Neobalanocarpus (PROSEA)

Plant Resources of South-East Asia
Introduction

Protologue: Fl. Malesiana, ser. I, 9: 388 (1982).

Family: Dipterocarpaceae

Chromosome number: x= 7; 2n= 14

Trade groups

Chengal: heavy hardwood, a single species, Neobalanocarpus heimii (King) P. Ashton, Fl. Malesiana, ser. I, 9: 388 (1982), synonym: Balanocarpus heimii King (1893).

Vernacular names

Chengal

Malaysia: chengai, penak
Thailand: takhian-chan, takhian-chantamaeo (peninsular), chi-ngamat (Narathiwat).

Origin and geographic distribution

Chengal occurs throughout Peninsular Malaysia and in the southernmost part of peninsular Thailand, where it may be extinct.

Uses

Chengal is a very durable and heavy timber and is therefore suitable for many heavy-duty purposes. It was the standard timber for durable heavy construction in Peninsular Malaysia and can be applied both indoors and outdoors. It is suitable for railway sleepers, piles, bridges, telegraph and power-line poles, vats, casks, tanks and frameworks, especially for wooden houses but even for e.g. lorries and buses. Indoors it is used for flooring (medium and heavy duty) and joinery. Chengal has been used in constructing wharves, ships and boats both in fresh and salt water conditions, with good results. Despite its hardness it is used for carving; carving is comparatively easy, especially when the wood is fresh.

Good-quality resin, known in Peninsular Malaysia as "damar penak", can be obtained by wounding the tree. It has been used only on a limited scale in the manufacture of certain classes of varnish.

Production and international trade

Chengal is a popular and well-known timber of Peninsular Malaysia. For the period 1986-1990 the average domestic log and sawn timber prices in December were US$ 123/m³ and US$ 242/m³ respectively. In this period Peninsular Malaysia exported an average of 28 500 m³of sawn timber annually, while 69 000 m³ or 71% was consumed domestically. In 1992 the export of sawn chengal timber was 8000 m³ with a value of US$ 2.1 million. Malaysia is the only exporter of chengal sawn timber; Thailand is the main importer. Because collecting the dammar is fairly labour-intensive, an attempt to create a firm trade has failed.

Properties

Chengal is a heavy hardwood. The sapwood is pale yellow with fine yellow ripple marks visible to the naked eye, distinctly demarcated from the heartwood. The colour of the heartwood is yellow-green when freshly cut, weathering to dark tan-brown. The density is 915-980 kg/m³ at 15% moisture content. The grain is interlocked, texture moderately fine and even.

At 15% moisture content the modulus of rupture is 149 N/mm², modulus of elasticity 19 600 N/mm², compression parallel to grain 75 N/mm², compression perpendicular to grain 12 N/mm², shear 14 N/mm², cleavage 55 N/mm radial and 49 N/mm tangential and Janka side hardness 9480 N. See also the table on wood properties.

Shrinkage is fairly low to moderate, averaging 1.1% radial and 2.6% tangential from green to 15% moisture content. The timber dries rather slowly. Air seasoning does not develop serious defects except for end and surface checks. Boards of 40 mm thick take about 6 months to air dry. The timber is subject to fungal infestation if stacked in badly ventilated locations. Chengal also kiln dries slowly and is extremely prone to surface checking. Radial boards tend to dry much slower than tangential boards. It takes 30 days for 25 mm thick boards to kiln dry from green to 10% moisture content. It is recommended that kiln-drying schedule B (Malaysia) is used and the timber should be air dried to below 30% moisture content before kilning.

Air-dried chengal is slightly difficult in rip-sawing but moderately easy in cross cutting especially in relation to other timbers of the same class. This ease may be partly attributed to the low content of silica and partly to the comparatively slight interlocking of the grain. Planing, boring and turning are rated as easy, giving a smooth finish. The resistance to splitting when nailed is rated as very poor.

