Okoumé (Aucoumea klaineana)
|Also known as:||Gabon mahogany, gaboon|
|Size||Height: up to 60 m (2)|
Trunk diameter: up to 2.4 m (2)
Classified as Vulnerable (VU) on the IUCN Red List (1).
This medium- to large-sized evergreen is Gabon’s most important commercial tree, contributing around 90 percent of the country’s total timber production (1) (3) (4). The trunk of okoumé is cylindrical and clear of branches up to about 21 metres, with wing-like buttresses up to about three metres high, in individuals over 30 to 40 centimetres in diameter. The smooth bark is greyish to orange-brown in colour, and lichens growing on young trees may result in spotting with white, yellow, orange or red bands. In older trees, the bark cracks and sheds in large vertical scales (2) (5). The heartwood is salmon-pink, and the narrow sapwood whitish or pale grey (5) (6). The leaves of okoumé are alternate and pinnate, bearing between 7 and 13 leaflets, which are ovate to oblong in shape and leathery in texture, with entire (unserrated) edges (2).
The natural range of okoumé is restricted to western and central Gabon and areas of Equatorial Guinea, Republic of Congo and Cameroon (1) (3). The species has also been introduced to Madagascar, Ivory Coast, Ghana, Central African Republic, French Guiana, Indonesia, Malaysia and Surinam (2) (5).
Lowland broadleaf forests up to elevations of 700 to 1,000 metres (3) (5). Okoumé grows well on a wide range of acid soils (2) (5), and is common in secondary forest (3), though it is generally absent from flooded areas (5).
Okoumé is a light-demanding species which requires full sun to grow well (2) (3), and as a pioneer species it readily colonises open spaces (2) (5). New leaves appear from September to December and are bright red for about a week. Flowering usually starts at the end of the dry season, in August, and may last up to two months, although individual flowers last for only a few days. The whitish flowers, which are insect-pollinated, are borne on branched inflorescences up to 20 centimetres long, with male and female flowers borne on separate trees. Although okoumé may begin to flower at about ten years old, it only starts to produce fruit after about fifteen years, or when the tree has reached 30 to 40 centimetres in diameter. After this, fruiting is usually annual, taking place between January and March, though large quantities of seeds are only produced every few years. The fruits comprise capsules up to five centimetres by three centimetres in size, each producing five spoon-shaped, winged seeds, which are dispersed by the wind up to 200 metres from the parent tree (2) (5). A mature okoumé tree may produce up to 20,000 seeds (2). Okoumé is a long-living tree, with individuals sometimes reaching up to 300 years old (5).
Okoumé produces a lightweight, relatively soft hardwood, which is considered excellent for veneer and plywood, and is also used in light construction and furniture (2) (3) (5). In Gabon and Equatorial Guinea, it is also used as firewood and for building dugout canoes, and the bark resin is used for torches and oil lamps. The bark itself may be used to treat wounds and abscesses and as a treatment for diarrhoea (2) (5).
Okoumé regenerates naturally when sufficient periods are left between logging cycles (2). However, repeated logging restricts regeneration and while some consider logging to be sustainable in Gabon, other fear for the long-term survival of this species (1) (3). There is also concern that repeated, selective felling of okoumé may be leading to deterioration of the gene pool in some areas (1) (3) (4). Some predict that okoumé forest will probably be exhausted in Equatorial Guinea and the Republic of Congo in the near future (7), and although the species remains abundant in Gabon, it appears logging restrictions, such as minimum logging diameters, are not always enforced (3).
Okoumé is considered a priority species for
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- Alternate: leaves that are located at alternating points along a stem, rather than in opposite pairs.
- Buttresses: the flared bases of certain tree trunks.
- Evergreen: a plant which retains leaves all year round. This is in contrast to deciduous plants, which completely lose their leaves for part of the year.
- Germination: the beginning of growth, usually following a period of dormancy and in response to favourable conditions. For example, the sprouting of a seedling from a seed.
- Heartwood: the inner layers of wood in a tree that no longer contain living cells or produce sap. Heartwood tends to be darker in colour than the outer ‘sapwood’.
- In situ: measures to conserve a species or habitat, that occur inside of the natural range of the species.
- Inflorescence: the reproductive shoot of a plant which bears a group or cluster of flowers.
- Leaflets: the individual ‘leaf-like’ parts of a compound leaf.
- Lichens: composite organisms made up of a fungus in a co-operative partnership with an alga. Owing to this partnership, lichens can thrive in harsh environments such as mountaintops and polar regions. Characteristically forms a crust-like or branching growth on rocks or tree trunks.
- Pinnate: in plants, a compound leaf where the leaflets (individual ‘leaves’) are found on either side of the central stalk.
- Sapwood: the living, soft wood between the bark of a tree and its inner, non-living heartwood. This outer layer of wood contains the sap and is generally lighter in colour than the heartwood.
- Secondary forest: forest that has re-grown after a major disturbance, such as fire or timber harvest, but has not yet reached the mature state of primary forest.
IUCN Red List (December, 2009)