Hopea (giam) (PROSEA)

Plant Resources of South-East Asia
Introduction

List of species

Hopea Roxb. (giam)

Protologue: Pl. Coromandel 3: 7 (1811).

Family: Dipterocarpaceae

Chromosome number: x= 7; Hopea nutans: 2n= 28

Trade groups

Giam: heavy hardwood, e.g. Hopea ferrea Lanessan, H. forbesii (Brandis) v. Slooten, H. helferi (Dyer) Brandis.

In Indonesia the wood of several species of Hopea is traded as "balau" because it closely resembles the wood of the heavy species of Shorea. In Indonesia the name "giam" is used for the wood of Cotylelobium spp. The wood of H. ferrea is sometimes traded separately and called "malut".

Vernacular names

Giam: heavy hopea (En).
Brunei: luis (Iban)
Indonesia: balau (partly)
Malaysia: selangan (Sabah, Sarawak)
Papua New Guinea: heavy hopea
Philippines: yakal
Burma: thingyan
Cambodia: kôki:(r)
Thailand: takhian-hin (peninsular), takhian-rak (peninsular), krabok-krang (Nan)
Vietnam: săng dào, sao xanh.

Origin and geographic distribution

Hopea consists of some 102 species. The section Hopea, to which most of the giam timbers belong, comprises about half of the total number of species and is distributed from Sri Lanka and southern and eastern India through mainland South-East Asia towards Malesia, where it occurs on all islands except for the Lesser Sunda Islands. The oldest fossil wood belonging to the genus Hopea was found on the east coast of southern India and dates from the Miocene.

Uses

Giam is a useful general-purpose timber for heavy construction. Its durability both in contact with the ground as well as in contact with water makes it suitable for purposes such as bridges, piers, wharves, piling, posts and electricity poles, beams and railway sleepers; it is in demand for boat building, specifically for boat keels. Giam is suitable for heavy-duty, industrial flooring. Other general applications of the timber are for vehicle bodies, furniture, wall plates and other interior finish, window and door frames and heavy-duty laboratory benches. Due to its hardness giam is generally not suitable for plywood or veneer nor for particle board.

Several species yield a clear crystalline resin known as "damar mata kucing" which is used for varnish manufacture and locally for torches and caulking boats.

Production and international trade

Giam is not an important export timber in Malaysia, Indonesia and the Philippines. It is probably mostly used locally, but small amounts may be exported mixed with other heavy hardwoods such as balau (from Shorea spp.). However, Hopea timber (both heavy and light) is one of the more important export timbers in Papua New Guinea; it is ranked in the MEP (Minimum Export Price) group 3 and fetched a minimum export price of US$ 50/m³ for saw logs in 1992.

Properties

Giam is a heavy hardwood. The yellowish-white sapwood is generally distinct from the yellowish-brown heartwood, sometimes with a greenish tinge, darkening to dark brown on exposure. The density is 875-1220 kg/m³ at 15% moisture content. Planed surfaces are usually not particularly lustrous; a stripe figure may be present. The grain of the wood is interlocked, texture fine and even.

When green, the modulus of rupture is 103-124 N/mm², modulus of elasticity 14 600-22 000 N/mm², compression parallel to grain 42-70 N/mm², compression perpendicular to grain 10-17 N/mm², shear 13-14 N/mm², cleavage 58-98 N/mm radial and 75-116 N/mm tangential, Janka side hardness 8700-9750 N and Janka end hardness 8100-8410 N.

The rates of shrinkage are moderate to fairly high, from green to 15% moisture content 1.4-2.0% radial and 2.6-4.4% tangential. Giam timber air dries slowly, often with slight end and surface checks and splits. Boards of 15 mm thick take about 6 months to air dry. Kiln-drying characteristics have not been assessed but in Malaysia kiln schedule B is recommended.

Giam is easy to difficult to resaw and cross cut. The sawteeth may become clogged with resinous sawdust. Planing is easy, giving a smooth finish. Boring is easy to slightly difficult but the finish is always smooth. Turning is difficult and the quality of finish ranges from smooth to rough. The resistance to splitting when nailed is rated as very poor.

Giam is very durable, even under exposed conditions. Test stakes in Malaysia showed an average service life in contact with the ground of over 10 years. The wood is resistant to pinhole borer and powder-post beetle attack, and probably also to marine borer attack. The heartwood of giam is very resistant to preservative treatment, but it has great natural durability. The sapwood absorbs preservatives fairly well, and the life of the sapwood in poles can be prolonged by preservative treatment.

