Shorea (balau) (PROSEA)

Plant Resources of South-East Asia
Introduction

Shorea Roxb. ex Gaertner f. (balau and red balau)

Protologue: Fruct. 3: 47 (1805).

Family: Dipterocarpaceae

Chromosome number: x= 7; 2n= 14 for the majority of species; counts of 2n= 20 for S. obtusa and 2n= 12 for S. siamensis need confirmation.

Trade groups

Balau: heavy hardwood, e.g. Shorea laevis Ridley, S. materialis Ridley, S. maxwelliana King and S. scrobiculata Burck.

Red balau: heavy hardwood, e.g. S. collina Ridley, S. guiso (Blanco) Blume and S. kunstleri King.

The wood of S. laevis is often traded under the distinctive name "bangkirai". Hopea species with heavy wood (giam) are often traded as balau.

The timber of some species (e.g. S. elliptica, S. kunstleri) is either traded as red balau or red meranti, depending on the density of the wood. Hence, the distinction between those trade groups is not sharp.

Vernacular names

Balau

Brunei: selangan batu
Indonesia: damar laut (Sumatra), anggelam (Kalimantan)
Malaysia: selangan batu (Sabah, Sarawak)
Philippines: malayakal, yakal, gisok
Burma: thitya
Cambodia: phchök
Thailand: takhian-samphon (Ranong), balao
Vietnam: cà chắc, sến.

Red balau

Brunei: red selangan, selangan merah
Indonesia: balau merah
Malaysia: balau laut merah (Peninsular), selangan batu merah (Sarawak, Sabah), red selangan batu (Sabah)
Philippines: guijo
Thailand: teng-tani (Lampang, Phrae), lantan (peninsular), chan
Vietnam: chai.

Origin and geographic distribution

Shorea consists of about 194 species, 163 of which occur in Malesia. The genus is distributed from Sri Lanka and India through Indo-China towards Malesia. Within Malesia the species occur eastward towards the Moluccas. The genus is absent from the Lesser Sunda Islands but fossil wood has been recorded from Timor.

The species of balau and red balau are found from Sri Lanka and southern India through Indo-China and western Malesia. Within Malesia 38 species occur. The greatest diversity is in Borneo (27 species) followed by Peninsular Malaysia (18 species), Sumatra (10 species) and the Philippines (5 species).

Uses

Shorea is economically the most important timber genus in the Asian humid tropics. Balau is particularly suited for all forms of heavy constructional work such as bridges, wharves, railway sleepers, telegraph and powerline posts, boat building and mine props. Its durability makes it particularly valuable in the tropics, where it can also be used in humid conditions and in contact with the ground. The timber is suitable for various applications in houses, such as wall plates, sills, floor joists, posts, beams, staircases, and door and window frames. It is often used for parquet floors or as a flooring timber, although only the heaviest grades are suitable for heavy duty industrial floors. Other applications of the timber are for launch keels and ribs, fence posts and gates, the framework of cars, railway carriages and wagons, motor lorries, vats and other containers, and joinery. Because of its often slippery surface when wet, it is not suited for ship decks. Being too hard and too dense, it is generally unsuitable for plywood and veneer manufacture, or for hardboard or pulp. When mixed with lighter material, the manufacture of satisfactory particle board is possible.

Red balau is generally less durable than balau; it is rated as moderately durable. Therefore applications of untreated material in contact with the ground or outdoors should be avoided. It is a timber for heavy and moderately heavy constructions and is regarded as a first class flooring and parquet timber with an exceptionally close and glossy surface. It is also a suitable timber for high grade utility furniture. Like balau, the wood is generally too dense for particle board and fibreboard, and its uncertain gluing property makes it less suitable for plywood and veneer.

Several species yield a dammar which is mostly of inferior quality and not useful for varnish. The dammar is, however, sometimes collected from natural exudations to form the main component of "damar laut" which is used locally for making torches.

The fruits of many species can be boiled and eaten (mainly as famine food). A few species yield fruits from which a fat similar to cocoa butter is obtained (e.g. S. seminis). It is used in Europe for manufacturing chocolates and cosmetics and was formerly used in soaps, candles and tallow. The fruits are often called "illipe nuts" which sometimes leads to confusion with the illipe nut from Madhuca spp. (Sapotaceae).

