Alstonia (PROSEA Timbers)

Plant Resources of South-East Asia
Introduction

Protologue: On Asclepiad.: 64 (1810).

Family: Apocynaceae

Chromosome number: x= 11; A. macrophylla: 2n= 22, A. scholaris: n= 20, 22, 2n= 22, 44

Trade groups

Pulai: (very) lightweight hardwood, e.g. Alstonia pneumatophora Backer ex den Berger, A. scholaris (L.) R.Br., A. spatulata Blume.

Hard alstonia: medium-heavy hardwood, e.g. A. macrophylla Wallich ex G. Don, A. spectabilis R.Br.

Vernacular names

Pulai

white cheesewood, white pine, milkwood, milky pine (En)
Shaitan (Fr)
Brunei: pelai (Malay)
Indonesia: kayu susu (general), rita (Sulawesi)
Malaysia: basong (Peninsular), mergalang (Sarawak)
Papua New Guinea: white cheesewood, milky pine
Philippines: dita (general)
Burma: lettok, sega, shaitan
Thailand: sattaban (central), thia
Vietnam: cây mò cua, cây sữa.

Hard alstonia

hard milkwood (En)
Malaysia: pulai bukit
Philippines: batino (Pilipino)
Thailand: thungfa (peninsular).

Origin and geographic distribution

Alstonia consists of about 40 species and occurs in a continuous belt in the paleotropics. It ranges from tropical West Africa to the Marquesas in the far eastern Pacific and from the Himalayas in the north to New South Wales in the south. Two species are native in tropical Africa, 4 in Australia, about 15 in the Pacific region, 12 in the Malesian region and the rest occur in continental Asia. A. scholaris is the most widespread species and occurs from India and Sri Lanka through Indo-China (including southern China) towards Malesia, south to Queensland and east to the Solomon Islands. Several species have been planted outside their natural area of distribution.

Uses

Due to its weakness, pulai is not recommended for structural purposes. It is suitable for boxes, crates, coffins, drawing boards, picture frames, matches, shuttering, interior trim, furniture components, prahus, foundry patterns and handicrafts such as wooden shoes, toys, puppets and masks. The occurrence of large latex traces makes it unsuitable for face veneers but it can be applied as core wood in plywood production. The pulp obtained from the wood has satisfactory paper-making qualities. The wood produces a poor-quality charcoal and as a match timber it is inferior to terentang ( Campnosperma spp.). The root wood of several species of pulai is amongst the lightest woods of the world. It is called "basong" and has been used for making pith helmets and floaters for nets; it is an inferior alternative to cork.

Hard alstonia, being stronger than pulai, can be applied for medium and sometimes even for heavy constructional work, railway sleepers and boarding. When properly protected against the weather and fungal and insect attacks, it can be used for house building; it has been used for beams, rafters and joists. Because of its wavy and attractive grain it is also used for making furniture and cabinets.

A latex which contains alkaloids can be tapped from the bark (though not from the bark of hard alstonia). The latex is important and is often used in traditional medicine. In Fiji it has been applied to people with eye troubles. Mixed with oil, it has been used to treat earache. The bark is used against malaria and is the source of a popular drug in the Philippines. It is also popular in India and Java to treat diarrhoea and dysentery. The leaves are used medicinally against all diseases of the skin. An extract of the roots, leaves and latex of A. scholaris is used as a febrifuge. The latex of that species is used for chewing gum. Outside Malesia other species are used for this purpose too. Some species of pulai are planted as ornamental trees because of their pagoda-like crown.

Production and international trade

The export of sawn pulai timber in Indonesia increased from 50 000 m³ (with a value of US$ 8.7 million) in 1987 to 70 000 m³ (with a value of US$ 12.3 million) in 1988 and 90 000 m³ (with a value of US$ 18.5 million) in 1989. Pulai ranks among the six most important export timbers of Indonesia. Because of its lightness and limited uses, sawn pulai timber does not fetch a high price compared with other export timbers: US$ 206/m³ in 1989.

