Tectona (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Tectona L.f.

Protologue: Suppl. pl. 20, 151 (1782).

Family: Verbenaceae

Chromosome number: x= unknown; T. grandis: 2n= 36

Teak: medium-weight hardwood, Tectona grandis L.f. and T. philippinensis Benth. & Hook.f.

Teak

• teck (Fr)
• Indonesia: jati (general), deleg, kulidawa (Java)
• Burma: kyun
• Laos: sak
• Thailand: sak (general), mai-sak
• Vietnam: cây tếch, giá tị.

Tectona consists of 3 species. The natural distribution of the genus is discontinuous. It occurs in the Indian peninsula, Burma, Laos, Thailand and the Philippines. In the Philippines teak is represented by a distinct and narrow endemic species. Teak is probably not indigenous to Indonesia; there are indications that it was introduced to Java 400-600 years ago. At present it is widely cultivated in many parts of the tropics. Within the Malesian area plantations have been established practically everywhere.

Teak is a well-known and very good general-purpose timber. Its favourable properties make it suitable for a wide variety of purposes. For the export market teak is recommended for ship decking and other constructional work in boat building. It is extensively used for deck houses, rails, bulwarks, latches, weather doors, etc. and for furniture and interior fittings of boats. Being classified as very resistant to teredo activity, teak is an excellent timber for bridge building and other construction in contact with water such as docks, quays, piers and floodgates in fresh water. In house building teak is particularly suitable for interior and exterior joinery (windows, solid panel doors, framing) and is used for floors exposed to light to moderate pedestrian traffic. It is also used quite extensively for the manufacture of furniture and garden furniture. Other applications of teak are for building poles, transmission line poles, fence posts, wall boards, beams, woodwork, boxes, musical instruments, toys, railway sleepers and railcar construction. It is brittle and therefore less suitable for articles requiring high resilience, such as tool handles and sporting goods. The high resistance of teak to a wide variety of chemicals make it ideal for laboratory and kitchen tables as well as for scrubbing towers, vats, pipes and fume ducts in industrial chemical plants. Figured wood produces a very attractive veneer which is extensively used in the manufacture of furniture and interior fitting. Teak is suitable for the manufacture of decorative plywood. Teak wood has also been used for the manufacture of charcoal and as a fuelwood, but is nowadays often considered too valuable for such usage.

Both the bark of the roots and the young leaves produce a yellowish-brown or reddish dye which is used for paper, clothes and matting. Sawdust from teak wood is used as an incense in Java. In traditional medicine a wood powder paste has been used against bilious headaches and swellings and internally against dermatitis or as a vermifuge. The charred wood soaked in poppy juice and made into a paste was used to relieve the swelling of eyelids. The bark has been used as an astringent and the wood oil as a hair tonic.

Burma produces most of the world supply of teak, followed by India, Thailand and Indonesia. The average annual teak timber production in Indonesia (Java) in the period 1984-1988 was 800 000 m³, which was processed into the following products (in terms of average annual production): 4.4 million m² veneer, 54 000 m² mosaic parquet, 140 000 m² laminated parquet and parquet blocks, 194 000 m² wall panelling, decking and finished flooring, 100 000 m skirting, 26 000 m² overlay plywood, 475 000 beams, and 580 solid doors. The export of sawn teak timber from Indonesia in 1989 was 46 000 m³ (with a value of US$ 29.4 million). Since 1990 the export of sawn teak timber from Indonesia has been restricted to meet the demand of the local furniture industry.

Teak was by far the most important export timber in Thailand until all logging in natural forest was banned in 1989. The highest production for export of teak from natural forest was reached in 1980 with 97 000 m³, but export decreased, with some fluctuations, to 39 000 m³ in 1985, and 25 000 m³ (all processed teak) in 1990. The above-mentioned ban, the depletion of natural teak stands and the high demand on the local market have caused the sharp decline of the amounts of teak exported.