The bark and wood of some species (e.g. S. robusta Gaertner f., S. obtusa and S. siamensis) contains tannin.

Production and international trade

No export figures for balau and red balau are available for Indonesia. The export of sawn balau timber from Peninsular Malaysia peaked in 1987 with 47 500 m³ (worth US$ 6.4 million) falling to 27 000 m³ (worth US$ 4.9 million) in 1990, and 17 500 m³ (worth US$ 3.8 million) in 1992. In Peninsular Malaysia the price of exported sawn balau timber was US$ 115/m³ in 1984 and US$ 220/m³ in 1992. The export of sawn timber of red balau increased in Peninsular Malaysia from only 2400 m³ (with a value of US$ 400 000) in 1983 to 12 000 m³ (worth US$ 2.5 million) in 1989; in 1990 the export was 10 500 m³ (worth US$ 1.8 million), and in 1992 5000 m³ (worth US$ 1.2 million). The export of balau and red balau is more important in eastern Malaysia. In 1987 export of round logs of balau from Sabah was 526 000 m³ (with a value of US$ 37.8 million), and of red balau was 33 000 m³ (with a value of US$ 2.2 million); in 1992 the export of balau logs was 90 000 m³ and of sawn timber 292 000 m³ (with a total value of US$ 93 million), and the export of red balau logs was 12 500 m³ and of sawn timber 750 m³ (with a total value of US$ 1.5 million).

The export of balau and red balau has never been important in the Philippines. In 1987 21 000 kg processed timber of S. astylosa (worth US$ 9100) was exported.

Properties

Balau is a heavy hardwood. The heartwood is yellowish- to reddish-brown when freshly cut, changing to red-brown, purple-brown or dark brown on exposure. The heartwood is moderately distinct from the sapwood, which is lighter and yellowish- to reddish- or purplish-brown. The radial section shows a stripe figure, the end surface shows a metallic lustre and is variably glossy. The density is (600-)850-1160 kg/m³ at 15% moisture content. The grain of the wood is straight to spiral or interlocked, texture moderately fine to moderately coarse and even.

At 40% moisture content the modulus of rupture is 115-125 N/mm², modulus of elasticity 18 400-22 100 N/mm², compression parallel to grain 60-71 N/mm², compression perpendicular to grain 7.5-12.5 N/mm², shear 11.5-13 N/mm², cleavage 54-88 N/mm radial and 58-133 N/mm tangential, and Janka side hardness 8010-9520 N.

The rates of shrinkage are high when compared, for instance, to the otherwise very similar chengal (Neobalanocarpus heimii (King) P. Ashton): from green to 15% moisture content 1.5-2.7% radial and 3.1-3.9% tangential, and from green to oven dry c. 4.2% radial and 9.3% tangential. Balau dries slowly with moderate to severe end checks and slight to severe splits; surface checks are moderate but the timber does not warp. The air drying of 15 mm and 40 mm thick boards takes about 4 months and 10 months, respectively. In Malaysia kiln-drying schedule B is recommended.

The working qualities of balau are rated as moderately difficult. Sawing properties are moderately easy to slightly difficult for green timber, but air-dried timber is slightly difficult to difficult to saw. Balau is easy to turn and gives a smooth finish. In green condition, it is easy to bore and the finishing is smooth, but boring of air-dried timber is slightly difficult. The planing properties in a green condition range from easy to slightly difficult, giving a smooth finish; the planing of air dried timber is more difficult. Among the species tested, S. laevis is the most easy to machine and S. maxwelliana the most difficult. The nailing property is rated as poor; the wood splits easily. Balau was found to be unsuitable for hardboard manufacture and for the production of veneer and plywood.

The heartwood is naturally durable, but the sapwood is liable to fungal infestation. In graveyard tests, untreated stakes (50 mm × 50 mm × 600 mm) of S. maxwelliana showed an average lifespan of 16 years and those of S. laevis of 7.5 years. Untreated railway sleepers of S. laevis and S. glauca lasted at least 15 years and 11 years, respectively, under tropical conditions. Laboratory tests in Indonesia showed that wood of S. laevis is resistant to wood-rotting fungi, but poorly resistant to dry-wood termites. The heartwood is difficult to treat with preservatives, but the sapwood is permeable.

