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Sterculia oblonga Mast.

Protologue
Oliv., fl. Trop. Afr. 1: 216 (1868).
Family
Sterculiaceae (APG Malvaceae)
Chromosome number
2n = 36
Synonyms
Eribroma oblonga (Mast.) Pierre ex A.Chev. (1917), Sterculia elegantiflora Hutch. & Dalziel (1928).
Vernacular names
Yellow sterculia, white sterculia (En). Eyong (Fr).
Origin and geographic distribution
Sterculia oblonga occurs in the forest zone from Guinea and Liberia east to the Central African Republic and south to Gabon, Congo and northern DR Congo.
Uses
The wood (trade names: eyong, okoko, ohaa) is used in West Africa for flooring, beams, planks and furniture. It is also suitable for construction, veneer, plywood, vehicle bodies, handles, sporting goods, toys, agricultural implements, hardboard and particle board.
The seeds are eaten. In Cameroon a mixture of pulped leaves and oil is applied to the chest of children as a dressing to cure chest complaints. In Gabon a bark decoction is drunk as a cure for acute stomach-ache. The fibrous bark of young trees is used as bark cloth for partitioning huts.
Production and international trade
Cameroon exported 40,550 m³ of logs in 1997, 29,280 m³ in 2000, 5850 m³ in 2003, and 9750 m³ in 2004. In 2005 it exported about 8000 m³ of logs at an average price of US$ 217/m³ and in 2006 about 14,000 m³ at US$ 485/m³. Cameroon exported 1120 m³ of sawn wood from July 2001 to June 2002, 260 m³ in 2003, 190 m³ in 2004 and 110 m³ in 2006. In 2005 it exported about 1000 m³ of veneer at an average price of US$ 951/m³ and in 2006 small amounts of veneer at an average price of US$ 623/ m³. Congo exported about 900 m³ of logs per year in 1967–1970, whereas Equatorial Guinea exported about 3440 m³ of logs per year in 1996–1998 and Gabon on average 3100 m³ per year in 2001–2005.
Properties
The heartwood is pale yellow with white streaks, and indistinctly demarcated from the 10–20 cm wide sapwood. The grain is straight or slightly interlocked, texture medium to fairly coarse. Quartersawn surfaces have an attractive figure. The wood is oily to the touch and fresh wood has an unpleasant smell.
The wood is medium-weight to moderately heavy, with a density of 680–840 kg/m³ at 12% moisture content. It air dries slowly, with a tendency for surface checking, distortion and development of shakes or collapse. The rates of shrinkage from green to oven dry are high: 4.5–5.0% radial and 10.2–12.2% tangential. Once dry, the wood is usually moderately stable in service.
At 12% moisture content, the modulus of rupture is 91–153 N/mm², modulus of elasticity 12,600–17,110 N/mm², compression parallel to grain 49–67 N/mm², shear 3–13 N/mm², cleavage 12–18 N/mm and Janka side hardness 4980 N.
The wood saws well, with moderate blunting effects on sawteeth. It works well with machine tools, but more difficultly with hand tools. A cutting angle of 20° is recommended in planing. It finishes with difficulty, and a filler is needed. Staining and polishing are satisfactory. Nailing and screwing properties are good, but quartersawn surfaces may split on nailing. The wood glues well. The peeling and slicing properties are good. Steam-bending properties are moderate.
The wood is not durable, being susceptible to attacks by fungi, dry wood borers and termites. The sapwood is susceptible to Lyctus borers. The heartwood is extremely resistant to impregnation with preservatives, the sapwood is permeable. The chemical composition of the oven-dry wood is: cellulose 36.2–46.2%, furfurals 11.5–12.4%, pentosans 19.8–21.2%, lignin 18.2–22.7%, ash 1.3–3.2%. The solubility in hot water is 2.7–6.2%, in alcohol-benzene 1.2–9.2% and in 1% NaOH 16–23.5%.
Adulterations and substitutes
The wood resembles that of Pterygota and Amphimas spp.
