4524

5(2): Timber trees; Minor commercial timbers

Pterocymbium R.Br.

Benn., R.Br. & Horsf., Pl. jav. rar. 3: 219 (1844).

STERCULIACEAE

x = unknown; 2n = unknown

Trade groups Amberoi: lightweight hardwood, e.g. Pterocymbium beccarii K. Schumann, Pterocymbium tinctorium (Blanco) Merr., Pterocymbium tubulatum (Masters) Pierre.

Amberoi. Indonesia: kelumbuk, papita (general). Malaysia: melembu (Peninsular), teluto (Sabah), keluak (Malay, Sarawak). Philippines: taluto (Filipino). Burma (Myanmar): sawbya. Thailand: oi-chang, po-ikeng, po-kradang.

Pterocymbium consists of 6 or 7 species and is confined to Burma (Myanmar), the Nicobar and Andaman Islands, Indo-China, Thailand, and throughout the Malesian region and Fiji.

Amberoi has uses similar to Scaphium wood (kembang semangkok), particularly for rotary veneer (both face and core veneer) and plywood, but also for temporary construction, scantlings, mouldings, interior finish, furniture, concrete shuttering, packing cases, fishing boats, fish-net floats, matchsplints and matchboxes, wooden shoes, pulp and paper, and wood-wool boards.
The bark of Pterocymbium tinctorium is used to improve black dyeing of cotton cloth. Strips of the bark are used locally for making rope.

The export of round logs from Sabah in 1987 was 19 000 m³ with a value of US$ 1.3 million (US$ 69/m³), and in 1992 the total export of amberoi from Sabah was 9100 m³ (61% as sawn timber, 39% as logs) with a total value of US$ 1.3 million (US$ 194/m³ for sawn timber, US$ 69/m³ for logs).
In Papua New Guinea, amberoi is an important export timber. It is ranked in MEP (Minimum Export Price) group 4; in 1992 saw logs fetched a minimum price of US$ 43/m³. It is imported in Japan mainly from Papua New Guinea, and in 1987 constituted 2.3% of the total timber import from Papua New Guinea.
Pterocymbium timber is traded in Thailand domestically together with the timber of other fast-growing species such as Bombax anceps Pierre, Lannea coromandelica (Houtt.) Merr. and Tetrameles nudiflora R.Br.

Amberoi is a lightweight hardwood. The heartwood is yellowish-white or greyish-white, and not distinctly demarcated from the white sapwood. The density is (230—)240—380(—450) kg/m³ at 12% moisture content. The grain is straight, texture moderately coarse to coarse. The wood is not lustrous, but an attractive oak-like figure is present on quarter-sawn surfaces.
At 12% moisture content, the modulus of rupture is 46—54 N/mm², modulus of elasticity c. 8405 N/mm², compression parallel to grain 30 N/mm², shear 4—7.5 N/mm², cleavage 23 N/mm radial and 23—34.5 N/mm tangential, and Janka side hardness 1625 N.
The rates of shrinkage are moderate: from green to 12% moisture content 1.9% radial and 5.0% tangential, and from green to oven dry 2.9% radial and 7.6% tangential. The wood air dries readily without much degrade. The moisture content of green timber is about 60%. The wood kiln dries fairly readily, but occasional end-splitting and twisting may occur. A temperature of 60—70°C gives good results. Boards 25 mm thick can be kiln dried to 12% moisture content in about 2 days. A high-humidity treatment is recommended after drying.
Amberoi has good sawing characteristics (silica is absent), and is easy to work, provided the wood is well seasoned, but it requires sharp tools to make a smooth cut, especially across the grain. A good finish can be obtained with both machine and hand tools. The nail-holding properties are moderate, but the wood glues fairly well. The steam bending properties are satisfactory. Amberoi is well suited for veneer and plywood, less suited for particle board and fibreboard making, and not suited for cement board production. The pulp is only of moderate quality.
Amberoi is non-durable. It is highly perishable in exposed situations and highly susceptible to termite, Lyctus and ambrosia beetle attack, and should only be used under cover. The wood is very prone to staining. Both sapwood and heartwood are permeable to preservatives when using a pressure treatment.
The wood contains 67—80% holocellulose, 18.2—25.5% lignin, 13—17.6% pentosan and 0.8—2.5% ash. The solubility is 1.4—3.3% in alcohol-benzene, 6—11% in hot water and 23.5—23.9% in a 1% NaOH solution. The wood is not suitable for making charcoal.