Red balau is also a heavy hardwood. The heartwood is light to dark red-brown or purplish-red, darkening on exposure and losing much of its red colour, fairly distinct from the lighter sapwood (pink, greyish-brown). Planed surfaces occasionally show a stripe figure. The density is generally somewhat less than that of balau: (675-)750-880(-1090) kg/m³ at 15% moisture content. The grain of the wood is deeply interlocked, texture moderately fine to slightly coarse and even. Generally speaking, red balau is slightly inferior to balau in mechanical properties and durability, but it is markedly superior to dark red meranti. At 55% moisture content the modulus of rupture is 84-105 N/mm², modulus of elasticity 13 700-19 000 N/mm², compression parallel to grain 43-58 N/mm², compression perpendicular to grain 5.5-9.5 N/mm², shear 9.5-10.5 N/mm², cleavage 67-75 N/mm radial and 77-93 N/mm tangential, and Janka side hardness 4490-6940 N.

The rates of shrinkage of red balau are comparatively high, but generally slightly less than those of balau: from green to 15% moisture content 1.4-2.2% radial and 3.2-3.6% tangential, and from green to oven dry 3.3-6.2% radial and 9.0-11.5% tangential. Red balau dries slowly with only slight seasoning defects. There may be slight cupping, bowing or springing, and moderate checking, slight splitting and surface checking may also occur. The air drying of 12 mm and 25 mm thick boards takes about 4 and 5 months, respectively. In Malaysia kiln-drying schedule G is recommended.

Red balau is usually easier to work than balau but the working qualities are rated as slightly difficult. It is slightly difficult to difficult to saw, but planing is easy, giving a smooth to slightly rough finish. Boring is easy to slightly difficult and turning is easy to difficult. The nailing property is rated from poor (for S. kunstleri) to good (S. guiso and S. ochrophloia).

The wood is moderately durable under exposed conditions and is subject to subterranean termite and fungal attack. In contact with the ground, stakes may last 2-7 years under tropical conditions; the average lifespan in contact with the ground of S. guiso wood in Indonesia is 7 years. Wood of S. elliptica and S. guiso was usually resistant to wood-rotting fungi in laboratory tests in Indonesia. The heartwood is very difficult to treat with preservatives.

The wood of S. laevis contains 53-58% cellulose, 24% lignin, 17% pentosan, 0.4-1% ash and 0.1-0.4% silica. The solubility is 3.0% in alcohol-benzene, 0.6-0.8% in cold water, 2.6-3.4% in hot water and 8.9-10.9% in a 1% NaOH solution. The energy value is 16 800-19 300 kJ/kg.

Description

Medium-sized to very large trees up to 60(-75) m tall; bole straight, cylindrical, branchless for 6-25(-40) m and with a diameter of up to 180(-300) cm; buttresses prominent, up to 5 m high and very thin, growing away from the bole more or less spirally; bark surface longitudinally cracked or square-section fissured and usually flaky, shedding in thin, flat scales, grey, red or brown, outer bark usually comparatively thin, inner bark yellowish to greenish-yellow or red, exuding a clear, sticky, pale yellowish or brownish resin; crown hemispherical or dome-shaped, sympodial.
Leaves alternate, simple, entire, glabrous, pinnately veined with scalariform tertiary venation, often glaucous on the lower surface; stipules and bracts small, fugaceous.
Inflorescences terminal or axillary, paniculate.
Flowers secund or distichous, bisexual, 5-merous, actinomorphic, scented; calyx lobes free, hirsute; petals free or connate at base, cream, often pink at base, the outer surface hirsute; stamens 15-60, the anthers with 4 pollen sacs, usually broadly oblong, both the appendages and pollen sacs usually barbate; ovary surmounted by a stylopodium, tomentose, style usually shorter than the ovary.
Fruit usually shortly stalked with the outer 3 or rarely all calyx lobes much elongated, these more or less thickened at base and saccate, sometimes all calyx lobes short and subequal; nut 1-seeded, free from the calyx, subglobose to ovate, with a long beak.
Seedling with epigeal germination; pericarp splitting irregularly; cotyledons reniform-sagittate, greenish-orange or red; first two leaves opposite, subsequent leaves arranged spirally, often larger than those on mature trees.

