Okoumé  (Aucoumea klaineana)

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 in situ conservation programmes (3) in order to protect its population long-term. Although it has been grown in plantations since 1944, only a small proportion of timber felled in natural forests has been replaced by plantation development (4). It has been suggested that the species should be listed on Appendix II of the Convention on International Trade in Endangered Species in Equatorial Guinea and the Republic of Congo, meaning international trade in the species should be carefully controlled in these states, and on Appendix III in Gabon, allowing a certain amount of controlled trade (7), although this has yet to be agreed.

For more information on conservation of the world’s threatened tree species and for advice on responsible timber buying, visit:

• Global Trees Campaign:
  http://www.globaltrees.org/
• Forest Stewardship Council:
  http://www.fsc.org/
• International Tropical Timber Organization:
  http://www.itto.or.jp/live/index.jsp