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Tieghemella africana Pierre

Protologue
Not. bot. 1: 18 (1890).
Family
Sapotaceae
Chromosome number
2n = 26
Synonyms
Dumoria africana (Pierre) Dubard (1915), Mimusops africana (Pierre) Lecomte (1921), Baillonella africana (Pierre) Baehni (1965).
Vernacular names
Douka (En). Douka (Fr).
Origin and geographic distribution
Tieghemella africana occurs in Cameroon, Equatorial Guinea, Gabon, Congo and DR Congo. However, some specimens have been reported from Côte d’Ivoire, where the closely related Tieghemella heckelii (A.Chev.) Roberty occurs.
Uses
The wood, traded as douka, but often also as makore or cherry mahogany (often without distinction from Tieghemella heckelii), is used for furniture, exterior and interior construction, flooring, doors, vehicle frames, sports goods, railway sleepers, ship building, turnery and sculptures, and makes good and decorative veneer, often used to face plywood.
The seed kernels are rich in an edible fat, which is locally popular as a cooking or seasoning oil. In Gabon the fat is also used externally to treat rheumatism.
Production and international trade
Douka is traded on the international timber market, but production is small due to limited supply from natural stands. It is often traded together with makore timber (from Tieghemella heckelii). The export from Gabon increased from 15,600 m³ in 1997 to 36,000 m³ in 2001, but decreased again to 25,000 m³ in 2003. The export from Cameroon is much lower: 390 m³ in 2003. In 1994 the price of sawn douka wood from Gabon was US$ 93/m³.
Properties
The data on wood properties of douka and makore cannot be separated in the literature, and the following description applies to both species. The wood resembles African mahogany (Khaya and Entandrophragma spp.), but the texture is finer. The heartwood is pinkish-, purplish- or reddish-brown with a silky lustre, often with a decorative figure in the form of flames or stripes; it is very distinctly demarcated from the up to 8 cm wide and pinkish white to greyish brown sapwood. The grain is straight or interlocked, texture fine and even.
The wood is medium-weight with a density of 600–800 kg/m³ at 12% moisture content. The shrinkage rates are low to moderate. In a test, shrinkage of the wood from 90% to 60% air moisture content was 1.1% radial and 1.8% tangential. Shrinkage from green to 12% moisture content was 3.0% radial and 4.5% tangential, and from green to oven dry 5.0–6.0% radial and 7.2–7.7% tangential. Usually, drying does not cause problems, although the wood dries slowly.
At 12% moisture content, the modulus of rupture is 96–138 N/mm², modulus of elasticity 10,100–13,850 N/mm², compression parallel to grain 51–59 N/mm², shear 12.6 N/mm², cleavage 27 N/mm and Janka side hardness 4940 N.
The wood is somewhat difficult to work due to the presence of silica; blunting effects are moderately severe when sawing, and stellite-tipped sawteeth are recommended. The wood finishes well. Staining and polishing give good results. Pre-boring for nailing and screwing is recommended to avoid splitting. Gluing properties are good. The timber can be peeled satisfactorily.
The heartwood is rated as one of the most durable African timbers. It is resistant to termites and fungi. Damage by pinhole borers and powder-post beetles has been recorded occasionally. Although it is resistant to marine borers in temperate waters, the wood is not very durable in tropical (especially brackish) waters. The heartwood is very difficult to impregnate, the sapwood moderately easy.
Dust from sawn wood may cause irritation to skin and mucous membranes. It has been suggested that this is caused by the presence of saponins or the contact allergen 2,6-dimethoxy-1,4-benzoquinone. A highly haemolytic saponin has been isolated from the wood; on hydrolysis it gave d-glucose, l-rhamnose and d-xylose. The resistance of the wood to termites has been demonstrated in toxicity tests of extracts.
The fatty oil from the seed kernel is yellowish and semi-fluid, has a pronounced flavour and taste, and consists of about 55% oleic acid, 21.5% stearic acid, 16.5% palmitic acid and 5% linoleic acid. The kernel comprises about 50% of fat.
Adulterations and substitutes
Douka is used for similar purposes as African mahogany (Khaya and Entandrophragma spp.), but it is more durable. It is sometimes even traded as African mahogany. It is very similar to the wood of makore (Tieghemella heckelii), which is often traded together with douka under the same commercial name of makore.
Description
