Pterospermum (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Pterospermum Schreb.

Protologue: Gen. pl. 2: 461 (1791).

Family: Sterculiaceae

Chromosome number: x= 19;P. acerifoliumand several non-Malesian species: 2n= 38

Vernacular names

• Bayur (trade name)
• Malaysia: bayor, litak (Sabah)
• Philippines: bayok (general)
• Vietnam: lòng mang.

Origin and geographic distribution

Pterospermum comprises about 40 species occurring in India, Burma (Myanmar), Indo-China, southern China, Thailand and throughout Malesia except for New Guinea. About 15 species are found in Malesia; the Philippines and Peninsular Malaysia are richest with about 9 and 6 species, respectively. Thailand is also rich in species (about 10).

Uses

The wood of Pterospermum is used for joinery, flooring, furniture, cladding, striking tool handles, implements and plywood; it is also used in ship and bridge building. It is suitable for construction under cover, e.g. for boards, beams, joists and rafters. The wood is suitable for matches and for the production of wood-wool board. The pulp is suitable for making paper.

The bark is sometimes used to obtain a yellow dye. Leaves and bark, which are rich in tannin, are occasionally applied in traditional medicine, e.g. as a poultice against itch and to treat wounds, and internally against dysentery. The bark is locally used for toughening fishing nets.

Production and international trade

In Peninsular Malaysia Pterospermum trees are too scattered and the form of the bole is often too poor to be of importance. In Borneo, particularly in Sabah, Pterospermum is locally abundant. In 1987 the export of round logs from Sabah was 17 000 m³with a value of US$ 1.05 million (US$ 62/m³), and in 1992 it was 24 000 m³(6% as sawn timber and 94% as logs) with a total value of US$ 1.7 million (US$ 151/m³for sawn timber and US$ 68/m³for logs). Japan imports this timber in comparatively small amounts from Sabah and Sarawak.

Properties

Pterospermum yields a lightweight to medium-weight hardwood with a density of 300-780 kg/m³at 15% moisture content. Heartwood pale brown to pale red-brown with a purplish tinge, not clearly demarcated from the paler sapwood; grain straight or shallowly interlocked; texture moderately fine to slightly coarse, even. Growth rings distinct to indistinct, boundaries irregular and fairly ill-defined; vessels moderately small to moderately large, solitary and in radial multiples of 2-3(-4), occasionally in clusters, open, sometimes with tyloses or pale brown deposits; parenchyma abundant, paratracheal vasicentric, apotracheal diffuse and diffuse-in-aggregates, both types rather indistinct with a hand lens; rays very fine; ripple marks present due to storeying of lower rays and axial parenchyma, rather inconspicuous; axial traumatic canals observed in P. javanicum .

Shrinkage of the wood upon seasoning is moderate and the only risk of degrade is stain, therefore stock should be treated with anti-stain chemicals immediately after sawing. The wood air dries fairly rapidly; air drying of 13 mm, 25 mm and 38 mm thick boards of P. javanicum takes 1.5 months, 2 months and 3.5 months, respectively. Kiln drying of 25 mm thick boards from green to 10% moisture content takes 5 days with a drying temperature of 54C to 83C and a relative humidity of 84% to 30%. The wood is soft to moderately hard, moderately strong and tough. It is easy to work and gives a smooth finish; the machining properties of P. celebicum are rated lowest and those of P. diversifolium highest. The wood is durable for interior use and reputedly for use under water. The sapwood is susceptible to moderately resistant to Lyctus . The resistance of the wood to termites is variable. The wood of P. javanicum is resistant to wood-rotting fungi. The wood is moderately easy to easy to treat with preservatives.

The gross energy value of the wood of P. diversifolium is 19 530-20 350 kJ/kg, that of the heartwood of P. javanicum is 20 350 kJ/kg.

See also the tables on microscopic wood anatomy and wood properties.