The allowable annual cut of teak in the natural deciduous forests of Burma is 350 000 t. The area planted with teak in Java is about 1 million ha, which is 45% of the total area of plantation forest. Natural stands of teak in Thailand cover about 2.5 million ha, the plantations 170 000 ha. In other South-East Asian countries, teak is planted on a comparatively small scale and the production is small. However, plantations receive great interest, e.g. in Papua New Guinea where teak fetches very high prices and where the export of teak logs is banned, in Peninsular Malaysia where plantations on an experimental scale in the far north-west show very encouraging results, and in Sabah where the export of sawn teak timber in 1992 was only 12 m³ with a value of US$ 4600 (US$ 383/m³).

Prices of teak wood are very high (e.g. even in 1989 as much as 640 US$/m³ for sawn Java teak on the export market), and hence teak is mainly used as a luxury wood.

Teak is a medium-weight timber which is rather soft and has a very characteristic appearance. The heartwood is often dull yellowish when freshly cut but it turns golden brown or sometimes dark greyish-brown after exposure, often streaked greyish or blackish; the sapwood is yellowish-white or pale yellowish-brown and up to 50 mm thick. The wood is oily to the touch, and when freshly cut it has a smell reminiscent of leather. The density is (480-)610-750(-850) kg/m³ at 12% moisture content. The grain of the wood is straight, wavy or slightly interlocked, texture rather coarse and uneven.

At 12% moisture content the modulus of rupture is 85-106(-148) N/mm², modulus of elasticity (8600-)10 000-13 400 N/mm², compression parallel to grain (43-)47-60(-72) N/mm², compression perpendicular to grain 6-7.5 N/mm², shear 8-14.5 N/mm², cleavage (60-)77-82 N/mm radial and (75-)87-91 N/mm tangential, Janka side hardness 3730-4510(-4800) N and Janka end hardness 4150-4500 N.

The rates of shrinkage of teak are very low, from green to 12% moisture content 0.7-1.5% radial and 1.1-2.5% tangential, and from green to oven dry 2.5-3.0% radial and 3.4-5.8% tangential. Teak dries very well but rather slowly. Boards of 1 cm thick take 15 days to air dry from 40% to 15% moisture content, boards of 2.5 cm thick 30 days and boards of 4 cm thick 50 days. Boards of 2.5 cm thick can be kiln dried from 40% to 10% moisture content in 5-6 days at a drying temperature of 60-80° C, and a corresponding relative humidity of 80% to 40%. In particular, care is required in determining initial and final moisture contents, as large variations in drying rates occasionally occur. The timber is very liable to colour change, and high initial temperatures should be avoided. During kiln drying a condensate of butyric acid is formed which may corrode metal kilns (unless made of aluminium or stainless steel). Teak has low movement values and a good form stability.

Teak is not difficult to work, but requires some effort, mainly because of the presence of silica (up to 1.5%). Tools tipped with tungsten carbide are recommended for sawing and planing operations. The wood is difficult to chisel with a hollow square mortiser, but turns well. The nail-holding capacity is good, but pre-boring is recommended; the screw- and staple-holding capacity is also good. Gluing is only successful on freshly machined or newly sanded surfaces. The wood bending properties vary and are usually classified as moderate; there is a tendency to buckle, and the wood is only suitable for bends of moderate curvature. Staining and polishing require freshly machined surfaces or a pretreatment with thinner. However, teak can be varnished and polished beautifully. It is easy to cut into smooth, tight veneer of uniform thickness at a temperature of 90-95° C. The veneer dries flat and split-free with low shrinkage. Owing to its beautiful figure, teak is in great demand as face veneer.

Teak heartwood is rated as durable to very durable. Stake tests show an average service life in contact with the ground of up to more than 10 years under tropical conditions and more than 25 years under temperate conditions. Graveyard tests in Indonesia indicate that the durability is significantly influenced by tree age; wood from 75-year-old trees has an average service life in contact with the ground of 7 years, but wood from 20-year-old trees only 2.5 years. Teak is very durable under cover. In India there are examples of teak wood several hundreds or even over 1000 years old, and still in good condition. The heartwood is resistant to termites, and, although not immune, to marine borer attack. The sapwood is reported to be liable to attack by powder-post beetles (Lyctus sp.). The heartwood is difficult to treat with preservatives, although carbolineum and natrium fluoride reportedly may penetrate to a fair depth.