Medium-sized to large, monoecious, deciduous trees up to 50 m tall; bole straight, branchless for up to 33 m, up to 90(—120) cm in diameter, with short rounded buttresses extending up the trunk as low ribs; bark surface smooth, hoop-marked, conspicuously dotted with dark warty protuberances, pale grey to orange-brown or pinkish-brown or dark brown, inner bark soft, fleshy red with white streaks, with yellowish exudate. Stellate hairs or scales present. Leaves arranged spirally, distinctly petiolate; blade simple and entire, ovate or broadly ovate, base cordate to truncate, apex acuminate, glabrescent, pinnately veined but with 3(—7) palmate veins at base, tertiary venation scalariform, slightly prominent below; stipules subulate, small, caducous. Inflorescence axillary or terminal, slightly pendulous, paniculate. Flowers unisexual, 5-merous, regular; calyx bell-shaped or tubular, hairy along the margin; petals absent; male flowers with a staminal column topped by 8—10 sessile anthers; female flowers with 5 superior, free, sessile, pubescent pistils on top of an androgynophore, each ovary with 2 ovules, style with recurved stigmas. Fruit consisting of 4—5 follicles within a persistent calyx, follicle papery, splitting open before ripening, boat-shaped with a prominent dorsal lobe. Seed 1 at the base of each follicle, not winged.

— Macroscopic characters:
Heartwood yellowish-white to pale yellow, not distinctly demarcated from the sapwood. Grain generally straight. Texture coarse; silver grain prominent on radial surfaces due to the wide rays. Growth rings indistinct to fairly distinct; vessels visible to the naked eye; large rays distinct to the naked eye on all surfaces; ripple marks distinct because of storied small rays and other elements.
— Microscopic characters:
Growth rings generally indistinct, if fairly distinct, marked by the interrupted arrangement of small flattened pores. Vessels diffuse, 1—2(—4)/mm², predominantly solitary, occasionally in radial multiples of 2—3, round or oval, up to 350 µm in tangential diameter; perforations simple; intervessel pits alternate, c. 6 µm in diameter; vessel-ray and vessel-parenchyma pits almost similar to intervessel pits but half-bordered; deposits and tyloses absent or scarce. Fibres 1.1—2.1 mm long, very thin-walled (walls 1—2 µm thick), with numerous minutely bordered to simple pits in the radial walls. Parenchyma abundant, diffuse-in-aggregates and narrowly vasicentric, in 2—4 celled strands. Rays 2—4/mm, of 2 distinct sizes, 1—2-seriate and up to 12(—20)-seriate, broad rays up to 5 mm (occasionally more) high, heterocellular with more than one row of square and/or upright marginal cells (Kribs type heterogeneous III or II); sheath cells present. Crystals present as druses, numerous, in sheath cells and also in other enlarged ray parenchyma cells, occasionally as prismatic crystals in procumbent ray cells. Silica inclusions absent. Traumatic axial canals with dark contents sometimes present in short arcs. All elements, except the broad rays, storied.
Species studied: Pterocymbium beccarii, Pterocymbium tinctorium.

Amberoi trees are fast growing. In an 11-year-old plantation of Pterocymbium tinctorium in the Philippines, trees had a mean height of 25.4 m, a bole branchless for 17.6 m on average and a mean diameter of 35.2 cm. A mean annual diameter increment of 2 cm has been reported over a period of 30 years.
Flowering occurs on the bare crown and trees are often leafless until fruit is set. The period between flowering and fruiting for Pterocymbium tinctorium is extremely short, being only about 3 weeks.

Pterocymbium is readily distinguishable by its characteristically shaped follicles, which is at the same time the main distinctive feature towards the closely related genus Scaphium. There is some dispute about species delimitation, because some authors value the variation in colour, size and form of the flowers at species level, while others lump the plants that are very similar in other respects into a single, variable species.

Amberoi is usually locally common but scattered in tropical evergreen to moist mixed deciduous forest. It is most common in the lowland but may extend to lower montane forest at 1000 m altitude. Amberoi occurs on a wide range of soils, varying from sandy alluvial flats to loamy or clayey soils.

Amberoi is propagated by seed. One kg contains about 8000 dry follicles of Pterocymbium tinctorium and about 9200 dry seeds. Seed germinates readily and rapidly; fresh seed of Pterocymbium tinctorium has 100% germination in 1—2 weeks, whereas seed stored for 1—2 months has 65—75% germination in 1—3 weeks. Seed is sown under shade and seedlings are pricked out and transferred to polybags. After 6 months the seedlings are 50 cm tall and ready for planting out in the field. Spacings applied are 2 m 3 m and 4 m 4 m. Pterocymbium tinctorium should not be planted on soils with a periodically high water table.

Natural regeneration is generally good. Being a pioneer species, amberoi needs plenty of light, especially in the seedling stage. Plantations need to be weeded during the first 1—3 years and should be thinned 5 and 10 years after planting. The rotation of amberoi in plantations is 30 years or less.

