Duabanga (PROSEA)

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Plant Resources of South-East Asia Introduction

List of species

Duabanga Buch.-Ham.

Protologue: Trans. Linn. Soc. Lond. 17: 177 (1837).

Family: Sonneratiaceae

Chromosome number: x= 12;D. grandiflora,D. moluccana: 2n= 48

Trade groups

Duabanga: lightweight hardwood, Duabanga grandiflora (Roxb. ex DC.) Walp. and D. moluccana Blume.

Vernacular names

• Duabanga
• Indonesia: benuang laki (Kalimantan), gayawas hutan (Moluccas), kalanggo (Sumbawa)
• Malaysia: magasawih, berembang bukit (Peninsular), magas (Sabah)
• Philippines: loktob (general). Burma (Myanmar): myaukngo
• Cambodia: dlom chloeu ter
• Laos: phay
• Thailand: lamphu-pa (peninsular), tum ten (northern), lamphaen (Trang)
• Vietnam: bông sư.

Origin and geographic distribution

Duabanga consists of 2 species and is distributed from the eastern Himalayas to New Guinea: eastern India, Burma (Myanmar), Indo-China, Thailand, and Malesia (except Sumatra and western Java). D. grandiflora is confined to mainland South-East Asia (south to central Peninsular Malaysia), D. moluccana to the eastern part of the geographical range of the genus (west to Borneo and the Philippines).

Uses

Duabanga timber is used for dugout boats, fishnet floats, floaters for the extraction of sinker logs, temporary construction, interior fittings and furniture, mouldings, cupboards, and matches and matchboxes. It has good properties for the production of veneer and plywood, being used for outer layers as well as core layers.

The young fruits are edible but sour. In Indonesia a decoction of the bark has been used in mixtures with other plants to dye matting black.

Production and international trade

Duabanga is only locally commercially important. In Sumbawa (Indonesia), it is locally gregarious; the production was about 9000 m³in 1983. In 1992, the export of logs from Sabah was 37 000 m³and of sawn timber 4500 m³with a total value of US$ 3.6 million. Its availability in Papua New Guinea is variable, but Duabanga is rated as having commercial potential. Small amounts are imported by Japan, mainly from Sabah and Sarawak.

Properties

Duabanga is a lightweight and comparatively soft wood. The heartwood is whiteor pale yellow to pale reddish-brown or greyish-brown, and not clearly demarcated from the 6-9 cm wide sapwood, which is slightly paler than the heartwood. The density is 270-560 kg/m³at 15% moisture content. The grain is usually shallowly interlocked, sometimes straight, texture coarse but even.

At 12% moisture content, the modulus of rupture is 43-90 N/mm², modulus of elasticity 6670-8285 N/mm², compression parallel to grain 30-44 N/mm², compression perpendicular to grain c. 7 N/mm², shear 6-11 N/mm², cleavage c. 37.5 N/mm tangential, Janka side hardness about 1380-4275 N and Janka end hardness c. 4740 N.

The rate of shrinkage is moderate: from green to oven dry about 3.7-3.9% radial and 6.6-7.2% tangential. The wood air dries rapidly and without serious degrade, but often darkens considerably on drying. Kiln drying may result in slight warping and splitting. In Burma (Myanmar), it is recommended to girdle the standing log several months before felling to facilitate drying.

The wood is easy to saw (it contains no silica), plane, shape, bore, turn and sand, but finishing is more difficult because of its softness. It holds nails and screws well and gluing is not a problem. Peeling properties are good, but care should be taken to prevent fungal attack when veneer or plywood is stacked tightly. Drying of veneer presents no problems.

The wood is perishable and susceptible to staining and termite attack. The wood of D. moluccana is reported as easy to impregnate, but that of D. grandiflora is sometimes more resistant to treatment with preservative.

Wood of D. moluccana contains 54% cellulose, 29% lignin, 16% pentosan and 0.6% ash. The solubility is 4.3% in alcohol-benzene, 4.4% in cold water, 11.5% in hot water and 20.6% in a 1% NaOH solution. The energy value is 19 660 kJ/kg.

Description

Medium-sized to fairly large trees, up to 35(-45) m tall; bole cylindrical, up to 100 cm in diameter, buttresses absent or insignificant; bark surface smooth, lenticellate, becoming rough, inner bark soft, fibrous, yellow or reddish; crown monopodial, tall, oblong, rather open; twigs pendulous, 4-angled or winged, later becoming terete, with reddish young leaves towards the tips. Leaves opposite, biseriate, simple and entire, leathery, ovate-oblong with cordate or rounded base, glabrous or very soon glabrescent, conspicuously veined with numerous secondary veins, glaucous beneath; petiole short, stipules absent. Flowers in terminal 5-many-flowered corymbs, bisexual, 4-8merous; calyx thickly leathery, gamosepalous, persistent, tube obconical or cup-shaped; petals equal in number to and alternating with sepals, broad and wrinkled, white; stamens 12 or numerous, inserted on the calyx, with long, slender filaments inflexed in bud; ovary superior, 4-8-celled, style long and robust with a capitate and lobed stigma. Fruit a loculicidally 4-8-valved capsule, many-seeded. Seed small, lacking albumen, tailed at both ends. Seedling with epigeal germination.