Burma teak is usually slightly superior to Java teak regarding strength properties, while teak from Thailand is slightly less strong and less heavy than Java teak. Java teak and Malabar teak are preferred for figured material.

The wood contains 47.5% cellulose, 30% lignin, 14.5% pentosan, 1.4% ash and 0.4-1.5% silica; the solubility is 4.6% in alcohol-benzene, 1.2% in cold water, 11.1% in hot water and 19.8% in a 1% NaOH solution. The fine dust produced in machining operations may cause irritation of the skin or bronchial asthma and rhinitis after inhalation; a well-functioning dust extractor fan is recommended. The substances responsible for the allergic reactions are probably lapachol and desoxylapachol, though they are not always present in the wood. The resistance of teak wood to termites and fungi is due to the presence of tectochinon and other anthrachinones; naphthochinones and naphtoles also seem to play a role in the resistance to fungal attack. The energy value of the wood is 21 350 kJ/kg.

• Small to large deciduous trees of up to 50 m tall; bole generally straight and branchless for up to 20(-25) m, diameter up to 150(-250) cm, at base fluted or with low buttresses; bark soft; branches tetragonal.
• Leaves deciduous, decussate or ternate, simple, the blade ovate-lanceolate to broadly ovate, cuneate at base, margin entire or denticulate, softly hairy on both surfaces, petiolate.
• Inflorescence with many flowers in terminal or axillary cymes, bracts very small.
• Flowers bisexual, actinomorphic, small; calyx gamosepalous, shortly 5-7-lobed, persistent, finally enclosing the fruit; corolla gamopetalous, 5-7-lobed with a short tube and patent or reflexed lobes, glabrous, white or bluish; stamens 5 or 6, inserted at the base of the corolla tube, exserted, anthers dorsifixed, 2-celled, opening by longitudinal slits; ovary ovoid, 2-carpellate, 4-celled, one ovule per cell, style terminal, with a shortly bifid stigma with subequal branches.
• Fruit drupaceous, subglobose or slightly tetragonal, woody, with a thin, subcarneous exocarp and thick, bony, 4-celled endocarp.
• Seed without endosperm.
• Seedling with epigeal germination; cotyledons equal, petiolate, with a notched or emarginate apex; all leaves decussate.

Macroscopic characters

• Sapwood white, yellowish-white to pale yellowish-brown; heartwood golden brown, dark golden brown, sometimes ageing to dark brown or dark greyish-brown, the colour varying considerably with locality.
• Grain straight or wavy, sometimes interlocked.
• Texture moderately coarse to coarse and uneven; wood generally dull with rather rough oily feel, strongly and characteristically scented when fresh.
• Growth rings distinct and generally conspicuous to the naked eye.

Microscopic characters

• Growth rings distinct, marked by thick-walled latewood fibres and differences in vessel diameter.
• Wood ring-porous; earlywood vessels extremely large to very large, with largest pores of 340-370μm in diameter, solitary or in radial rows of 2-3 (mostly 2), transition from the earlywood to latewood gradual to more or less abrupt, latewood vessels medium-sized to small or very small with maximum diameter of 50-290μm, solitary or in radial rows of 2-5; perforations simple; intervessel pits alternate, mainly round, 5-7μm; helical thickenings absent; yellowish or reddish-brown gummy deposits mainly present in the smaller vessels; tyloses fairly abundant.
• Fibres 700-1400μm long, septate, walls variable in thickness with thicker walls towards the latewood, interfibre pits simple to minutely bordered and confined to the radial walls.
• Parenchyma both apotracheal and paratracheal; apotracheal parenchyma extremely sparse, restricted to occasional diffuse strands of 4(-8) cells; paratracheal parenchyma in thin vasicentric sheaths, but in the earlywood region in the form of a wide, 2-10(-20)-seriate paratracheal band in which the first row of earlywood vessels is partially or wholly embedded.
• Rays 4-7/mm, 1-6 or more cells wide (mostly 4-seriate or more), mostly about 0.5 mm in height but up to 0.9 mm in some samples, heterogeneous, with one row of upright to square cells but some rays tending to be homogeneous.
• Crystals absent.
• Vitreous silica present in some vessels and parenchyma.
• Yellowish or reddish-brown gummy deposits fairly abundant in the parenchyma and rays of heartwood.

