23

5(1): Timber trees; Major commercial timbers

Eusideroxylon Teijsm. & Binnend.

Natuurk. Tijdschr. Ned. Ind. 25: 292 (1863).

LAURACEAE

x = unknown

Trade groups Ulin: a single species, Eusideroxylon zwageri Teijsm. & Binnend., Natuurk. Tijdschr. Ned. Ind. 25: 292 (1863), synonym: Bihania borneensis Meissner (1864).

Ulin: ironwood, billian (En). Bilian, bois de fer (Fr). Brunei: belian. Malaysia: belian (Sarawak, Sabah), tambulian (Sabah), im muk (Cantonese, Sabah). Indonesia: belian (general), onglen (Sumatra), tulian, tebelian (Kalimantan). Philippines: tambulian, sakian, biliran (Sulu).

Eusideroxylon is monotypic and occurs in eastern and southern Sumatra, Bangka, Belitung, Borneo and the Sulu archipelago and Palawan (the Philippines).

Ulin is one of the heaviest and most durable timbers of South-East Asia. As such, it is preferably used in marine constructions such as pilings, wharfs, docks, sluices, dams and ships (keels, ribs and decking), or in heavy constructions such as bridges, power line poles, masts, piles and house posts. Ulin is also used for the traditional houses ('longhouses') of the Dayak in Borneo. Another major use of ulin is for roof shingles ('sirap') which are reported to last 50 years to more than a century. Less important is the use of ulin as frame, board, for heavy duty flooring, floodgates, road pavement and foundations, railway sleepers, fencing, printing blocks, vehicle bodies, sleds for log skidding, furniture, chopsticks, blowpipes, poles (in pepper cultivation) and survey pegs. The wood is not suitable for plywood or particle board production.
The large fruits are poisonous and pulverized fruits have been used medicinally against swellings.

Ulin is primarily used locally, and in several areas it receives some protection. In 1981 the total amount of 'sirap' pieces produced was about 50 million. It is not exported on a large scale and only a few statistics are available. Sabah exports ulin; in 1987 the export of round logs was 38 000 m³ with a value of US$ 3 million, and in 1992 the export of sawn timber was 7350 m³ with a value of US$ 2.3 million.

Ulin is a heavy hardwood. The heartwood is yellowish-brown to reddish-brown when freshly cut, but it becomes silvery brown, dark brown or almost black on exposure; the sapwood is sharply differentiated from the heartwood and bright yellow when freshly cut, darkening to yellowish-brown on exposure. The density is (830-)880-1190 kg/m³ at 15% moisture content. Surfaces show some lustre, and there is no distinct figure except for an inconspicuous ray figure on quarter-sawn surfaces. Freshly cut wood has a fresh, slightly lemon-like odour. The grain is straight, occasionally slightly interlocked, texture moderately coarse and even. In green condition, the modulus of rupture is 135 N/mm², modulus of elasticity 17 400-18 100 N/mm², compression parallel to grain 67-80 N/mm², compression perpendicular to grain 17.5 N/mm², shear 9.5-14 N/mm², cleavage 61-70 N/mm radial and 90-122 N/mm tangential, Janka side hardness 9730-12 150 N and Janka end hardness 10 700 N. See also the table on wood properties.
The rates of shrinkage are rather high, from green to 15% moisture content 2.0% radial and 4.5% tangential, from green to oven dry 4.2-4.3% radial and 7.5-8.3% tangential. Ulin dries slowly, although the moisture content of green wood is comparatively low (about 38%); it is liable to surface and end checking during drying. Air seasoning of 2.5 cm thick boards to 16% moisture content takes approximately 75 days. The recommended kiln schedule in Malaysia is B, in Indonesia a temperature of 40-60 °C and corresponding relative humidity of 85% to 50% are suggested. Kiln drying of 2.5 cm thick boards takes about 8 days. Ulin tends to split when too dry.
Ulin can be sawn with good result, but it blunts sawteeth fairly rapidly, owing to its hardness; the sawteeth should be kept clean from accumulating oily deposits. Tests on the machining show good results for planing, shaping, boring, mortising, turning and sanding. Too high speeds in boring may cause burning. Because it tends to split in the radial plane when screwed or nailed, the wood must be pre-bored. The easy splitting in radial direction makes ulin excellent for making shingles, although sometimes pieces of wood with interlocked grain may cause problems. The wood is difficult to glue with synthetic adhesives; furniture, for instance, often fails at glued joints. In a general sense, ulin is too dense for plywood manufacture and insufficiently ornamental for sliced veneer, but tests indicate that good veneer can be made at a peeling angle of 92 ° after boiling for 24 hours, and that gluing of the veneer with urea-formaldehyde produces good plywood. The wood is unlikely to be suitable for the production of pulp, paper or fibreboard.
Ulin is rated as very durable. Graveyard tests with stakes showed an average service life in contact with the ground of 17.5 years under tropical conditions. Stockades and posts have been reported to last over 100 years, and pepper (Piper nigrum L.) support posts and shingles over 30 years. A life of up to 20 years can be expected in marine works. The wood is resistant to termite attack, although after long periods of exposure attack may occur. Ambrosia beetle attack is rare, but ulin is more commonly attacked by longicorn beetles, and the sapwood also by powder-post beetles. The wood is very resistant to wood-rotting fungi. The heartwood is extremely resistant to preservative treatment.
Ulin wood contains 58% cellulose, 29% lignin, 12.5% pentosan, 1.0% ash and up to 0.5% silica. The solubility is 5.2% in alcohol-benzene, 2.9% in cold water, 6.8% in hot water, and 18.2% in a 1% NaOH solution. The energy value is about 21 300 kJ/kg.