Very large tree up to 55 m tall; bole up to 250 cm in diameter, sometimes much more, straight and cylindrical, often swollen in lower part, reaching up to 30 m to the first branches, sometimes with buttresses; bark surface brown to red-brown, deeply furrowed with rectangular scales, inner bark fibrous but brittle, exuding a sticky latex; crown heavy, rounded, heavy branches often abruptly spreading. Leaves arranged spirally, more or less in tufts at the ends of branches, simple; stipules absent; petiole 1.5–3.5 cm long, slender; blade elliptical to obovate, 8–16 cm × 4–7 cm, cuneate at base, rounded or obtusely acuminate at apex, with entire to slightly undulate margin, thinly leathery, glabrous, lateral veins numerous. Flowers in fascicles of 2–3 in the leaf axils, bisexual, regular; pedicel 1.5–2.5 cm long; calyx with 2 whorls of 4 lobes c. 6 mm long, outer ones glabrous but softly hairy at margins, inner ones softly hairy outside; corolla with c. 1.5 mm long, fleshy tube and 8 lobes, each lobe with 1 filiform median segment and 2 large, fleshy, imbricate lateral segments c. 4 mm long, creamy white; stamens 8, inserted on the corolla tube in front of the corolla lobes, free, filaments short, 8 longer staminodes alternating with the stamens; ovary superior, conical, softly hairy, 8-celled, each cell with 1 ovule, style short. Fruit a large, ovoid, smooth berry c. 8 cm long, brownish yellow when ripe, containing 1–3 seeds in a yellowish pulp. Seeds broadly ellipsoid or ovoid, slightly laterally compressed, 5–7 cm long, testa thick, woody, smooth, shining and brown in dorsal part, rough and bullate in ventral part (scar); endosperm absent. Seedling with epigeal germination; hypocotyl stout, up to 17 cm long, epicotyl up to 17 cm long; cotyledons thick, sessile, c. 4 cm × 1 cm, green.
Other botanical information
The genus Tieghemella consists of 2 species and is closely related to Mimusops, which differs in having less-developed corolla tubes, smaller fruits, and seeds with smaller scars, copious endosperm and thin cotyledons. Tieghemella heckelii from West Africa resembles Tieghemella africana and may be conspecific. The former differs in the smaller median segment of the corolla lobes, smaller staminodes and larger seed scar. A taxonomic study is needed to clarify the species limits and the status of the genus, which is complicated by the fact that the name Tieghemella was first published for a genus of fungi.
Anatomy
Wood-anatomical description (IAWA hardwood codes):
Growth rings: 2: growth ring boundaries indistinct or absent. Vessels: 5: wood diffuse-porous; 7: vessels in diagonal and/or radial pattern; 13: simple perforation plates; 22: intervessel pits alternate; (23: shape of alternate pits polygonal); 26: intervessel pits medium ( 7–10 μm); 30: vessel-ray pits with distinct borders; similar to intervessel pits in size and shape throughout the ray cell; 31: vessel-ray pits with much reduced borders to apparently simple: pits rounded or angular; 32: vessel-ray pits with much reduced borders to apparently simple: pits horizontal (scalariform, gash-like) to vertical (palisade); (33: vessel-ray pits of two distinct sizes or types in the same ray cell); 42: mean tangential diameter of vessel lumina 100–200 μm; 47: 5–20 vessels per square millimetre; 56: tyloses common; (58: gums and other deposits in heartwood vessels). Tracheids and fibres: 61: fibres with simple to minutely bordered pits; 66: non-septate fibres present; 69: fibres thin- to thick-walled; (70: fibres very thick-walled). Axial parenchyma: 86: axial parenchyma in narrow bands or lines up to three cells wide; 87: axial parenchyma reticulate; 92: four (3–4) cells per parenchyma strand; 93: eight (5–8) cells per parenchyma strand; 94: over eight cells per parenchyma strand. Rays: 97: ray width 1–3 cells; 107: body ray cells procumbent with mostly 2–4 rows of upright and/or square marginal cells; 108: body ray cells procumbent with over 4 rows of upright and/or square marginal cells; 115: 4–12 rays per mm; (116: 12 rays per mm). Mineral inclusions: 159: silica bodies present; 160: silica bodies in ray cells.
(L.N. Banak, H. Beeckman & P.E. Gasson)
Growth and development
Young douka trees were on average 9 m tall 6 years after planting in Gabon. The survival rate was about 90% and was almost equal when planted exposed to full sunlight in comparison with planting in the shade of forest cleared from undergrowth. The young trees grow faster when planted in light shade; 11-year-old trees were on average 18.5 m tall and 13 cm in diameter when planted in light shade, and 15.5 m tall and 9 cm in diameter in full sunlight. In a 66-year-old plantation in Gabon the mean annual increment is 0.4 cm in diameter and 1.8 m³/ha in wood volume. The fruits are eaten by elephants, which are probably the main seed dispersers.
Ecology