Species studied: T. grandis.

The fruit splits open on one or two sides when germination starts; the radicle emerges first, and soon afterwards the cotyledons emerge. A single fruit often produces several seedlings (usually 2). The primary root is long, but gradually disappears after lateral roots have developed. The root system is superficial, often not deeper than 50 cm, and roots may extend laterally up to 15 m from the stem.

The central axis is sympodial and all side axes are orthotropic and equal. Young shoots are formed from lateral buds at the base of the terminal inflorescence. Consequently, the central axis branches after flowering. Its length at the moment of first flowering is very important in silviculture. When it is long (it may reach up to 10 m), the final bole form is positively affected, but early flowering trees may develop extremely wide crowns and short boles. The occurrence of the first inflorescence is determined by both genetic and environmental factors.

Teak is a strong light demander, and the optimum for its growth lies at 75-100% of full sunlight. Seedlings are very intolerant of shade. In seasonal climates teak is deciduous. Trees grown in non-seasonal climates are semi-deciduous. However, teak continues to develop growth rings. Young trees usually easily recover from damage by fire. Frequent fires may even result in a thickened rootstock from which, under favourable conditions, a new, more vigorous shoot may develop. In Thailand flowering normally starts at the age of 8-10 years. However, trees have been observed to flower at the age of 3 months, while a few specimens of superior phenotype did not flower before the age of 27 years. Flowers usually appear during the rainy season, and trees tend to flower synchronously. In Thailand, flowering occurs particularly in June - September and fruiting in November - January. In Java, teak flowers every year at the beginning of the rainy season (October - November), and only a few flowers (about 1%) develop into fruits. Fruits fall gradually during the dry season (May - September).

Pollination is by insects; in Thailand in particular by bees. The individual flower has a one-day cycle and the optimum pollination period is between 11.30 h and 13.00 h. Teak is mainly self-incompatible (96-100%). Although fruit set in Thailand is low (0.5-5%), 6-60% of fruit set can be achieved by artificial pollination. Fruits develop to full size in about 50 days after pollination, but are mature at 120-200 days after pollination. They are dispersed by wind over 10-15 m, but fruits are also transported by running water after heavy rainfall.

The initial growth of teak is rapid. At an age of 5 years an average height of 13 m and a stem diameter of 10 cm is not unusual, after 10 years 16.5 m and 15 cm, and after 20 years 21.5 m and 23.5 cm. After 15-20 years growth slows down. In stands of 80 years old the maximum height of trees is about 45 m, with a maximum diameter of 75 cm.

Tectona is the only genus of the tribe Tectonae which is classified within the subfamily Viticoideae. It differs from other tribes in this subfamily by the deviating type of the drupe. Features of the wood anatomy indicate that Tectona is closely related to the genera Clerodendrum , Gmelina and Premna and enable the genus to be divided into two sections, viz. sect. Tectona (with T. grandis) and sect. Leiocarpae Briq. (with T. philippinensis and T. hamiltoniana Wallich). Like T. philippinensis , T. hamiltoniana has a very localized natural distribution, i.e. in central Burma.