In the nursery damping-off is a risk, but it can be prevented by avoiding excessive watering and allowing for air ventilation. Although larvae of the moth Arthroschista hilaralis have been found to damage terminal buds and Meloidogyne nematodes may destroy roots of amberoi trees, these pests are never very serious.

Logs should be extracted from the forest within a day after felling as the timber is very susceptible to attacks by Lyctus, ambrosia beetles, and blue stain. The cut ends of logs should therefore be coated with tar or lime to prevent damage.

In Papua New Guinea, the estimated maximum timber volume of Pterocymbium beccarii is 2.6 m³/ha, but in New Britain it is 17.6 m³/ha. In the evergreen forest of Burma (Myanmar), approximately 0.65 amberoi trees/ha are found, with a timber volume of 0.88 m³/ha. For Thailand a mean annual increment of 2 m³/ha has been recorded, but this seems to be very low as amberoi is known for its rapid growth.

Logs of amberoi float in water and can be transported by rivers. Amberoi is used for floating heavier timber in rafts.

Amberoi does not seem to be in immediate danger of genetic erosion. It is often a pioneer and it regenerates readily after logging, and some species (especially Pterocymbium tinctorium) are common over large areas. However, some species are much less common and widespread (e.g. Pterocymbium tubulatum), and plantations have only been established as trials on a small scale.

Amberoi seems to have promising prospects for planting in logged-over forest and for reforestation, as it grows fast and is adapted to open and fairly dry soil conditions. Rotations of less than 30 years are needed to produce fair amounts of timber, which is particularly suitable for manufacturing veneer.

All Nippon Checkers Corporation, 1989. Illustrated commercial foreign woods in Japan. Tokyo. p. 131.
Ashton, P.S., 1988. Manual of the non-dipterocarp trees of Sarawak. Vol. 2. Dewan Bahasa dan Pustaka, Kuala Lumpur. pp. 398-400.
Bolza, E. & Kloot, N.H., 1966. The mechanical properties of 81 New Guinea timbers. Division of Forest Products Technological Paper No 41. Commonwealth Scientific and Industrial Research Organization, Melbourne. pp. 32-35.
Eddowes, P.J., 1977. Commercial timbers of Papua New Guinea. Their properties and uses. Office of Forests, Department of Primary Industry, Port Moresby. pp. 18-19, 81, 100, 107.
Keating, W.G. & Bolza, E., 1982. Characteristics, properties and uses of timbers. Vol. 1: South-east Asia, Northern Australia and the Pacific. Division of Chemical Technology, Commonwealth Scientific and Industrial Research Organization. Inkata Press, Melbourne, Sydney, London. p. 286.
Kochummen, K.M., 1983. Sterculiaceae. In: Whitmore, T.C. (Editor): Tree flora of Malaya. A manual for foresters. 2nd edition. Vol. 2. Malayan Forest Records No 26. Forest Research Institute Malaysia. Longman Malaysia SDN. Berhad, Kuala Lumpur. pp. 366-367.
Kostermans, A.J.G.H., 1950. Notes on Pterocymbium R.Br. (Sterculiaceae). Reinwardtia 1: 41-49.
Streimann, H., 1974. Amberoi, Pterocymbium beccarii, Sterculiaceae. Timber Species Leaflet No 10. Division of Botany and Forest Products Research Centre, Department of Forests, Port Moresby. 4 pp.
Sun, K.K. et al., 1983. Studies on the end-use development of lesser-known tropical timbers II. Studies on five species Amberoi (Pterocymbium beccarii K. Schum.), Celtis (Celtis nymannii K. Schum.), Dillenia (Dillenia papuana Martelli), Malas (Homalium foetidum Benth.), Spondias (Spondias dulcis Forst.), grown in Kapuluk district, New Britain, Papua New Guinea. Research Reports No 30. Forest Research Institute Korea, Seoul. pp. 191-212.
van Royen, P., 1964. Manual of the forest trees of Papua and New Guinea. Part 3 - Sterculiaceae. Division of Botany, Department of Forests, Lae. pp. 24-28.

C. Phengklai (general part), S.I. Wiselius (properties), S. Sudo (wood anatomy), M.S.M. Sosef (selection of species)

Pterocymbium beccarii
Pterocymbium splendens
Pterocymbium tinctorium
Pterocymbium tubulatum

Phengklai, C., Wiselius, S.I., Sudo, S. & Sosef, M.S.M., 1995. Pterocymbium R.Br.. In: Lemmens, R.H.M.J., Soerianegara, I. and Wong, W.C. (Editors): Plant Resources of South-East Asia No 5(2): Timber trees; Minor commercial timbers. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea

The following species in this genus are important in this commodity group and are treated separatedly in this database:
Pterocymbium beccarii
Pterocymbium splendens
Pterocymbium tinctorium
Pterocymbium tubulatum