Botany

Medium-sized to large trees up to 45 m tall; bole short or crooked but sometimes fairly straight and branchless for up to 30 m, often fluted, up to 100(-120) cm in diameter, buttresses usually present, short to stout (up to 2 m high), rounded; bark surface smooth, distantly scaly or shallowly fissured, lenticellate, pale brown to grey or sometimes dark brown, inner bark fibrous, red or red-brown with white streaks; crown usually becoming somewhat flattened, coppery. Leaves alternate, simple, often unequal at base (often peltate in young trees), entire, wavy or toothed, densely hairy below; stipules present. Flowers solitary or up to 3 together in leaf axils or pseudoterminal, generally large and showy, bisexual, 5-merous, white or yellow; calyx appearing tubular with cohering or free sepals; petals strap-shaped; short androgynophore present; stamens in 5 bundles of 3, staminodes 5; ovary superior, 5-locular with many ovules in each cell, style slender. Fruit an oblong, woody, many-seeded capsule. Seed flattened, winged on one side. Seedling with epigeal germination; cotyledons emergent, leafy; hypocotyl elongated; leaves conduplicate, all arranged spirally.

The leaves of saplings are different from those of mature trees; they are often peltate and lobed or toothed. Growth is rapid, as observed in trials in Java. The mean height and mean diameter of P. javanicum trees are 11.9-12.5 m and 11.4-11.8 cm when 5.5 years old and 18.1 m and 24.3 cm when 13 years old. In another trial 17-year-old trees even measured 24 m in height and 40 cm in diameter. The trees flower every year or sometimes even twice a year. In Java P. javanicum flowers in June-July and bears ripe fruits in October-December. In Thailand P. diversifolium flowers in February-April and fruits in March-May.

P. javanicum var. montanum Koord. & Valeton has been described from Java. No complete taxonomical revision exists. It seems probable that the number of species will be considerably reduced when specimens and species from different regions are compared.

Ecology

Pterospermum occurs scattered in primary forest or locally abundantly in secondary forest and especially on river banks, often on alluvial soils, up to 1400 m altitude.

Silviculture Pterospermum can be propagated by seed. P. diversifolium has about 19 500 dry seeds without wings per kg, for P. javanicum the range is wide, being 7000-54 000 dry seeds/kg. Seeds can be stored for a maximum of two weeks, hence they should be transported in the form of fruits. Seeds of P. javanicum gave 45-100% germination in 4-20 days. They should be sown in the shade and at the final spacing in nursery beds, as the young seedlings cannot withstand being pricked out. Direct sowing or planting of wildlings has been done, in the latter case development of the seedlings is fairly slow. When seedlings are planted in the field at 3 m × 1 m or 3 m × 2 m, the canopy closes after three years and the first thinning is necessary after five years. Early thinning is important to prevent the formation of too slender stems which tend to bend. The yield in these trials was 51-64 m³/ha when 8 years old and 98 m³/ha when 13 years old, irrespective of the stem wood volume of thinnings. Trees generally coppice well and resprout after fire. Pterospermum trees are fast-growing and light-demanding and regeneration in natural forest is restricted to gaps and forest fringes. P. lanceaefolium Roxb. originating from Vietnam has been planted in Java and measured 13.0 m in height and 21.5 cm in diameter at the age of 24 years.

Genetic resources and breeding

Several Pterospermum species are at least locally common, and they do not seem endangered. However, other species are now considered as rather narrow endemics, especially in the Philippines, and this calls for caution, at least as long as a thorough taxonomical revision is wanting. The major drawback for its use for timber is the often poor form of the bole. P. javanicum var. montanum , however, has a superior bole form and could be of interest for future breeding activities.

Prospects

Pterospermum seems to have good prospects for enrichment planting in selective logging systems and for plantations, as it regenerates usually well in disturbed forest and grows fast. Moreover, the wood is of fair quality, but breeding for a better bole form seems essential.

Literature

40, 61, 70, 101, 130, 151, 163, 198, 209, 235, 259, 260, 267, 376, 387, 405, 406, 427, 436, 464, 488, 633, 678, 740, 741, 757, 758, 780, 783, 829, 831, 861, 888, 933, 934, 947, 1177, 1199, 1221, 1239, 1242.