Description
Deciduous medium-sized to large tree up to 45 m tall; bole branchless for up to 21 m, up to 150 cm in diameter, straight, cylindrical, with buttresses up to 3.5 m high; bark surface greyish, with small scales, inner bark fibrous, white to yellow with orange streaks, strongly resinous, with distinctive smell; crown narrow, branches whorled. Leaves alternate, simple and entire; stipules early caducous; petiole 2–7 cm long; blade elliptical, 6–15 cm × 3–8 cm, rounded to obtuse at base, short-acuminate at apex (3-pointed in saplings), densely stellate hairy below when young, pinnately veined with 10–14 pairs of lateral veins. Inflorescence an axillary, narrow panicle 3–10 cm long; bracts lanceolate, hairy, c. 3 mm long, caducous. Flowers unisexual, regular, 5-merous, cream to greenish yellow, c. 6 mm long; perianth consisting of free tepals, stellate hairy inside; male flowers with c. 10 anthers borne on a long common stalk, stalk with long hairs in basal part; female flowers with ovary consisting of 5 carpels united loosely. Fruit consisting of (4–)5 woody follicles 10–15 cm long, glabrescent, green-yellow to yellow-brown, many-seeded. Seeds ovoid, compressed, 2–2.5 cm × c. 1 cm, with bright yellow, fleshy seed coat. Seedling with epigeal germination.
Other botanical information
Sterculia is found throughout the tropics and comprises about 150 species, with about 25 of them in tropical Africa.
Anatomy
Wood-anatomical description (IAWA hardwood codes):
Growth rings: 2: growth ring boundaries indistinct or absent. Vessels: 5: wood diffuse-porous; 13: simple perforation plates; 22: intervessel pits alternate; 23: shape of alternate pits polygonal; 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; 42: mean tangential diameter of vessel lumina 100–200 μm; 43: mean tangential diameter of vessel lumina 200 μm; 46: 5 vessels per square millimetre. Tracheids and fibres: 61: fibres with simple to minutely bordered pits; 66: non-septate fibres present; 70: fibres very thick-walled. Axial parenchyma: 85: axial parenchyma bands more than three cells wide; 87: axial parenchyma reticulate; 92: four (3–4) cells per parenchyma strand; (93: eight (5–8) cells per parenchyma strand). Rays: 98: larger rays commonly 4- to 10-seriate; 99: larger rays commonly > 10-seriate; 102: ray height > 1 mm; (103: rays of two distinct sizes); 107: body ray cells procumbent with mostly 2–4 rows of upright and/or square marginal cells; 110: sheath cells present; 114: 4 rays per mm; (115: 4–12 rays per mm). Storied structure: 120: axial parenchyma and/or vessel elements storied. Mineral inclusions: 136: prismatic crystals present; 137: prismatic crystals in upright and/or square ray cells; 141: prismatic crystals in non-chambered axial parenchyma cells; 142: prismatic crystals in chambered axial parenchyma cells; 154: more than one crystal of about the same size per cell or chamber.
(E. Uetimane, H. Beeckman & P.E. Gasson)
Growth and development
Sterculia oblonga is classified as a non-pioneer light demander. This means that seedlings are found in full shade, but saplings only grow up under small gaps in the forest canopy. In Ghana average increase in height is about 30 cm during the first year with 9-year-old trees 3–15 m tall. Under the forest canopy in Guinea saplings were 50 cm tall 1 year after planting and 125 cm tall after 2 years. In Côte d’Ivoire trees showed a mean annual increment in bole diameter of 13 mm in the first 14 years after planting. In the Central African Republic the mean annual diameter increment was 1.7–7.3 mm for trees of about 25 cm in bole diameter, the fastest growth occurring in an exploited and thinned forest. Annual diameter increment in secondary forest in Cameroon averaged 18.6 mm. In this forest individuals of Sterculia oblonga were present as emergents with an average height of 41 m, whereas the main canopy of the forest was at 15–30 m. In Ghana flowering occurs in September, October and January and fruits are encountered from September to January. Dispersal of the seeds is probably done by birds.
Ecology
Sterculia oblonga is most commonly found in semi-deciduous forest, particularly in secondary forest. It prefers drier localities.
Propagation and planting
The 1000-seed weight is about 1100 g. Seeds have to be sown immediately after harvest. Germination begins after 8–15 days, but the germination rate can be low. In the nursery, the seedlings need to be kept in the shade. When they are 25–30 cm tall they can be planted out under the forest canopy cover or in forests paths. It is recommended to refrain from planting in the full sun.
