Upuna (PROSEA)

Plant Resources of South-East Asia
Introduction

Protologue: Bull. Jard. Bot. Buitenzorg, sér. 3, 17: 88, f. I-II, pl. 1-3 (1941).

Family: Dipterocarpaceae

Chromosome number: x= 11; 2n= 22

Trade groups

Upun: heavy hardwood, a single species, Upuna borneensis Sym., Bull. Jard. Bot. Buitenzorg, sér. 3, 17: 88, f. I-II, pl. 1-3 (1941).

Vernacular names

Upun

Brunei: upun batu
Indonesia: balau penyau (general), cangal tanduk (South Kalimantan), penyau tanduk (West Kalimantan)
Malaysia: penyau (Sarawak).

Origin and geographic distribution

The monotypic genus Upuna is endemic to Borneo where it occurs in South and West Kalimantan, Sarawak, Brunei and Sabah; it is rare in East Kalimantan. It is the only Malesian genus of the family Dipterocarpaceae which is not recorded (presently and fossil) from mainland South-East Asia or Sri Lanka.

Uses

Upun is suitable for all heavy constructional work where strength and durability are essential, such as bridges, wharves and mining timber. Locally (e.g. in Brunei), it is popular for boat building, and it is suited for heavy-duty furniture and heavy-duty flooring, although it is rather brittle and does not take glue well.

Production and international trade

Upun is not an export timber. This is due to its scattered occurrence and to its popularity for local uses. Upun is possibly sometimes traded as balau (Shorea spp.), giam (Hopea spp.) or resak (Cotylelobium spp. and Vatica spp.)

Properties

Upun is a heavy and hard timber. The colour of the heartwood is dark brown, and the heartwood is clearly demarcated from the much lighter (light yellow-brown) sapwood. The density is 935-1040(-1140) kg/m³ at 15% moisture content. The grain is straight to shallowly interlocked, texture fine to slightly coarse and even.

At 15% moisture content the modulus of rupture is 156-163 N/mm², modulus of elasticity 17 300-17 800 N/mm², compression parallel to grain 87-95 N/mm² and shear 18-20.5 N/mm². See also the table on wood properties.

Shrinkage of upun during drying is low when compared to similar timbers such as balau or resak: from green to 15% moisture content 0.5-1.8% radial and 1.5-3.2% tangential. The timber air dries moderately slowly, but faster than other heavy timbers, and without many seasoning defects, although slight checks and end splits may develop. Boards of 15 mm thick take about 3 months to air dry from green to 15% moisture content, 40 mm thick boards take 4-5 months.

Although upun does not contain silica, it is difficult to saw owing to the dense and somewhat resinous nature of the wood. Saws should be cleaned from resin regularly. Planing and boring are easy and give a smooth finish, although grain pick-up may occur on the radial surface during planing, and the finish after boring may be slightly rough. The nailing properties are rated as poor. It does not glue well, and has proved to be rather brittle.

Upun is a very durable timber. Graveyard tests with stakes in Malaysia showed an average service life in contact with the ground of 10 years. The wood is resistant to attack by termites, powder-post beetles and fungi, but logs are slightly susceptible to pinhole borer attack. Upun is very difficult to treat with preservatives, but this is usually not necessary as the wood has great natural durability. Using the open tank method and an equal mixture of creosote and diesel fuel the heartwood absorbs hardly any preservative, and even the sapwood is resistant to preservative treatment.

Description

Large trees up to 55 m tall; bole tall, cylindrical, branchless for up to 25 m, up to 190 cm in diameter, buttresses many, single or grouped, up to 2 m high, blunt; bark surface with square-section fissures and flat-topped flaking ridges, dark purple-brown to chocolate-brown, outer bark up to 1.5 cm thick, hard, inner bark up to 1 cm thick, pale yellow to cream; branches ascending, bending down at the tips, rather crooked, twigs terete, densely tomentose.
Leaves alternate, simple, entire, softly leathery, oblong to obovate, 9-24 cm × 4-9.5 cm, with a cordate base and an up to 5 mm long acumen, with 12-20 pairs of veins curving near the margin, lower surface white tomentose with a prominent midrib; petiole geniculate, 1-3 cm long; stipules subpersistent, subulate, up to 2 cm long, scar small.
Inflorescences cymose, borne in the axils of the uppermost leaves, many-branched, up to 15 cm long, densely pale chocolate-brown tomentose and glandular; bracts up to 10 cm × 3.5 cm.
Flower bud narrowly ovoid, acute, up to 5 mm × 2 mm; calyx lobes fused at base, imbricate, densely tomentose outside; petals 5, broadly ovate, subacute, becoming reflexed apically, sparsely tomentose on the parts exposed in bud, deep purple with dark yellow margins; stamens 25-30, in several verticils, filaments broad at base, those of the outer row tapering abruptly, anthers subglobose with a slender, glabrous appendage about 3 times longer than the anther; ovary ovoid-globose, without a distinct stylopodium, tomentose, style 2-3 times longer than the ovary, pubescent in the lower half.
Fruit a triangular nut, enclosed by a fruit calyx with a narrowly cuneate base, the lobes valvate, united into a basal cup but not fused with the nut, unequal, lanceolate, the larger 2 up to 13 cm × 2.7 cm, subacute, the smaller 3 up to 7.5 cm × 1.7 cm; nut narrowly ovoid, acute, up to 3.2 cm × 1.5 cm, densely fulvous tomentose, with a distinct style remnant.
Seed with a distinct arillode.
Seedling with epigeal germination; cotyledons subequal, cordate; first pair of leaves opposite, subsequent leaves arranged spirally, often much larger than those of mature trees.