Teak occurs naturally in various types of tropical deciduous forest. It is often a dominant member of mixed deciduous forest, where its main associates are Xylia spp., Afzelia xylocarpa (Kurz) Craib, Terminalia spp. and Lagerstroemia spp. The forest floor is often covered by bamboos. The various teak forest formations can be grouped into three main types: moist natural teak formations (annual rainfall of (1300-)1500-2500 mm), dry natural teak formations (annual rainfall 760-1500 mm) and Indonesian teak formations (annual rainfall 1200-2000 mm). Teak thrives best and reaches its largest dimensions in a humid tropical climate but it needs a marked dry season. Optimal growth is attained with an annual rainfall of 1200-2500 mm of which 75% falls in the rainy season. Teak generally occurs scattered but can form almost pure stands under favourable conditions. Teak forests are generally situated on hilly or undulating country but are known from alluvial flats as well. Their altitudinal limit lies around 1000 m where they give way to oak and pine forests. The most suitable soil is a deep and well-drained, fertile alluvial-colluvial soil with a pH of 6.5-8.0 and a relatively high Ca and P content. Teak does not tolerate flooding or infertile lateritic soils. Young teak plants show a remarkable capability to recover after fire. Teak is a pioneer species, but with a long lifespan. In contrast to many other pioneer species, teak is able to persist and dominate and to naturally regenerate towards the climax phase of succession in most parts of its natural range.

Natural regeneration of teak is particularly abundant in forests exposed to fires, and often occurs patchwise. Seeds collected from the forest floor are generally used to establish plantations. It is recommended to collect seeds from trees older than 20 years. The weight of 1000 seeds of T. grandis is 500-1250 g. Seed is often collected from selected seed stands. The seeds have a rather low germination rate, usually less than 50%, but sometimes up to 80%. Germination usually starts after 10 days but may extend over 2-3 months. In Thailand seedlings are kept in nursery beds for about one year. Then the rootstock is dug up, the stem cut off, and the stump is planted into the field. Direct sowing into the field at the beginning of the rainy season is often practised in Java. Soaking the seeds for 2 days, drying them for 1 day, and repeating this procedure 4 times promotes germination. Seeds can be stored for up to several years without difficulty, provided they are kept under cover. Stumps can be stored for up to one year.

Teak can be successfully propagated by tissue culture. Stem segments and leaf stalks taken from seedlings or trees yield callus when cultured on a modified Murashige and Skoog medium. Root formation occurs within 2 months after planting the explants on the same medium with 3.5 ppm naphthalene acetic acid and 0.25 ppm benzylamino purine.

Normal spacing in the field is 2 m × 2 m, 3 m × 1 m, 3 m × 3 m, 4 m × 2 m or 4 m × 4 m, depending on site conditions.

In natural teak forest in Thailand a selective cutting system is used, with minimum girth limit of 180 cm at breast height. For teak plantations the clear-cutting system is used. Replanting is often carried out after cutting. The cutting cycle for plantations is 50-80 years. The site is completely cleared before planting, usually by means of fire.

Frequent weeding in the first years after planting is necessary, as seedlings are easily suppressed by weeds. Regular thinnings are needed to obtain well-shaped logs. In plantations in Java with an initial spacing of 3 m × 1 m, thinning starts 3-4 years after planting, with a frequency of 4 years until the age of 15 years, from then on with a frequency of 5 years until the age of 25 years, and thereafter once every 10 years until the felling age, which is usually 80 years. Frequency of thinning depends on site conditions, i.e. more frequent in better sites. Teak trees coppice well; regrowth from the stumps of felled trees is sometimes a real problem in the establishment of new plantations.

Teak plantations must be protected from fire and grazing animals, as the soil is often susceptible to erosion. Interplanting with other species is difficult because of the fast initial growth of teak, but with Leucaena spp., Acacia spp. and perhaps Shorea spp. it seems possible. It is sometimes underplanted with bamboos. In Java, teak is often planted in the "tumpangsari system". In this agroforestry system teak is planted together with agricultural crops, and often also Leucaena leucocephala (Lamk) de Wit. However, after about 2 years the shade under the young trees usually precludes sufficient growth of the crop.

