Koompassia (PROSEA)

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Plant Resources of South-East Asia
List of species

Koompassia Maingay ex Benth.

Protologue: Hooker's Icon. pl.: t. 1164 (1873).
Family: Leguminosae
Chromosome number: x= unknown

Trade groups

  • Kempas: medium-heavy timber, Koompassia malaccensis Maingay ex Benth.
  • Tualang: medium-heavy timber, K. excelsa (Becc.) Taubert.

Vernacular names


  • Brunei: impas
  • Indonesia: (m)engris (Aceh, Bangka, Belitung, Kalimantan), (h)ampas (Sumatra, Kalimantan), keranji (Sumatra)
  • Malaysia: impas (Sabah, Sarawak), mengris (Peninsular, Sarawak), makupa (Peninsular)
  • Thailand: thongbung (Phuket), makupa (Malay, Narathiwat), sifai (Patthalung).


  • Brunei: mangaris
  • Indonesia: mangaris (Kalimantan), sialang (Sumatra)
  • Malaysia: sialang (Peninsular), kayu raja (Sabah, Sarawak, Peninsular), tapang, kussi (Sarawak), mengaris (Sabah)
  • Philippines: manggis (Sulu, Tagbanua), ginoo (Palawan)
  • Thailand: yuan, tolae (Yala, Pattani).

Origin and geographic distribution

Koompassia consists of 3 species, 2 of which are distributed over southern Thailand, Peninsular Malaysia, Sumatra, Borneo and Palawan. The third (K. grandiflora) occurs in the western part of New Guinea (Irian Jaya).

Fossil wood resembling that of K. malaccensis has been described from the Tertiary of West Bengal, indicating a formerly more widespread or different distribution of the species or its ancestors.


Koompassia timber is suitable for structural usage. For outdoor usage the timber should be treated with appropriate wood preservatives. Treated kempas is suitable for all heavy construction purposes such as railway sleepers, telegraph and transmission posts, beams, joists, rafters, piling, heavy duty columns, fender supports, pallets, door and window frames and sills, tool handles and marine constructions. When not treated it can be used for structural purposes under cover such as parquet and strip flooring (especially when resistance to acids and chemicals is needed), panelling, vehicle bodies and heavy duty furniture.

Tualang timber is used for the same purposes as kempas but it is less useful in severe conditions because it is moderately durable and it is difficult to apply preservatives.

Kempas wood produces charcoal of high quality.

Tualang is used for firewood, although the presence of tall buttresses in large trees (thus hindering felling) and its hardness make it unpopular. The bark of tualang is used traditionally among Malays to prepare a medicinal bath against fever. Large branches often bear masses of honeycombs containing honey produced by wild bees (Apis cerana). Villagers value tualang trees as sources of honey, which accounts for their objection to the felling of these trees.

Production and international trade

Average annual log production of kempas and tualang for Peninsular Malaysia for the period 1982-1987 was 571 000 m3 and 77 000 m3, respectively. In that period the average price for logs was US$ 68/m3for kempas and US$ 45/m3for tualang. The average annual export of sawn timber in Peninsular Malaysia over the same period was 126 000 m3 (average price US$ 108/m3) for kempas and 34 000 m3 (average price US$ 86/m3) for tualang. The export of sawn timber of kempas from Peninsular Malaysia in 1990 was 114 000 m3 (with a value of US$ 14.6 million) and that of tualang 71 000 m3 (with a value of US$ 8 million), and in 1992 the export amounted to 49 000 m3 (with a value of US$ 9.2 million) for kempas and 71 000 m3 (with a value of US$ 9.5 million) for tualang. Major export destinations are eastern Asia, Europe, North America and western Asia.

Production and export figures from other regions are not available, except for Sabah: export of round logs of tualang in 1987 was 4000 m3 with a value of US$ 260 000; in 1992 the export of kempas was 29 000 m3 of logs and 23 000 m3 of sawn timber (with a total value of US$ 6.3 million), and of tualang 70 000 m3of logs and 69 000 m3 of sawn timber (with a total value of US$ 16.9 million). Kempas and tualang probably are much less important for timber production elsewhere, as the trees are protected in several areas. At this moment there are no reports of the species being grown in plantations except for 9 ha of kempas and 1.6 ha of tualang at the Forest Research Institute Malaysia (FRIM).


Kempas is a medium-weight hardwood. The heartwood is orange-red or red-brown, darkening on exposure, with numerous yellow-brown streaks, clearly defined from the very pale brown or pale yellowish sapwood. The density is (670-)770-1150(-1290) kg/m3 (averaging 880 kg/m3) at 15% moisture content. The grain is interlocked, sometimes wavy, texture coarse but even.

