4995

5(3): Timber trees; Lesser-known timbers

Bombax L.

Sp. pl. 1: 511 (1753); Gen. pl., ed. 5: 227 (1754).

BOMBACACEAE

x = unknown; B. ceiba: 2n = 72

Kekabu (trade name). Cottonwood (En). Indonesia: randu alas. Malaysia: kekabu hutan (Peninsular), kapok, tambaluang (Sabah). Papua New Guinea: bombax, kapok. Philippines: malabulak. Burma (Myanmar): didu, letpan, thinbaw. Thailand: ngiu. Vietnam: g[aj]o d[or], g[aj]o hoa trang, p'lang.

Bombax comprises 8 species occurring in the Old World tropics from tropical Africa to Indo-China, throughout the Malesian area towards northern Australia. Three species are native to Malesia.

In the Malesian region Bombax is used as a low grade utility timber only. It has been applied for packing cases, matchboxes, matches, core veneer, temporary construction, musical instruments, mouldings, household appliances, buoys, novelties and, when treated, for low grade furniture and interior partitioning. Locally it is used for making canoes. In Papua New Guinea large logs of B. ceiba were formerly peeled for plywood and veneer production. In India, where B. ceiba is much more common, it is the major indigenous source of wood for the production of matches.
The kapok from the fruits of B. ceiba can be used for stuffing pillows etc., and the tree is sometimes planted as an ornamental for its bright red flowers; in Vietnam it is also planted around temples. In Java Bombax is grown in cemeteries and the trees are considered sacred. The gum from the bark and roots has been used as a medicine against diarrhoea, dysentery and fever. Fibres from the bark of B. ceiba are used for making paper pulp, oil from the seed is used in food and for soap making and the flowers are eaten after boiling. Leaves and twigs may be used as a forage for cattle.

Within the Malesian region supplies are generally very limited and trade is only local. In Peninsular Malaysia Bombax is often traded as "durian"" wood in small proportions in mixed consignments mainly comprising wood of Durio spp. In 1996 Papua New Guinea exported about 1050 m³ of Bombax logs at an average free-on-board (FOB) price of US$ 97/m³.

Bombax yields a lightweight hardwood with a density of 120-545 kg/m³ at 15% moisture content. Heartwood straw-coloured, sharply differentiated (B. valetonii) or not (B. ceiba) from the white sapwood; grain straight or slightly interlocked; texture moderately coarse and even. Growth rings indistinct; vessels medium-sized to large, solitary and in radial multiples of 2-4, rarely in clusters; parenchyma abundant, apotracheal diffuse to diffuse-in-aggregates, visible with a lens; rays medium-sized, conspicuous on radial surface, and fine, hardly visible even with a lens; ripple marks present, but not always distinct due to vertical fusion of rays.
Shrinkage is low to moderate and the wood seasons fairly rapidly with negligible degrade except for fungal and insect attacks. Board 13 mm and 38 mm thick boards take respectively 2.5 months and 3.5 months to air dry. The wood is soft and weak. It is easy to work in green as well as in seasoned condition. The wood is non-durable, with an average service life of 0.9 years in a graveyard test in Peninsular Malaysia. It is extremely easy to treat with preservatives: an average absorption of 592 kg/m³ of creosote by the open-tank method is reported, whereas an average absorption of 415 kg/m³ is obtained by the hot and cold tank process using 50% creosote and 50% diesel oil. The sapwood is susceptible to Lyctus and blue stain. The large difference in wood properties between wood samples of B. ceiba originating from India and those from the South-East Asian region, which is often mentioned in literature, is only slightly reflected by data on mechanical properties, the wood from India being only slightly stronger.
See also the tables on microscopic wood anatomy and wood properties.