Management
In the Central African Republic, the natural regeneration of Sterculia oblonga is good and better in exploited forest than in unexploited forest. In natural forest on average 9.7 trees per ha were counted in 1995, with a volume of 4.24 m³ per ha. The average volume of timber of Sterculia oblonga in Gabon was measured in 1963 to be 0.11 m³ per ha. Burning the undergrowth in forest has a negative effect on regeneration of Sterculia oblonga although it seems to be less sensitive to fire than Sterculia rhinopetala K.Schum.
Yield
A tree with a diameter of 60 cm yields about 3.3 m³ of log, and trees 100 and 150 cm in diameter yield 11.6 and 27.8 m³ of logs, respectively.
Handling after harvest
Freshly harvested logs sink in water, so they cannot be transported by river. To prevent blue stain and pinhole borer attack, logs must be treated with a preservative as soon as possible after felling and be removed from the forest, sawn and dried rapidly.
Genetic resources
The timber of Sterculia oblonga is valuable and is selectively exploited. This has led to the species becoming rarer in Limbe Region, Cameroon and probably elsewhere as well. It is classified as vulnerable in the IUCN Red list, because of habitat decline.
Prospects
The wood of Sterculia oblonga has good strength properties, but it is difficult to dry and it has a low natural durability. Overexploitation must be avoided as the species is considered vulnerable. Because of its slow growth it does not seem to have much potential as a plantation species.
Major references
• 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, 2003. Eyong. [Internet] Tropix 5.0. http://tropix.cirad.fr/ afr/eyong.pdf. Accessed July 2008.
• Farmer, R.H., 1972. Handbook of hardwoods. 2nd Edition. Her Majesty’s Stationery Office, London, United Kingdom. 243 pp.
• Hallé, N., 1961. Sterculiacées. Flore du Gabon. Volume 2. Muséum National d’Histoire Naturelle, Paris, France. 150 pp.
• Hawthorne, W.D., 1995. Ecological profiles of Ghanaian forest trees. Tropical Forestry Papers 29. Oxford Forestry Institute, Department of Plant Sciences, University of Oxford, United Kingdom. 345 pp.
• Hawthorne, W. & Jongkind, C., 2006. Woody plants of western African forests: a guide to the forest trees, shrubs and lianes from Senegal to Ghana. Kew Publishing, Royal Botanic Gardens, Kew, United Kingdom. 1023 pp.
• Irvine, F.R., 1961. Woody plants of Ghana, with special reference to their uses. Oxford University Press, London, United Kingdom. 868 pp.
• Laird, S.A., 2000. L’exploitation du bois d’oeuvre et des produits forestiers non ligneux (PFNL) dans les forêts d’Afrique Centrale. In: Sunderland, T.C.H., Clark, L.E. & Vantomme, P. (Editors). Recherches actuelles et perspectives pour la conservation et le devéloppement. FAO, Rome, Italy. pp. 53–64.
• Normand, D. & Paquis, J., 1976. Manuel d’identification des bois commerciaux. Tome 2. Afrique guinéo-congolaise. Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 335 pp.
• Takahashi, A., 1978. Compilation of data on the mechanical properties of foreign woods (part 3) Africa. Shimane University, Matsue, Japan, 248 pp.
Other references
• African Regional Workshop (Conservation & Sustainable Management of Trees, Zimbabwe), 1998. Eribroma oblonga. In: IUCN. 2007 Red list of threatened species. [Internet] http://www.iucnredlist.org. Accessed July 2008.
• ATIBT (Association Technique Internationale des Bois Tropicaux), 1986. Tropical timber atlas: Part 1 – Africa. ATIBT, Paris, France. 208 pp.
• Bedel, F., Durrieu de Madron, L., Dupuy, B., Favrichon, V., Maitre, H.F., Bar Hen, A. & Narboni, P., 1998. Dynamique de croissance dans des peuplements exploités et éclaircis de forêt dense africaine: le dispositif de M’Baïki en République Centrafricaine (1982–1995). Document Forafri 1. Cirad-Forêt, Montpellier, France. 72 pp.
