Testulea gabonensis (PROTA)

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Plant Resources of Tropical Africa
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Testulea gabonensis Pellegr.


Protologue: Bull. Soc. Bot. France 71: 76 (1924).
Family: Ochnaceae

Origin and geographic distribution

Testulea gabonensis is restricted to western Central Africa, occurring in south-western Cameroon, Equatorial Guinea, Gabon and Congo.

Uses

The wood, traded as ‘izombé’, is used for construction, flooring, joinery, panelling, windows, doors, stairs, ship building, vehicle bodies, furniture, cabinet work, sporting goods, sculptures, carvings, turnery and sliced veneer. It is suitable for mine props, boxes, crates, toys, novelties and pattern making.

The bark is used in traditional medicine. Ground in water, it is applied to the nostrils to treat headache, and it is also used as aphrodisiac.

Production and international trade

Testulea gabonensis is available at the international timber market in limited quantities. In 1999 Testulea gabonensis ranked 14th on the list of most important export timbers of Gabon, with an export volume of 19,250 m³. In 2003, 5000 m³ of logs were exported from Gabon at an average price of US$ 135/m³, and in 2005 18,000 m³ at US$ 64/m³. In 2004 Congo exported 1000 m³ of sawn wood at an average price of US$ 155/m³.

Properties

The heartwood is straw-coloured, becoming orange-yellow to yellowish brown or pink-yellow with greyish tinge upon exposure, and indistinctly demarcated from the 2–5 cm wide sapwood. The grain is usually straight, occasionally slightly interlocked, texture fine and even. The wood shows an indistinct figure and has no distinct smell. Resinous deposits may be present.

The wood is medium-weight to moderately heavy, with a density of 630–840 kg/m³ at 12% moisture content. It air dries moderately easily with slight risks of distortion and checking; it is recommended to dry carefully and slowly. Kiln drying is moderately easy. Quarter-sawn boards dry faster and with lesser degrade than flat-sawn boards. The rates of shrinkage are moderate, from green to oven dry 3.6–4.5% radial and 6.3–9.5% tangential. Once dry, the wood is moderately stable to stable in service, but somewhat fissile and brittle.

At 12% moisture content, the modulus of rupture is 109–173 N/mm², modulus of elasticity 7850–13,100 N/mm², compression parallel to grain 49–73 N/mm², shear 6–11 N/mm², cleavage 12–22 N/mm and Chalais-Meudon side hardness 3.2–6.1.

The wood is easy to saw and work with both hand and machine tools. The blunting effect on saw teeth and cutting edges is moderate. The wood planes to a good finish, except when interlocked grain is present. It can be sanded to a high polish. It holds nails generally well with occasional tendency of splitting; pre-boring is therefore advised, especially in wood of small dimensions. The wood glues, paints and varnishes well. The steam-bending properties are good. The wood has good slicing properties when it has been steamed for 2–3 days. The heartwood is durable, being resistant to fungal, termite, powder-post beetle and dry-wood borer attacks. It is not resistant to marine borers. It is resistant to impregnation with preservatives.

The wood contains about 35% cellulose, 39% lignin, 14% pentosan, 0.4% ash and 0.01% silica. The solubility is 6.7% in alcohol-benzene and 1.9% in water.

Several alkaloids have been isolated from the bark, with Nb-methyltryptamine as main alkaloid. The triterpenes friedeline and friedelinol have also been identified.

Adulterations and substitutes

The wood of Testulea gabonensis with its good durability and stability and nice colour can be used as a substitute of teak, for instance in ship building and for high-quality furniture. It is similar to but harder than the wood of Lophira alata Banks ex P.Gaertn.

Description

Medium-sized to fairly large tree up to 40(–50) m tall; bole branchless for up to 20 m, usually straight and cylindrical, up to 100(–120) cm in diameter, with steep buttresses up to 3 m high, often with horizontal ridges on the buttresses; bark scaly, exfoliating in small irregular patches, yellowish brown to yellowish grey, inner bark granular, brittle, pinkish to reddish with whitish spots, becoming brownish upon exposure; crown irregular; branches glabrous, with distinct leaf scars. Leaves arranged spirally, clustered near tips of branches, simple; stipules fused, triangular, axillary; petiole up to 3 mm long; blade oblanceolate, 20–35 cm × 4–8 cm, rounded at base, short-acuminate at apex, margins entire but slightly wavy, glabrous, pinnately veined with numerous distinct lateral veins. Inflorescence a terminal false raceme up to 35 cm long, with flowers in groups of 3–4. Flowers bisexual, zygomorphic, 4-merous, yellowish white to pinkish; pedicel slender, c. 1.5 cm long; sepals free, unequal, largest one c. 12 mm long; petals free, 2 larger ones c. 1.5 cm long and 2 smaller ones c. 1 cm long; stamen 1, nearly sessile, opening with 2 pores at apex, with 2 appendages at base, staminodes numerous, fused into a long tube but free near apex; ovary superior, cylindrical, 1-celled, style long, curved. Fruit a rounded, inflated, flattened capsule 3–6 cm in diameter, notched at apex, with thin wall, dehiscing with 2 valves, many-seeded. Seeds cylindrical, c. 1 cm long, with papery wing c. 1.5 cm long.

