Hopea (merawan) (PROSEA)

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Plant Resources of South-East Asia
Introduction
List of species


Hopea Roxb. (merawan)

Protologue: Pl. Coromandel 3: 7 (1811).
Family: Dipterocarpaceae
Chromosome number: x = 7; Hopea beccariana: 2n = 20 22, H. latifolia: 2n = 21, H. nervosa: 2n = 14, H. odorata: 2n = 14, 20 22, H. sangal: 2n = 14

Trade groups

Merawan: lightweight to medium heavy hardwood, e.g. Hopea beccariana Burck, H. dryobalanoides Miq., H. mengarawan Miq., H. odorata Roxb., H. sangal Korth.

Timber of H. sangal is sometimes traded separately in Indonesia as "cengal".

Vernacular names

Merawan:

  • light hopea (En).
  • Brunei: selangan, damar kemantok, luis.
  • Indonesia: damar mata kucing (Sumatra), gagil (Kalimantan).
  • Malaysia: gagil, selangan, mang (Sarawak, Sabah) luis (Sarawak).
  • Papua New Guinea: light hopea.
  • Philippines: manggachapui.
  • Burma: thingan. Cambodia: kôki:(r).
  • Laos: kh'è:n.
  • Thailand: takhian thong (central).
  • Vietnam: sao den.

Origin and geographic distribution

Hopea consists of some 102 species. The section Dryobalanoides (Miq.) Burck, to which most of the merawan timbers belong, comprises about half of the total number of species and is distributed from mainland South East Asia towards Peninsular Malaysia, Sumatra, Borneo, the Philippines and New Guinea. The oldest fossil wood belonging to the genus Hopea was found on the east coast of southern India and dates from the Miocene.

Within South East Asia several species (especially H. odorata and H. mengarawan) are being used for reforestation.

Uses

Merawan is a very useful general purpose timber for light and medium heavy construction; some of the heavier species are even suitable for heavy construction under cover. Its generally good working properties make it suitable not only for house construction, where it is e.g. used for joists, rafters, beams, columns, boards, stairs and door and window frames, but also for general joinery and turnery, although not for high class furniture. Its comparatively high resistance to fungal attack makes merawan superior to e.g. meranti for uses such as weatherboarding and tiling battens. Merawan, especially wood of H. odorata, is often used for light or medium traffic flooring or for light industrial floors. Its generally high durability, including in contact with water, makes it suitable for boat and ship building and water barrels. It is satisfactory for the manufacture of plywood, veneer and particle board.

Several species yield a clear resin known as "damar mata kucing" which is used to manufacture varnish and locally for torches and caulking boats. This resin was formerly used as a medicine applied to sores and wounds. The bark sometimes contains tannin which gives good results when applied to tan leather and is used for the manufacture of tannin formaldehyde adhesive. The bark is also used for walls and partitions of local houses.

Production and international trade

Merawan timber is usuallly not available in large quantities and large sizes. Therefore, it is rarely traded separately in Malaysia and Indonesia. Small quantities are sometimes mixed with timber of Shorea spp. and sold as meranti (Peninsular Malaysia, Indonesia) or selangan (Sabah). However, merawan is exported separately (as "gagil") from Sabah and in 1987 the export of round logs was 118 000 m3 with a value of US$ 7.6 million (US$ 64/m3). In 1992 the export of merawan logs from Sabah was 16 000 m3 and of sawn timber 15 500 m3, with a total value of US$ 3.7 million. In the Philippines merawan ("manggachapui") occurs locally abundantly, but no export figures are available. Hopea (both heavy and light) is one of the more important export timbers in Papua New Guinea, and 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. However, it constitutes less than 1% of the total amount of timber imported in Japan from Papua New Guinea.

Properties

Merawan is a light to medium heavy hardwood. The sapwood is light yellow and distinct from the usually yellowish brown heartwood (sometimes olive brown or reddish brown); on exposure the heartwood often darkens to dark brown. The density is (420—)490—980(—1155) kg/m3 at 15% moisture content. Planed surfaces are glossy and the radial surface often shows a stripe figure. The grain of the wood is interlocked, texture moderately fine and even.