An evergreen tree of up to 40(-50) m tall; bole straight, branchless for up to 20 m but usually less, sometimes slightly fluted at the base, up to 150(-220) cm in diameter; buttresses many, small, rounded, giving the base an elephant-foot like appearance, in moist places the base often characteristically set with a mattress of slender rootlets; bark surface red or grey-brown with thin cracks, debarking in small scab-like subquadrangular pieces which are turned up at the lower side; exudate absent; crown dense, globular; twigs smooth, slightly angular, tomentellous. Leaves arranged spirally, simple, entire, leathery, elliptical to ovate, 14-18 cm x 5-11 cm, base rounded-subcordate, the apex obtuse to shortly acuminate, upper surface glabrous, lower surface hairy on the larger veins; petiole 6-15 mm; stipules absent. Inflorescence axillary, paniculate, dense, drooping, 10-20 cm long, densely short-hairy. Flowers bisexual, actinomorphic, on a 3-11 mm long pedicel; perianth tube shallow, tepals 6, in 2 whorls, imbricate, caducous, 3-3.5 mm long, greenish, yellow or purplish, puberulous outside; stamens without glands, in 4 whorls, in the outer 2 whorls staminodial and petaloid, 1.5 mm long, yellowish with a purple tip, ciliate, those of the third whorl fertile, thick, with minute red or white anthers with a pink hue, anther cells 4, in 1 horizontal row, the central 2 extrorse, the lateral 2 sublatrorse, stamens of the inner whorl staminodial, subulate, small; ovary superior, sessile, unilocular, with a single ovule, tapering into the subulate style; stigma small, discoid. Fruit drupaceous, on a thick pedicel, 1 or 2 in each panicle, completely included in and adnate to the accrescent perianth tube, ellipsoid to ovoid or globular, 7-16 cm x 5-9 cm, glossy black at maturity, containing a single seed. Seed very large, seed-coat very hard, furrowed, brittle, pale bony; embryo very small. Seedling with hypogeal germination; cotyledons often partly fused, succulent but tough and long persistent; internodes sparsely adpressed pubescent; leaves all arranged spirally, conduplicate or induplicate when young, provided with a lateral branch in each axil.

-Macroscopic characters: Heartwood dark yellowish-brown or reddish-brown with a greenish tinge, turning dark brown or chocolate brown on exposure, distinctly demarcated from the yellowish-brown sapwood. Grain straight or sometimes interlocked. Texture moderately coarse. Growth rings not distinct; tyloses visible to the naked eye.
- Microscopic characters: Growth rings indistinct. Vessels diffuse, 5-10/mm², solitary and in radial multiples of 2-3, 150-300 µm in tangential diameter; perforations simple; intervessel pits alternate, bordered, 8-10 µm; vessel-ray and vessel-parenchyma pits simple or with reduced borders, enlarged, narrowly oval to scalariform; reddish contents present; tyloses abundant and sometimes sclerotic. Fibres 1.2-1.9 mm long, thick-walled (wall 5-12 µm thick), with minutely bordered to simple pits, confined to the radial walls. Parenchyma occasionally in apotracheal bands and diffuse, and aliform and confluent forming wavy tangential bands; oil cells frequent. Rays 8-10/mm, (1-)4-seriate, up to 2300(-2800) µm high, homocellular and occasionally heterocellular, with one row of marginal square cells (Kribs type homogeneous to heterogeneous III), cells with reddish contents. Crystals and silica bodies absent.

Seedlings and saplings demand some shade, but older saplings and young trees require plenty of light for vigorous growth. Mean annual diameter increment of young trees may be 9.5 mm under good conditions, but usually it is less. Trees can reach a height of 8 m in 8 years, and usually they are 9-14 m high after 16 years. The growth rate seems to be rather uniform during the life of a tree, but it will probably slow down slightly when the tree becomes older. The maximum diameter of 40-year-old trees is reportedly 36 cm, and probably trees need over 100 years to reach a diameter of 50 cm. This means that growth is slow, even under optimal conditions.
Trees may begin to flower at an age of 15-20 years. They bear fruits at irregular intervals, often every 2-3 years, sometimes annually. In southern Sumatra fruits are often found in July - August, in Kalimantan in October - November. Fruits ripen within 3 months after flowering. Seed dispersal is apparently often by water; rich pockets of ulin forest are often found at places where the fruits wash ashore in large quantities along rivers. Procupines may also disperse the seeds.