Wood anatomy

Macroscopic characters

Heartwood yellowish- to reddish-brown when freshly cut, darkening to dark brown or dark purplish-brown on exposure, moderately distinctly demarcated from the lighter sapwood (yellowish-, red- or purplish-brown).
Grain straight, spiral or interlocked.
Texture varying from fine to coarse, generally moderately coarse to coarse; quarter-sawn surface often with a stripe figure, end grain shiny with a metallic lustre.
Growth rings absent, but the long tangential bands of resin canals with white contents and the parenchyma associated with them may have the appearance of growth rings; vessels fairly evenly distributed, but with a tendency to form short, oblique lines mostly filled with tyloses, but without deposits, visible to the naked eye; parenchyma not distinct without a lens; rays visible to the naked eye but not conspicuous on the radial surface, containing brown deposits.
Ripple marks mostly absent.

Microscopic characters

Growth rings absent.
Vessels diffuse, 2-10(-14)/mm², mostly solitary but also in radial or oblique multiples of 2-4, round to oval, with a tangential diameter of 75-300 μm; perforations simple; intervessel pits alternate, dense and vestured, with an average diameter of 5-7 μm; vessel-ray and vessel-parenchyma pits large, round or gash-like, simple; helical thickenings absent; vessels mostly filled with tyloses.
Fibres 900-1600 μm long, 14-16 μm in diameter, non-septate, walls 5-7 μm thick, pits minutely bordered, largely confined to the radial walls.
Parenchyma scarce to moderately abundant, occasionally abundant (e.g. in S. exelliptica, S. falciferoides, S. foxworthyi), mainly paratracheal consisting of narrow incomplete sheaths around the vessels, often distinctly aliform (e.g. in S. laevis), but sometimes (locally) confluent; apotracheal parenchyma diffuse and diffuse-in-aggregates or as concentric bands containing the vertical resin canals, as occasional terminal bands, and as short fine lines of varying widths.
Rays 5-12/mm, mostly multiseriate, 3-4(-5)-seriate and frequently under 30 cells high (350-650 μm); uniseriate margins of rays typically only 1 or 2 cells high, with occasional margins 3-4 cells high; most of the rays similar (usually Kribs type heterogeneous II-III, rarely homogeneous).
Crystalliferous axial parenchyma strands and/or ray cells with solitary prismatic crystals usually abundant.
Silica bodies absent.
Intercellular canals smaller than vessels and arranged in long or short concentric (tangential) bands filled with white resin.

Species studied: S. astylosa, S. ciliata, S. exelliptica, S. falciferoides, S. foxworthyi, S. glauca, S. havilandii, S. inappendiculata, S. laevis, S. lumutensis, S. malibato, S. maxwelliana, S. scrobiculata, S. seminis, S. submontana, S. superba.

Red balau differs from balau by its more reddish-brown colour, fewer tyloses, and often larger vessel diameter, from red meranti by its greater density, and usually more numerous rays. Balau differs from giam (heavy Hopea timber) particularly by less numerous vessels, broader rays and coarser texture.

Growth and development

Optimal growth of seedlings of S. materialis in terms of increases in height, stem diameter, leaf area and overall dry matter was observed between 30-55% relative light intensities. Seedling growth of S. laevis is best under moderate shading and is considerably better than when grown in full sunlight or under heavy shading. As in all dipterocarps, mycorrhizae are essential for good growth. Research in the forest understorey showed that 42% of S. maxwelliana seedlings had no ectomycorrhizae. Infected seedlings are taller than seedlings without ectomycorrhizae. Once established, balau saplings are able to persist for a number of years in the understorey under heavy shade, but they need moderate to high light intensities for rapid growth. Balau-producing species grow slowly. Annual diameter growth of S. siamensis in Thailand is reported to be only 1-2 mm. In Peninsular Malaysia planted trees of S. geniculata and S. scrobiculata reached bole diameters of only 27 cm and 18 cm respectively in 40 years. The red balau S. guiso grows considerably faster; the annual girth increment of this species was 1.6-2.0 cm in Peninsular Malaysia. Other red balau-producing species also grow comparatively fast, e.g. S. kunstleri and S. ochrophloia, which may reach a bole diameter of 55 cm in 40 years. Large balau trees can be very old, several hundreds of years at least.