At 15% moisture content the modulus of rupture is 122-133 N/mm2, modulus of elasticity 18 100-20 900 N/mm2, compression parallel to grain 66-73 N/mm2, compression perpendicular to grain 7.5 N/mm2, shear 8-14 N/mm2, cleavage 54-60 N/mm radial and 62-67 N/mm tangential, Janka side hardness 6000-7630 N and Janka end hardness 7700-8500 N.

Kempas timber needs 2-6 months to achieve air dry moisture content in Malaysia (18.1%) in air seasoning. Radial and tangential shrinkage from green to air dry averages 2.0% and 3.0%, respectively. It takes about 8 days to kiln dry 25 mm thick boards from about 50% to 10% moisture content. Kiln schedule E is used in Malaysia. Apart from springing and splitting of boards containing included phloem, the timber is free from defects in drying.

Kempas is somewhat difficult to machine and turn due to the interlocked grain and fibrous texture. The silica content is about 0.1%. Blunting of sawteeth is moderate to severe. When planing, the cutting angle should be reduced to 20° to avoid tearing. The wood can be satisfactorily stained and polished. Pre-boring is advisable before nailing. Good veneer of 1.5 mm thick can be made at a peeling angle of 92° without pretreatment. Wood without included phloem is suitable for plywood that meets the standards of Indonesia, Germany and Japan.

The heartwood of kempas is durable in temperate climates, but in tropical climates it is moderately durable. Graveyard tests in Indonesia showed an average service life in contact with the ground of 2 years. Treatment with preservatives is easy. Using the open tank method and an equal mixture of creosote and diesel, kempas can absorb 160 kg/m3 on average. Using copper-chromium-arsenic preservatives, kempas can easily be treated to more than 16 kg/m3 dry-salt retention. The sapwood is liable to attack by powder-post beetles and fungi. The heartwood is readily destroyed by termites. Kempas has shown a large and unexplained variability in natural resistance to marine borer attack.

Tualang is also a medium-weight hardwood. The heartwood is reddish-brown darkening to dark brown on exposure and distinctly demarcated from the greyish-white sapwood. The density is (570-)800-900(-1120) kg/m3 at 15% moisture content. The grain is interlocked, texture moderately coarse to coarse and even.

At 15% moisture content the modulus of rupture is 121 N/mm2, modulus of elasticity 17 800 N/mm2, compression parallel to grain 62 N/mm2, compression perpendicular to grain 8 N/mm2, shear 16 N/mm2, cleavage 57 N/mm radial and 59 N/mm tangential, Janka side hardness 7230 N and Janka end hardness 8900 N.

Usually tualang dries well, but the wood may split along included phloem. The shrinkage from green to air dry is 1.5% radial and 1.7% tangential. Tualang is easy to turn and plane to a moderately smooth finish. Nailing is easy but boring slightly difficult. The wood is seldom used for veneer and plywood.

The heartwood of tualang is moderately durable in contact with the ground, having an expected lifespan of 3-4 years under tropical conditions. Tualang is classified as moderately easy to treat with preservative. Using the open tank method, it absorbs about 130 kg/m3 of an equal mixture of creosote and diesel. The frequent presence of included phloem is a major defect when large sizes of timber are required, as is often the case with tualang.

The chemical composition of kempas and tualang wood has been investigated in Malaysia. Kempas wood contains 76% holocellulose, 54% alphacellulose, 26% lignin, 4.2% alcohol-benzene solubles, 7.4% of 1% alkali solubles, 1.6% hot water solubles, 12% pentosans and 0.3% ash. Tests in Indonesia showed 47% cellulose, 29% lignin, 17% pentosan, 0.7% ash and 0.1% silica. The solubility is 3.1% in alcohol-benzene, 1.1% in cold water, 2.4% in hot water and 9.0% in a 1% NaOH solution. Tualang wood contains 66% holocellulose, 46% alphacellulose, 27% lignin, 2.0% alcohol-benzene solubles, 10.7% of 1% alkali solubles, 4.4% hot water solubles, 14% pentosans and 1.0% ash. The energy value of kempas wood is about 19 300 kJ/kg.


