Dialium (PROSEA)

Plant Resources of South-East Asia
Introduction

List of species

Dialium L.

Protologue: Mant. pl. (Syst. Nat. ed. 12, Vol. 2): 3 (1767).

Family: Leguminosae

Chromosome number: x= probably 14 (2n= 28 counted for three African species)

Trade groups

Keranji: heavy hardwood, e.g. Dialium indum L., D. platysepalum Baker, D. procerum (v. Steenis) Stey.

Vernacular names

Keranji

velvet tamarind, tamarind plum (En)
Indonesia: kranji (Sumatra)
Burma: taung-kaye
Cambodia: krâlanh, krâlanh lomië
Laos: kheng
Thailand: kayi-khao (peninsular), yi-thongbung (Nakhon Si Thammarat)
Vietnam: xoay, xây, nhội.

Origin and geographic distribution

Dialium has a pantropical distribution and consists of about 30 species. Of these, 7 species occur within the Indo-Malesian area whereas some 20 are present in Africa and Madagascar and only 1 in Central and South America. Within Malesia the genus is confined to the western half (Peninsular Malaysia, Sumatra, Java and Borneo) and does not cross Wallace's line, an important biogeographical barrier which lies between Borneo and Sulawesi. The absence from eastern Malesia and areas further east and south implies that the Malesian species have a western origin.

Uses

Keranji is a good general-purpose timber. Because of its moderate natural durability and strength it has a limited suitability for purposes in contact with the ground such as poles and piles, fences, railway sleepers, telegraph and power transmission posts and cross-pieces, bridges, and sledges used in logging. Locally the timber is used for ship and boat building and for vehicle bodies (framework and floor boards). Keranji is chiefly used in construction, e.g. as mine timber, for joinery, beams, door and window frames, sills, posts, joists, rafters, fender supports, columns, and various parts of staircases. Keranji is also very suitable for purposes where toughness and resilience is required, such as gymnasium equipment, agricultural implements, tool handles (heavy impact), mallets, oil presses and industrial flooring. Due to the attractive sheen which is usually dark red or brown, keranji is suitable for decorative panelling, cabinet and furniture making, toys and novelty items. Due to the hardness of the timber it is not recommended for veneer and plywood production, neither is it suitable for particle board or pulp production.

The pulpy fruits of some species are edible and are generally sold dry. The bark is rich in tannins but has been used for tanning on a very limited scale. The bark has also been used as a substitute for betel nut and medicinally against diarrhoea and herpes.

Production and international trade

Keranji is especially exported from Sabah and Sarawak to Japan, but in fairly small amounts. The export of round logs from Sabah in 1987 was 63 500 m³with a value of US$ 4 million (US$ 63/m³), but in 1992 it was only 17 000 m³(logs) and 13 500 m³(sawn timber) with a total value of US$ 3.5 million. Export of keranji is not significant elsewhere. During the late 19th Century and the beginning of the 20th Century, logs were exported from Peninsular Malaysia to China, but when the number of large trees diminished, keranji timber lost its importance.

Properties

Keranji is a heavy, hard and fairly strong timber. The heartwood is generally golden brown to reddish-brown, becoming darker upon exposure, and clearly distinct from the lighter (white to yellowish-white) sapwood. The planed surface is usually lustrous; the radial surface often shows a stripe figure, the tangential surface a faint zig-zag design. The density is 750-1100(-1250) kg/m³at 15% moisture content. The grain is generally interlocked or wavy, sometimes straight, texture fine to moderately coarse and even.

At 15% moisture content the modulus of rupture is 134-166 N/mm², modulus of elasticity 19 400-20 100 N/mm², compression parallel to grain 72-91 N/mm², shear 16-23 N/mm², cleavage c. 56 N/mm radial and 67 N/mm tangential, and Janka side hardness 10 600-11 300 N.

The rates of shrinkage are usually high, from green to 15% moisture content (1.0-)3.7% radial and (1.7-)6.6% tangential. Keranji dries moderately slowly. During drying the wood is liable to split, and there is a tendency to moderate surface and end checking, and to slight warping. Warping and checking can be prevented by quarter-cut sawing and slow and careful seasoning techniques. Boards 15 mm and 40 mm thick take respectively 2 and 6 months to air dry. In Malaysia kiln schedule E is recommended. Seasoned wood is stable in service.

Keranji is difficult to saw, especially when seasoned. The wood blunts sawteeth and cutter edges rapidly, and chromium-plated teeth are recommended. It produces a moderately smooth finish in planing, but it has tendency to grain pick-up on radial faces; a 20cutting angle is recommended. The wood turns well. Pre-boring is needed for nailing and screwing.

The wood is usually rated as moderately durable in contact with the ground under tropical conditions. Graveyard tests with stakes in Malaysia showed a maximum service life in contact with the ground of 5.5 years. Logs, particularly the sapwood, may be attacked by pinhole borers, marine borers and termites. Under temperate conditions keranji is durable in exposed situations or in contact with the ground. The heartwood is very difficult to impregnate.