Regrowth from stumps does occur after coppicing, e.g. in S. siamensis. The best coppicing power is found in small trees (up to 20 cm in diameter). Coppice shoots grow well. Coppicing may be applied for firewood production.

Balau-producing species flower at irregular intervals of several years with varying intensity, though gregariously, like other Shorea species. In a year of heavy flowering, nearly all species in a given area flower. In Peninsular Malaysia and Borneo flowering may occur between March and July. In the Philippines the balau-producing trees usually flower from June to August.

Seed dispersal is usually only over short distances from the mother trees, generally not more than 30 m, as in other Shorea species.

Other botanical information

Anatomical features of the wood and bark provide useful evidence for the classification of species at infrageneric level. The division of the genus Shorea into 4 major timber groups (red meranti, white meranti, yellow meranti, and balau and red balau) coincides in broad outline with the division of the genus into botanical sections. Timbers of the balau group belong to the sections Shorea and Neohopea P. Ashton. The section Pentacme (A.DC.) P. Ashton contains two species, S. siamensis and S. contorta S. Vidal. The first is classified as a balau; the second, however, is classified as a light red meranti, white meranti or a white lauan (this being the timber trade name for species of the genus Parashorea). The section Pentacme is botanically rather aberrant from the other sections.

Timber of the red balau group originates mostly from species in section Shorea. S. elliptica is placed within the section Rubella P. Ashton (red meranti timber) but the wood of this species is usually traded as a red balau. In terms of wood anatomy, this species resembles species of the section Shorea , which is in accordance with the trade classification. The timber of S. kunstleri and S. inaequilateralis Sym. is traded either as red balau or red meranti. However, these species belong in the section Brachypterae Heim, which otherwise includes red meranti timbers. The distincion between red balau and red meranti is not sharp. Several species may yield both types of timber (depending on the density). Their classification in either one of the groups, as presented here, is debatable. S. kunstleri is treated as red balau, S. inaequilateralis as red meranti, together with some other species producing both types of timber ( S. albida, S. balangeran).

The wood of several species of Hopea, of Parashorea aptera v. Slooten and of Upuna borneensis Sym. is sometimes traded as balau as well.

The timber of S. robusta ("sal") is much used in India.

Ecology

Shorea species are confined to the tropics with average annual rainfall exceeding 1600 mm and a dry season of less than 6 months. Most species occur below 1000 m altitude. They reach the largest number of species and individuals per species on deep, well-drained soils in the lowland. Comparatively few species are restricted to a single vegetation type or substratum, whereas some species are common to gregarious in a certain habitat but are also found scattered in others. A few species are confined to specific edaphic habitats such as heath (kerangas) forest (e.g. S. materialis) or sandy soils (e.g. S. falcifera, S. geniculata).

Propagation and planting

Trials on propagation of balau and red balau have been carried out occasionally. Like other Shorea species, the seeds lack dormancy. Experiments in Indonesia showed a maximum germination rate of 70% within 6 days for S. laevis seeds after 4 days of storage; the fruit wings were removed and the seeds were sown in shaded nursery beds. However, the survival rate of seedlings is usually low. A maximum of 40% was observed in seedlings of S. astylosa in the Philippines, transplanted when about 20 cm tall. Seedlings of S. guiso raised in the nursery had a survival rate of only 20%. Attempts to propagate S. seminis from cuttings in Malaysia failed. S. guiso and S. seminis are commercially propagated in East Kalimantan.

