Diospyros (PROSEA Timbers)

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Plant Resources of South-East Asia Introduction

List of species

Diospyros L.

Protologue: Sp. pl. 2: 1057 (1753); Gen. pl. (Ed. 5): 478 (1754).

Family: Ebenaceae

Chromosome number: x= 15; 2n= 30 for most of the species, D. ebenum: 2n= 90, D. kaki: 2n= c. 54-56, 90

Trade groups

• Black ebony: heavy hardwood, e.g. Diospyros ebenum Koenig, D. ferrea (Willd.) Bakh.

• Streaked ebony: heavy hardwood, e.g. D. blancoi A.DC., D. celebica Bakh., D. pilosanthera Blanco.

• White Diospyros wood: medium-weight hardwood, e.g. D. discocalyx Merr., D. rigida Hiern.

Black and streaked ebony is the corewood of the species involved. In species producing white ebony, this corewood has developed only slightly or is absent, and the remainder of the wood is pale.

Vernacular names

Black ebony:

• East Indian ebony, Ceylon ebony (En)
• Ebène noir (Fr)
• Indonesia: kayu arang, kayu eboni
• Philippines: kamagong, camagon.
• Burma (Myanmar): mepyaung
• Cambodia: trayung
• Thailand: maklua, lambit.

Streaked ebony:

• Macassar ebony, Andaman marblewood, zebrawood (En).
• Ebène de Macassar, coromandel (Fr)
• Indonesia: kayu hitam, kayu eboni
• Malaysia: buey (general), merpinang (Iban, Sarawak)
• Philippines: kamagong, camagon
• Thailand: kaling.

White Diospyros wood:

• persimmon (Am)
• Malaysia: kayu arang, kayu malam
• Philippines: ata-ata, malatinta, bolong-eta
• Thailand: tako-na.

Origin and geographic distribution

Diospyros consists of over 300 species and occurs throughout the tropics. Some 170 species have been recognized within the Malesian region; 70 species occur within Peninsular Malaysia and about 100 in Indonesia.

Uses

In South-East Asia, the fancy wood of black and streaked ebonies is in great demand for high quality sculptures and carving. It is also valued for furniture, cabinet work, interior fittings, fans, decorative articles, turnery, brushware, household utensils, tool handles, machete handles and sheaths, decorative veneer, musical instruments (e.g. pianoforte keys, stringholders in violins), toys, chisels, bowling alleys and pins, canes, inlaying, but also for boxes, construction (posts, poles) and bridges. The light-coloured wood is used for furniture, pallets and other utility purposes. The sapwood of several species is reported to be strong and tough and is used for tool handles and shoe trees.

The fruits of many Diospyros species are edible; the most important fruit trees are D. blancoi, D. digyna Jacq. and D. kaki L.f. The unripe fruits of a few species (D. malabarica (Desr.) Kostel. var. malabarica and var. siamensis (Hochr.) Phengklai, and D. mollis Griffith) are used to dye cloth black and for tanning nets and sometimes hides. The tannin in young fruits has medicinal uses, as does an extract of the bark. Fruits are also used as a source of fish poison. D. malabarica is sometimes planted as an ornamental tree.

Production and international trade

The timber of D. celebica was already being exported from Sulawesi in the 18th century. It is reported to be the most valuable timber species in Indonesia. Around 1920 exports were about 2300 m³/year, increasing to 8200 m³in 1928, and from then on were 6000 m³/year on average. In 1973 exports peaked at 26 000 m³, and in 1978 were still 23 000 m³. By then, stands had been heavily depleted and exports decreased considerably.

The export of white Diospyros wood ("kayu malam") from Sabah was about 1060 m³ in 1992 (86% as sawn timber, 14% as logs) with a total value of US$ 500 000 (US$ 540/m³ for sawn timber and US$ 70/m³ for logs). In Papua New Guinea, ebony also fetches high prices and is classified as very high quality wood; the export of logs is banned. Most of the ebony timber is exported to Japan, but smaller amounts are sold to Europe and the United States.