Douka is an emergent tree of primary rain forest. It is most common in coastal lowland and diminishes towards the eastern parts of Cameroon, Equatorial Guinea and Gabon. It occurs scattered in the forest, but may locally be more abundant. Young trees are tolerant of shade, but can survive in full sun.
Propagation and planting
The seeds are heavy: 15–20 g. They should be planted within a few weeks because viability decreases rapidly.
Management
The density of douka in the forest is generally low. The average of 14 inventories in western Gabon was 0.5 m³ of timber per ha. The total volume of douka timber in Gabon was estimated at 6 million m³. The minimum diameter allowed for exploitation is 70 cm in Gabon and 60 cm in Cameroon. Douka has been planted on a small scale (37 ha in 1988 and 1989) near Ekouk (Gabon), and still smaller plantations exist elsewhere in Gabon, where the results indicate that douka is one of the best indigenous species for planting after okoumé (Aucoumea klaineana Pierre).
Handling after harvest
Care should be taken when sawing douka wood. Nasal and respiratory irritation with haemoptysis occurred in men sawing wood from Equatorial Guinea.
Genetic resources
Although Tieghemella africana is also included in the IUCN red list of threatened species, it is probably less liable to genetic erosion than Tieghemella heckelii. It suffers less from habitat destruction than its West African relative, but is subject to selective logging in many regions.
Prospects
The prospects for planting programmes using douka are good in the light of the experiences in Gabon and with makore in West Africa. Like the latter species it may be suitable for use in agroforestry programmes, being not only important for its timber, but also for fat production from the seeds.
Major references
• Aubréville, A., 1964. Sapotacées. Flore du Cameroun. Volume 2. Muséum National d’Histoire Naturelle, Paris, France. 143 pp.
• CIRAD Forestry Department, 2003. Makore. [Internet] Tropix 5.0. http://tropix.cirad.fr/ afr/makore.pdf. Accessed July 2004.
• de Saint-Aubin, G., 1963. La forêt du Gabon. Publication No 21 du Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 208 pp.
• Koumba Zaou, P., Mapaga, D., Nze Nguema, S. & Deleporte, P., 1998. Croissance de 13 essences de bois d’oeuvre plantées en forêt Gabonaise. Bois et Forêts des Tropiques 256(2): 21–32.
• Louppe, D., Deleporte, P., Vigneron, P. & Béhaghel, I., 1999. Projet OIBT PD 10/95 REV. 2 (F). Evaluation des essences indigènes de bois d’œuvre en vue du développement des plantations forestières au Gabon. Rapport final Assistance technique du CIRAD-Forêt, Libreville – Montpellier. 201 pp.
• Raponda-Walker, A. & Sillans, R., 1961. Les plantes utiles du Gabon. Paul Lechevalier, Paris, France. 614 pp.
• Richter, H.G. & Dallwitz, M.J., 2000. Commercial timbers: descriptions, illustrations, identification, and information retrieval. [Internet]. Version 18th October 2002. http://delta-intkey.com/wood/index.htm. Accessed July 2004.
• Wilks, C. & Issembé, Y., 2000. Les arbres de la Guinée Equatoriale: Guide pratique d’identification: région continentale. Projet CUREF, Bata, Guinée Equatoriale. 546 pp.
Other references
• Aubréville, A., 1961. Sapotacées. Flore du Gabon. Volume 1. Muséum National d’Histoire Naturelle, Paris, France. 162 pp.
• Bilé Allogho, J., 1999. Etude des ressources forestières du Gabon. DIARF, Libreville, Gabon. 108 pp. + annexes.
• Bokdam, J., 1977. Seedling morphology of some African Sapotaceae and its taxonomical significance. Mededelingen Landbouwhogeschool Wageningen 77–20. Wageningen, Netherlands. 84 pp.
• Cassagne, C., 1966. Contribution à l’étude des lipides de trois graines oléagineuses africaines: Dumoria africana, Dumoria heckelii et Irvingia gabonensis. Thèse, Faculté des sciences de l’Université de Bordeaux, France. 89 pp.
• Gassita, J.N., Nze Ekekang, L., De Vecchy, H., Louis, A.M., Koudogbo, B. & Ekomié, R. (Editors), 1982. Les plantes médicinales du Gabon. CENAREST, IPHAMETRA, mission ethnobotanique de l’ACCT au Gabon, 10–31 juillet 1982. 26 pp.
• InsideWood, undated. [Internet] http://insidewood.lib.ncsu.edu/search/. Accessed May 2007.
• Takahashi, A., 1978. Compilation of data on the mechanical properties of foreign woods (part 3) Africa. Shimane University, Matsue, Japan, 248 pp.
• Vivien, J. & Faure, J.J., 1988. Fruitiers sauvages du Cameroun. Fruits Paris 44(5): 281–288.
Sources of illustration
• Aubréville, A., 1964. Sapotacées. Flore du Cameroun. Volume 2. Muséum National d’Histoire Naturelle, Paris, France. 143 pp.
• Wilks, C. & Issembé, Y., 2000. Les arbres de la Guinée Equatoriale: Guide pratique d’identification: région continentale. Projet CUREF, Bata, Guinée Equatoriale. 546 pp.
Author(s)
R.H.M.J. Lemmens
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands


