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Ochroma pyramidale (Cav. ex Lam.) Urb.

Protologue
Repert. Spec. Nov. Regni Veg., Beih. 5: 123 (1920).
Family
Bombacaceae (APG: Malvaceae)
Chromosome number
2n = 72, 78, 88, 90
Synonyms
Ochroma lagopus Sw. (1788).
Vernacular names
Balsa wood tree, corkwood, cork tree, down tree (En). Balsa (Fr). Pau de balsa, pata de lebre, pau de jangada (Po).
Origin and geographic distribution
The natural distribution of Ochroma pyramidale is in tropical Central and South America from southern Mexico to Bolivia. It is planted in many tropical countries, including tropical Africa (e.g. Cameroon and Zimbabwe) and South Africa. It has locally become naturalized.
Uses
The extremely lightweight wood (trade name: balsa) is used for buoys, life-jackets and life-belts, surf boards, aircraft construction, ship and boat building, toys, model making, laboratory mounting boards, core stock in sandwich construction, surgical splints, packaging of fragile articles and as insulation for temperature, vibration, sound and formerly also for electricity. Slightly heavier wood is suitable for matches, popsicle sticks and toothpicks, and for the production of pulp and paper.
The floss from the fruit is suitable for filling pillows and mattresses. Rope is made from the fibrous bark. The tree is sometimes planted as an ornamental or to provide shade.
Production and international trade
Ecuador is the main exporting country of balsa wood, supplying 80–90% of the volume traded on the world market.
Properties
The heartwood is white to grey-white, sometimes with a pinkish tinge near the heart in older trees; it is not clearly demarcated from the sapwood. The grain is straight, texture coarse and even. The wood has a silky lustre. Heartwood is too heavy to be of economic importance and most of the commercial stock is sapwood.
The wood is extremely lightweight with a density of (40–)70–250(–320) kg/m³ at 12% moisture content. High-grade timber weighs less than 150 kg/m³ at 12% moisture content and is generally produced by young trees (8–9 years old), whereas older trees produce heartwood, which is heavier and is considered of secondary quality. Large differences exist between the outermost sapwood and that from nearer the centre, the new wood (outer 3 cm) being on average 2.2 times heavier than the old wood (inner 3 cm) as determined for wood samples from Costa Rica.
Air drying from green to 15% moisture content takes 1–3 weeks. The rates of shrinkage from green to oven dry are small to medium: 2.1–3.0% radial and 2.8–7.6% tangential. Kiln drying is preferable to air drying, to minimize splitting and warping. Movement in service is small.
The wood is very soft and weak, and that from old trees tends to be brittle. At 12% moisture content, the modulus of rupture is 14–57 N/mm², modulus of elasticity 2100–6400 N/mm², compression parallel to grain 6–24 N/mm², compression perpendicular to grain 5 N/mm², shear 2–3 N/mm², cleavage 2–11 N/mm, Janka side hardness 330–450 N, Janka end hardness 2410 N and Chalais-Meudon side hardness 0.1–0.2.
The wood is very easy to work with hand and machine tools, but sharp tools are needed to prevent crumbling. It takes nails and screws readily, but is too soft to hold them well. Planing is almost impossible. Gluing properties are good, and the wood stains, polishes and paints satisfactorily, but it is very absorbent. Bending properties are poor. The wood has good insulating properties and can be used at very low temperatures (down to –250°C). Wood from old trees is brittle and decayed.
The wood is non-durable and prone to attack by Anobium and Lyctus borers, termites and longhorn beetles. The sapwood is permeable to impregnation with preservatives, absorbing about 560 kg/m³; the heartwood is more resistant.
The average fibre length of wood from Belize is 1.9 mm, with a diameter of 36.1 μm, a lumen diameter of 28.3 μm and a cell wall thickness of 3.9 μm. The wood contains 74% holocellulose, 38% α-cellulose and 1% ash; the solubility in 1% NaOH is 21%, and that in ethanol-benzene 1%. The wood is suitable for pulping by chemical and semi-chemical processes, yielding 45–50% pulp with good strength characteristics. The pulp can be easily bleached without loss of strength, making it suitable for printing and writing papers.