Properties

Black and streaked ebony are heavy, hard and strong woods. The heartwood is dark brown or black and may have reddish stripes, sometimes with pale green, distinctly demarcated from the usually wide sapwood which is yellowish-white to pale reddish-brown. The density is 640-1270 kg/m³ at 15% moisture content. The grain is straight to shallowly interlocked, texture fine to very fine and even. The wood is lustrous and has no distinct odour or taste.

At 15% moisture content, the modulus of rupture is c. 110 N/mm², modulus of elasticity 14 700 N/mm², compression parallel to grain 60 N/mm², shear 6 N/mm², cleavage 49 N/mm radial and 67.5 N/mm tangential, Janka side hardness 6420 N and Janka end hardness 7205 N.

The rates of shrinkage are moderate to high: from green to 15% moisture content up to 5.5% radial and 8.7% tangential, and from green to oven dry 6.2-8.7% radial and 7.8-13.3% tangential. Black and streaked ebony is difficult to dry; it may develop deep checks and has a tendency to warp and cup. It is recommended to convert the logs in green condition to small sizes and dry slowly. For kiln drying, a temperature of 30-50C and corresponding relative humidity of 88% to 31% are recommended.

The heartwood is generally difficult to work with hand and machine tools because of its high density, especially when air dry. It dulls tool edges and the wood requires considerable pressure bar loading and power in sawing; stellite-tipped saws are necessary for good results. The wood is somewhat brittle but saws to a good finish. It turns and planes well, taking a high polish; to plane wood with a slightly interlocked grain the cutting angle must be reduced to prevent the grain picking up. Pre-boring is necessary for nailing and screwing, but the wood holds nails and screws fairly well. It is reputed to be difficult to glue. Very beautiful veneer can be made by slicing, but pretreatment is required; the veneer is usually used as face veneer.

The heartwood of black and streaked ebony is very durable. The service life in contact with the ground under tropical conditions is over 25 years. Sapwood is not durable when exposed or in contact with the ground but is durable when used indoors. The wood may be moderately susceptible to dry-wood termites and Lyctus beetles. The heartwood is extremely resistant to preservative treatment and the sapwood is moderately resistant.

Wood of D. celebica contains 46.5% cellulose, 28.5% lignin, 18.5% pentosan, 1.7% ash and no silica. The solubility is 7.1% in alcohol-benzene, 2.0% in cold water, 4.1% in hot water, and 11.1% in a 1% NaOH solution. The energy value is about 19 500 kJ/kg. The wood dust sometimes causes dermatitis.

White Diospyros wood is a medium-weight hardwood. The heartwood is greyish or yellowish-white to buff-coloured but often with a streaky or black core up to 10 cm in diameter; it is not distinctly demarcated from the sapwood. The density is (440-)540-945(-1065) kg/m³ at 15% moisture content. Most properties of the wood are comparable with black and streaked ebony, but the wood usually seasons more easily (although slowly), works more easily, is less durable and more easy to treat with preservatives.

Description

Evergreen, usually dioecious or sometimes monoecious or polygamous shrubs or small to large trees up to 40(-50) m tall; bole branchless for up to 24 m, up to 70(-85) cm in diameter, usually without buttresses, though if present these are short, up to 2(-4) m high; crown monopodial, with branches in pseudowhorls; bark surface smooth, fissured, or cracked, black, hard and brittle.

• Leaves alternate, distichous, simple, pinnately veined, without stipules.
• Inflorescence axillary or cauliflorous on older branches or rarely on the trunk, cymose, 1-many-flowered, multi-bracteate.
• Flowers usually unisexual, actinomorphic, 3-5(-8)-merous; pedicel articulate; sepals united at base, sometimes free, the lobes valvate or imbricate, persistent in fruit; petals basally united into a tube, with patent lobes; stamens (3-)12-20(-100), often inserted at the base of the corolla tube, sometimes on the receptacle, rarely higher up on the corolla tube, often in 2 whorls, anthers basifixed, 2-locular, longitudinally dehiscent, staminodes usually present in female flowers; ovary rudimentary in male flowers, in female ones superior, multilocular, 2-8-carpellate, each carpel corresponding to a 2-ovulate locule or more commonly to a pair of uni-ovulate locules, resulting from the presence of false septae, ovules pendulous, styles 2-8.
• Fruit a berry, with fibrous to fleshy pericarp.
• Seeds 1-16, with a thin leathery testa, and thick, horny, smooth or ruminate endosperm; cotyledons leafy, flat.
• Seedling usually with epigeal germination, sometimes hypogeal (cotyledons remaining within the seed-coat and hypocotyl not elongated) or with the durian type of germination (cotyledons remaining within the seed-coat and hypocotyl elongated); first 2 leaves opposite or alternate, subsequent leaves alternate.