Description

Small to fairly large trees of up to 48 m tall; bole usually tapering, frequently branching low with a diameter of up to 160 cm, exuding a pale clear dammar; buttresses usually thin, sometimes thick, bole sometimes stilt-rooted or with flying buttresses; bark surface usually flaky when mature, chocolate and grey mottled, hoop-marked, inner bark pink or greenish-yellow, close textured; crown of the smaller trees lanceolate, monopodial with slender, more or less horizontal and pendant branches, in large trees becoming hemispherical with many small straight branches radiating from the bole apex.
Leaves alternate, simple, small or medium-sized, sometimes large and narrowly oblong, usually with domatia on the lower surface, usually with scalariform tertiary venation, but venation sometimes "dryobalanoid", i.e. secondary veins numerous and of varying length, more or less indistinct and with indistinct tertiary venation; petioles never geniculate; stipules linear, fugacious (subpersistent in saplings).
Inflorescence paniculate, rarely fascicled, irregularly branched, terminal or axillary, many-flowered, slender, generally tomentose.
Flower buds small, ovoid or rarely globose; flowers secund or distichous, bisexual, actinomorphic, 5-merous, pale, scented; sepals imbricate, 2 outer ones ovate, more or less obtuse, thickened, 3 inner ones suborbicular, frequently mucronate, thin at margins; petals oblong, connate at base and shed as a rosette, often persistently pubescent on the parts exposed in bud; stamens 10 or 15, in 1-3 verticils or irregular, filaments broad and compressed at base, tapering medially and filiform apically, anthers subglobose, with 4 pollen sacs, the outer pair somewhat larger, appendage to connective slender, usually at least twice as long as the anther, glabrous or minutely glandular tuberculate; ovary ovoid, glabrous or tomentose, a distinct stylopodium sometimes present and then pear-shaped to cylindrical, style long or short, glabrous, with a minute stigma (except H. ferrea).
Fruit comparatively small, 2 outer fruit calyx lobes prolonged, spatulate, 3 inner ones short, sometimes all 5 lobes short and subequal, lobes thickened and saccate at base; nut ovoid, usually glabrous, with a distinct apical stylopodium if present in the flower; pericarp splitting irregularly at germination (rarely into 3 valves).
Seedling with epigeal germination; cotyledons subequal; first pair of leaves opposite, followed by spiral leaves or an initial whorl of 3.

Wood anatomy

Macroscopic characters

Heartwood yellowish-brown, often with a green tinge, turning dark yellowish-brown or red-brown upon exposure, usually distinctly demarcated from the yellowish-white sapwood.
Grain shallowly to strongly interlocked.
Texture fairly fine to fine; concentric lines composed of white dots and lighter coloured parenchyma distinct to indistinct.
Growth rings usually not distinct.

Microscopic characters

Growth rings indistinct.
Vessels diffuse, usually 10-20/mm², mostly solitary, with a small number of radial multiples of 2(-3), less than 150μm in tangential diameter; perforations simple; intervessel pits alternate, vestured, round, usually 5-8μm; vessel-ray and vessel-parenchyma pits round to oval, simple to half-bordered; tyloses often abundant.
Fibres 1.2-2.2 mm long, 18-25μm in diameter, non-septate, usually thick-walled, with infrequent, small simple pits confined to the radial walls.
Parenchyma vasicentric, aliform, short confluent and in tangential bands surrounding the intercellular canals.
Rays 8-11/mm, 1-5-seriate, mostly 1000-2000μm high, usually heterocellular, mostly with 1 and/or 2-4 rows of upright and/or square marginal cells (Kribs type heterogeneous III and II).
Prismatic crystals sporadic or absent in axial parenchyma, usually found in ray parenchyma cells.
Axial intercellular canals of the concentric type, with whitish contents, surrounded by tangential parenchyma bands.

Species studied: H. nutans, H. semicuneata.

Giam differs from balau (heavy Shorea timber), particularly in having more numerous vessels, narrower rays and a finer texture. Macroscopic identification is often difficult, and giam and balau are often not separated in trade.

Growth and development

Seedlings need ectomycorrhizal infection for optimal growth. Most species regenerate prolifically under natural conditions and are shade-tolerant. Plagiotropic branching of Hopea saplings is mainly at the apex of the leader shoot at the initiation of each growth period; hence, the sapling has a pagoda-like appearance.

Giam trees usually grow slower than merawan ( Hopea species with lighter wood) trees. H. andersonii is reported to reach a maximum diameter of 39 cm at an age of 40 years, H. nutans of 35 cm. However, for 40-year-old planted trees of H. helferi an astonishingly large maximum diameter of 82 cm has been reported in Malaysia.

The flowering periodicity of the various giam species is not known. Thrips are pollinators of many Hopea species. The interval between anthesis and mature fruits is about 3 months. The abundance of seedlings below trees indicates that most fruits fall directly beneath the mother tree.