Wood anatomy

• Macroscopic characters:

Heartwood comparatively soft, white or grey to pale reddish-brown, often streaked or tinted with yellow to pale brown, indistinctly demarcated from the paler sapwood. Grain straight to shallowly interlocked or wavy. Texture coarse. Growth rings indistinct or absent; vessels visible to the naked eye, with occasional tyloses visible with hand lens; parenchyma sometimes visible to the naked eye as pale halos around the vessels; rays not visible to the naked eye, barely distinct with a hand lens; ripple marks absent.

• Microscopic characters:

Growth rings indistinct or absent. Vessels diffuse, mostly 2-7/mm², usually in short radial multiples of 2-4, mostly 160-250μm in diameter (sometimes up to 350μm); perforation plates simple; intervessel pits alternate, circular or oval, vestured, 8-12(-14)μm; vessel-ray pits simple or with much reduced borders, enlarged, round to somewhat horizontally to vertically elongated (sometimes difficult to locate); tyloses common to infrequent. Fibres typically 1.2-1.4(-2.3) mm long, non-septate, very thin-walled to thick-walled, with simple to minutely bordered pits mainly confined to the radial walls. Parenchyma scarce to frequent, vasicentric to slightly aliform (lozenge type), 8 or more cells per parenchyma strand. Rays mostly 8-10/mm, exclusively uniseriate or nearly so, (400-)600-1200(-1600)μm high, homocellular to heterocellular with one row of upright and/or square marginal cells; storied structure absent. Prismatic crystals in upright and/or square marginal ray cells and in procumbent ray cells of D. grandiflora , and in non-chambered parenchyma cells of D. moluccana , mostly one crystal per cell or chamber, but sometimes two distinct sizes of crystals in one cell or chamber. Silica absent.

Species studied: D. grandiflora , D. moluccana .

Growth and development

Duabanga trees are light-demanding and fast growing. The average annual increment in height and in diameter is reported as 67 cm and 2.5 cm, respectively, for D. moluccana in Indonesia; it grows to 60-70 cm in diameter in 25 years. In open places in India, an annual growth rate in height of almost 3 m has been achieved for D. grandiflora in a 10-year-old plantation. The latter species can reach a diameter more than 50 cm in 40 years inunthinned stands. Logs of up to 35 cm diameter and a merchantable height of 17.5 m have been obtained from an 11-year-old plantation of D. moluccana in the Philippines.

The architecture of D. grandiflora trees is according to Massart's model. The trunk is orthotropic and monopodial with leaves arranged spirally. It produces close series of branches as a result of rhythmic growth; the trunk shows regular tiers of 3-5 branches and proceeds to the top of the crown. The branches are plagiotropic, have opposite leaves and become pendulous with age.

The trees are evergreen or leafless for a short period in the dry season. They start to flower at an age of about 4-6 years. Trees often flower more or less continuously. The flowers, which are borne at the tips of branches, open after sunset and have a strong, sour to musty smell. They are pollinated by bats (e.g. Eonycteris spelaea and Macroglossus sobrinus for D. grandiflora in Peninsular Malaysia) and fall the next morning. The very light seeds have wings and are dispersed by wind.

Other botanical information

Together with Sonneratia , a genus of mangrove trees, Duabanga constitutes the family Sonneratiaceae . These genera are sometimes placed in Lythraceae , and occasionally Duabanga is considered to represent a separate family: Duabangaceae .

A third species has been described in the genus from trees growing in a botanical garden in Sri Lanka (probably raised from seeds from the botanical garden in Bogor, Indonesia): D. taylorii Jayaweera. It shows several intermediate characters between the other 2 species and is possibly of hybrid origin. Its pollen and seed, however, showed good fertility.

Ecology

Duabanga is characterized as a pioneer or early successional species just like kadam ( Anthocephalus chinensis (Lamk) A. Rich. ex Walp.) and Trema and Macaranga species, and is found up to 1200 m altitude. The seedlings are very light-demanding and grow only in open sites. After the original forest has been disturbed, D. moluccana may form an almost pure stand (e.g. in Sumbawa), which is, however, not stable and gradually becomes dominated by other species such as Syzygium spp. In Papua New Guinea, D. moluccana usually occurs on the edges of freshwater swamps and floodplains. D. grandiflora occurs more scattered in Peninsular Malaysia along rivers, especially in hilly country.

Propagation and planting

The winged seed of Duabanga is very small and a single fruit contains 7000-8000 seeds. The weight of 10 000 seeds is about 1 g. Since Duabanga starts to flower when about 4 years old and ripe fruits can be harvested twice a year, it is usually easy to obtain seed for propagation.

