is highly prized for use in wood carving, musical instruments, and furniture. 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. It is one of the fastest-growing Hawaiian trees, capable of reaching over 20 feet in 5 years, but still requires 50 years or more to reach the size required by most users, making farming of koa difficult. 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 Halakau National Wildlife Refuge have shown that ʻōhiʻa, the dominant tree in most Hawaiian forests, survives best in pasture when planted under koa.
A closely related species, koaiʻa or koaiʻe (A. 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 strongly sickle shaped, though this character is variable in both species. The wood has a different structure, and is harder than koa. Koaiʻa has been much more heavily impacted by cattle and is now rare, but can be seen on ranch land in North Kohala.
[edit] External links
- Photos of Acacia koa at Hawaiian Ecosystems at Risk Project (HEAR)
- UCLA botanical garden
[edit] References
- Wilkinson, Kim M. and Elevitch, Craig R. : Growing Koa : a Hawaiian Legacy Tree. Permanent Agriculture Ressources (PAR), Holualoa, 2003. ISBN 0-9702544-2-3 .