Other botanical information

Testulea comprises a single species. The tree has some resemblance to Lophira alata Banks ex P.Gaertn. (also Ochnaceae), which occurs in the same region.

Anatomy

Wood-anatomical description (IAWA hardwood codes):

  • Growth rings: 2: growth ring boundaries indistinct or absent.
  • Vessels: 5: wood diffuse-porous; (12: solitary vessel outline angular); 13: simple perforation plates; 22: intervessel pits alternate; 24: intervessel pits minute ( 4 μm); 25: intervessel pits small (4–7 μm); 30: vessel-ray pits with distinct borders; similar to intervessel pits in size and shape throughout the ray cell; 41: mean tangential diameter of vessel lumina 50–100 μm; 49: 40–100 vessels per square millimetre; 58: gums and other deposits in heartwood vessels. Tracheids and fibres: (60: vascular/vasicentric tracheids present); 62: fibres with distinctly bordered pits; 63: fibre pits common in both radial and tangential walls; 66: non-septate fibres present; 69: fibres thin- to thick-walled; 70: fibres very thick-walled.
  • Axial parenchyma: 78: axial parenchyma scanty paratracheal; 84: axial parenchyma unilateral paratracheal; 93: eight (5–8) cells per parenchyma strand; 94: over eight cells per parenchyma strand.
  • Rays: 97: ray width 1–3 cells; 98: larger rays commonly 4- to 10-seriate; 104: all ray cells procumbent; 106: body ray cells procumbent with one row of upright and/or square marginal cells; (107: body ray cells procumbent with mostly 2–4 rows of upright and/or square marginal cells); 115: 4–12 rays per mm.
  • Mineral inclusions: 136: prismatic crystals present; 138: prismatic crystals in procumbent ray cells.

(E. Uetimane, P. Baas & H. Beeckman)

Growth and development

Trees usually flower in December–April. The seeds are dispersed by wind, and are a favourite food of grey parrots.

Ecology

Testulea gabonensis usually occurs in primary humid rainforest on well-drained localities.

Management

Testulea gabonensis is found scattered in the forest in low densities. In Gabon the average wood volume of trees with a bole diameter of more than 60 cm is 0.1–1.0 m³/ha.

Harvesting

The high buttresses give some problems in felling and harvested logs may be fluted. The minimum bole diameter allowed for harvesting in Gabon is 70 cm.

Handling after harvest

Although the heartwood is quite durable, logs should not be left in the forest too long because the sapwood can be attacked by fungi and insects, which on the longer term can also affect the heartwood. Logs often do not float in water and therefore cannot be transported by river.

Genetic resources

Testulea gabonensis has been subjected to overexploitation in most regions within its area of distribution. Its occurrence in a small area and low densities make it even more vulnerable. It is classified as endangered in the IUCN Red List of threatened species.

Prospects

Testulea gabonensis produces a good-quality timber. However, it is clearly threatened by genetic erosion or even extinction and research should focus on proper management measures to ensure sustainable exploitation. This would imply very low production levels for the near future. Testulea gabonensis deserves more research on seed harvesting, nursery techniques, silviculture and growth rates.