Wood anatomy

• Macroscopic characters:

Heartwood black (e.g. D. ebenum) or black with pale yellow streaks (D. ferrea) or black with pinkish streaks (D. blancoi), or practically without dark-coloured heartwood and grey to almost white (e.g. D. papuana), usually distinctly demarcated from the yellowish-white or pinkish sapwood. Grain straight or shallowly interlocked. Texture fine; wood lustrous. Growth rings usually indistinct; vessels in the sapwood often dark stained; parenchyma reticulate, visible with a hand lens; ripple marks uncommon but present in some species.

• Microscopic characters:

• Growth rings usually indistinct but, if present, marked by flattened fibres.
• Vessels diffuse, the number varying with species, solitary (percentage varying with species) and in radial multiples of 2-5(-7), 80-190μm in tangential diameter; perforations simple; intervessel pits non-vestured, alternate, fine, 3-5μm in diameter, often with coalescent apertures; vessel-ray and vessel-parenchyma pits almost similar to intervessel pits; vessels filled or coated with dark-coloured substances; tyloses often present.
• Fibres 650-1350μm long (D. ferrea), mostly thick-walled, with numerous, small slit-like pits.
• Parenchyma scanty paratracheal and abundant apotracheal, reticulate, in bands 1-2 cells wide, often seemingly in long concentric bands; in 4-8-celled strands.
• Rays 11-16/mm, uniseriate (D. blancoi, D. ebenum), 1-2-seriate (D. ferrea) or 1-3(-5)-seriate (D. papuana), 260-1500μm high, heterocellular with low or high marginal rows of upright cells (Kribs type heterogeneous II, rarely I).
• Prismatic crystals present, scarce in ray cells and scarce to fairly numerous in chambered axial parenchyma cells, in chains of 4-5, sometimes up to 20.
• Silica bodies absent.

Species studied: D. blancoi, D. ebenum, D. ferrea, D. papuana.

Growth and development

Most Diospyros species have epigeal germination, but in D. maingayi germination is of the "durian type", whereas D. pendula shows hypogeal germination. In the latter food reserves are transferred to the taproot (which becomes swollen) during the first weeks of growth. In some species from Peninsular Malaysia, the cotyledons are shed almost immediately after emergence without ever turning green, thus not exploiting the photosynthetic advantage of epigeal germination; this phenomenon is only known for Diospyros. However, the first two leaves develop precociously as if to compensate for the early loss of the cotyledons.

The growth of young plants is slow and in a plantation trial of D. celebica under teak in Java the young trees were 30-100 cm tall after 2 years, 40-190 cm at the age of 4 years, 60-300 cm at the age of 6 years, and 70-450 cm when 8 years old. The mean annual height increment was 90 cm during the first 10 years, then it decreased, whereas the mean annual diameter increment was 1.5 cm during the first 20 years then decreasing to 0.5 cm. Diameters recorded for D. ebenum at different ages are: 46 cm when 25 years old, 91 cm when 75 years old, 137 cm when 135 years old and 183 cm when 200 years old.

All Diospyros species are characterized by the architectural growth model of Massart, i.e. an orthotropic, monopodial trunk with rhythmic growth producing regular tiers of branches.

Trees of D. celebica may already start to flower and fruit at the age of 5-7 years. The period from anthesis to fruit ripening takes 6 months in D. celebica, 9-11 months in D. maingayi and 5 months in D. pendula. The seeds are dispersed by birds, bats and monkeys.

