Local names:
English (okoume,Gabon mahogany), French (okoumé), Trade name (okoumé)
Aucoumea klaineana is a dioecious, medium-sized to large evergreen tree up to 50(-60) m tall; bole cylindrical, often contorted and bent, up to 110(-240) cm in diameter, with buttresses up to 3 m high, and clear of branches up to 21 m. The bark 0.5-2 cm thick, greyish to orange-brown, smooth and spotted with white, yellow, orange or red bands (resulting from lichens) in young trees, detaching in more or less thick rectangular brown scales revealing orange bark in adult trees, lenticellate, slash strongly resinous, pinkish-red, fibrous; crown rather open structured. Leaves alternate, imparipinnate; stipules absent; rachis up to 40 cm long; leaflets 7-13, petiolule up to 4 cm long, blade ovate to oblong, 1030 cm × 4-7 cm, rounded at base, acuminate at apex, margin entire, leathery. Inflorescence an axillary or terminal panicle up to 20 cm long; male inflorescence comprising up to 5 times more flowers than the female. Flowers unisexual, regular, 5-merous; sepals lanceolate, up to 5 mm long, tomentose, greenish; petals spatulate, 5-6 mm long, tomentose on both sides, whitish; extra-staminal disk present consisting of 2-lobed nectaries; male flowers with 10 stamens and rudimentary pistil; female flowers with 10 staminodes and a superior, 5-locular ovary, each locule with 2 ovules but only 1 ovule developing. Fruit a capsule up to 5 cm × 3 cm, opening with 5 valves from the base, 5-seeded. It is monotypic, and characterized by its extra-staminal disk and dry, dehiscent fruit (pseudocapsule), which after opening releases 5 seeds covered by a winged endocarp. Seeds enclosed by endocarp (‘pyrenes’), ovoid extending into a wing 2-3 cm × 0.5 cm; cotyledons suborbicular, thin and foliaceous.
Ecology
Okoumé is a long-lived pioneer of, in particular, large forest clearings and fire-protected savanna edges, where it often becomes mono-dominant. It requires full sun to grow well but seedlings and saplings can, however, survive in shade. It is abundant in Hygrophilous coastal evergreen Guineo-Congolian rain forest especially in old secondary forest on well-drained sites where huge individuals occur in what seems to be virgin forest. It regenerates naturally where the recuperation period between logging cycles is sufficient.
Native range
Cameroon, Cote d'Ivoire, Democratic Republic of Congo, Equatorial Guinea, Gabon, Nigeria
Tree management
Good regeneration requires a sufficient number of seed trees, large canopy openings or clearings (>2500 m²) and clean soil during the fruiting season. These conditions are found in shifting cultivation or in logged areas (e.g. log yards and wide logging tracks). Selective logging or natural tree fall events do not produce sufficiently large canopy openings. If site conditions are favourable, okoumé dominates re-growth. Two main site preparation methods are used for establishing plantations. The first is mechanised clear felling, in which existing woody vegetation is cleared using bulldozers and placed into windrows and burned. Seedlings are planted between the windrows. The second consists of cutting the vegetation to 50 cm above the ground to allow re-sprouting and re-growth. Seedlings are planted in lines cut through the re-growth. In both methods, existing large trees are killed. Recommended spacing for seedlings is in the range of 625–950 trees/ha. It is necessary to eliminate climbers, especially Mikania species, and trees such as Musanga cecropioides, which competes for light and space, for up to 5 years after planting. Thinning in both natural and artificial stands is advisable but should be conducted carefully to avoid increased sensitivity to black canker attack resulting from lateral illumination of the stem. In both mixed and almost pure stands, thinning is beneficial for diameter growth, but the resulting extractable wood volume may vary. Suppressed trees are more responsive to thinning than dominant ones. In almost pure stands, thinning should be restricted to those young stands of less than 15 years, because in older stands thinning will remove potentially commercial volumes of wood. In plantations, it is recommended that a thinning regime to reduce stem density to 350 stems/ha after 5 years, 200-250 stems/ha after 10 years and 150 stems/ha after 15 years. If resources only allow 2 thinning operations, stand density can be reduced to 250-300 stems/ha after 5 years and 150 stems/ha after 13 years. In all cases, thinning should involve girdling okoumé trees, or girdling and poisoning other species, taking care to avoid intense bole illumination of lower strata trees. Okoumé trees should not be poisoned because of the risk of affecting adjacent trees via the connected root systems.
Seed storage behaviour is intermediate. Seeds lose viability within 1 month in the field, but can be stored at 4°C in airtight containers for up to 3 years after being dried to 8% moisture content. There is a 10000 seeds per kg.
Okoumé is a long-lived pioneer of, in particular, large forest clearings and fire-protected savanna edges, where it often becomes mono-dominant. It requires full sun to grow well but seedlings and saplings can, however, survive in shade. It is abundant in Hygrophilous coastal evergreen Guineo-Congolian rain forest especially in old secondary forest on well-drained sites where huge individuals occur in what seems to be virgin forest. It regenerates naturally where the recuperation period between logging cycles is sufficient.
Propagation by seed is the preferred method. Seeds do not require pre-treatment and can be sown directly in polythene bags (20-30 cm high, 10-15 cm in diameter) filled with a mixture of sand and clay. Two seeds are placed per bag; one seedling is selected after 3-4 weeks. After 2.5 months, the seedlings are 20-25 cm tall, have 5-7 simple leaves and are ready for transplanting. Propagation by grafting and cuttings is possible.
The wood, which is used as firewood has an energy value of 29 970 kJ/kg
Timber: Okoumé is a lightweight, comparatively soft hardwood with a density of (320-)430-450(-570) kg/m³ at 12% moisture content. Okoumé is a major commercial timber in Gabon and Equatorial Guinea, representing more than 70% of timber production, while it is of lesser importance in Congo. The timber is mainly exported as logs to Europe. It is made into blockboard, particle board and veneer, and is widely used in boat building for decorative interior paneling and for exterior applications. The wood is also suitable for light interior construction, carpentry, furniture, sports equipment, cigar boxes and packing cases. Logs are traditionally used for the construction of canoes. The wood is suitable for the production of pulp for papermaking.
Medicine: Bark is applied to treat superficial wounds and abscesses. The astringent bark is used to treat diarrhea.
Gum or resin: Bark resin is used for torches and oil lamps in Gabon and Equatorial Guinea.