Major references

  • ATIBT (Association Technique Internationale des Bois Tropicaux), 1986. Tropical timber atlas: Part 1 – Africa. ATIBT, Paris, France. 208 pp.
  • Bolza, E. & Keating, W.G., 1972. African timbers: the properties, uses and characteristics of 700 species. Division of Building Research, CSIRO, Melbourne, Australia. 710 pp.
  • CIRAD Forestry Department, 2009. Izombe. [Internet] Tropix 6.0. http://tropix.cirad.fr/ africa/ izombe.pdf. April 2011.
  • CTFT (Centre Technique Forestier Tropical), 1952. Izombé. Bois et Forêts des Tropiques 24: 256–259.
  • CTFT (Centre Technique Forestier Tropical), 1990. Izombé. Bois et Forêts des Tropiques 225: 65–72.
  • de Saint-Aubin, G., 1963. La forêt du Gabon. Publication No 21 du Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 208 pp.
  • Takahashi, A., 1978. Compilation of data on the mechanical properties of foreign woods (part 3) Africa. Shimane University, Matsue, Japan. 248 pp.
  • UNEP-WCMC, 2006. Contribution to an evaluation of tree species using the new CITES Listing Criteria. UNEP World Conservation Monitoring Centre, Cambridge, United Kingdom. [Internet]. http://www.unep-wcmc.org/ species/tree_study/pdfs/ 1.pdf. February 2010.
  • White, L. & Abernethy, K., 1997. A guide to the vegetation of the Lopé Reserve, Gabon. 2nd edition. Wildlife Conservation Society, New York, United States. 224 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.

Other references

  • Adjanohoun, E.J., Ahyi, A.M.R., Aké Assi, L., Baniakina, J., Chibon, P., Cusset, G., Doulou, V., Enzanza, A., Eymé, J., Goudoté, E., Keita, A., Mbemba, C., Mollet, J., Moutsamboté, J.-M., Mpati, J. & Sita, P. (Editors), 1988. Médecine traditionnelle et pharmacopée - Contribution aux études ethnobotaniques et floristiques en République Populaire du Congo. Agence de Coopération Culturelle et Technique, Paris, France. 606 pp.
  • African Regional Workshop (Conservation & Sustainable Management of Trees, Zimbabwe), 1998. Testulea gabonensis. In: IUCN. 2011 IUCN Red list of threatened species. Version 2011.1. [Internet] http://www.iucnredlist.org. April 2011.
  • Christy, P., Jaffré, R., Ntougou, O. & Wilks, C., 2003. La forêt et la filière bois au Gabon. Projet Aménagement Forestier et Environnement, Libreville, Gabon. 389 pp.
  • Chudnoff, M., 1980. Tropical timbers of the world. USDA Forest Service, Agricultural Handbook No 607, Washington D.C., United States. 826 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.
  • Gérard, J., Edi Kouassi, A., Daigremont, C., Détienne, P., Fouquet, D. & Vernay, M., 1998. Synthèse sur les caractéristiques technologiques des principaux bois commerciaux africains. Document Forafri 11. Cirad, Montpellier, France. 185 pp.
  • Leboeuf, M., Cavé, A., Mangeney, P. & Bouquet, A., 1977. Alcaloïdes et triterpènes du Testulea gabonensis. Plantes médicinales et Phytothérapie 11(3): 230–235.
  • Neuwinger, H.D., 2000. African traditional medicine: a dictionary of plant use and applications. Medpharm Scientific, Stuttgart, Germany. 589 pp.
  • Raponda-Walker, A. & Sillans, R., 1961. Les plantes utiles du Gabon. Paul Lechevalier, Paris, France. 614 pp.
  • Sallenave, P., 1955. Propriétés physiques et mécaniques des bois tropicaux de l’Union française. Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 129 pp.
  • Sallenave, P., 1964. Propriétés physiques et mécaniques des bois tropicaux. Premier supplément. Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 79 pp.
  • Sallenave, P., 1971. Propriétés physiques et mécaniques des bois tropicaux. Deuxième supplément. Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 128 pp.
  • Tailfer, Y., 1989. La forêt dense d’Afrique centrale. Identification pratique des principaux arbres. Tome 2. CTA, Wageningen, Pays-Bas. pp. 465–1271.
  • Vivien, J. & Faure, J.J., 1985. Arbres des forêts denses d’Afrique Centrale. Agence de Coopération Culturelle et Technique, Paris, France. 565 pp.

Sources of illustration

  • CTFT (Centre Technique Forestier Tropical), 1952. Izombé. Bois et Forêts des Tropiques 24: 256–259.
  • 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)

  • K.A. Oduro, Forestry Research Institute of Ghana (FORIG), University P.O. Box 63, KNUST, Kumasi, Ghana

Correct citation of this article

Oduro, K.A., 2012. Testulea gabonensis Pellegr. In: Lemmens, R.H.M.J., Louppe, D. & Oteng-Amoako, A.A. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. Accessed 14 November 2018.