Other botanical information

The genus Hopea belongs to the tribe Shoreae and is very closely related to Shorea. The distinction is made by a single character: in Hopea the two outer sepals are slightly or markedly thicker than the three inner ones, and only they develop into wings in fruit. In Shorea the three outer sepals are thicker and larger than the two inner ones, and normally develop into fruit wings (or lobes). In both genera species with only short and subequal fruit sepals occur and these are assigned to one of the two by comparison of other floral characters. All but a few Shorea species are emergent trees, whereas all but a few Hopea species are main canopy or understory trees.

The groups distinguished commercially, the giam timbers and the more variable merawan timbers, correspond to some degree to the botanical subdivision of the genus Hopea. Most giam timbers (except H. coriacea and H. malibato) belong to section Hopea, most merawan timbers to section Dryobalanoides (Miq.) Burck. Section Hopea is characterized by its scalariform leaf venation, smooth or evenly flaky bark, bole usually without stilt roots and wood with markedly heterogeneous rays and usually without chambered parenchyma strands.

Some Hopea species (H. depressinerva and H. glabrifolia) cannot be assigned to either of the two commercial groups. Since they belong to section Hopea, it seems justifiable to deal with these species under giam.

Ecology

Giam is found in lowland and hill forest from sea-level up to 1000 m altitude. It occurs as a main canopy or understorey, rarely as an emergent tree in evergreen or seasonal, semi-evergreen forest. The semi-evergreen forest accommodates the majority of the species, often narrow endemics. The different species occur in a wide variety of forest types ranging from mixed dipterocarp forest to heath forest and mixed peat-swamp forest and, consequently, on a wide variety of soil types, including limestone. Some species occur markedly gregariously with comparatively large gaps between the groups.

Propagation and planting

The viability of seeds under natural conditions is short. Seeds of H. helferi show a germination rate of over 90% at temperatures between 5°C and 35°C; the germination rate drops sharply above 40°C. The weight of 1000 seeds of H. helferi is about 125 g. When H. helferi seeds are dried at 35°C to 25% moisture content, they can be kept viable in sealed polyethylene bags for 2 months at 15°C. Seeds of H. ferrea can also be stored, but survival at 4°C does not exceed 3 months. H. plagata can be vegetatively propagated by air layering; in tests 15% of the branches developed roots.

Yield

Yields are generally low. The trees often occur scattered in the forest, and very locally there may be 10-13 trees of over 40 cm diameter per ha.

Genetic resources

Hopea is a large genus, and some of the species are common and widespread, but others are scattered or rare. Large-scale logging without identification of species, as commonly practised, could easily endanger the less common species.

Prospects

Few timbers are as strong and durable as giam. The establishment of plantations is desirable, but more research is needed on propagation techniques and silvicultural aspects, since information about giam is scarce. The growth rates, gathered from the few data available, seem to be acceptable for such a heavy timber. H. helferi has been recommended for planting in Peninsular Malaysia.

Literature

Ashton, P.S., 1964. Manual of the dipterocarp trees of Brunei State. Oxford University Press, London. pp. 89-114.
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, Boston, London. pp. 237-552.
Bolza, E. & Kloot, N.H., 1966. The mechanical properties of 81 New Guinea timbers. Technological Paper No 41. Division of Forest Products, CSIRO, Melbourne. pp. 24-27.
Browne, F.G., 1955. Forest trees of Sarawak and Brunei and their products. Government Printing Office, Kuching. pp. 123-126.
Burgess, P.F., 1966. Timbers of Sabah. Sabah Forest Records No 6. Forest Department, Sabah, Sandakan. pp. 135-140.
de Guzman, E.D., Umali, R.M. & Sotalbo, E.D., 1986. Guide to Philippine flora and fauna. Vol. 3: Dipterocarps, non-dipterocarps. Natural Resources Management Center, Ministry of Natural Resources and University of the Philippines, Manila. pp. 26-41.
Lim, S.C., 1984. Malaysian timbers - giam. Malaysian Forest Service Trade Leaflet No 84. Malaysian Timber Industry Board, Kuala Lumpur. 8 pp.
Reyes, L.J., 1938. Philippine woods. Technical Bulletin No 7. Commonwealth of the Philippines, Department of Agriculture and Commerce. Bureau of Printing, Manila. pp. 296-305.
Tang, H.T. & Tamari, C., 1973. Seed description and storage tests of some dipterocarps. Malaysian Forester 36: 38-53.
Zabala, N.Q., 1986. Vegetative propagation of some dipterocarp species. Philippine Lumberman 32(7): 13-16.

Selection of species

Authors

K.M. Kochummen (general part, selection of species),
W.C. Wong (properties),
S. Sudo (wood anatomy),
F.T. Frietema (selection of species)