The production and trade of pulai in Malaysia is less than in Indonesia; Sarawak and Sabah export small amounts of this timber (e.g. in 1992 the export of round logs of pulai from Sabah was 20 000 m³ and of sawn timber 9500 m³, worth US$ 3.1 million). In Papua New Guinea pulai is not ranked among the most important export timbers; it is in MEP (Minimum Export Price) group 5 and fetched a minimum export price of US$ 40/m³for saw logs in 1992. Papua New Guinea exports small amounts of hard alstonia timber, mainly to Japan. In the Philippines pulai seldom reaches the market.

Properties

Pulai is a lightweight hardwood. The heartwood is cream-white, sometimes weathering to yellow-brown, and not clearly differentiated from the sapwood. The density of the wood is 210-500 kg/m³ at 15% moisture content. However, the root wood may be much lighter, 48-80 kg/m³ at 15% moisture content. The grain is straight or interlocked, texture moderately fine to moderately coarse. Planed surfaces are moderately lustrous, the tangential surface occasionally with zigzag markings.

At 15% moisture content, the modulus of rupture is 33-52 N/mm², modulus of elasticity 6300-9000 N/mm², compression parallel to grain 22-32 N/mm², compression perpendicular to grain 2-4 N/mm², shear 5-7 N/mm², cleavage 26-45 N/mm radial and 30-51 N/mm tangential, Janka side hardness 725-2000 N and Janka end hardness 1315-3225 N.

The rates of shrinkage are moderately low, from green to 15% moisture content about 2.3% radial and 2.8% tangential, and from green to oven dry 3.1-3.4% radial and 4.9-6.1% tangential. Pulai air dries fast and easily, and without defects except for slight cupping, bowing, twisting and end checking. Boards of 15 mm thick take 1-1.5 months to air dry, boards of 40 mm thick approximately 2.5 months. In Malaysia, kiln schedule J is recommended; boards of 25 mm thick can be kiln dried from 50% to 10% moisture content in about 5 days. Pulai is very susceptible to fungal and insect attack during drying; it should be treated chemically or dried quickly.

Pulai is easy to saw, plane and bore in green as well as in air-dried condition; dry wood is easy to turn. The surfaces produced are generally smooth. The wood has an excellent resistance to splitting when nailed. Tests in Indonesia on the machining properties of wood of A. pneumatophora showed good results for sanding, planing, turning and shaping, and moderate results for boring and mortising. Tests on A. angustiloba wood showed good results for turning, but moderate for planing and poor for shaping, boring, mortising and sanding. In Indonesia, veneer with a smooth surface has been made at a 90peeling angle from A. scholaris without pretreatment; glued with urea-formaldehyde, the veneer makes good plywood. On the other hand, tests in Malaysia showed that pulai is easy to peel but produces veneer with fuzzy grain; clean veneer is difficult to obtain due to the presence of traces of latex. In Malaysia, pulai is considered unsuitable for producing veneer. The wood gives a sulphate pulp with satisfactory paper-making qualities.

Pulai is non-durable; it is very perishable in exposed conditions and in contact with the ground. Graveyard tests in Indonesia and Malaysia showed an average service life in contact with the ground of 6-16 months. The wood is very susceptible to blue stain and dry-wood borer attack. It is poorly to moderately resistant to dry-wood termites. Pulai is easy to treat with preservatives. Using the open tank method, the wood absorbs 300-560 kg/m³of an equal mixture of creosote and diesel fuel. The wood is also easy to treat by the vacuum-pressure process with CCA preservative.

Wood of A. scholaris contains 54% cellulose, 25% lignin, 15% pentosan, and 0.9% ash. Pulai contains no silica. The solubility is 1.4% in alcohol-benzene, 0.3% in cold water, 3.6% in hot water and 11.1% in a 1% NaOH solution. The energy value is 19 900 kJ/kg.

