Shorea Roxb. (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Shorea Roxb. ex Gaertner f.

Protologue: Fruct. 3:47 (1805).

Family: Dipterocarpaceae

Chromosome number: x= 7; 2n= 14

Major species and synonyms

• Shorea macrophylla (de Vriese) P. Ashton, Gard. Bull. Sing. 20: 278 (1963), synonyms: Hopea macrophylla de Vriese (1861), Shorea gysbertsiana Burck (1886), Pachychlamys gysbertsiana (Burck) Ridley (1922).

• Shorea splendida (de Vriese) P. Ashton, Gard. Bull. Sing. 20: 279 (1963), synonym: S. martiniana R. Scheffer (1873).

• Shorea stenoptera Burck, Meded.'s-Lands Plantent. 3:11 (1886).

Vernacular names

• General: tengkawang (En). Illipe (Fr)
• Indonesia: tenkawang. Brunei, Malaysia: engkabang, illipe, singkawang.

• S. macrophylla . Brunei: kawang jantong
• Indonesia: awang katolok, tengkawang buah (East Kalimantan), tengkawang hantelok (Kalimantan)
• Malaysia: engkabang jantong, engkabang ringgit (Sarawak), kawang jantong (Sabah).

• S. splendida
• Indonesia: tengkawang bani, tengkawang goncang, tengkawang rambai (West Kalimantan)
• Malaysia: engkabang bintang, melindang (Sarawak).

• S. stenoptera
• Indonesia: tengkawang tayau, tengkawang tungkul (West Kalimantan)
• Malaysia: engkabang kerangas (Iban), engkabang rusa (Sarawak).

Note: in the literature the name illipe nut is sometimes used for Shorea nuts. Illipe nut however, is the fruit of Madhuca and other Sapotaceae ; their fat is buttery while the fat of tengkawang fruit is more solid and has a higher melting point.

Origin and geographical distribution Many Shorea species including S. macrophylla , S. splendida , S. stenoptera and most other tengkawang species are endemic to Borneo where also the greatest diversity occurs. A few of the in total 200 species occur in India and Sri Lanka, the rest in South-East Asia (only some in continental South-East Asia, the majority in Borneo, several in Sumatra, Java, Moluccas and the Philippines).

Uses

Several species of Shorea produce edible fruits (nuts) that are rich in fat, commonly known as tengkawang fat or butter, illipe butter, green butter or Borneo tallow. The extraction of fat from these nuts is an old tradition in Borneo. The indigenous people consider traditionally-extracted tengkawang fat as a delicacy and commonly add it to food such as rice. In Peninsular Malaysia and Sumatra, tengkawang fat is only used occasionally. Tengkawang fat is an excellent substitute for cocoa butter in the manufacture of chocolate. Its composition is very similar to cocoa butter so that its addition hardly alters the properties and taste and is difficult to detect. It can also be used in the confectionery industry and in the manufacture of cosmetics particularly creams and lipsticks. Medicinally, tengkawang fat is applied to treat thrush and sprue and as an ointment on wounds. The meal remaining after oil extraction can be used as a 10% feed supplement for pigs.

Shorea is the most important source of timber in South-East Asia and the species yielding tengkawang fat also yield timber, mostly classified in the trade groups "balau" (e.g. some minor species mentioned in other botanical information) or "red meranti" (e.g. the 3 major species mentioned). Some species grow into large trees with excellent boles that are in high demand by the plywood and veneer industry. All timber aspects of Shorea are given in PROSEA 5(1): Timber trees: major commercial timbers, and are not repeated here.

In Borneo, tengkawang trees play a role in religious tradition, land tenure and shifting agriculture and are therefore often regarded as family heirlooms and banned from logging. However, they are still cut for their valuable timber even where collection of tengkawang nuts is an economically important activity. In Indonesia and Sarawak, the main tengkawang species are protected and their logging is banned in most regions. Tengkawang species are used in reforestation, agroforestry activities and rehabilitation of land that has been subjected to shifting cultivation.