Tests of merawan wood in green condition in Indonesia, Malaysia, Papua New Guinea and the Philippines showed the following mechanical properties: modulus of rupture (64—)77—110 N/mm2, modulus of elasticity 12 000—15 500 N/mm2, compression parallel to grain (33—)42—51 N/mm2, compression perpendicular to grain 5—9 N/mm2, shear (4—)5—11 N/mm2, cleavage 35—65 N/mm radial and 44—84 N/mm tangential, Janka side hardness 3010 5525 N and Janka end hardness (2710—)3910—6110 N.

Tests in Indonesia at 15% moisture content gave the following results: modulus of rupture 94—117 N/mm2, modulus of elasticity 13 000—14 000 N/mm2, compression parallel to grain (46—)51—58 N/mm2, shear 4—12 N/mm2, cleavage 26—43 N/mm radial and 31—66 N/mm tangential, Janka side hardness (2200—)3800—4870 N and Janka end hardness (4200—)5150—6180 N.

The rates of shrinkage are small to moderate, from green to 15% moisture content 0.9—1.3% radial and 2.2—3.3% tangential, and from green to oven dry 2.7—3.6% radial and 6.1—7.5% tangential. Merawan air dries comparatively slowly, but rarely develops serious seasoning defects except for slight cupping; sometimes end and surface checks and warping occur, especially on wide boards. Boards of 15 mm and 40 mm thick of H. sulcata wood take respectively 4 months and 6 months to air dry. In Malaysia kiln drying schedule H is recommended. It takes 5 days for 25 mm thick boards to kiln dry from 50% to 10% moisture content.

Merawan is usually easy to resaw and cross cut. Planing is also easy, giving a smooth finish. Boring is recorded as slightly difficult for H. nervosa, but easy for H. mengarawan and H. sulcata, and the surface produced is usually smooth. Turning is easy and the finish is smooth. H. sulcata is rated as very poor in resistance to splitting when nailed. Merawan is suitable to be peeled for veneer. Veneer 1.5 mm thick can be made satisfactorily with a peeling angle of 91°. Gluing with urea formaldehyde extended with 20% wheat flour produces good quality plywood. The pulping and paper making properties of merawan are rated as satisfactory; the paper is suitable for writing, printing and wrapping.

Merawan is moderately durable under exposed conditions. Graveyard tests with stakes in Malaysia showed an average life in contact with the ground of 3—3.5 years, but in Indonesia up to 7.5 years (H. mengarawan) or even 10 years (H. dasyrrhachis). The wood is resistant to fungal infection under normal conditions but some species are very susceptible to damage by ambrosia beetles. The sapwood is susceptible to severe damage by termite and (in damp situations) fungal attack. Most species are immune to powder post beetle attack. The wood is not resistant to marine borer attack. It is difficult to treat with preservatives. When the open tank process is used, the wood absorbs only 32—48 kg/m3 of a mixture of creosote and diesel fuel, and under heavy pressure in the full cell process absorption will be about 80 kg/m3. However, in spite of the low absorption, treated wood is very durable in exposed conditions or in contact with the ground.

Merawan wood contains 54 60% cellulose, 27—29% lignin, 13—13.5% pentosan, 0.6—0.8% ash and about 0.2% silica. The solubility is 5.2—7.1% in alcohol benzene, about 1% in cold water, 2.1—4.5% in hot water and 13.3—13.4% in a 1% NaOH solution. The energy value of H. mengarawan wood is 19 600 kJ/kg.