Chengal is classified as naturally durable and is normally very resistant to termite attack and fungal infestation. Under graveyard test conditions, untreated stakes of 50 mm × 50 mm × 600 mm lasted 9 years. Treated stakes of the same size and under the same test conditions lasted about 19 years. Untreated railway sleepers (238 mm × 125 mm × 1950 mm) laid under severe environmental conditions had an average life of 19 years. Chengal is rated as moderately difficult to treat with preservatives. Using test sticks of 900 mm × 65 mm × 65 mm, and applying the standard open tank treatment using a mixture of equal parts of creosote and diesel fuel, an average absorption of 68 kg/m³ was obtained.

After 6 hours extraction, chengal flour was found to have 23% hot water extractives and 32.6% methanol extractives. Impregnation of these extractives into rubberwood conferred a certain degree of resistance to the fungus Coriolus versicolor, while chengal wood blocks extracted with water or methanol retained their resistance to the same fungus.

When dry-wood termites (Cryptotermes cynocephalus) are exposed to wood blocks and wood extractives of N. heimii and the light red meranti Shorea ovalis (Korth.) Blume, the termites' survival and wood consumption is significantly higher in the meranti than in chengal. The bioassays with sawdust, extracted sawdust and treated filter paper further indicated that the dry-wood termites survived significantly better on S. ovalis than on N. heimii test material.

Early reports of a comparatively poor resistance of chengal to salt water have been contradicted by more recent results.

The best grades of the dammar are pale and transparent but it darkens when stored. It is a usable material for making spirit-varnish, normally with turpentine or naphtha as a solvent. The usual melting point of 90-100° C and its hardness make it superior to other dammars of the same type. The defect of cloudiness in no way detracts from the utility of the varnish, which is to produce a lustrous coating.

Description

A large tree, sometimes over 60 m tall; bole straight and cylindrical, unbranched for 30 m or more (but sometimes irregular and low-branched), with an average diameter of 90 cm, prominently buttressed; outer bark hard, shallowly irregularly longitudinally fissured, becoming shaggy in old specimens, falling in long scales, dark-coloured; inner bark 1.5 cm thick, fibrous, yellow, exuding a clear, colourless or golden dammar; twigs slender, ribbed, glabrescent.
Leaves alternate and simple, leathery, elliptical-lanceolate, 7-17 cm × 2.3-5 cm, acuminate, at base rounded to cuneate, unequal, pinnately veined with 9-12 pairs of ascending and arched veins, slightly sunken on the upper surface, but prominent and glabrous or only sparsely pubescent on the lower, tertiary venation reticulate-scalariform; petiole 5-10 mm long; stipules narrowly oblong, to 12 mm long, spreading, early caducous.
Inflorescence paniculate, terminal or axillary, up to 9 cm long, singly branched, puberulent.
Flowers bisexual, actinomorphic, ovoid in bud, up to 4 mm × 3 mm; sepals 5, subequal, imbricate at base, broadly ovate, acute, outside caducous puberulent; petals 5, elliptical, cream-white or greenish-yellow, outside densely buff pubescent; stamens 15, glabrous, filaments slender and tapering, anthers linear-oblong, yellow, with small, straight appendages; ovary single, ovoid, glabrous, surmounted by a filiform style with a minute stigma.
Fruit an oblanceolate, cylindrical nut on a short, stout stalk, up to 5.5 mm × 2.5 mm, shortly apiculate, shining, embraced at the base by a cup formed by the enlarged, woody, saccate sepals, the outer 2 of which are slightly smaller and thicker than the inner 3.
Seedling with epigeal germination; cotyledons very unequal, only the dorsal one reaching the apex of the nut; first 4-5 leaves in a whorl, subsequent ones arranged spirally.

