Khaya senegalensis

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Khaya senegalensis flower
© Joris de Wolf, Patrick Van Damme, Diego Van Meersschaut

© Joris de Wolf, Patrick Van Damme, Diego Van Meersschaut
Khaya senegalensis foliage
© Joris de Wolf, Patrick Van Damme, Diego Van Meersschaut
Khaya senegalensis bark
© Joris de Wolf, Patrick Van Damme, Diego Van Meersschaut

Khaya senegalensis is a deciduous evergreen tree, 15-30 m high, up to 1 m in diameter, with a clean bole to 8-16 m, buttresses not prominent or absent; bark dark grey, with small, thin, reddish-tinged scales; slash dark pink to bright crimson, exuding a red sap.
 
Leaves alternate, compound, stipules absent; petiole and rachis 13-33 cm long; leaflets 3-4 (max. 7) usually opposite pairs, oblong to narrowly oblong-elliptic, 4-12 x 2-5 cm, apex acute to shortly acuminate, base rounded, margins entire, pale green, lateral nerves 8-16, petiolules about 3.5 cm long. 

Inflorescence a lax, much-branched axillary panicle up to 17 cm long; flowers tetramerous, monoecious but with well-developed vestiges of those of the opposite sex with very little external differences between sexes. Calyx pale green, lobed almost to the base, lobes subcircular, about 1 x 1 mm, imbricate; petals cream, free, oblong-ovate, 4 x 2.5 mm, contorted in bud; orange disk around the ovary. 

Fruit an upright, almost spherical, woody capsule, 4-6 cm in diameter, opening by 4 valves from the apex (a distinction from K. ivorensis, which is closely related but has 5 valves). Seeds brown, 6 or more per cell, broadly transversely ellipsoid to flat, about 25 x 18 mm, margins narrowly winged. 
The specific name means ‘of Senegal’, which is where the type specimen was collected.

Ecology

K. senegalensis occurs in riverine forests and is scattered within the higher-rainfall savannah woodlands. In moister areas, K. senegalensis is found on uplands, but it is restricted to riparian habitats or stream bottoms that extend into the savannah in the drier portions of the range. During the 1st year, the seedling develops a strong, deep taproot, which makes it the most drought hardy of all the Khaya species. It is also very resistant to flooding and can be considered for planting on swampy soils. Moderately shade tolerant. Except where selectively removed by logging, dry-zone mahogany remains a dominant species in most of its range.

Successful plantations of dry-zone mahogany in other parts of the world have generally been in areas with short dry seasons and high rainfall.

Native range
Cameroon, Central African Republic, Chad, Cote d'Ivoire, Equatorial Guinea, Gambia, Ghana, Guinea, Guinea-Bissau, Mali, Niger, Nigeria, Senegal, Sierra Leone, Sudan, Togo, Uganda

Tree management

Strategies to obtain sufficient regeneration on poor sites should include liberation cutting of stands with advanced regeneration. Common spacings on cleared and prepared sites are 5 x 5 m and 5 x 10 m. A spacing of 5 x 20 m is used when planting in riparian forests. Hoeing and weeding are recommended at the onset of the dry season. K. senegalensis coppices well. Although older trees are resistant to fire, seedlings are fairly susceptible.

Seed storage behaviour is intermediate; seeds tolerate desiccation to 6% mc; 81% germinate following 3 years of subsequent storage at 2 deg. C; seeds tolerate desiccation to 5.7% mc (in equilibrium with 54.4% rh), little loss (about 3%) on desiccation to 2.1% mc (in equilibrium with 11.8% rh at 20 deg. C), complete loss in viability following 24 months of hermetic storage at 10 deg. C, 0 deg. C and -20 deg. C with 10% mc; it appears to 0 deg. C is optimal storage temperature for seeds at 2.2-5.6% mc, whereas -20 deg. C is damaging. Normally there are 6000-7000 seed/kg, but occasionally as few as 3000.

K. senegalensis occurs in riverine forests and is scattered within the higher-rainfall savannah woodlands. In moister areas, K. senegalensis is found on uplands, but it is restricted to riparian habitats or stream bottoms that extend into the savannah in the drier portions of the range. During the 1st year, the seedling develops a strong, deep taproot, which makes it the most drought hardy of all the Khaya species. It is also very resistant to flooding and can be considered for planting on swampy soils. Moderately shade tolerant. Except where selectively removed by logging, dry-zone mahogany remains a dominant species in most of its range.

Successful plantations of dry-zone mahogany in other parts of the world have generally been in areas with short dry seasons and high rainfall.

Natural regeneration from seed is poor, although it grows from pretreated seed and transplants well. Seed yield is usually heavy. Germination is epigeal, about 90% of fresh seed germinate within 18 days. Seedlings can survive light to moderate shade. Containerized stock is best; however, bare-root and stump plantings give satisfactory results. Reproduction may also occur from root suckers. 

Establishment of new seedlings can be encouraged by disturbances such as cultivation or prescribed fire just before seed fall. After seedlings have emerged, a partial cut applied to allow light to reach the forest floor improves seedling establishment well before the final harvest of the existing stand.

Poison: K. senegalensis is used in Cote d’Ivoire as an ingredient in arrow poison. Bark scales are sometimes used as a fish poison.

It largely reproduces itself from suckers and is recommended for reforestation purposes.

Fodder: Young leaves contain fairly large amounts of digestible crude protein. The leaves are used as a fodder for cattle and camels, although they are not very palatable.

Only limited quantities are available for fuelwood, and trees of larger dimensions are undesirable because of difficulties with splitting and crosscutting. Hence, even if fuelwood is in short supply, larger-diameter sections are not utilized. The gross energy value of the wood is 19 990 kJ/kg.

Fibre: The wood is used in West Africa for pulp.

Timber: One of the hardest African mahoganies and the hardest of the Khaya species. It is widely used on a commercial scale, particularly in West Africa. The wood density ranges from 0.6 to 0.85, depending on locality. The sapwood is pinkish-tan in colour and the heartwood an attractive dark red-brown. It is moderately resistant to fungi, insects and termites. The sapwood is moderately resistant to preservation treatment, the heartwood extremely so. The timber saws well except for a tendency to be woolly in cross grain. It seasons rapidly, with little degradation; however, tension may occasionally cause splitting and warping. It is favoured for furniture, high-class joinery, trim and boat building. The wood is also used locally for railroad ties, flooring, turnery and veneer. Because of its decorative appearance, the wood of K. senegalensis is a very popular timber.

Tannin or dyestuff: The bark is used in tanning. 

Lipids: The seeds have an oil content of 67% and are rich in oleic acid (66%). The oil is used in West Africa for cooking.

Medicine: The very bitter bark has a considerable reputation in its natural range as a fever remedy. The bark is also used as a vermifuge, taenicide, depurative and for treating syphilis. Bark extract is used for treating jaundice, dermatoses, scorpion bite, allergies, infection of the gums, hookworm, bleeding wounds (disinfectant), and as a laxative. Seeds and leaves are used for treating fever, headache; roots against sterility, for the treatment of mental illness, against syphilis, leprosy and as an aphrodisiac. Crushed bark and seeds are regarded as emmenagogue. Bark also used in traditional veterinary practice, for example for cattle suffering from liver fluke, for ulcers in camels, donkeys and horses, and in horses for internal ailments associated with mucous diarrhoea.

Gum or resin: The presence of oleoresin in the vessels of Khaya species accounts for the durability of the timber and its resistance to insect and fungal attack.

Ornamental: Dry-zone mahogany is an important urban tree in West Africa.