Description

  • Small to fairly large, occasionally large, trees of up to 40(—60) m tall; bole usually tapering, frequently branching low but sometimes branchless for up to 20(—30) m, with a diameter of up to 100(—180) cm, often exuding a pale or white clear dammar, sometimes in globular or stalactitic masses; buttresses present, often small but sharp and stilted, sometimes with adventituous stilt roots; bark surface regularly, closely, rather deeply fissured, or comparatively smooth at maturity, sometimes irregularly fissured or cracked with age, dark chocolate brown with greenish yellow areas, inner bark pink, dull sandy brown or dull light brown tinged pink, close textured; crown in small 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 lower surface; secondary veins sometimes comparatively few with scalariform tertiary venation (H. nervosa, H. papuana and H. sublanceolata), more often numerous and of varying length, more or less indistinct and with indistinct tertiary venation ("dryobalanoid"), superficially resembling Dryobalanops, or intermediate between these two types ("subdryobalanoid"); petiole never geniculate; stipules linear, fugacious (subpersistent in saplings).
  • Inflorescence paniculate, regularly branched with short branchlets, terminal or axillary, many flowered, slender; bracts fugacious or subpersistent.
  • Flower buds small, ovoid or rarely globose; flowers secund or distichous, bisexual, actinomorphic, 5 merous, pale or dark coloured, 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 falling in a rosette, often persistently pubescent on the parts exposed in bud; stamens 10 or 15 (rarely up to 38), in 1—3 verticils or irregular, filaments broad and compressed at base, tapering medially and filiform apically, anthers usually 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, without or with a distinct stylopodium and then pear shaped or truncate, style long or short, glabrous, with a minute stigma.
  • Fruit comparatively small, 2 outer fruit calyx lobes prolonged, spatulate, 3 inner ones short, sometimes all 5 fruit calyx lobes short and subequal, all 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.
  • 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, usually with a greenish tinge, but H. sangal wood with a pinkish tinge and H. nervosa wood reddish brown with darker streaks, darkening to brown with a greenish tinge or dark reddish brown on exposure, distinctly demarcated from the yellowish white sapwood.
  • Grain shallowly or deeply interlocked, sometimes wavy.
  • Texture moderately fine; irregularly spaced, light coloured concentric lines surrounding white dots visible to the naked eye, usually less clearly than in giam.
  • Growth rings 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), usually 140—200 μm in tangential diameter; perforations simple; intervessel pits alternate, vestured, round, usually 5—10 μm; vessel ray and vessel parenchyma pits round to oval, simple to half bordered; tyloses often abundant.
  • Fibres 1.2—2.2 mm long, c. 25 μm in diameter, non septate, thin to thick walled, much thinner walled than fibres of giam (walls c. 2.5 μm thick in H. sangal), with infrequent, small, simple to minutely bordered pits confined to the radial walls.
  • Parenchyma vasicentric, aliform and short confluent, and also often apotracheally diffuse in aggregates, partly forming a reticulate pattern (H. acuminata, H. odorata, H. sangal), and in irregularly spaced tangential bands surrounding the intercellular canals.
  • Rays 5—7/mm, 1—4 seriate (H. acuminata) or 1—7 seriate (H. odorata), mostly 1000—2000 μm high, the multiseriate part of some species (e.g. H. acuminata, H. odorata) often heterocellular, with 1 and/or 2—4 rows of square and/or upright marginal cells (Kribs type heterogeneous III and II).
  • Prismatic crystals present in axial parenchyma cells, in long chains (H. ferruginea), or absent (H. mengarawan, H. sangal); druses present in addition in H. ferruginea; prismatic crystals generally present in ray parenchyma cells, often alligned radially.
  • Axial intercellular canals of the concentric type surrounded by tangential parenchyma bands, with whitish contents.

Species studied: H. acuminata, H. ferruginea, H. mengarawan, H. nervosa, H. odorata, H. sangal.

Merawan differs from giam by its larger vessels, thinner walled fibres and fewer rays.