Editors
D. Louppe
CIRAD, Département Environnements et Sociétés, Cirad es-dir, Campus international de Baillarguet, TA C-DIR / B (Bât. C, Bur. 113), 34398 Montpellier Cedex 5, France
A.A. Oteng-Amoako
Forestry Research Institute of Ghana (FORIG), University P.O. Box 63, KNUST, Kumasi, Ghana
M. Brink
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
General editors
R.H.M.J. Lemmens
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
L.P.A. Oyen
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
J.R. Cobbinah
Forestry Research Institute of Ghana (FORIG), University P.O. Box 63, KNUST, Kumasi, Ghana
Photo editor
E. Boer
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

Correct citation of this article:
Lemmens, R.H.M.J., 2005. Tieghemella africana Pierre. In: Louppe, D., Oteng-Amoako, A.A. & Brink, M. (Editors). Prota 7(1): Timbers/Bois d’œuvre 1. [CD-Rom]. PROTA, Wageningen, Netherlands.
Distribution Map wild


1, base of bole; 2, flowering twig; 3, flower; 4, fruit; 5, seed
Redrawn and adapted by Achmad Satiri Nurhaman



plantation of 66 years


plantation of 11 years


stem, 6 m in diameter


leaves


fruit for sale along the road


opened fruit with seed


wood in transverse section


wood in radial section


wood in tangential section