Hard alstonia is a moderately heavy hardwood. The heartwood is yellowish-white to pale yellowish-brown and not distinctly demarcated from the sapwood. The density of the wood is 560-850 kg/m³ at 15% moisture content. The grain is moderately interlocked, texture moderately fine. This timber is much stronger and much harder than pulai. The shrinkage rates are low to moderately low, from green to 15% moisture content 1.4% radial and 2.7% tangential, and from green to oven dry 3.2% radial and 4.7% tangential. Hard alstonia seasons well, although warping and checking occur. It is easy to work and takes a good finish. It is fairly durable, even when exposed to the weather or in contact with the ground.

The latex contains triterpenes, particularlyα-amyrin, ß-amyrin and lupeol. Leaves and bark contain alkaloids which have medicinal and poisonous properties.

Description

Shrubs or small to large, evergreen or (rarely) deciduous, laticiferous trees of up to 50 m tall; bole straight, generally coarsely fluted at the base and up to 125 cm in diameter; bark surface generally tessellated with small scales or shallowly fissured, appearing smooth at a distance, variable in colour, generally pale or purplish-black, outer bark granular, inner bark cream, soft, frequently conspicuously exuding sticky white latex; branches verticillate, mostly 4-5 together, distant.
Leaves verticillate (or sometimes opposite) in verticils of 2-8, simple, entire, with very variable shape (even in the same tree), from lanceolate to obovate and obtuse to acute or acuminate, glabrous or sometimes hairy, generally fleshy but drying papery; venation pinnate, with many parallel secondary veins often linked near the margin by a hardly looped intramarginal vein; petiole generally short and unswollen, with or without intrapetiolar stipules.
Inflorescence cymose, terminal, usually 1-5 together, thyrsoid or compound-subumbellate.
Flowers actinomorphic, bisexual, protandrous, generally small and fragrant; calyx 5-lobed, united at base into a short tube; corolla white, yellow or red, with 5 rotate, contorted, imbricate and spreading lobes, tube long, cylindrical, widening around the anthers, thickened at the throat, rather densely pubescent inside just below the stamens and on the lobes; stamens included, inserted on the corolla tube, with short but distinct filaments, anthers basifixed, introrse, triangular to narrowly triangular, apices touching each other above the stigma in bud; disk annular, entire or lobed, free or adnate to the ovary, often indistinct; ovary superior, with 2 carpels, apocarpous or syncarpous, with 2 placentas per locule, ovules numerous, in 2-many rows, style 1, long and filiform to very short, glabrous, with 2 short stigmas.
Fruit composed of 2 follicles, free or connate at the base (sometimes united into a single capsule), woody, long and slender, dehiscent along an adaxial suture, inconspicuously striate outside, containing many seeds.
Seed with endosperm, thin, flattened, minutely foveolate, glabrous or (often dorsally) pubescent, ciliate at both ends, sometimes winged.
Seedling with epigeal, erect hypocotyl; cotyledons leaf-like, thin, oblong or ovate-oblong with an obtuse top and rounded base; leaves decussate, exstipulate.

Wood anatomy

Macroscopic characters

Sapwood very wide, not well defined from the yellowish, cream-white or straw-coloured to pale yellow-brown heartwood; in the pulai group, true heartwood is often not present. Grain straight to interlocked. Texture moderately fine to moderately coarse, variable; wood with an attractive figure in species with higher density. Growth rings generally not evident, sometimes with a tendency to indistinct rings, particularly in species with denser wood; vessels intermediate to small in size, distinct or indistinct to the naked eye; parenchyma bands sometimes evident; rays not evident without lens. Characteristic latex traces appear as open slit-like radial passages.