Silviculture and management

Under selective cutting systems, natural regeneration may be good, at least locally, but is often unevenly distributed (e.g. S. laevis). If natural regeneration is inadequate, enrichment planting may be practised using seedlings 20-25 cm high from the forest or nursery. Since most species are slow growers, cutting cycles should be adequately long.

Diseases and pests

Seeds and seedlings are regularly attacked by insects. The weevil Nanophyes shoreae has been reported to attack and destroy large numbers (more than 90%) of seeds of S. laevis in East Kalimantan. Feeding of insects on S. maxwelliana seedlings of 10-40 cm tall was found to be less severe than in some red meranti-producing species (S. leprosula Miq., S. acuminata Dyer), probably because of a higher content of essential oils in the former.

Yield

The estimated average standing stock of balau in Indonesia is 4 m³/ha for trees with a diameter exceeding 50 cm and 4.5 m³/ha for trees with a diameter exceeding 35 cm.

Genetic resources

Balau and red balau as timber groups include many species. Some of them occur widespread and gregariously (e.g. S. guiso, S. laevis, S. maxwelliana), but others are much less common or occur only locally (e.g. S. collina, S. elliptica, S. falciferoides, S. geniculata, S. inappendiculata, S. lumutensis, S. malibato). Since identification at species level is usually not made before logging, the latter group of species may be liable to genetic erosion or even extinction. Some species are threatened in specific areas and should be protected there, e.g. S. materialis and S. scrobiculata in Peninsular Malaysia.

Prospects

The greatest species diversity of Shorea in general and of the balau and red balau groups in particular is found in lowland forest, which is threatened with clearence for agriculture and development projects. In order to protect the various Shorea species, immediate steps should be taken to preserve large tracts of lowland forest in different ecological habitats. In these reserves the forest should be kept free from any human disturbance.

Balau- and red balau-producing Shorea species are not promising for the establishment of plantations. The more quickly growing meranti-producing species, with lighter timber, are better suited for planting.

Literature

Ashton, P.S., 1964. Manual of the dipterocarp trees of Brunei State. Oxford University Press, London. pp. 115-227.
Ashton, P.S., 1982. Dipterocarpaceae. In: van Steenis, C.G.G.J. (Editor): Flora Malesiana. Ser. 1, Vol. 9. Martinus Nijhoff/Dr. W. Junk Publishers, The Hague, Boston, London. pp. 237-552.
Browne, F.G., 1955. Forest trees of Sarawak and Brunei and their products. Government Printing Office, Kuching. pp. 164-171.
Burgess, P.F., 1966. Timbers of Sabah. Sabah Forest Records No 6. Forest Department, Sabah, Sandakan. pp. 173-181, 202-217.
Durand, P.Y., 1985. Commercial nomenclature of Shorea and Parashorea. Revue Bois et Forêts des Tropiques 210: 59-66.
Kosasih, A.S. & Tarigan, Y.T., 1981. Pengaruh pelepasan sayap buah dan tingkat naungan pada perkecambahan Shorea laevis Ridl. dengan beberapa tahap lama penyimpahan buahnya [The effects of fruit wings separation and shade levels on the germination of Shorea laevis Ridl. seeds of various storage duration]. Laporan No 385. Lembaga Penelitian Hutan, Bogor. 20 pp.
Lopez, D.T., 1981. Malaysian timbers - red balau. Malaysian Forest Service Trade Leaflet No 45. Malaysian Timber Industry Board, Kuala Lumpur. 7 pp.
Lopez, D.T., 1983. Malaysian timbers - balau. Malaysian Forest Service Trade Leaflet No 78. Malaysian Timber Industry Board, Kuala Lumpur. 9 pp.
Martawijaya, A., Kartasujana, I., Kadir, K. & Prawira, S.A., 1986. Indonesian wood atlas. Vol. 1. Forest Products Research and Development Centre, Bogor. pp. 15-23. | 10 | Sandrasegaran, K., 1965. A note on the growth of Shorea guiso (Blanco) Bl. (membatu). Malayan Forester 28: 320-325.

Selection of species

Authors

K.M. Kochummen (general part),
W.C. Wong (properties),
J.M. Fundter (wood anatomy),
M.S.M. Sosef (selection of species)