Production and international trade

Production and trade volumes of Shorea vary widely from year to year, due to the gregarious flowering habit of many dipterocarp species with intervals of 2-7 years. During good years production is 20 000-30 000 t and 5000-20 000 t from main exporters Sarawak and West Kalimantan, respectively. Exports in 1968, 1970, 1973, 1977, 1980, 1983 and 1987 were good but they were nearly nil in other years. Prices also fluctuate and drop drastically in high-production years. As tengkawang fat is a substitute for cocoa butter, its price is further subject to the mechanisms of the cocoa market. This market, in turn, is dependent on world demand for cocoa products and the production in the major cocoa growing countries.

Properties

Tengkawang nuts have a fat content of about 50% (on dry weight basis). The proximate fatty acid composition is: palmitic acid 18-21%, stearic acid 39-43% and oleic acid 37-38%. Tengkawang fat has an iodine value of 29-38. Its pronounced melting point is 33-36°C which is just below the temperature of the human body. It is slightly higher than that of cocoa butter and the consistency of tengkawang fat is consequently slightly harder. This is important in the manufacture of chocolate, particularly for warm and tropical countries. The high latent heat of both cocoa and tengkawang fat is freed when they melt and this creates the fresh and cool sensation associated with the taste of chocolate. This property also imparts a creamy, solid characteristic to cosmetics when applied on the skin. The fat keeps for a very long time without a change in properties and smell. Poorly prepared tengkawang fat with a free fatty acid content of over 5% is not suitable for human consumption.

Description

Medium-sized to very large trees up to 75 m tall; bole straight, cylindrical, branchless for 10-40 m, diameter up to 3 m; buttresses usually prominent, up to 5 m tall; bark surface smooth, prominently fissured or becoming flaky, sometimes scaly, grey or brown; inner bark reddish, pink, orange or yellow, exuding a brown, reddish or yellowish resin; mature crown hemispherical or dome-shaped, sympodial. Leaves alternate, stipules and bracts persistent or fugacious, usually petiolate; blade simple, entire, glabrous, pinnately veined with scalariform tertiary venation, often glaucous on the lower surface. Inflorescences terminal or axillary, paniculate; flowers secund or distichous, usually rather crowded, hermaphrodite, 5-merous, actinomorphic, scented; calyx lobes free, hirsute; petals free or connate at base, cream suffused with pink, the outer surface hirsute; stamens usually 15, sometimes up to 70, usually strap-shaped, the anthers with 4 pollen sacs, linear-oblong to subglobose, with short to long, glabrous appendages; ovary with or without a stylopodium. Fruit a usually short stalked, subglobose to ovoid nut, sharply pointed, with the outer 3 or rarely all calyx lobes much elongated, these more or less thickened and saccate at the base. 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.

- S. macrophylla . Tree up to 50 m tall, bole up to 130 cm in diameter, buttresses up to 2 m tall. Leaves coriaceous; stipules persistent, broadly hastate, up to 5 cm × 1.3 cm; petiole 1.5-3 cm long; blade elliptical-oblong, 17-35 cm × 10-14 cm, base obtuse to subcordate, apex acuminate, secondary veins 11-20 pairs. Panicle up to 17 cm long; flower bud ellipsoid, up to 8 mm × 5 mm; petals pale pink; stamens 15, of which inner 5 long and outer 10 short, filaments adnate forming a tube around the ovary, tapering distally, becoming filiform below the anthers; anthers with long appendages, stylopodium pyriform; larger calyx lobes 3, in fruit up to 11 cm × 3 cm, 2 shorter lobes up to 8 cm × 1.5 cm. Nut obovoid, up to 6 cm × 4 cm, yellow-brown, soft pubescent.

• S. splendida. Tree up to 30 m tall, bole up to 65 cm in diameter, buttresses low. Leaves chartaceous, lustrous; stipules subpersistent, cordate, up to 2.5 cm long; petiole 1-2 cm long; blade oblong, 8-23 cm × 4-11 cm, base cordate, apex acuminate, secondary veins 9-12 pairs. Panicle up to 20 cm long; flower bud conical, up to 10 mm × 3 mm; petals lanceolate; stamens 15, inner 5 longer than outer 10, filaments adnate forming a tube around the ovary, anthers with long, slender appendages, stylopodium spindle-shaped; larger calyx lobes 3, oblong, in fruit up to 7.5 cm × 2.3 cm, 2 smaller lobes up to 6.5 cm × 1.2 cm. Nut ovoid, 5.5 cm × 3 cm, pale yellow-brown pubescent.