Microscopic characters

Growth rings not evident, sometimes vaguely indicated, particularly in species with denser wood, due to zones of thicker-walled fibres.
Vessels diffuse, few (2-3/mm²) to numerous (more than 20/mm²), evenly distributed, typically in radial multiples of 2-3(-6) and sometimes in clusters, solitary vessels few, rather angular in transverse section, small to large, tangential diameter ranging from 70-220μm, generally with maximum tangential diameter of 150-220μm in the pulai group and less than 120μm in the hard alstonia group; perforation plates simple, markedly oblique; intervessel pits alternate, vestured, small (c. 3μm); vessel-ray pits half-bordered, otherwise similar to intervessel pits, occasionally unilaterally compound.
Fibres 1200-1760μm long, non-septate, thin- to moderately thick-walled, pits small but distinctly bordered; tension wood fibres often present.
Parenchyma abundant apotracheal, diffuse or in fine, numerous, wavy or discontinuous lines of 1 cell wide in species with small pores, or in 1-2 cell wide moderately closely spaced bands, irregular to loosely regular in other species; paratracheal parenchyma sparse to absent, strand length 5-10 cells. Rays 6-7/mm, (1-)2-3(-4)-seriate, uniseriate rays few, generally 20-30 cells high, occasionally up to 40 cells high, uniseriate rays heterocellular with 3-4 rows of marginal upright cells and 2-3 rows of marginal procumbent cells of larger vertical dimensions than the central procumbent cells; with small latex tubes only in the pulai group.
Chambered prismatic crystals moderately abundant in parenchyma strands, central ray cells and sometimes in the marginal rays cells of the hard alstonia group.
Silica absent.

Species studied: A. angustiloba, A. macrophylla, A. scholaris, A. spatulata, A. spectabilis.

The wood of Dyera costulata (Miq.) Hook.f. (jelutong) is very similar to pulai wood, but it can usually be distinguished by its very fine, regularly spaced uniseriate bands forming a reticulate pattern with the rays.

Growth and development

Seedlings are vigorous and hardy, and young trees demand full light in order to grow vigorously. Under favourable conditions they are undoubtedly fast growers, although no data are available on growth rates. Young trees of most species have a pagoda-like crown with a monopodial appearance (according to Prévost's architectural tree model). The growth of branches is intermittent. However, crowns of A. angustifolia and A. macrophylla are of normal sympodial structure, even when young (Koriba's architectural tree model).

The trees are often deciduous at irregular intervals. They do not flower at every leaf-change, but only after marked periods of dry weather. The large branches of big pulai trees provide favourable nesting sites for wild bees.

Pollination is by insects; when flowering, trees are often surrounded by butterflies and bees. The fruits open on the tree and the seeds, which have a tuft of silky hairs at each end, are dispersed by wind.

Other botanical information

The genus Alstonia is divided into 5 sections, mainly on the basis of seed morphological characteristics. The sections Alstonia and Monuraspermum Monach. occur in Malesia. They mainly differ from each other by the number of secondary veins, direction of the contortion of the corolla lobes, shape of the seed and architecture. Pulai trees often resemble jelutong (Dyera costulata) trees, but they can be distinguished by their usually tall buttresses and typically fluted stems. Within South-East Asia Alstonia can also be confused with the genera Rauvolfia, Tabernaemontana and Ochrosia, which all have verticillate leaves, but Alstonia can be distinguished by its slender fruits and ciliate seeds. The name Alstonia R.Br. is conserved as a later homonym of Alstonia Scop. which is a synonym of Pacouria Aublet (Apocynaceae). Giant stomata have been observed in A. macrophylla.

Ecology

Species of Alstonia grow in both primary and secondary lowland evergreen to deciduous rain forest. They occur on humus-rich clayey soils but also on sandy or even limestone soils and in places which are periodically inundated and carry swamp or peat-swamp forest, to comparatively dry areas with savanna woodlands. In Sarawak several distinct subtypes of mixed peat-swamp forest can be distinguished, in one of which pulai (A. pneumatophora) occurs in association with terentang (Campnosperma spp.) and in another in association with meranti (Shorea spp.). The species occur from sea-level to up to 1000 m altitude, and in the area of distribution the annual number of dry months ranges from 0 to 3.