The second species of the genus often mentioned in literature, Eusideroxylon melagangay Sym., has been transferred to the monotypic genus Potoxylon (Potoxylon melagangay (Sym.) Kosterm.). The two genera constitute the subtribe Eusideroxylineae in the tribe Cryptocaryeae.
Several varieties can possibly be distinguished within ulin, based on the form and size of the fruits. In practice, 'bulian sirap', having wood suitable for the manufacture of shingles, is sometimes distinguished from 'bulian tanduk' or 'bulian daging', which is suitable only for the production of timber. However, the large variation in fruit shape does not seem to be correlated with the variation in wood properties. Smooth, grey- or white-barked trees are sometimes encountered. The abnormal bark formation is likely to be induced by external factors (fungi).

Ulin is a constituent of primary or old secondary tropical rain forest. It thrives in a climate with an average annual rainfall of 2500-4000 mm. It prefers well-drained soils in valleys or on hillsides or even low ridges when soil moisture is sufficient. It is found from sea-level up to 500(-625) m altitude. Ulin generally occurs on sandy soils of Tertiary origin, on clay-loam soils or on sandy silt-loam soils, but large specimens have also been found on limestone.
Ulin occurs scattered or gregarious and is often the dominant canopy species. It sometimes forms almost pure stands. In Sumatra the 'ironwood forest' is recognized as a distinct forest type characterized by an exceptionally low species diversity. Ulin occurs also in mixed dipterocarp forest and has been found associated with Koompassia, Shorea, and Intsia species.

Ulin can be propagated by seed, but nursery-raised wildlings are also often used for planting. Seeds are often placed horizontally between two beds of grass, or they are covered with 2-5 cm of soil. Germination usually starts after about 2 weeks (but it may take 6-12 months) and the germination rate is approximately 40%. Scarification (cutting off the top of the seed or removing the whole outer shell) may improve the germination rate to 70%.
Nursery-raised seedlings or wildlings of about 40 cm tall, a height reached after 1-1.5 years, are planted into the field at a spacing of 3 m x 4 m and need shade. In experiments, seedlings of 10-15 mm diameter gave significantly higher survival and height growth than thinner ones (5-10 mm).

In natural forest ulin is usually cut selectively with a diameter limit of 50 cm. Regeneration in logged-over forest is often not sufficient, although ulin may coppice freely and can be persistent. In South Kalimantan, for instance, seedlings of ulin often dominate the regeneration in virgin forest, together with meranti (Shorea spp.), but in logged-over forest regeneration of ulin is often considerably less prolific. In such situations, enrichment planting in strips or lines is advisable. Systems with poison-girdling of unwanted tree species can be successful as long as sufficient shade is maintained for the ulin seedlings and saplings. As the trees are slow growers, rotation should be adequately long. Ulin could be grown in pure plantations, but the plantations would require very long cutting cycles to provide larger dimensions of timber.

No serious diseases and pests are reported, although deer and boars may damage seedlings and saplings, and seeds are often destroyed by porcupines. In East Kalimantan 45% of the unsound fruits proved to be attacked by insect borers.

Since ulin is exploited separately from other species in forest concessions, just like ebony (Diospyros celebica Bakh.), harvesting is mostly done manually. Ulin logs sink in water. They are transported over land or rafted fastened to floater boles.

The standing timber volume of ulin trees with a diameter of over 50 cm can be as much as 90 m³/ha in natural forest in Sarawak or even more: 112 m³/ha in Jambi, Sumatra.

Originally, ulin was a common species of primary forest, but over-exploitation for its valuable timber has caused a serious depletion of stands and many stands are in critical condition. Moreover, as ulin often occurs near rivers, places which are easily accessible, stands are also endangered by shifting cultivation. Control of exploitation and trade together with enrichment planting after logging is desirable.

Ulin is one of the most important timbers for local use, and future supplies should be guaranteed. Forests containing much ulin seem to be best suited for management under selective felling systems with enrichment planting. Long cutting cycles are probably needed to obtain a sustainable yield. More research on appropriate management systems and appropriate methods of propagation is needed. Ulin does not seem to be very suitable for large-scale plantation establishment, as it grows too slowly.

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A.J.G.H. Kostermans (general part), B. Sunarno (general part), A. Martawijaya (properties) & S. Sudo (wood anatomy)

Kostermans, A.J.G.H., Sunarno, B., Martawijaya, A. & Sudo, S., 1993. Eusideroxylon Teijsm. & Binnend.. In: Soerianegara, I. and Lemmens, R.H.M.J. (Editors): Plant Resources of South-East Asia No 5(1): Timber trees; Major commercial timbers. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea