Acrocarpus (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Acrocarpus Wight ex Arn.

Protologue: Mag. Zool. Bot. 2: 547 (1838).

Family: Leguminosae

Chromosome number: x= unknown;A. fraxinifolius: 2n= 24

• Pink cedar, shingle tree (En)
• Indonesia: delimas (Javanese), madang pariek (Minangkabau, Sumatra). Burma (Myanmar): yetama
• Laos: ket 'hoy (Sayaboury), khan khak (Luang Prabang)
• Thailand: kang khimot, khang chang (northern), sadao chang (eastern).

Acrocarpus is a monotypic genus distributed in eastern India, Burma (Myanmar), Laos, southern China, Thailand, Sumatra and central Java. Its only species is A. fraxinifolius Arn., which is planted in many areas within and outside its natural area of distribution (e.g. in India, Africa and Central America).

The wood of A. fraxinifolius is suitable for indoor construction, furniture, plywood, packing cases, beehives and fence posts; it is also used as fuelwood and to produce charcoal.

The tree has been recommended for reinforcing river banks and to stabilize terraces, and for use in agroforestry. It is grown for shade in coffee and tea plantations, and is a good source of nectar. The foliage can be used as forage.

Acrocarpus timber is probably used on a local scale only.

A. fraxinifolius yields a medium-weight hardwood with a density of 520-700 kg/m³at 12% moisture content. Heartwood pale pinkish, bright red to reddish-brown with darker streaks, sharply differentiated from the pale yellowish sapwood; grain straight to slightly interlocked, sometimes wavy; texture coarse and even; wood lustrous. Growth rings indistinct, delimited by a fine, interrupted line of parenchyma; vessels medium-sized to very large, solitary and in radial multiples of 2-3(-more), occasionally with white deposits; parenchyma paratracheal vasicentric and aliform, visible to the naked eye; rays very fine to moderately fine and moderately broad, forming conspicuous flecks on radial surfaces.

Shrinkage upon seasoning is moderate. The wood seasons well when not too rapidly dried. In India boards 2.5 cm thick took 9 months to air dry. The wood is soft to moderately hard and strong. It is easy to work, saw and peel, especially when green. It finishes fairly well and takes a high polish. The wood is generally rated as non-durable, but Indonesian samples have been rated moderately durable. Graveyard tests in India showed an average service life of 41 months. Impregnation of the sapwood is easy, but that of the heartwood is erratic. The sapwood is highly susceptible to fungal and insect attacks.

The seed oil was found to contain 84% of lupeol.

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

A deciduous, medium-sized or sometimes large tree up to 30(-50) m tall; bole columnar, branchless for up to 10(-30) m, up to 100(-400) cm in diameter, often with small buttresses; bark surface smooth or slightly rough, pale grey or pale brown. Twigs often prominently lenticellate. Leaves bipinnate with (2-)3-5 pairs of pinnae and 4-7(-9) pairs of leaflets per pinna, with or without a terminal leaflet; petiole and main rachis up to 80 cm long; stipules small, caducous. Flowers in paniculate inflorescence in the axil of fallen leaves, bisexual, 5-merous; calyx lobes and petals imbricate; petals dark red; stamens exserted; ovary stiped. Fruit an elongated and flattened pod, long-stipitate, narrowly winged, (3-)10-18-seeded. Seed slightly lens-shaped, brown. Seedling with epigeal germination; cotyledons free, foliaceous, slightly fleshy; hypocotyl elongated; first leaves paripinnate.

Early growth is very rapid. In India seedlings were 1 m tall after 5.5 months whereas in Malawi a mean annual increment of 2-year-old plants of 2.7-3.3 m in height and 6.1-7.1 cm in diameter was reported. Growth of older trees is still rapid, as observed in India where the mean annual increment of 13-year-old trees was 1.1 m in height and 2.9 cm in diameter and that of 23-year-old trees 0.8 m and 2.2 cm, respectively. Young leaves are characteristically bright red. The trees flower after shedding their leaves. In India flowering and fruiting occur almost every year. Apparently, A. fraxinifolius does not have nitrogen-fixing nodules.

A. fraxinifolius grows best in submontane areas in the humid and subhumid tropics with a short dry spell, but is very sensitive to frost. It is rare in Sumatra and Java where it occurs on fertile and constantly wet soils in the forest, sometimes on abandoned agricultural land, at 600-1200 m altitude. In Thailand it occurs in evergreen gallery forest. In India and Burma (Myanmar) it is more frequent and occurs in regions with an annual precipitation of over 2000 mm, growing best in deep, well-drained, clay-loam soils with a pH of 4-7. It regenerates primarily in small, burnt areas, on open patches where fresh soil has been exposed and along newly constructed roads. A. fraxinifolius is a light demander and a pioneer, but can tolerate slight shade when young.

Silviculture A. fraxinifolius can be propagated by seed; the use of wildlings is reported for India. Patch budding gave 80% success when establishing seed orchards. Collected seed should be left to air dry for about 10 days and can then be stored for many years in airtight containers when kept cool. There are 13 000-47 000 dry seeds/kg. Seed should be pretreated with sulphuric acid for 10 minutes or by hot water and left to imbibe in water for 24 hours before it is sown in the shade. A germination of 80-95% within only 2-7 days is achieved after this pretreatment. Under natural conditions some seeds may germinate within a week, while others may lie dormant for one year before germinating. The seedlings are pricked out into beds or containers and placed in full sunlight. Seedlings are ready for planting when 3 months old and 30-45 cm tall. Seedlings from the nursery beds can be planted bare-rooted or as stumps or striplings. Periodic weeding is required and the first thinning must be performed 3-4 years after planting. As the trees require a large crown for optimal growth, regular thinnings are necessary until the stand is fully developed. On favourable sites a mean annual increment of 10 m³/ha may be expected. In Malawi 2-year-old trees yielded 33 t/ha of total above-ground biomass. Young trees are susceptible to termite attack, and in India Atractomorpha crenulata , a grasshopper, and the caterpillar of Eurema blanda defoliated seedlings in nurseries and young plantations. A. fraxinifolius is also a host for the wood borer Xylosandrus compactus , a small ambrosia beetle. When rainfall is insufficient (less than 1500 mm/year) and a pronounced dry season occurs, the fast early growth may be followed by stagnation and high mortality. The tree coppices vigorously. In India natural regeneration is favoured by clearing the forest floor of weeds and by raking the soil, after which the canopy is gradually removed as young trees become established.

A. fraxinifolius is rare in Malesia where it occurs only very locally. It would be worthwhile establishing germplasm collections from the Malesian populations to obtain planting material adapted to the ecological conditions in this region. This material could be used to establish timber plantations. A germplasm bank of 17 clones and a seed orchard of 16 clones have been established in Arunachal Pradesh in India. India and Kenya are the major seed-exporting countries.

A. fraxinifolius is promising for timber plantations. It is easy to raise in the nursery, its survival after planting is generally very high and it grows fast. No trial plantations have been established in the Malesian area, however.

70, 104, 130, 152, 163, 276, 343, 364, 370, 405, 436, 465, 658, 735, 861, 919, 920, 924, 928, 1039, 1064, 1104, 1177, 1190.

E. Boer & R.H.M.J. Lemmens