  • Very large deciduous trees, up to 85 m tall, bole columnar, unbranched for up to 30 m and up to 290 cm in diameter, with large, steep buttresses sometimes exceeding 4 m in height; outer bark thin, hard and brittle, inner bark normally less than 12.5 mm thick, hard, yellowish-brown or orange-fawn; crown made up of a few large branches.
  • Leaves alternate, imparipinnate; leaflets 5-14(-17), more or less alternate, elliptical, more or less leathery, often with a blunt protruding apex, midrib sunken on the upper surface; stipules free, very small and early deciduous.
  • Inflorescence an axillary or terminal panicle with many small flowers.
  • Flowers bisexual, sessile or shortly pedicellate; calyx narrowly imbricate having 5 acute to acuminate and hairy sepals; petals 5, subequal, about as long as the sepals, glabrous, with an indistinct claw; stamens 5, alternating with the petals, anthers opening by 2 apical pores, usually followed by 2 basal pores; ovary sessile, with a single ovule, style and stigma very short and small.
  • Fruit a flat, more or less elliptical pod, twisted 180° near the base, surrounded by a broad, veined and brittle wing, 1-seeded.
  • Seed flat.
  • Seedling with epigeal germination, phanerocotylar; first 2 leaves opposite, next leaves arranged spirally.

Wood anatomy

Macroscopic characters

  • Heartwood reddish-brown, distinctly demarcated from the very light brown (almost whitish) to light yellowish-brown sapwood.
  • Grain interlocked.
  • Texture coarse to very coarse.
  • The outer part of the mature stem with wide distinct concentric brown-coloured bands, if dried often with splits (not examined in K. grandiflora).
  • Growth rings sometimes discernible; parenchyma bands visible to the naked eye.

Microscopic characters

  • Growth rings, if present, marked by differences in wall thickness on either side of the ring boundary and/or by the periodic variation in the length of aliform and/or confluent parenchyma bands.
  • Vessels diffuse, normally 1-6/mm2, solitary and in radial multiples of 2-3 and rarely in clusters, usually 220-300(-360)μm in tangential diameter; perforations simple; intervessel pits alternate, non-vestured, 6-8μm; vessel-ray and vessel-parenchyma pits almost similar to intervessel pits.
  • Fibres 1.2-2.5 mm long, 3-4μm wide, thick- to very thick-walled; pits small and minutely bordered, infrequent, confined to radial walls.
  • Parenchyma vasicentric, winged-aliform, occasionally to short confluent (K. malaccensis) or confluent, more or less concentric and wavy, with periodical change in the band length (K. excelsa, K. grandiflora) and apotracheally diffuse-in-aggregates or in discontinuous lines, in 4-8-celled strands.
  • Rays 7-11/mm, (1-)2-4(-5)-seriate, maximum height 600-800(-1100)μm, obscurely storied, homocellular and occasionally with one row of square marginal cells (Kribs type homogeneous to heterogeneous III).
  • Included phloem in irregularly spaced concentric bands, usually present in the outer part of stem.
  • Prismatic crystals numerous in axial parenchyma (more sporadic in K. malaccensis) and ray parenchyma cells (much more sporadic in K. malaccensis), in chambered cells, in long chains of up to 20 chambers; aliform and confluent parenchyma usually including the crystals in the cells of their outer layers.
  • Druses rarely present in ray cells (K. grandiflora).

Species studied: K. excelsa, K. grandiflora, K. malaccensis.

Growth and development

Taproot and hypocotyl emerge laterally from the fruit. The germination period for kempas is 2-8 weeks, for tualang 1-3 weeks. A high percentage of germination has been observed. The growth of saplings of kempas is fairly rapid, 1.5 m in the first 2 years. Saplings of tualang grow well but not as quickly as those of kempas. Saplings are common on the floor of virgin forest but they may grow very slowly in the initial stages. Twenty 15-year-old saplings in a 17-year-old natural regrowth had reached an average height of only 1.85 m. The current annual diameter increment of kempas at the age of 17 years was recorded to be about 1.9 cm/year, but its growth decreased to about 0.9 cm/year from the age of 18-39 years. Kempas trees planted in Malaysia reached a maximum diameter of 64 cm at an age of 40 years, but tualang trees reached only 36 cm.

The lateral roots of kempas have been observed to run along rather than beneath the soil surface.

Koompassia trees shed all their leaves every year and remain leafless for a few days (kempas) or weeks (tualang). The flowers appear just after the new leaves, and the fruits ripen several months later. Kempas has been found flowering in Malaysia in the months May, July, August and September and bearing fruit throughout the year. Tualang flowers in May and June and fruits in August and September. Tualang has been observed to flower at irregular intervals of 5-6 years. Natural dispersal of the fruits of Koompassia species is by wind; the fruit has a papery wing and the seed is flattened.