Growth and development

The growth of seedlings is enhanced by inoculation with ectomycorrhizae. The fungi significantly promote the uptake of macronutrients in the tissues of seedlings. For H. odorata, inoculation with Scleroderma sp. gives better results than inoculation with Russula and Boletus sp. Most species regenerate prolifically under natural conditions. In natural forest in Malaysia, 75% of the seedlings of H. pedicellata survived 2 years after germination. Mortality was highest among seedlings 10—20 cm tall. Seedlings of H. foxworthyi are shade tolerant; they have a survival rate of 85% a few months after germination when growing under heavy shade. On the other hand, seedlings of H. sangal survive remarkably well when planted in full sunshine. The sapling branches mainly at the apex of the leader shoot at the initiation of each growth period; this gives the sapling a pagoda like appearance.

Growth rates of trees vary considerably between species. At an age of 40 years, H. mengarawan and H. myrtifolia are reported to reach a maximum diameter of 60 cm, H. beccariana, H. ferruginea and H. latifolia reach 50 cm, H. nervosa 42 cm, and H. pubescens only 26 cm, whereas H. sangal trees may reportedly reach a maximum diameter of 40—70 cm. H. odorata is reported to reach a diameter of 53 cm in 25 years. In East Kalimantan H. dryobalanoides showed a mean annual height increment of 1.3 m and mean annual diameter increment of 1.0 cm, in a 4 year period. Data from three 20 year old plantations of H. mengarawan in Indonesia show corresponding values of 1.1 m and 1.0—1.3 cm.

Merawan trees flower at more or less regular intervals. The flowering periodicity of the various species is unknown. H. odorata, planted at the Forest Research Institute Malaysia (Kepong) flowers and fruits almost regularly every 2 years. Many Hopea spp. are pollinated by thrips (Thysanoptera). The period between anthesis and maturity of the fruit is about 3 months. Even though the fruits have 2 long wings and thus seem adapted to dispersal by wind, they generally fall directly below the mother tree in the aseasonal, almost windless rain forest. This is evident from the abundance of regeneration of Hopea seedlings below mother trees.

Polyembryony has been reported in H. odorata. This species has found to be triploid, effectively confirming that it is apomictic.

Other botanical information

The genus Hopea belongs to the tribe Shoreae and is very closely related to the genus Shorea. The two genera are distinguished by a single character. In Hopea the two outer sepals are slightly or markedly thicker than the inner three and only they develop into wings in fruit. In Shorea the three outer sepals are thicker than the inner two and they normally develop into the large wings (or lobes) in fruit. In both genera species with only short and subequal fruit sepals occur and these are assigned to one of the two genera 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 division of the genus Hopea. Most giam timbers belong to the section Hopea, most merawan timbers (except H. acuminata, H. dasyrrhachis, H. glaucescens, H. odorata, H. papuana, H. philippinensis, H. sangal) to the section Dryobalanoides (Miq.) Burck. The latter is characterized by dryobalanoid or subdryobalanoid venation (scalariform in H. nervosa and H. sublanceolata), smooth, fissured or cracked, not evenly flaky bark, bole often stilt rooted and wood with numerous chambered parenchyma strands and not markedly heterogeneous rays.

There are some Hopea species that cannot be assigned to either of the two commercial groups. Since they all belong to the section Hopea, they are treated under the giam timber. The density range of the wood of H. pierrii is very wide, making it a heavy merawan or giam.

In Malaysia, the scaly barked species all belong to the giam group, those with smooth or fissured bark belong to merawan. These field characters can probably also be applied to Hopea species growing outside Malaysia.

Ecology

Merawan is found from sea level to 1650 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 more Hopea species, often narrow endemics. The different species occur in a wide variety of forest types, ranging from mixed dipterocarp forest to heath forest and swamp forest. Consequently, merawan occurs on a wide variety of soil types, often on well drained clayey soils but also on sandy, alluvial soils, podzols or on limestone. Few species extend their range towards swampy or inundated habitats. Merawan is usually not dominant, but some species occur markedly gregariously, especially in Papua New Guinea, with comparatively large gaps between the groups.