Wood anatomy

Macroscopic characters

Heartwood dark brown, light yellow-brown when fresh; sapwood pale yellow and distinct from the heartwood.
Grain generally shallowly to deeply interlocked, rarely straight.
Texture fine; planed surface lustrous, often with vague stripe figure.
Growth rings indistinct or absent; vessels not visible to the naked eye, tyloses visible with hand lens; parenchyma barely visible with a lens, generally in very fine, short tangential lines, marginal parenchyma rarely present; rays visible with a lens, rather narrow and short; ripple marks distinct and visible to the naked eye.
Intercellular canals visible with a lens in long tangential rows appearing as white lines, sometimes infrequent.

Microscopic characters

Growth rings indistinct or absent.
Vessels diffuse, (7-)11-14(-18)/mm², often solitary, but occasionally in short radial multiples, 120-220μm in diameter, 400-700μm in vessel element length; perforation plates simple; intervessel pits alternate, vestured, circular to oval, 6-8μm; vessel-ray pits with much reduced borders to apparently simple, rounded or angular (occasionally horizontal to vertical and of two distinct sizes, sometimes difficult to find); tyloses common.
Vasicentric tracheids present.
Fibres 1.2-2.0 mm long, non-septate, thin- to very thick-walled, with simple to minutely bordered pits.
Axial parenchyma predominantly diffuse to diffuse-in-aggregates, occasionally scanty paratracheal to vasicentric, with 4-8 cells per parenchyma strand.
Rays 6-8/mm, 330-380μm in height, mostly heterocellular with 1(-3) rows of upright and/or square marginal cells, often procumbent, square and upright cells mixed throughout the ray, mostly 3-5 cells wide; sheath cells often present; all rays storied, 3 tiers/mm.
Prismatic crystals generally in ray cells (upright/square cells and procumbent cells), often not common.
Silica bodies absent.
Intercellular canals in long tangential lines, infrequent to occasional, often occluded with white deposits.

Growth and development

As in most Dipterocarpaceae, germination of chengal seeds is rapid, almost without any dormancy. Germination is similar to that in Hopea. The radicle extrudes from the apex of the nut, splitting it into 3 equal valves. Seedling leaves have very long drip-tips and are purple-bronze or bluish when young. Saplings are frequently sympodial in growth which is the result of their intermittent growth. Shoot elongation takes place in flushes during which several nodes and leaves are produced in rapid sequence. These periods alternate with dormancy, during which the apical bud is aborted. The branchlets are drooping.

Growth is comparatively slow. It is estimated that chengal will attain a diameter of 64 cm in 75 years under optimal conditions. A tree planted in Kepong (Peninsular Malaysia) had a diameter of 48 cm after 40 years.

Chengal populations flower sporadically. Usually years with heavy flowering and fruiting occur at intervals of several years. Flowering appears to take place over about 3 weeks at some time between November and May, and fruiting in January-June. As in most Dipterocarpaceae the flowers are fragrant. Pollination is by insects, most particularly honey bees. The only method of dispersal of the heavy, wingless seeds of chengal might be by rolling down hill slopes or by means of animals.

Other botanical information

The chief diagnostic features of chengal are the dark coloured, scaly bole, the exudation of transparent, almost colourless dammar, the yellow inner bark, the hard, pale yellow sapwood with fine ripple marks, the 15 stamens with slender filaments and short terminal appendages and the acorn-like, large, wingless fruits.

The taxonomic position of Neobalanocarpus is dubious but it is believed to be closely related to Hopea section and subsection Hopea. The highly irregular pattern of meiosis might be a reflection of hybridity which may account for the doubt about its taxonomic position.

The generic name Neobalanocarpus was invalidly published by Ashton in 1978 (a Latin description is lacking); the new combination of N. heimii was therefore also invalid. Later, in 1982, the generic and specific names were validated.

Ecology

Chengal is widespread in mixed dipterocarp forest below 1000 m, especially on well-drained friable soils on undulating land. In peninsular Thailand it occurs frequently in hill dipterocarp forest along slopes and in valleys, and is often found together with Shorea curtisii Dyer ex King.