• Berti, S., Massei, M., Berti, R.N. & Topa, G., 1982. Tavole di cubatura di diciotto specie tropicali. Annali Accademia Italiana di Scienze Forestali 31: 345–380.
• Burkill, H.M., 2000. The useful plants of West Tropical Africa. 2nd Edition. Volume 5, Families S–Z, Addenda. Royal Botanic Gardens, Kew, Richmond, United Kingdom. 686 pp.
• Chudnoff, M., 1980. Tropical timbers of the world. USDA Forest Service, Agricultural Handbook No 607, Washington D.C., United States. 826 pp.
• CTFT (Centre Technique Forestier Tropical), 1960. Résultats des observations et des essais effectués au Centre Technique Forestier Tropical sur Eyong – Sterculia oblonga = Sterculia elegantiflora. Note Technique 70. Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 6 pp.
• de la Mensbruge, G., 1966. La germination et les plantules des essences arborées de la forêt dense humide de la Côte d’Ivoire. Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 389 pp.
• de Saint-Aubin, G., 1963. La forêt du Gabon. Publication No 21 du Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 208 pp.
• Durand, P.Y., 1978. Propriétés physiques et mécaniques des bois de Côte d’Ivoire: moyennes d’espèce et variabilité intraspécifique. Centre Technique Forestier Tropical, Abidjan, Côte d’Ivoire. 70 pp.
• Durrieu de Madron, L. & Daumerie, A., 2004. Diamètre de fructification de quelques essences en forêt naturelle centrafricaine. Bois et Forêts des Tropiques 281(3): 87–95.
• Germain, R. & Bamps, P., 1963. Sterculiaceae. In: Robyns, W., Staner, P., Demaret, F., Germain, R., Gilbert, G., Hauman, L., Homès, M., Jurion, F., Lebrun, J., Vanden Abeele, M. & Boutique, R. (Editors). Flore du Congo belge et du Ruanda-Urundi. Spermatophytes. Volume 10. Institut National pour l’Étude Agronomique du Congo belge, Brussels, Belgium. pp. 205–316.
• InsideWood, undated. [Internet] http://insidewood.lib.ncsu.edu/search/. Accessed May 2007.
• Keay, R.W.J., 1958. Sterculiaceae. In: Keay, R.W.J. (Editor). Flora of West Tropical Africa. Volume 1, part 2. 2nd Edition. Crown Agents for Oversea Governments and Administrations, London, United Kingdom. pp. 310–332.
• Neuwinger, H.D., 2000. African traditional medicine: a dictionary of plant use and applications. Medpharm Scientific, Stuttgart, Germany. 589 pp.
• Oluwadare, A.O., 1998. Evaluation of the fibre and chemical properties of some selected Nigerian wood and non-wood species for pulp production. Journal of Tropical Forest Resources 14: 110–119.
• Parant, B., Boyer, F., Chichignoud, M. & Curie, P., 2008. Présentation graphique des caractères technologiques des principaux bois tropicaux. Tome 1. Bois d’Afrique. Réédition. CIRAD-Fôret, Montpellier, France. 186 pp.
• Sallenave, P., 1964. Propriétés physiques et mécaniques des bois tropicaux. Premier supplément. Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 79 pp.
• Vivien, J. & Faure, J.J., 1985. Arbres des forêts denses d’Afrique Centrale. Agence de Coopération Culturelle et Technique, Paris, France. 565 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.
• Worbes, M., Staschel, R., Roloff, A. & Junk, W.J., 2003. Tree ring analysis reveals age structure, dynamics and wood production of a natural forest stand in Cameroon. Forest Ecology and Management 173: 105–123.
Sources of illustration
• Hallé, N., 1961. Sterculiacées. Flore du Gabon. Volume 2. Muséum National d’Histoire Naturelle, Paris, France. 150 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)
C.H. Bosch
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
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


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
G.H. Schmelzer
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

Correct citation of this article:
Bosch, C.H. & Louppe, D., 2008. Sterculia oblonga Mast. 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 branch; 3, part of fruit.
Redrawn and adapted by Achmad Satiri Nurhaman



wood


wood in transverse section


wood in tangential section