Propagation and planting

Seeds are difficult to collect, as the fruits open while still on the trees. The weight of 1000 seeds is about 1.5-2 g. The germination rate of fresh seeds is high, nearly 100%. Seeds can be stored in closed tins for 2 months, maintaining a germination rate of 90%. Seeds of A. angustiloba germinate in 2-8 weeks after sowing. In Indonesia, seedlings are planted into the field when they are 15-25 cm tall, with spacing of 1 m × 2 m and interplanted with Leucaena leucocephala (Lamk) de Wit.

A. scholaris has been grafted. Cleft grafting and inverted T-grafting have been found to be most appropriate.

Silviculture and management

Natural regeneration of pulai is often scarce, and seedlings are found scattered or in groups, particularly in open places at forest edges and in secondary forest. Regeneration can be enhanced by enrichment planting using the strip system, but sufficient opening of the canopy is essential for optimal growth of the seedlings. There is hardly any experience with silviculture of pulai. Young pulai trees coppice well.

Harvesting

In most countries of South-East Asia pulai is harvested selectively from natural forest, with a diameter limit of 40 cm, 50 cm or 60 cm. Pulai logs float easily in water when freshly cut, but they tend to become waterlogged and to sink after some weeks. The logs are very susceptible to insect and fungal attack and should be dried quickly or treated with preservatives after felling. The latex is harvested by making incisions in the bark.

Genetic resources

Most Alstonia species are common and widely distributed, although they occur scattered, and do not seem immediately liable to genetic erosion, largely because they often easily invade severely disturbed places. However, stands are heavily depleted locally as a result of deforestation caused by logging and shifting cultivation (e.g. in the Philippines) and the remaining stands need protection.

Prospects

As a fast-growing tree, pulai seems to have good prospects for timber production, notwithstanding the limited uses of the timber. Research on all silvicultural aspects is highly desirable, and experimental plantations should be established and studied.

Literature

Ashton, P.S., 1988. Manual of the non-dipterocarp trees of Sarawak. Vol. 2. Sarawak Branch for Forest Department, Sarawak. pp. 18-26.
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. 8-11.
Browne, F.G., 1955. Forest trees of Sarawak and Brunei. Government Printing Office, Kuching. pp. 63-66.
Cockburn, P.F., 1976. Trees of Sabah. Vol. 1. Forest Department, Sabah, Kuching. pp. 15-18.
Markgraf, F., 1974. Florae Malesianae praecursores LIV. Apocynaceae III. 9. Alstonia. Blumea 22: 20-29.
Martawijaya, A., Kartasujana, I., Kadir, K. & Prawira, S.A., 1986. Indonesian wood atlas. Vol. 1. Forest Products Research and Development Centre, Bogor. pp. 115-119.
Meniado, J.A., America, W.M. & Tamolang, F.N., 1976. Technical information on dita (Alstonia scholaris (L.) R.Br.). Forpride Digest 5: 53-58.
Monachino, J., 1949. A revision of the genus Alstonia (Apocynaceae). Pacific Science 3: 133-182.
Sim, H.C., 1982. Malaysian timbers - pulai. Malaysian Forest Service Trade Leaflet No 64. Malaysian Timber Industry Board, Kuala Lumpur. 7 pp.
Whitmore, T.C., 1983. Apocynaceae. In: Whitmore, T.C. (Editor): Tree flora of Malaya. A manual for foresters. 2nd edition. Vol. 2. Longman Malaysia SDN Berhad, Kuala Lumpur. pp. 7-12.

Selection of species

Authors

Rudjiman (general part, selection of species),
N. Gintings (general part),
A. Martawijaya (properties),
J. Ilic (wood anatomy)