Propagation and planting

It is recommended to begin collecting seed as soon as the seed wings start turning brown. The weight of 1000 seeds of H. mengarawan is about 155 g, that of H. odorata is about 130 g. Merawan seeds exhibit no dormancy and germinate quickly after maturation. Seeds of H. odorata from Thailand have a high moisture content (about 50%); they die quickly through dehydration and lose their viability within 5 days when kept in the open air at 20°C. However, seeds of H. odorata dried at 35°C to 33% moisture content could be kept viable in Malaysia for 1—2 months at 15°C, maintaining a germination rate of over 60%. Long term storage of seeds at 21°C in closed polyethylene bags proved possible for some species (e.g. H. nervosa); after almost one year the germination rate may still be 20% provided that fungal infection is prevented. Seeds of H. latifolia, H. odorata and H. nervosa survive at 4°C in sealed polyethylene bags for various periods, but not exceeding 3 months.

In Indonesia seedlings are planted into the field when they are 30—40 cm high. They are planted in cleared strips (1—2 m wide) in the forest at a distance of 5 m within the strip and 6—8 m between strips. For enrichment planting, wildlings are also used (e.g. of H. mengarawan). The application of naphthalene acetic acid (125 ppm) stimulates root growth in wildlings. Bare root transplanting of H. odorata results in almost 100% survival if pruned seedlings are used. The pruned seedlings can be stored in polyethylene bags at 25°C for long periods; viability is over 50% after 7 months.

Merawan can be propagated vegetatively, though often with a low success rate. Experiments with stem cuttings taken from vertical axes of 3—4 year old saplings treated with growth hormones (e.g. indole acetic acid and/or indole-3-butyric acid) showed successful rooting in only up to 40% of the cuttings. Stump planting of H. beccariana and H. nervosa shows high mortality. H. foxworthyi has been propagated by air layering, but only 20% of the branches developed roots.

Silviculture and management

In a 30 year old plantation in Indonesia trees of H. mengarawan planted at a density of 600 trees/ha produced 760 000 seedlings/ha. In Malaysia the survival rate of planted trees of H. vesquei after 15 years was 91%, whereas that of H. andersonii was 80%. Because of its good prospects H. mengarawan is recommended in Indonesia for reforestation programmes.

Diseases and pests

The fungus Cylindrocarpon destructans causes brown leaf spots and defoliation of seedlings of H. mengarawan. Seeds of H. odorata are reported to be attacked by the weevil Nanophyes shoreae.

Harvesting

Logs should be removed rapidly from logging areas as they are sometimes very susceptible to attack by ambrosia beetles and blue stain infection (particularly the sapwood). Fresh logs often sink in water (e.g. H. nervosa) and cannot be transported by river. Large logs are often hollow.

Yield

Yields are usually not high. Merawan trees are often scattered in the forest, and stands with 10—13 trees over 40 cm in diameter per ha occur only very locally.

Genetic resources

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

Prospects

More research on propagation and silviculture of merawan is desirable. The establishment of large scale plantations could be profitable, as some species grow quickly (e.g. H. mengarawan, H. odorata, H. sangal) and the durability of the wood is often superior to meranti.

Literature

  • 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.
  • Corbineau, F. & Come, D., 1989. Experiments on germination and storage of the seeds of two dipterocarps: Shorea roxburghii and Hopea odorata. Malaysian Forester 49: 371—381.
  • Ho, K.S., 1981. Malaysian timbers — merawan. Malaysian Forest Service Trade Leaflet No 53. Malaysian Timber Industry Board, Kuala Lumpur. 10 pp.
  • Martawijaya, A., Kartasujana, I., Kadir, K. & Prawira, S.A., 1986. Indonesian wood atlas. Vol. 1. Forest Products Research and Development Centre, Bogor. pp. 97—101.
  • 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.
  • Santoso, E., 1989. Pengaruh mikoriza terhadap diameter batang dan bobot kering anakan Dipterocarpaceae [The effect of mycorrhizae on the stem diameter and dry weight of dipterocarp seedlings]. Buletin Penelitian Hutan No 504: 11—21.
  • Sasaki, S., 1980. Storage and germination of dipterocarp seeds. Malaysian Forester 43: 290 308.
  • 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)