Botany
Deciduous or evergreen, medium-sized tree up to 30(–50) m tall; bole straight, usually short, cylindrical, up to 100(–180) cm in diameter, with short buttresses in older trees; bark surface smooth, grey-white mottled; crown spreading, large; branchlets stellate hairy. Leaves arranged spirally, simple; stipules broadly lanceolate, c. 1.5 cm × 1 cm; petiole 3–40 cm long; blade ovate, slightly 3–5-lobed, 10–40 cm × 11–35 cm, base cordate, apex acute or acuminate, margin wavy, glabrescent above, hairy beneath, palmately and pinnately veined with 7–9 pairs of lateral veins. Flowers solitary, axillary, bisexual, regular, 5-merous; pedicel 4–11 cm long; calyx tubular, 8–12 cm long, with unequal lobes 2.5–4 cm long, hairy outside and inside; petals 11–15 cm × c. 5 cm, whitish; stamens many, fused to the petals at their base, united into a briefly 5-lobed staminal column 10–12.5 cm long bearing sessile wavy anthers from the middle to the apex; ovary superior, 5-celled, style club-shaped and 9–10 cm long, stigma spiralled. Fruit an oblong capsule 12–25 cm × c. 2.5 cm, ribbed, 5-valved, dehiscent, densely woolly hairy inside, many-seeded. Seeds pear-shaped, 4–5 mm × c. 1.5 mm, covered in abundant pale brown floss.
Growth of Ochroma pyramidale trees can be extremely fast. In South America mean annual diameter increment is up to 10 cm, and after 10–12 years, when growth stabilizes, trees can be 20–25 m tall and about 100 cm in diameter. A mean annual volume increment of 17–30 m³/ha can generally be expected, although increments of up to 90 m³/ha have been achieved. After 12–15 years growth slows down and the trees deteriorate rapidly. Only under specific circumstances may trees reach 50 m in height. In Indonesia and Malaysia Ochroma pyramidale flowers throughout the year and is pollinated by bats. Trees start producing viable seed after (2–)3–4 years; the seeds are dispersed by wind.
Ochroma only comprises a single species. Ochroma pyramidale is highly variable, and the genus was formerly thought to comprise at least 11 species.
Ecology
Ochroma pyramidale is a typical pioneer, colonizing clearings. In natural conditions it occurs up to 1000 m altitude, in areas with an annual precipitation of 1250–3000 mm and a mean annual temperature of 22–28°C. It tolerates a dry season of up to 5 months, but only if the relative humidity does not normally drop below 75%. It grows gregariously with a preference for alluvial flats, on deep, rich, well-drained or volcanic soils. Inferior sites retard growth and produce wood with a higher density (over 160 kg/m³), which is not of commercial interest. In Cameroon Ochroma pyramidale is naturalized, occurring frequently in woodland and secondary forest.
Management
Ochroma pyramidale can be propagated by seed. The 1000-seed weight is 5–15 g. The very small seeds should be collected from standing trees and can be stored for several years in jute bags or in closed containers. They can be sown directly in the field or in the nursery. Seeds contain an impervious testa which must be ruptured by heat (boiling water, fire) before they will germinate. Under natural conditions forest clearance exposes the soil to the sun and this triggers germination of the seeds. In the nursery, seeds are sown in lines 3–4 cm apart under slight shade and in sterilized soil to prevent damping-off. Pretreated seeds show 65–75% germination in 5–28 days. When they are 3–4 months old and 20–25 cm tall, the seedlings are planted out in the field at a spacing of (2–)4–5 m × (3–)4–5 m. As the roots of young plants are extremely sensitive to damage, bare-rooted plants cannot be used and direct seeding is preferred, with 15–20 seeds per hole, later thinned to one plant per hole. Plantations should be weeded 2–3 times during the first year. When the trees are about 4 years old, the density should be about 400 trees/ha, to create enough growing space for the trees to allow for rapid growth. Great care should be taken to avoid damage to the remaining trees, as they heal very poorly or not at all. Pruning should therefore not be carried out. Rotations do not generally exceed 7–8 years. At this age heartwood development starts, and heartwood has a much higher density and a darker colour rendering it less suitable for the special purposes. The tree is liable to fungal and insect attacks via damage in the bark. Throughout Central and South America a shoot borer (Anadasmus porinodes) causes severe damage in plantations. The wood is highly prone to blue stain, and it should be converted rapidly after felling to prevent extensive splitting and staining.