Other botanical information

The large genus Diospyros has been subdivided into 5 subgenera: Eudiospyros (which should actually be called Diospyros), Maba, Hierniodendron, Cargillia, and Mabacea. The first two are subdivided further into many sections. The distinction between the subgenera and sections is not always clear. Several cultivars of species producing edible fruits are known, including cultivars with seedless fruits.

Ecology

Most ebony species occur in primary or rarely secondary lowland to hill evergreen rain forest up to 900 m altitude. Some species occur in lower montane or montane forest up to 1700 m, in peat-swamp forests, in kerangas forest or on limestone hills and ultrabasic soils. The important ebony-producing species, however, are mainly confined to lowland and hill rain forest. Exceptions are D. pilosanthera, which is often found in peat-swamp forest, and the important D. celebica, which grows naturally in humid as well as in markedly seasonal climates, where it occurs as a constituent of the rain and monsoon forest. D. celebica grows on a variety of soils, e.g. latosols, calcareous soils, and podzolic soils.

Propagation and planting

Propagation is from seed or stumps. Species producing edible fruits may also be propagated by air layering, budding, grafting or separation of root suckers. Ebony is reported to coppice well.

Seed should be extracted from fruits harvested from the tree when mature and dark brown, or collected from the ground. Pulp and seed can be separated by maceration. One kg contains about 9000 seeds of D. ebenum, about 800 of D. celebica from South Sulawesi and about 1150 of D. celebica from Central Sulawesi. Seed is recalcitrant and looses its viability very rapidly, although when kept in the ripe fruits it can be stored for longer. Seed sun-dried for three days does not germinate. Soaking in water for 24 hours slightly improves the germination rate and slightly shortens the germination period. Seed should be sown in shaded beds. When seed of D. celebica was sown one day after being collected, germination was 85% in 17-65 days; when stored in wet charcoal powder during 12 days 70% germination was achieved, whereas after storage for 20 days the germination rate dropped to 28%. For D. maingayi in Malaysia 55% of the seed germinate in 1-5 months, but for most Diospyros species 45-95% of the seed germinate in 2-8 weeks. Seed sown with the pulp still attached takes somewhat longer to complete germination. Freshly germinated seed requires a high humidity so that the testa remains soft and can be shed. Otherwise, young seedlings may have their cotyledons and epicotyl trapped in the testa; this often occurs in seedlings of D. pendula and D. sumatrana, even when watered twice a day. When planted or transplanted, care should be taken not to harm the taproot. Stumps of 1-3 cm diameter showed 85% survival after being planted out. In Sulawesi, seedlings of 6-7 months old and 20-30 cm tall and wildlings of 15-20 cm tall were successfully used for planting. Seedlings or stumps should be planted under light shade (e.g. under Pinus merkusii Junghuhn & de Vriese or Paraserianthes falcataria (L.) Nielsen). D. celebica can be planted at 1 m × 2 m under shade of Leucaena leucocephala (Lamk) de Wit planted 2-3 years earlier, or by planting between rows of Leucaena leucocephala. Seedlings at least one year old may be planted in the open. In Sulawesi, enrichment planting of secondary forest by line or strip planting has been successfully conducted with a spacing of about 7.5 m × 4 m.

Silviculture and management

In Indonesia, natural forest with Diospyros spp. is selectively cut under the Indonesian selective felling and replanting system (TPTI). Natural regeneration is enhanced by clearing the undergrowth and by opening up the canopy after logging. Diospyros spp. are generally shade tolerant and very persistant growers. Seed germinates readilyif sufficient light is available. In forest where commercial tree species grow slowly and where it is difficult to find trees with a diameter at breast height of over 50 cm, the diameter limit for selective felling may be lowered to 35 cm, leaving 25 healthy smaller trees per ha with a diameter of 15-34 cm. This is the case in mixed D. celebica forest. Enrichment planting is required if logged-over stands are poorly stocked by natural regeneration. The cutting cycle is extended to 45 years instead of the 35 years generally adopted in Indonesia.