• S. stenoptera . Tree up to 25 m tall, bole up to 60 cm in diameter, buttresses small or absent. Leaves thickly coriaceous; stipules subpersistent, ovate, up to 2 cm × 1 cm; petiole 2-5 cm long; blade oblong, 18-40 cm × 8-22 cm, base cordate to cuneate, apex acuminate, secondary veins 10-14 pairs. Panicle up to 35 cm long; flower bud conical, up to 7 mm × 3 mm; petals deep pink, lanceolate; stamens 15, inner 5 somewhat longer than outer 10, filaments connate for 3/4 of their length, tapering abruptly below the anthers, anthers with long slender appendages, stylopodium spindle-shaped; larger calyx lobes 3, in fruit up to 7.5 cm × 2 cm, 2 shorter lobes 5.5 cm × 0.8 cm. Nut ovoid, up to 5 cm × 3 cm, pale yellow-brown pubescent.

Growth and development

Seed dispersal in Shorea is usually only over short distances, generally not more than 30 m from the mother tree. Seed is recalcitrant and loses its viability within a month and on drying. Seedlings often grow faster in sunny than in shaded sites, but seedlings of many species suffer severe damage from prolonged exposure to full sunlight. Seedlings usually survive best in intermittent sunlight. Full sunlight causes the soil temperature near the seedlings to rise, inactivating the mycorrhizae which are essential for good growth of tengkawang. Infected seedlings grow faster and are taller. Once established, tengkawang saplings persist for a number of years in the understorey under heavy shade, but they can respond to moderate to high light intensities with rapid growth. Nursery-grown seedlings of S. stenoptera grow considerably better after inoculation with the mycorrhiza Scleroderma sp.; seedlings of S. pinanga respond best to inoculation with Russula sp.

As with most Shorea , there is little reliable information about rates of growth and development in natural stands. In planting trials in Sarawak, the annual average diameter growth of major tengkawang species ranged from 1.0-1.9 cm DBH (average of the best 10% of samples between 30-132 trees). The most important species S. macrophylla and S. stenoptera reached increments of 1.9 cm and 1.1 cm, respectively. In a plantation in Semengoh Forest Reserve (Malaysia) the mean annual growth rates varied from 1.2 cm for S. macrophylla to 0.8 cm for S. pinanga . In trial plantations in Java S. stenoptera had an average annual growth of 26.7 m³/ha over a period of 30 years. These exceptional values show the potential of this species under optimal conditions. In 40 years, red meranti trees may sometimes reach a diameter of up to 80 cm ( S. scaberrima ). Good seed production tends to reduce the growth of the tree and consequently also timber production.

For commercial nut production, age at first flowering is very important. Flowering generally starts when the tree crown reaches the canopy storey, which may be 10-15 years after germination for solitary specimens of fast-growing species. In the forest, most tengkawang species flower for the first time at the age of 20-30 years. Early flowering in plantations is reported for S. macrophylla , S. pinanga and S. sumatrana with special shade or fertilizer treatments. Trees of S. pinanga planted in Malaysia flowered and fruited after only 6 years because growth was enhanced by fertilizers. As in all dipterocarps flowering and fruiting of tengkawang occurs periodically with an average of 1 year of abundant fruit production (mast year) every 3-6 years, often after a pronounced dry season or drought, e.g. those caused by the El Niño weather system. Closely related species may differ in flowering periodicity. For several tengkawang up to 50% of the trees flower during years of gregarious flowering. During these years, there is only a slight overlap in the peak blooming periods of different species, but ripening of fruits is simultaneous. In mast years fruit production in the forest may be very abundant. In Peninsular Malaysia and Borneo S. sumatrana flowers between March and July. In the Philippines S. seminis usually flowers from June to August. Most dipterocarps are predominantly outbreeders, with high within-population variability. Pollination is generally by insects including thrips, psyllid bugs and honey-bees ( Apis spp.). Tengkawang grows slowly and large specimens can be very old, several hundred years at least. Regrowth from stumps occurs after coppicing. The best coppicing ability is found in small trees (up to 20 cm in diameter) and coppice shoots grow well. Coppicing is done for firewood production.