It is recommended to select superior mother trees to obtain good-quality seed. Sowing in open seedbeds gives poor results, because seeds are washed away or seedlings are destroyed by rain. In India, the best results are obtained either by mixing seed with fine sand and sowing on very fine porous soil on raised seedbeds, on powdered charcoal or on fine sand in covered boxes. Water should be applied by spraying. Seeds will germinate within 20 days. The germination rate of D. grandiflora is 65-75% after 8 days. Weeding is recommended 2 months after germination as weed competition may reduce seedling growth by up to 30%. The seedlings are transplanted into polyethylene bags towards the end of the following rainy season, when they are 3-6 cm tall. The can be planted out in the 3 months after this, preferably at the beginning of the rainy season. Wildlings and stumps are also commonly planted. The planting distance is 4-7 m × 4-7 m. Thinning is practised to obtain an eventual spacing of 15 m × 15 m or about 40 trees/ha.

Silviculture and management

Selective logging does create open areas where the light-demanding Duabanga seedlings can establish, but in areas with a low logging intensity other species which are more adapted to shade will predominate. Partial logging or group logging was adopted in Sumbawa (Indonesia) where areas of 5-10 ha were almost clear cut and subsequently planted with D. moluccana . A rotation of 50-70 years is recommended.

Diseases and pests

Insects, deer and cattle feed on seedlings and young plants. In South Kalimantan (Indonesia), an unidentified stem borer was found to attack trees in the field, disturbing their growth and reducing the quality of the timber. Tunnels made by this insect were about 30 cm long and 1.5 cm in diameter.

Harvesting

In Sumbawa (Indonesia), bulldozers are used for clear cutting and yarding. On slopes yarding is done by sky-line cables minimize forest destruction. However, mechanized harvesting was noted to destroy approximately 115 m³/ha of other timber species.

Yield

D. moluccana has a mean annual increment of 4 m³/ha. In a 50-year-old plantation with about 40 trees/ha, the logs had a diameter of 70-100 cm: with a timber volume of 5-10 m³/tree the total standing stock was 200-250 m³/ha. A 10-year-old plantation in India is reported to have produced 160 m³/ha.

Handling after harvest

Duabanga timber should be removed rapidly from logging areas, as it is susceptible to fungal and insect attack. The initial moisture content of timber can be very high (up to 120%) and fresh logs may even sink in water.

Genetic resources and breeding

Duabanga easily invades disturbed areas and does not seem to be at immediate risk of genetic erosion. The occurrence of variation in density of greentimber (about 90% of fresh logs float in water, about 10% sink) and of a putative hybrid may offer possibilities of breeding to obtain good planting stock for timber plantations.

Prospects

Duabanga is a fast-growing tree with promising economic prospects for timber plantations. It may be suitable for reforestation of denuded areas. However, not much is known about silvicultural aspects and more research is needed.

Literature

• Balai Teknologi Reboisasi Banjarbaru, Kalimantan Selatan, 1992. Pengelolaan hutan Duabanga di Calabai - Nusa Tenggara Barat [Management of Duabanga forest in Calabai - West Nusa Tenggara]. Penerbitan No 1: 43-49.
• Dahms, K.-G., 1982. Asiatische, ozeanische und australische Exporthölzer [Asiatic, Pacific and Australian export timbers]. DRW-Verlag, Stuttgart. pp. 106-107.
• Desch, H.E., 1954. Manual of Malayan timbers. Malayan Forest Records No 15. Vol. 2. Malaya Publishing House LTD., Singapore. pp. 564-567.
• Jayaweera, D.M.A., 1967. The genus Duabanga. Journal of the Arnold Arboretum 48: 89-100.
• Manan, S., 1991. Tinjauan silvikultur dan suksesi hutan alam Duabanga moluccana di Sumbawa [A review of the silviculture and succession of Duabanga moluccana natural forest in Sumbawa]. Kehutanan Indonesia 1991/1992 No 1: 3-7.
• Sagala, A.P.S., 1992. Pengelolaan hutan alam Duabanga dan pembangunan tanaman Duabanga supplement di Calabai - Nusa Tenggara Barat [The management of Duabanga natural forest and the establishment of supplementary Duabanga plantations in Calabai - West Nusa Tenggara]. Kehutanan Indonesia 1991/1992 No 1: 9-10.
• Susila, I.W.W., 1991. Model taksiran isi dolok kalanggo (Duabanga moluccana) di HPH VPI Sumbawa [Log volume estimation models of kalanggo (Duabanga moluccana) for the VPI forest concession in Sumbawa]. Santalum 7: 1-7.
• Troup, R.S., 1921. The silviculture of Indian trees. Vol. 2: Leguminosae (Caesalpiniaceae) to Verbenaceae. Clarendon Press, Oxford. pp. 605-608.
• Backer, C.A. & van Steenis, C.G.G.J., 1951. Sonneratiaceae. In: van Steenis, C.G.G.J. (Editor): Flora Malesiana. Ser. 1, Vol. 4. Noordhoff-Kolff N.V., Djakarta. pp. 280-289.
• Whitmore, T.C., 1983. Sonneratiaceae. In: Whitmore, T.C. (Editor): Tree flora of Malaya. A manual for foresters. 2nd Edition. Vol. 1. Forest Research Institute Malaysia. Longman Malaysia SDN. Berhad. pp. 442-444.