Diseases can be conveyed by bacteria such as Pseudomonas solanacearum and fungi such as Corticium salmonicolor. Wood borers frequently attack the stems, e.g. Xyleutes ceramicus in Thailand and Xyleborus destruens in Indonesia. Leaf-eating caterpillars such as Hyblaea puera and Pyrausta machaeralis may defoliate branches. Termites such as Neotermes tectonae may damage the trees, although many provenances show a high resistance. Seeds can be infested by larvae of Lepidoptera and Coleoptera (longhorn beetles). Crowns are often infested by semi-parasitic mistletoes ( Loranthus spp.).

Stems are usually girdled two years before logging. This practice kills the trees, and makes felling and transport easier; the logs dry and are then transportable by water. With modern felling and transportation techniques, girdling is nowadays redundant. Fresh logs are sometimes coated with tar or lime at both ends to prevent splitting. Cattle and buffalo are still often used to transport of the logs over short distances; for long-distance transportation trucks or trains are used. Sometimes transport is by river.

The average yield of teak plantations in Java is 60-100 m³/ha, including thinnings. Occasionally the final harvest may yield as much as 390 m³/ha in stands 80 years old. The mean annual volume increment is (1-)3-6(-15) m³/ha.

The natural area of distribution of T. grandis is large, and it often occurs commonly or even gregariously or is dominant. Therefore, it is not easily liable to genetic erosion. Its occurrence in different habitats, resulting in substantial provenance variation, gives potential for selection. This has been recognized in Indonesia and Thailand, where there are ongoing selection programmes and clonal seed orchards are being established.

The two other Tectona species, T. hamiltoniana and T. philippinensis, have a small area of distribution and need conservation. They are rarely planted, but their potential value for teak breeding should be investigated.

Breeding programmes have been established in Thailand, Indonesia and Papua New Guinea. In Thailand there is a long-term teak-breeding project, using 400 selected trees. The improvement programmes mainly concentrate on breeding for superiority in vigour and form, and also for pest resistance (e.g. against Xyleutes ceramicus) and preferred wood characteristics (e.g. colour, texture and hardness).

Teak is a good example of a high-quality timber which can be obtained from plantations. Adequate methods of vegetative propagation are indispensable for large-scale establishment of plantations with superior trees. Tissue culture on an experimental scale shows promising results with shoot tips and nodal segments, but more research is needed, especially on the behaviour of trees resulting from tissue culture.

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• Haslett, A.N., 1986. Properties and uses of the timbers of western Samoa. Plantation-grown exotic hardwoods. Ministry of Foreign Affairs, Wellington. pp. 22-24.
• Hedegart, T., 1976. Breeding systems, variation and genetic improvement of teak (Tectona grandis L.f.). In: Burley, J. & Styles, B.T. (Editors): Tropical trees. Variation, breeding and conservation. Linnean Society, London. pp. 109-123.
• Kaosa-ard, A., 1981. Teak (Tectona grandis), its natural distribution and related factors. Natural History Bulletin of the Siam Society 29: 55-72.
• Krishna Murty, A.V.R.G., 1975. Bibliography on teak, Tectona grandis Linn.f.: a survey of the world literature covering about 2961 references with abstracts to the more important ones. Kishore, Dehra Dun. 402 pp.
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• Ng, F.S.P, 1979. Teak. Nature Malaysiana 4(3): 36-41.
• Noerhadi, E., 1980. Vegetative propagation of Tectona grandis L. and Pinus merkusii Jungh. et de Vriese using tissue culture. Duta Rimba 42: 11-15.
• van Alphen de Veer, E.J., 1957. Teak cultivation in Java. Tropical Silviculture. FAO Forestry and Forest Products Studies 2, No 13. FAO, Rome. pp. 216-232. | 10 | Webb, D., Wood, P.J. & Smith, J., 1980. A guide to species selection for tropical and sub-tropical plantations. Tropical Forestry Papers No 15. Commonwealth Forestry Institute, University of Oxford. p. 249.

• C. Phengklai (general part),
• T. Smitinand (general part),
• J. Kartasubrata (general part),
• P.B. Laming (properties),
• S.C. Lim (wood anatomy),
• M.S.M. Sosef (selection of species)