Genetic resources and breeding
Differences in wood density may be a starting point for further selection and breeding.
Prospects
Ochroma pyramidale has lost importance due to the increased use of synthetic materials, but it will probably remain the best material for some special applications, e.g. model making. Increased use for niche applications and as pulpwood is even possible, in view of the current trends of using bio-based and biologically degradable materials instead of synthetic ones. It is not clear to what extent and where exactly the tree occurs planted or naturalized in tropical Africa, but it may have some potential here for plantations. An important advantage is its fast growth, as the wood can be harvested at 7–8 years rotation in timber plantations.
Major references
• Beentje, H. & Smith, S., 2001. FTEA and after. Systematics and Geography of Plants 71(2): 265–290.
• Farmer, R.H., 1972. Handbook of hardwoods. 2nd Edition. Her Majesty’s Stationery Office, London, United Kingdom. 243 pp.
• Keating, W.G. & Bolza, E., 1982. Characteristics, properties and uses of timbers. Vol.1: South East Asia, northern Australia and the Pacific. Inkata Press, Melbourne, Australia. 362 pp.
• Villiers, J.-F., 1975. Bombacaceae. Flore du Cameroun. Volume 19. Muséum National d’Histoire Naturelle, Paris, France. pp. 71–98.
• Wiselius, S.I., 1998. Ochroma Sw. In: Sosef, M.S.M., Hong, L.T. & Prawirohatmodjo, S. (Editors). Plant Resources of South-East Asia No 5(3). Timber trees: Lesser-known timbers. Backhuys Publishers, Leiden, Netherlands. pp. 414–416.
Other references
• Burkill, H.M., 1994. The useful plants of West Tropical Africa. 2nd Edition. Volume 2, Families E–I. Royal Botanic Gardens, Kew, Richmond, United Kingdom. 636 pp.
• Chittenden, A.E. & Palmer, E.R., 1990. Pulping characteristics of five low density wood species grown in Belize. Tropical Science 30(2): 167–177.
• CTFT (Centre Technique Forestier Tropical), 1961. Ochroma lagopus Swartz (balsa): caractères sylvicoles et méthodes de plantation. Bois et Forêts des Tropiques 80: 27–32.
• Dahms, K.-G., 1991. Neue Importholzkunde 4: Balsa. Holz-Zentralblatt 117(153): 2490.
• Lamprecht, H., 1989. Silviculture in the tropics: tropical forest ecosystems and their tree species, possibilities and methods for their long-term utilization. Deutsche Gesellschaft für Technische Zusammenarbeit (GTZ) GmbH, Eschborn, Germany. 296 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 mecaniques des bois tropicaux. Deuxième supplément. Centre Technique Forestier Tropical, Nogent-sur-Marne, France. 128 pp.
• Villavelez, L.V. & Meniado, J.A., 1979. Notes on balsa (Ochroma pyramidale Cav.). Forpride Digest 8(3–4): 25–30.
• Webb, D.B., Wood, P.J., Smith, J.P. & Henman, G.S., 1984. A guide to species selection for tropical and sub-tropical plantations. 2nd Edition. Tropical Forestry Papers No 15. Commonwealth Forestry Institute, University of Oxford, United Kingdom. 256 pp.
• Wiemann, M.C. & Williamson, G.B., 1988. Extreme radial changes in wood specific gravity in some tropical pioneers. Wood and Fiber Science 20(3): 344–349.
Sources of illustration
• Wiselius, S.I., 1998. Ochroma Sw. In: Sosef, M.S.M., Hong, L.T. & Prawirohatmodjo, S. (Editors). Plant Resources of South-East Asia No 5(3). Timber trees: Lesser-known timbers. Backhuys Publishers, Leiden, Netherlands. pp. 414–416.
Author(s)
M. Brink
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
Based on PROSEA 5(3): ‘Timber trees: Lesser-known timbers’.

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:
Brink, M., 2008. Ochroma pyramidale (Cav. ex Lam.) Urb. In: Louppe, D., Oteng-Amoako, A.A. & Brink, M. (Editors). Prota 7(1): Timbers/Bois d’œuvre 1. [CD-Rom]. PROTA, Wageningen, Netherlands.
1, tree habit; 2, flowering twig; 3, leaf; 4, flower; 5, flower in longitudinal section; 6, dehisced fruit.
Source: PROSEA



planks
obtained from
Arnhemse Fijnhouthandel


wood
obtained from
Arnhemse Fijnhouthandel


wood
obtained from
Carlton McLendon, Inc.