Deciduous, small to large trees up to 35(-45) m tall; bole straight, branchless for up to 20(-25) m, up to 150(-400) cm in diameter, with large buttresses, up to 6 m high, often fluted, bole or sometimes only the branches armed with sharp woody knobs or spines, often in rows; bark surface shallowly fissured, whitish to pale brownish-grey, inner bark soft and fibrous, red to orange or pink or straw, with slight cream and reddish flames; crown flat. Leaves arranged spirally, palmately compound; leaflets 5-9, entire; stipules caducous. Flowers solitary or in fascicles, large; epicalyx lacking; calyx cup-shaped with 2-4 lobes; petals 5, hairy; stamens numerous, the filaments joined into a short tube and forming 5 bundles, anthers 1-celled; ovary superior, 5-locular with many ovules in each cell, style club-shaped. Fruit a large woody capsule splitting into 5 parts, the inner walls covered with cottony down. Seed embedded in dense woolly hairs. Seedling with epigeal germination; cotyledons heart-shaped; hypocotyl elongated; first leaves alternate and with 3 leaflets up to about the 4th node, then the number of leaflets increases.
Growth is according to Aubréville's architectural tree model, characterized by a monopodial trunk with rhythmic growth, branches with rhythmic growth but modular, each branch plagiotropic by apposition. In a trial in Java growth was very slow and B. ceiba attained a height of 1-4.5 m 5.5 years after planting. For India very fast growth is reported; a mean annual diameter increment of 2.5 cm is not at all exceptional. In Peninsular Malaysia under natural forest conditions mean annual diameter increment of B. valetonii as a dominant or co-dominant tree is 1.2-1.6 cm. Flowers appear when the leaves have fallen. New growth commences after the fruits have matured. In Peninsular Malaysia flowering is from November-February, in Java from April-November and in Papua New Guinea from June-September. Nectar is collected from the flowers by bees, butterflies, birds and bats. Grafted plants start producing viable seed after three years. Seed is dispersed by wind.
The family Bombacaceae is sometimes incorporated in the Malvaceae.

Bombax can be found in primary and secondary forest, often near rivers, up to 750 m altitude (within Malesia). B. ceiba is often found at forest edges or disturbed forest and can be locally dominant.

Bombax can be propagated by seed, including direct sowing, and by vegetative means through cuttings and grafting. For B. ceiba there are about 28 000 seeds/kg. To obtain seeds the fruits are dried in the sun and when they open the seeds are removed. Seed can be stored in closed receptacles for 1-2 years. About 90% of B. ceiba seeds germinate in 6-18 days. Seedlings can be planted out as bare-rooted stock, as container stock or as stumps. Container stock is not successful in India due to slow development after planting, but 82% survival has also been reported. For stumps, the fleshy taproot should be 50-60 cm long, and the diameter at the collar should be 1-2.5 cm. Direct sowing in lines 45-60 cm apart after the harvest of a field crop showed very good results in India. Cuttings were not effective; high mortality occurred after planting out in the field. For B. ceiba as an ornamental tree, however, propagation by cuttings under mist is very successful and 100% rooting is obtained even without the application of growth hormones. Patch budding is used to establish seed orchards of B. ceiba in India; about 80% of the grafted plants survive, provided they are not transplanted. Weeding and thinning is necessary for up to three years. B. ceiba in India is characterized as a strong light-demander with abundant natural regeneration on open sites and easy natural pruning under forest conditions. It coppices well but only for the first few years. Bombax at first shows pioneer characteristics, but later develops those of a mature phase emergent. Fomes lignosus, a fungal wound parasite causing wood decay, and Dysdercus cingulatus (red cotton bug) nymphs and adults which feed on the sap of tender parts, have been observed on B. ceiba.

A germplasm bank has been established in Arunachal Pradesh (India) where 22 clones of B. ceiba are available, and 15 clones are present at the Forest Research Institute at Dehra Dun. Seed orchards have been established at 6 locations in the states of Arunchal Pradesh and Uttar Pradesh. B. ceiba shows both self- and cross-pollination, but the rate of outcrossing is unknown.

Judging by the experiences gained in India with B. ceiba prospects are promising. The large differences in growth rate reported for B. ceiba in South-East Asia and India, however, need reconfirmation; research is needed to determine whether these differences can be attributed to genetic variation.

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Nguyen Ba & Nguyen Nghia Thin

Bombax ceiba
Bombax valetonii

Ba, N. & Thin, N.N., 1998. Bombax L.. In: Sosef, M.S.M., Hong, L.T. and Prawirohatmodjo, S. (Editors): Plant Resources of South-East Asia No 5(3): Timber trees; Lesser-known 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:
Bombax ceiba
Bombax valetonii