Other botanical information

Other tengkawang species with fruits that are also occasionally used for fat production, are:

• S. lepidota (Korth.) Blume; synonyms: S. nitens Miq., S. megistocarpa Foxw., Vatica lepidota Korth.; vernacular names: Malaysia: meranti langgong, meranti pala, meranti sega. Sumatra: meranti katuko, meranti sitarah, meranti sabat. S. lepidota is restricted to Peninsular Malaysia and Sumatra. It is a large buttressed tree; leaves subcoriaceous, stipule lanceolate, 20 mm × 4 mm, persistent, petiole 7-11 mm long, blade obovate to oblong, 6-14 cm × 3-6 cm, base cuneate, apex acuminate, veins 14-16 pairs; panicle up to 7 cm long, petals cream, stamens 15, 3 longer calyx lobes in fruit 11 cm × 2.5 cm, 2 smaller ones 7 cm × 0.7 cm; nut ovoid, up to 16 mm × 11 mm, pointed. S. lepidota is common in lowland dipterocarp forest on undulating land and low hills below 350 m altitude. Its wood is traded as red meranti.

• S. pinanga R. Scheffler; synonym: S. compressa Burck; vernacular names: Brunei: kawang, meranti langgai bukit
• Indonesia: awang boi (south-eastern Kalimantan), tengkawang biasa, tengkawang rambai (West Kalimantan)
• Malaysia: kawang pinang (Sabah), meranti langgai bukit (Sarawak). S. pinanga is an endemic species of Borneo. It is a large tree, up to 50 m tall, with bole up to 125 cm in diameter, buttresses small, up to 1.5 m tall; leaves thinly leathery, stipules up to 6 cm long, petiole 1-2 cm long, blade elliptical to narrowly ovate, 11-24 cm × 4-9 cm, with 10-20 pairs of secondary veins; panicle up to 24 cm long, petals deep pink, stamens 15, filaments adnate forming a ring around the ovary, anthers subglobose with long, slender appendages, stylopodium long and slender, larger calyx lobes 3, in fruit up to 28 cm × 3.5 cm, 2 smaller ones 17 cm × 1.2 cm; nut broadly ovoid, 2.3 cm × 2.3 cm, yellow-brown pubescent. S. pinanga grows on clay-rich soils, especially on ridges below 700 m altitude. Variability in tomentum density and leaf shape is great. Where habitats overlap, S. pinanga can have characters in common with S. macrophylla , suggesting hybridization. Its wood is traded as red meranti.

• S. scaberrima Burck; vernacular names: Brunei: meranti paya bersisek
• Indonesia: kontoi entimus, tengkawang kijang (West Kalimantan), meranti sandakan (northern Kalimantan)
• Malaysia: engkabang pinang, kawang bukit (Sabah), meranti paya bersisek (Sarawak). S. scaberrima is an endemic species of Borneo. It is a tree up to 40 m tall, bole up to 110 cm in diameter, buttresses up to 1.5 m tall, bark appearing smooth; leaves thinly leathery, stipules hastate, 18 mm × 8 mm, caducous, petiole 2-2.5 cm long, blade oblong-ovate, 7-20 cm × 4-9 cm, with 14-17 pairs of secondary veins, lower surface tawny tomentose; panicle up to 8 cm long, petals pink, stamens 15, anthers oblong with long appendages, stylopodium narrow, 3 larger calyx lobes in fruit up to 4.5 cm × 1 cm, 2 smaller ones 3 cm × 0.3 cm; nut obovoid, 5 cm × 2.5 cm, fulvous pubescent. S. scaberrima occurs on sandy clay soils on low hills, on alluvium, on ridges and volcanic plateaux up to 850 m altitude. Its wood is traded as red meranti.