Description

Evergreen or more rarely deciduous, unarmed, small to large trees of up to 45 m tall or occasionally large shrubs; bole columnar but often slightly twisted above, branchless for up to 21 m, up to 120 cm in diameter and usually prominently buttressed with plank-like forked buttresses; bark surface generally smooth, often rugose or rugulose and occasionally flaking with small, thick scales, rarely lenticelled and hoop-marked, inner bark hard, brown, finely mottled, producing a little clear exudate soon turning red, sapwood hard, cream to yellowish-brown, ripple-marked; twigs terete, lenticellate, generally hairy when young and glabrescent; indumentum consisting of simple, patent or adpressed hairs.
Leaves alternate, either unifoliolate or simply imparipinnate; stipules small, linear-triangular, very early caducous; leaflets alternate or sometimes opposite to subopposite, entire, subleathery, hairy above when young, indumentum beneath generally persistent.
Inflorescences axillary or terminal, consisting of many-branched and many-flowered panicles; bracteoles very early caducous.
Flowers bisexual, irregular; sepals (in Asiatic species) 3 or 5; petals (in Asiatic species) 0 (5 in D. modestum ), when present not conspicuous, clawed; disk present or absent; stamens (in Asiatic species) 2 or 6 (5 in D. modestum), anthers basifixed, dehiscing by longitudinal slits; ovary sessile or sometimes shortly stipitate, with (1-)2 ovules, densely adpressed hairy, style solitary, excentric or central, with a punctiform stigma.
Fruit an indehiscent, ellipsoid or ovoid to subglobose or slightly compressed berry-like pod, hard, brittle and glabrescent outside, sometimes glaucous, the 1-2 seeds entirely embedded in a dry mealy reddish-brown pulp.
Seed usually reniform with a smooth testa, usually dark brown when dry, areoles absent, endosperm present.
Seedling with epigeal germination; hypocotyl elongated; cotyledons large, succulent; first two leaves opposite.

Wood anatomy

Macroscopic characters

Heartwood generally uniformly brown or reddish-brown when freshly cut, often darkening on exposure, sometimes becoming almost black with age, distinctly demarcated from the creamy white or yellowish sapwood.
Grain generally interlocked or wavy, sometimes straight.
Texture fine to moderately coarse.
The radial surface usually displays a ribbon figure, tangential surface with dark markings or ripple marks caused by storied elements, especially rays and parenchyma.
Vessels not visible to the naked eye.

Microscopic characters

Growth rings absent.
Vessels diffuse, 3-7(-11)/mm², 50-70% solitary and in radial multiples of 2-3 (sometimes more), round to oval, average tangential diameter (75-)120-190(-390)μm; perforations simple; intervessel pits alternate, 7-11(-13)μm, usually vestured; vessel-ray pits similar to intervessel pits; helical thickenings absent; whitish, yellowish or yellowish-brown gum-like deposits usually present, tyloses usually absent.
Fibres (800-)900-1100(-1500)μm long, non-septate, usually thick-walled and with very narrow lumen, with simple pits.
Parenchyma abundant, basically apotracheal, banded, usually one side of the band touching the vessels, bands usually 2-3 cells wide, usually broken or discontinuous and irregularly spaced from each other, 3-5 bands per radial mm, in (3-)4(-8)-celled strands.
Rays 9-11(-18)/mm, (1-)2-3(-4)-seriate, (100-)210-320(-560)μm high, storied, essentially homocellular with procumbent cells but sometimes marginal cells twice as high as body cells.
Prismatic crystals present in chambered axial parenchyma cells.
Silica bodies sometimes present in axial parenchyma cells (e.g. D. kunstleri ).

Species studied: D. indum, D. kunstleri, D. platysepalum.

Growth and development

During germination, the testa breaks at soil level, exposing the creamy white, thick cotyledons. As the seedling grows, the hypocotyl elongates and lifts the cotyledons above the soil level, leaving the testa behind on (or sometimes partly in) the soil. The clasping cotyledons then spread and do not change colour immediately but remain creamy white for some time until the first leaves start to develop. Then the cotyledons turn green and remain attached to the hypocotyl until the first leaves are fully developed.

Keranji trees are moderately slow growers. A tree of D. platysepalum in Malaysia reached a bole diameter of 49 cm after 40 years.

The fruits are dispersed by animals (e.g. monkeys) which like to eat the pulp embedding the seeds. However, the fruits are also capable of being transported by water, since they float. Transport by sea currents may lead to long-distance dispersal.