Other botanical information

Koompassia is a well defined genus of forest trees of exceptional beauty. It has affinities to Cassia and Dialium. Sometimes a fourth species called K. borneensis is recognized. This species, bearing the vernacular name "impas", is said to be slightly different from kempas. This has, however, never been confirmed by botanists and, moreover, the Latin name has never been validly published.


Koompassia is a tree of primary tropical rain forest below 650 m altitude. It is widespread and sometimes abundant, and is occasionally the dominant upper-storey tree. K. malaccensis is found on both dry land as well as in peat-swamp and freshwater swamp forest.

Propagation and planting

Freshly-collected fruits are used for propagation in Malaysia. No pretreatment is applied except for the removal of the wing. The average weight of a kempas seed is 1.2 g. Seeds can be sown on a seed-bed or directly in a polyethylene bag. A mixture of topsoil, sand and sawdust is generally used as a seed-bed medium.

The seeds of kempas have a moisture content of 15%. Koompassia seeds are not protected by a hard seed-coat. In order to ensure a high germination rate, the seed should not be stored for a long period. When stored, seeds are susceptible to fungus infection and should therefore be treated with a fungicide. Storage at low humidity is advised.

Silviculture and management

No specific information is available. In Malaysia kempas is categorized as a preferred species for regeneration while tualang is an acceptable species. Kempas seedlings grow well in regeneration plots with increased light treatment.

Diseases and pests

So far no serious diseases or pests have been reported.


Kempas is harvested similar to other timber species. The logs of tualang, however, are known to be brittle and frequently shatter on falling. In sawn timber processing, debarking of Koompassia is unnecessary. However, logs can easily be debarked by using a hammer.


Kempas is probably the third most abundant tree species in Peninsular Malaysia. A valuation survey has shown that it comprises up to 3.7% of the total number of trees and 6.1% of the wood volume in a generally rich forest. In Borneo it is usually a solitary tree with an average density of 1.1 trees per ha. In a superior hill forest of Peninsular Malaysia the stocking with a diameter of 15 cm and more ranges from 2.1 m3/ha to 6.1 m3/ha for kempas and from 3.1 m3/ha to 6.3 m3/ha for tualang.

Genetic resources

No special in situ or ex situ conservation action has been taken in Peninsular Malaysia except the establishment of a few virgin jungle reserves and big tree plots. In Borneo Koompassia species are locally protected (e.g. in Sarawak and East Kalimantan).


Koompassia timber is currently gaining importance due to the shortage of heavy hardwood timbers. Kempas is becoming a valuable and highly valued species in the wood processing industry. The timber is much in demand for railway sleepers. Research priorities should be given to breeding, management and silvicultural and conservation aspects of the species.


  • Burgess, P.F., 1966. Timbers of Sabah. Sabah Forest Records No 6. Forest Department, Sabah, Sandakan. pp. 361-371.
  • Burkill, I.H., 1966. A dictionary of the economic products of the Malay Peninsula. 2nd edition. Vol. 2. Ministry of Agriculture and Co-operatives, Kuala Lumpur. pp. 1305-1307.
  • de Wit, H.C.D., 1947. Revision of the genus Koompassia Maingay ex Bentham (Legum.). Bulletin of the Botanic Gardens, Buitenzorg, ser. 3, 17: 309-322.
  • Foxworthy, F.W., 1927. Commercial timber trees of the Malay Peninsula. Malayan Forest Records No 3. Federated Malay States Government, Forest Department, Kuala Lumpur. 195 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 Proprietary Ltd., Melbourne, Sydney and London. pp. 215-216.
  • Malaysian Timber Industry Board, 1986. 100 Malaysian timbers. Kuala Lumpur. 226 pp.
  • Martawijaya, A., Kartasujana, I., Mandang, Y.I., Prawira, S.A. & Kadir, K., 1989. Atlas kayu Indonesia [Indonesian wood atlas]. Vol. 2. Forest Products Research and Development Centre, Bogor. pp. 68-73.
  • Ser, C.S., 1981. Malaysian timbers - kempas. Malaysian Forest Service Trade Leaflet No 44. Malaysian Timber Industry Board, Kuala Lumpur. 7 pp.
  • Ser, C.S., 1984. Malaysian timbers - tualang. Malaysian Forest Service Trade Leaflet No 83. Malaysian Timber Industry Board, Kuala Lumpur. 6 pp.
  • Whitmore, T.C., 1972. Leguminosae. In: Whitmore, T.C. (Editor): Tree flora of Malaya, a manual for foresters. Vol. 1. Longman Malaysia SDN Berhad, Kuala Lumpur. pp. 264-266.

Selection of species


  • Wan Razali Wan Mohd. (general part, properties, selection of species),
  • S. Sudo (wood anatomy)