• S. seminis (de Vriese) v. Slooten; synonyms: S. schefferiana Hance, Isoptera borneensis Scheffer ex Burck, I. seminis (de Vriese) Burkill; vernacular names: Brunei: engkabang terendak, kawang tikus
• Indonesia: tengkawang ayer, tengkawang pelepak, tengkawang terindak (Kalimantan)
• Malaysia: engkabang chengai, engkabang terindak (Sarawak), selangan batu terendak (Sabah)
• Philippines: gisok-tapang (Sulu), malayakal (Tagalog), yakal (Chabacano). S. seminis is found in Borneo and in the Philippines. It is a tree up to 60 m tall with bole branchless for 25-30 m and up to 130 cm in diameter but usually much less, with prominent buttresses up to 2.5 m tall; leaves thinly leathery, stipules oblong, 7 mm × 3.5 mm, caducous, petiole 1-1.5 cm long, blade oblong-ovate to lanceolate, 9-18 cm × 2.5-8 cm, secondary veins 9-15 pairs; panicle up to 10 cm long, petals narrow, cream, stamens 30-40, the appendages with a few bristles, calyx lobes subequal, in fruit up to 2 cm × 1.8 cm; nut ovoid to globose, 1 cm in diameter, style remnant up to 1 cm long. S. seminis often grows gregariously on alluvium banks of sluggish rivers. The fat from S. seminis is said to have the best taste among all the tengkawang fats, but the nuts are too small to be valued for export. Its wood is traded as balau.

• S. singkawang (Miq.) Miq.; synonyms: Hopea singkawang Miq., Pachychlamys thiseltonii (King) Ridley, Shorea thiseltonii King; vernacular names: Indonesia: sengkawang pinang, singkawang daun halus (Sumatra)
• Malaysia: meranti bahru, meranti sengkawang merah, siput melantai (Peninsular)
• Thailand: maak on (peninsular). S. singkawang is found in Sumatra, Peninsular Malaysia and south-eastern peninsular Thailand. It is a tree up to 30 m tall, bole branchless for 12-21 m and up to 95 cm in diameter, buttresses up to 3.5 m tall; leaves coriaceous, stipules lanceolate-falcate, up to 12 mm × 6 mm, fugaceous, petiole 6-17 mm long, blade oblong-lanceolate, 8-24 cm × 2-9 cm, secondary veins in 7-17 pairs; panicle up to 8 cm long, petals red to purple-red, stamens 15, anthers subglobose with short appendages, stylopodium indistinct, the 3 larger calyx lobes in fruit up to 8 cm × 0.8 cm, only slightly longer than the nut, the 2 smaller ones 3 cm × 0.8 cm; nut ellipsoid to ovoid or obovoid, 6 cm × 2.5 cm, apex pointed. S. singkawang is frequent in lowland mixed dipterocarp forest on well drained undulating land, below 400 m altitude. Its wood is traded as red meranti.

• S. sumatrana (v. Slooten ex Thorenaar) Sym. ex Desch; synonyms: Isoptera sumatrana v. Slooten ex Thorenaar; vernacular names: Indonesia: kedawang, sengkawang (Sumatra)
• Malaysia: balau sengkawan air, sengkawang, tengkawang batu (Peninsular)
• Thailand: palosale, teng-dong (Pattani). S. sumatrana occurs in Sumatra, Peninsular Malaysia and south-eastern peninsular Thailand. It is exactly the same as S. seminis , only the number of stamens is 25, and perhaps it is not a different species. S. sumatrana grows semi-gregariously on alluvium banks of sluggish but not brackish rivers. Its wood is traded as balau.

Ecology

Shorea is confined to tropical climates with a mean annual rainfall exceeding 1600 mm and a dry season of less than 6 months. Most species occur below 1000 m altitude. Species and individual trees are most numerous on deep, well-drained yellow or red soils in the lowland. Most species are restricted to a single vegetation type or substratum. Some are common to gregarious in a certain habitat. S. macrophylla and S. splendida occur on periodically flooded, clayey alluvial soils, S. stenoptera on poorly-drained sandy alluvia. S. pinanga and S. scaberrima are found on ridges, while S. seminis and S. sumatrana often grow on the banks of sluggish flowing rivers.