Diseases and pests

No serious diseases or pests attack D. celebica plantations. Seed from fallen fruits is frequently infested by the fungus Penicilliopsis clavariaeformis, which is specific to ebony seeds.

Harvesting

Before 1972 the diameter limit for D. celebica in Indonesia was 55-60 cm. This regulation was followed consistently, because smaller logs, weighing less than 700 kg could not be exported. The diameter limit has now been lowered to 35 cm, although small logs may have insufficient streaked ebony heartwood. People felling the trees prefer to use an axe instead of a saw, as the wood dust irritates the skin, eyes and respiratory organs. After felling the sapwood is removed, because only the heartwood is marketed. Large-diameter D. celebica and D. rumphii trees are reported to be hollow for a large part.

Yield

So far, D. celebica has not been planted on a large scale, but in trial plantations in West Java the estimated mean annual increment is 6 m³/ha. In natural forest D. celebica trees are very scattered and irregular, but locally in Central Sulawesi the estimated timber volume of ebony is 60 m³/ha. Reputedly, the more stony and rough the site, the more heartwood is present. The heartwood in D. celebica trees measures 10-25 cm in diameter in logs of 60 cm diameter.

Genetic resources

The logging of black or streaked ebony-producing Diospyros species should be carefully controlled and monitored. The resources have been depleted for centuries, because the wood has long been in great demand. D. celebica was once widespread in Sulawesi, but has now become comparatively rare, especially in South Sulawesi, and has been proposed for inclusion in Appendix II of the CITES convention (which means controlling the timber trade). Small trial plantations have been established in Indonesia, e.g. in West Java. D. philippinensis is a protected species in the Philippines.

Prospects

The establishment of large-scale plantations of ebony seems promising as the timber is so highly valued. This should be coupled with conservation of the existing resources. Tree improvement programmes may result in superior stock for planting. However, the trees grow comparatively slowly and it takes a long time to produce sufficient amounts of heartwood. This makes the economic feasibility dubious, as very long cutting cycles are needed and the timber production will be comparatively low.

Literature

• All Nippon Checkers Corporation, 1989. Illustrated commercial foreign woods in Japan. Tokyo. pp. 143-144.
• Alrasjid, H., 1985. Percobaan penanaman kayu eboni (Diospyros celebica) di bawah tegakan jati di Jawa [Plantation trial of ebony (Diospyros celebica) under a teak stand in Java]. Buletin Penelitian Hutan 464: 23-37.
• Bolza, E. & Kloot, N.H., 1966. The mechanical properties of 81 New Guinea timbers. Division of Forest Products Technological Paper No 41. Commonwealth Scientific and Industrial Research Organization, Melbourne. pp. 16-19.
• Burgess, P.F., 1966. Timbers of Sabah. Sabah Forest Records No 6. Forest Department Sabah. pp. 235-243.
• Malaysian Timber Industry Board, 1986. 100 Malaysian timbers. Kuala Lumpur. pp. 54-55.
• Martawijaya, A., Kartasujana, I., Kadir, K. & Prawira, S.A., 1986. Indonesian wood atlas. Vol. 1. Forest Products Research and Development Centre, Bogor. pp. 32-36.
• Ng, F.S.P., 1991. Manual of forest fruits, seeds and seedlings. Vol. 1. Malayan Forest Record No 34. Forest Research Institute Malaysia, Kepong. pp. 61-62, 319-327.
• Phengklai, C., 1981. Ebenaceae. In: Smitinand, T. & Larsen, K. (Editors): Flora of Thailand. Vol. 4. TISTR Press, Bangkok. pp. 281-392.
• Reyes, L.J., 1938. Philippine woods. Technical Bulletin 7. Commonwealth of the Philippines, Department of Agriculture and Commerce. Bureau of Printing, Manila. pp. 404-415.
• Soerianegara, I., 1967. Beberapa keterangan tentang djenis-djenis pohon eboni Indonesia [Some information on the Indonesian ebony tree species]. Rimba Indonesia 12(2-4): 29-54.