Propagation and planting

Natural regeneration beneath parent trees is rarely abundant in virgin rain forest except on ridges in hill forest. The few seedlings usually encountered beneath a parent tree are capable of surviving for very long periods under dense shade, but light is required for further development. Well-established young trees are found in felling gaps, although they respond slowly to an opening in the canopy and readily become smothered. When very young, chengal seedlings are sensitive to drought and overexposure. Planting has been attempted in Peninsular Malaysia with indifferent results. Insects attacked the seedlings badly. Planting in open, unshaded conditions, in association with rubber, has failed. Planting in secondary forest was carried out successfully. The seedlings need shaded conditions.

The fruits are best stored at about 14° C. After storing the fruits at this temperature for 50 days with a loss of 18.7% of the original moisture content and application of a fungicide, they showed no damage. Further reducing of the moisture content to just over half of that of fresh fruits did not kill them either.

Diseases and pests

Chengal fruits are often attacked by a seed beetle, Coccotrypes graniceps, and its larvae. A Laspeyresia species (Lepidoptera-Tortricidae) is a shoot-borer often causing severe damage to saplings 1-3 m high. It shows a marked preference for strong, sappy shoots. A pinhole borer attacks the living tree; it has not yet been collected but it is presumed to be a species of Diapus (Coleoptera-Platypodidae).

Genetic resources

Chengal is much rarer nowadays than it was early in the 20th Century. Because of its limited distribution in combination with its great commercial value, chengal might become endangered in the near future. In 1987 the Forestry Department of Peninsular Malaysia took steps to ensure some protection of chengal by increasing the cutting limit to 60 cm diameter at breast height.

Prospects

Chengal is a highly valued timber. Demand will always remain high but availability is expected to decrease due to exploitation, and efforts should therefore be made to replenish the species.

Literature

Ashton, P.S., 1982. Dipterocarpaceae. In: van Steenis, C.G.G.J. (Editor): Flora Malesiana. Ser. I, Vol. 9. Martinus Nijhoff/Dr. W. Junk Publishers, The Hague, Boston, London. pp. 237-552.
Balan Menon, P.K., 1967. Structure and identification of Malesian woods. Malaysian Forest Records No 25. Forest Research Institute, Kepong. 121 pp.
Burkill, I.H., 1966. A dictionary of the economic products of the Malay Peninsula. 2nd edition. Vol. 1. Ministry of Agriculture and Co-operatives, Kuala Lumpur. pp. 286-289.
Lopez, D.T., 1983. Malaysian timbers - chengal. Malaysian Forest Service Trade Leaflet No 72. Malaysian Timber Industry Board, Kuala Lumpur. 7 pp.
Smitinand, T., Santisuk, T. & Phengklai, C., 1980. The manual of Dipterocarpaceae of mainland South-East Asia. Thai Forestry Bulletin 12: 1-110.
Symington, C.F., 1941. Foresters' manual of dipterocarps. Malayan Forest Records No 16. Forest Department, Kuala Lumpur. 244 pp.
Thomas, A.V., 1955. Malayan timbers - chengal. Malayan Forester 18: 103-105.
Yamamoto, K. & Hong, L.T., 1988. Decay resistance of extractives from chengal (Neobalanocarpus heimii). Journal of Tropical Forest Science 1(1): 35-41.
Yap, S.K., 1981. Collection, germination and storage of dipterocarp seeds. Malaysian Forester 44: 281-300.
Yap, S.K., 1985. Gregarious flowering of dipterocarps: some observations based on fixed tree populations in Selangor and Negeri Sembilan, Malay Peninsula. In: Kostermans, A.J.G.H. (Editor): Proceedings of the third round table conference on dipterocarps, Samarinda. UNESCO-ROSTSEA, Jakarta & SEAMEO-BIOTROP, Bogor. pp. 305-317.

Other selected sources

6, 32, 96, 144, 159, 190, 297, 359, 417, 473, 511, 809.

Authors

W.C. Wong (general part, properties),
R.B. Miller (wood anatomy)
G. dos Santos (wood anatomy)