Propagation and planting

There is much traditional knowledge about the enhanced natural regeneration, planting and seeding of the more important tengkawang species because of their potential as multipurpose trees. This is particularly true for S. macrophylla , S. seminis (in East Kalimantan) and S. stenoptera (in Western Borneo). The best time to collect fruits of S. pinanga and S. stenoptera is when part of the wing colour changes to brown. Fresh seed of S. pinanga has a germination rate of 93% while that of S. stenoptera seed is 96%. All seeds are recalcitrant; they should be planted within 4 weeks after harvest. After this period, germination rates drop drastically. Eight-week old seedlings can be transplanted into the field. Vegetative propagation is also possible. Single-node leafy cuttings from 8- and 15-month old seedlings of S. macrophylla root easily under continuous mist with or without auxin treatment.

Husbandry

The best known tengkawang plantation is probably the collection in the Hourbentes Forest Station near Bogor in West Java. It is an excellent example of the early ex-situ conservation and proof that regeneration of dipterocarps, often regarded as difficult and sensitive, is abundant under favourable conditions. Other trial plantations of tengkawang are in Sarawak and Peninsular Malaysia. Intensive cultivation with application of fertilizer induced and enhanced early flowering in S. pinanga . Providing some shade during the early stages of the plantation can give the same effect. Trees of S. macrophylla started fruiting after 6 years when their seeds were planted in the open. A stand of S. pinanga with fertilizer treatment yielded at the same age.

Tengkawang cultivation has been a traditional smallholder activity for more than 100 years but a few larger plantations also exist. Smallholders in Kalimantan cultivate S. macrophylla , S. pinanga , S. seminis , S. splendida and S. stenoptera in traditional plantations along rivers and streams. Planting trees is one way to claim land and to prove ownership or usufruct rights, acknowledged by traditional law. New gardens are usually established in shifting cultivation schemes.

Diseases and pests

Fusarium fungi may kill tengkawang seedlings. Seeds and seedlings of S. pinanga are also occasionally attacked by the fungus Cylindrocarpon destructans . Weevils such as Alcidodes dipterocarpi and Nanophyes shoreae are major pests of seeds, occasionally damaging up to 85% of the seeds. Other seed-attacking insects include Microlepidoptera moths of the families Pyralidae and Totricidae , and beetles of the family Scolytidae . Terrestrial vertebrates, particularly pigs and squirrels feed on fallen seeds and are the major cause of seed mortality. Ants and termites also feed on fallen seeds. Some caterpillars eat seedlings, although seedling predation is generally low.

Harvesting

Nuts of tengkawang are usually collected from the ground or scooped out of streams when a tree grows on a stream bank. This should be done soon after nut fall to avoid predation and seed germination (seed germinates rapidly). The periodic character of flowering is a deterrent to the establishment of a regular and profitable chain of harvesting, processing and commercialization for nuts and fat. Hence, investment in post-harvest processing and storage is almost absent.

Yield

There is no information on the yield of natural tengkawang stands. A trial plantation of 20-year old S. macrophylla in Peninsular Malaysia produced 1140 kg/ha of nuts. Another trial plantation of 32-year old S. macrophylla in Sarawak yielded 1120 kg/ha of nut and one of S. pinanga gave 2280 kg/ha of nuts. These figures refer to yields in mast years and indicate the potential rather than actual yields in natural stands.

Handling after harvest

After collecting the fruits of tengkawang, the wings are broken off the nut. Then nuts are soaked in water for 30-40 days (in bamboo baskets in a river); this treatment loosens the nutshell for its easy removal. Afterwards, the kernel (which usually splits into 4 parts) is dried. The dried parts ("padi tengkawang") are marketed; the blacker they are the better because it means that they have been dried without decay. They are suitable for oil extraction, or can be safely stored for up to a year. As an alternative to this long soaking period, the unwinged nuts are also roasted over a fire (and marketed as such), or boiled or soaked in boiling water to remove the shell more easily. Formerly the fruits were piled in a humid place to induce germination. The fruit wall splits open as soon as the seedling reached 10-20 cm in length, the kernel could then be freed and dried, while the shell and sprout were removed. This method resulted in a lower fat content. Drying the cotyledons in the sun is better than drying them over a fire. The long soaking method is advantageous because the padi tengkawang is less severe attacked by insects. To obtain the fat, the dried cotyledons are crushed, heated in boiling water and the fat skimmed off. This fat is suitable for burning, soap or candle production; the fat solidifies into greenish or yellow-white clumps. For home use, the oil is filtered first. It can be stored for a long time without deterioration.