Wood anatomy

Macroscopic characters

Sapwood light yellow-brown, sharply differentiated from the heartwood which is greenish- or yellowish-brown when freshly cut and darkens on exposure.
Grain straight to shallowly interlocked.
Texture moderately fine and even.
Wood almost featureless except that because of their large size the intercellular canals stand out clearly on longitudinal surfaces.
Stripe figure usually inconspicuous, planed surface sometimes glistening because of the abundance of tyloses, radial longitudinal surfaces often with a slightly mottled "silver figure".

Microscopic characters

Growth rings indistinct.
Vessels diffuse, 5-11/mm², exclusively solitary, round to oval, average tangential diameter 210 μm; perforations simple; intervessel pits alternate, vestured, round to oval, 6-10 μm; vessel-ray and vessel-parenchyma pits similar but half-bordered; helical thickenings absent; tyloses abundant.
Fibres 1200-2000 μm long, non-septate, thick-walled, with moderately conspicuously bordered pits in both radial and tangential walls.
Parenchyma moderately abundant to rather sparse; apotracheal parenchyma diffuse, diffuse-in-aggregates, or in uniseriate discontinuous lines or in marginal bands associated with the resin canals, in 5-10-celled strands; paratracheal parenchyma scanty to vasicentric.
Rays, 6-12/mm (average 9/mm), of two distinct sizes, fine rays uniseriate (rarely 2-seriate), broad rays 3-4(-6) cells wide, up to 1.5 mm high, Kribs type heterogeneous II with 3-4 rows of upright marginal cells; sheath cells usually present.
Crystals and silica absent.
Vertical intercellular canals present, variable in size, diffuse, in short or long tangential lines; canals empty or filled with white gum-like resin.
All elements non-storied.
Upun wood differs from balau and giam by its solitary vessels and diffuse resin canals, from resak by generally fewer vessels.

Growth and development

The trees grow slowly, as can be expected from such a heavy and hard timber. The scanty information available indicates that after 40 years upun may have reached a bole diameter of only 28 cm; the growth rate is comparable with that of many balau-producing species.

Other botanical information

The genus Upuna is remarkable botanically. It has several features which are regarded as comparatively primitive, such as the presence of multicellular glandular hairs and the cymose inflorescence. On the other hand, it possesses derived characters such as the curving corolla lobes and the fused base of the calyx. The arillode on the seed is a rare feature within the family Dipterocarpaceae. The genus shows similarities with Monotes of the African subfamily Monotoideae but also with the genera Anisoptera, Cotylelobium, Stemonoporus and Vatica of the subfamily Dipterocarpoideae. Features of the wood anatomy point to a closer relationship to the latter four genera, especially to Anisoptera and Vatica.

Ecology

Upun occurs scattered and is only very locally abundant, in primary lowland mixed dipterocarp forest. It prefers well-drained, deep, sandy soils with a low clay content, on hills (often subcoastal) and ridges up to 350 m altitude.

Propagation and planting

As in other dipterocarp species, the seeds of upun have no dormancy. They germinate rapidly and lose their viability within a few weeks.

Silviculture and management

Natural regeneration is reported to occur frequently and locally abundantly.

Harvesting

Upun logs sink in water and therefore cannot be transported by river.

Genetic resources

As upun has only a limited area of distribution and is generally not common, but is locally a popular timber, it is at risk of genetic erosion and extinction.

Prospects

Although upun shows very interesting wood properties, particularly concerning strength and durability, not much is known about this timber. This is because of its limited area of distribution and scattered occurrence. It does not seem to be a promising species for cultivation in timber plantations as it is a very slow grower.

Literature

Ashton, P.S., 1964. Manual of the dipterocarp trees of Brunei State. Oxford University Press, London. pp. 7-8.
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.
Browne, F.G., 1955. Forest trees of Sarawak and Brunei and their products. Government Printing Office, Kuching. pp. 171-172.
Burgess, P.F., 1966. Timbers of Sabah. Sabah Forest Records No 6. Forest Department, Sabah, Sandakan. pp. 226-235.
Dahlan, M.J. & Tam, M.K., 1985. Natural durability of some Malaysian timbers by stake tests. Malaysian Forester 48: 154-159.
Malaysian Timber Industry Board, 1986. 100 Malaysian timbers. Kuala Lumpur. pp. 30-31.
Ng, F.S.P. & Tang, H.T., 1974. Comparative growth rates of Malaysian trees. Malaysian Forester 37: 2-23.
Symington, C.F., 1941. Upuna, a new genus of the Dipterocarpaceae. Bulletin of the Botanical Garden Buitenzorg, ser. 3, 17: 88-95.
Thomas, A.V., 1953. The timber of upun batu (Upuna borneensis). Malayan Forester 16: 163-165.
Wood, G.H.S. & Meijer, W., 1964. Dipterocarps of Sabah (North Borneo). Sabah Forest Records No 5. Forest Department, Sandakan. p. 327.

Other selected sources

258, 578.

Authors

M.S.M. Sosef (general part),
J.E. Polman (properties),
S.C. Lim (wood anatomy)