Other botanical information

The genus Dialium belongs to the subtribe Dialiinae together with 12 other genera, among which is Koompassia (kempas and tualang). The genus is very heteromorphic in the number of floral parts, but can be accurately defined by its characteristic fruit. The genera Arouna, Dansera and Uittienia have been merged with Dialium and recognized as separate subgenera. This resulted in 4 subgenera: Dialium, Arouna (Aublet) Stey., Dansera (v. Steenis) Stey. and Uittienia (v. Steenis) Stey., respectively. Dialium subgenus Arouna is confined to tropical Africa and Madagascar. This subdivision is confirmed by anatomical characters as well as pollen morphology. The merging of Uittienia (comprising only one species: U. modesta v. Steenis) with Dialium is, however, debatable because of its unique fruit characters.

Ecology

Most species of keranji inhabit primary rain forest. Because of the hardness of the wood, specimens are often left by loggers or in shifting cultivation and they become relicts in secondary forest. Keranji occurs scattered, not gregarious as do many other related species, sometimes along river banks and in low-lying swampy areas and peat swamps but also on well-drained land. Keranji is generally found in the lowlands, but occasionally up to 1150 m altitude.

Propagation and planting

Germination of untreated seeds of D. platysepalum is staggered over a period of about 17 months; 75% of the seeds have germinated after 50 weeks. Mechanical scarification (cutting with secateurs on one side of the seed) is the best treatment to promote germination. About 70% of the scarified seeds germinate within a month. Treatment with concentrated sulphuric acid (H₂SO₄) is much less effective.

The seeds can be sown in beds containing a mixture of equal parts of forest topsoil and river sand. They are buried just below the soil surface and a layer of sawdust is spread on top. The beds should be shaded and watered regularly (twice a day).

There are no records of the establishment of plantations, except for D. cochinchinense, which is reported to be planted in villages in northern Peninsular Malaysia for its edible fruits.

Harvesting

Keranji trees are difficult to cut because of the dense wood. They often have tall buttresses, and these have to be slashed before cutting as much wood would be wasted if the trunk were cut above the buttresses. This, and its scattered occurrence, make keranji timber not very valuable commercially.

The logs cannot be transported by river because they sink in water; they are therefore transported over land.

Genetic resources

Keranji trees are found scattered in the forest. Large-scale logging may endanger the individual species.

Prospects

Two facts discourage exploitation of keranji trees: they occur scattered in primary forest, and are difficult to cut because of their hardness. Moreover, when keranji trees are found near villages, people prefer gathering the fruits above cutting the trees. However, timber is becoming more and more valuable, and there is a tendency to view any timber species left in the forest as worth harvesting. In addition, keranji wood is very suitable for special uses such as tool handles, cross ties and flooring. Therefore, research is desirable, especially on silvicultural and management aspects.

Literature

Ani Sulaiman & Lim, S.C., 1990. Malaysian timbers - keranji. Timber Trade Leaflet No 112. Malaysian Timber Industry Board, Forest Research Institute Malaysia. 7 pp.
Burgess, P.F., 1966. Timbers of Sabah. Sabah Forest Records No 6. Forest Department Sabah, Sandakan. pp. 350-355.
Cockburn, P.F., 1976. Trees of Sabah. Vol. 1. Forest Department Sabah, Kuching. pp. 163--169.
Desch, H.E., 1954. Manual of Malayan timbers. Vol. 1. Malayan Forest Records No 15. Malaya Publishing House Ltd., Singapore. pp. 274-278.
Keating, W.G. & Bolza, E., 1982. Characteristics, properties and uses of timbers. Vol. 1. South-east Asia, northern Australia and the Pacific. Inkata Press Proprietary Ltd., Melbourne, Sydney & London. pp. 119-120.
Rahman bin Chik, E.A. & Choong Ngok, W., 1975. Preliminary studies on some Malaysian timbers for plywood manufacture. Part 10 - keranji (Dialium platysepalum). Malaysian Forester 38: 17-23.
Rojo, J.P., 1982. Studies in the genus Dialium (Cassieae -Caesalpinioideae). Unpublished thesis. University of Oxford. 282 pp.
Sabah Forestry Department, 1989. Forestry in Sabah. pp. 130, 137.
Sabariah, A., 1978. Pretreatment of Dialium (keranji) and Sindora (sepetir) seeds to promote germination. Malaysian Forester 41: 26-28.
Whitmore, T.C., 1983. Leguminosae, Dialium. In: Whitmore, T.C. (Editor): Tree flora of Malaya. 2nd edition. Vol. 1. Malaysian Forest Records No 26. Longman Malaysia SDN Berhad, Kuala Lumpur. pp. 255-262.

Selection of species

Recently the genus was fully revised by Rojo but his results have not been published to date. He has merged many of the formerly recognized taxa, because they lack distinctive characters. The treatment of the species below follows Rojo's revision and hence many names are treated here as synonyms of others for the first time.

Authors

J.P. Rojo (general part, wood anatomy, selection of species),
D.S. Alonzo (properties)