Genetic resources

Large live germplasm collections of tengkawang trees are present in several botanic gardens like in Bogor (Indonesia) and Kepong (Malaysia). They are important sources of seeds, although there is growing evidence that such seeds may be inferior because of inbreeding.

Breeding

Proposals have been made to select trees for intensive cultivation among those that flower early, but no selection programmes are known to exist. Some natural hybridization occurs between species where habitats overlap. S. splendida probably occasionally hybridizes with S. pinanga and S. stenoptera.

Prospects

Although restrictions on the use of cocoa butter substitutes in manufacturing chocolate in the European Union have been eased, the potential of tengkawang for the international market remains limited. It not only has to compete with cocoa and shea butter, but the fluctuations in its production also make it difficult to develop reliable markets. The long juvenile period of tengkawang trees does not make it an attractive crop for plantations. However, tengkawang fat will continue to contribute to the productivity of managed forests and shifting cultivation systems.

Literature

• Anderson, J.A.R., 1975. Illipe nuts (Shorea spp.) as potential agricultural crops. In: Williams, J.T., Lamoureux, C.H. & Wulijarni-Soetjipto, N. (Editors): Proceedings of a symposium on South-East Asian plant genetic resources. Bogor, Indonesia, 20-22 March 1975. Food and Agriculture Organization of the United Nations, SEAMEO Regional Centre for Tropical Biology/BIOTROP and Lembaga Biologi Nasional-LIPI, Bogor, Indonesia. pp. 217-230. | 2| Ashton, P.S., 1964. A manual of the dipterocarp trees of Brunei State. Oxford University Press, Oxford, United Kingdom. 242 pp.
• 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, the Netherlands. pp. 237-552.
• Hamzah, Z. et al., 1978. Laporan: Feasibility study pembangunan kebun benih tengkawang di Kalimantan Barat [Report: Feasibility study for the establishment of a tengkawang seed garden in West Kalimantan]. Lembaga Afiliasi IPB, Bogor, Indonesia. 152 pp.
• Jafarsidik, Y.S., 1982. Inventarisasi jenis-jenis pohon penghasil tengkawang di hutan Mentatai (Melawi) Kalimantan Barat [Inventory of tengkawang nut producing tree species in the Mentatai forest (Melawi), West Kalimantan]. Laporan No 387. Balai Penelitian Hutan, Bogor, Indonesia. 23 pp.
• Kochummen, K.M., Wong, W.C., Fundter, J.M. & Sosef, M.S.M., 1993 . Shorea Roxb. ex Gaertner f. (balau and red balau). In: Soerianegara, I. & Lemmens, R.H.M.J. (Editors): Plant resources of South-East Asia 5(1): Timber trees: major commercial timbers. Pudoc Scientific Publishers, Wageningen, the Netherlands. pp. 421-434.
• Kochummen, K.M., Wong, W.C., Fundter, J.M. & Sosef, M.S.M., 1993 . Shorea Roxb. ex Gaertner f. (red meranti). In: Soerianegara, I. & Lemmens, R.H.M.J. (Editors): Plant resources of South-East Asia 5(1): Timber trees: major cmmercial timbers. Pudoc Scientific Publishers, Wageningen, the Netherlands. pp. 384-403.
• Seibert, B., 1996. Food from dipterocarps: utilization of the tengkawang species group for nut and fat production. In: Schulte, A. & Schöne, D. (Editors): Dipterocarp forest ecosystems - towards sustainable management. World Scientific, Singapore. pp. 616-626.
• Warsopranoto, S. & Suhaendi, H., 1977. Kemungkinan membudidayakan tengkawang [The possibilities to cultivate tengkawang]. Lembaran Pengembangan 1. Lembaga Penelitian Hutan (LPH), Bogor, Indonesia. 20 pp.

Authors

B. Seibert & A.T. Salang