6489

5(3): Timber trees; Lesser-known timbers

Xylia Benth.

Journ. Bot. (Hooker) 4: 417 (1842).

LEGUMINOSAE

x = 12; X. xylocarpa: n = 12

Burma (Myanmar): pyinkado. Cambodia: sô-kra:ch, sô-krâm krâhâ:m, sô-krâm sâ:r. Laos: dêng. Thailand: daeng (general). Vietnam: c[aw]m xe.

Xylia comprises about 12 species, most of which occur in tropical Africa and Madagascar. Only one species occurs in South-East Asia: X. xylocarpa (Roxb.) Taubert (synonym: X. dolabriformis Benth.); it is not found in the wild in Malesia, but occurs in India, Burma (Myanmar), Indo-China and Thailand. It is also planted within its natural area of distribution, rarely outside this region, occasionally so in Singapore and Peninsular Malaysia.

The hard and durable wood of X. xylocarpa is used for heavy construction, e.g. for posts and flooring, bridges, marine piling, railway sleepers, boat construction, freshwater locks, paving blocks, rubbing fenders, chutes and for furniture, turnery and household implements.
The bark and fruits are used in local medicine; in Indo-China in a decoction against haemoptysis.

Large supplies of timber of X. xylocarpa are available, particularly in Burma (Myanmar). At the beginning of the 1980s the annual production of logs in Burma (Myanmar) was about 20 000 t.

X. xylocarpa yields a heavy hardwood with a density of 880-1170(-1330) kg/m³ at 15% moisture content. Heartwood reddish-brown to dark brown, distinct from the up to 2.5 cm wide paler sapwood; grain interlocked or wavy; texture moderately fine to medium and even; surface somewhat gummy causing a speckled appearance. Growth rings distinct to indistinct, when distinct indicated by narrow parenchyma bands; vessels moderately small to moderately large, solitary and in radial multiples of 2-4, occasionally in oblique arrangement, frequent orange-brown gum deposits and chalky white deposits; parenchyma moderately abundant to abundant, paratracheal vasicentric, aliform and confluent, with occasional apotracheal parenchyma in very narrow marginal or seemingly marginal bands; rays very fine, visible with a hand lens; ripple marks absent.
Shrinkage is low, but the wood requires careful and slow seasoning to prevent checking and splitting; in kiln drying it needs a mild and slow drying schedule. The wood is very hard and very strong. It is difficult to work and plane and has a serious blunting effect on tools, but a good finish can be obtained. Green stock, however, is easier to saw. The wood is very durable: untreated sleepers lasted for 12 years in Thailand and for 20-24 years in India. The heartwood is very resistant to preservative treatment, the sapwood is readily treatable. The wood is susceptible to longhorn and buprestid beetle attack, the sapwood to Lyctus, but the wood is resistant to termites and marine borers.
See also the tables on microscopic wood anatomy and wood properties.

A deciduous, medium-sized tree up to 25(-40) m tall; bole straight and cylindrical, sometimes fluted, branchless for up to 12(-25) m and up to 75(-120) cm in diameter, buttresses small or absent; bark surface flaky, with small lenticels, greyish to reddish or yellow-brown, inner bark pinkish; crown dense. Leaves arranged spirally, bipinnate with 1 pair of pinnae, rachis and pinnae glandular; leaflets opposite, 3-6 pairs per pinna, entire; stipules filiform. Flowers in stalked globose heads, male or bisexual, 5-merous; calyx funnel-shaped, hairy, with valvate lobes; petals free, hairy; stamens 10, free; ovary superior, sessile, hairy, 2-locular, style 1. Fruit a boomerang-shaped, flat, woody pod, dehiscing from the apex in 2 recurving valves, 7-10-seeded. Seed ellipsoid, flat, testa hard and brown, with pleurogram. Seedling with epigeal germination; cotyledons emergent; hypocotyl elongated; first pair of leaves opposite, with 1(-2) pairs of leaflets, sometimes 3-foliolate, subsequent leaves arranged spirally.
The growth rate of young trees is reportedly fairly high: in India trees were on average 5.7 m tall and 8 cm in diameter after 5 years, in Bangladesh 16 m tall and 19 cm in diameter after 10 years. In Malaysia a 23-year-old tree grown in the arboretum of the Forest Research Institute Malaysia, Kepong measured 22 m tall and 30 cm in diameter. Flowering is in March-June, fruiting in November-December.
Xylia belongs to the tribe Mimoseae of the subfamily Mimosoideae, and seems most closely related to the West African genus Calpocalyx. Within X. xylocarpa two varieties are distinguished: var. xylocarpa from India and Burma (Myanmar) with subglabrous leaflets and glandular anthers, and var. kerrii (Craib & Hutch.) I.C. Nielsen (synonym: X. kerrii Craib & Hutch.) from Burma (Myanmar), Indo-China and Thailand with hairy leaflets and eglandular anthers.

X. xylocarpa occurs in dry evergreen forest, mixed deciduous forest and dry deciduous dipterocarp forest, on well-drained, sandy and rocky soils, up to 850 m altitude.

X. xylocarpa can be raised from seed, which can be stored for 1 year if kept dry. Seed viability is high and germination occurs readily when sown under shade and with adequate watering. Direct seeding is recommended, as seedlings do not stand the shock of planting well, probably because the taproot develops rapidly and attains 30 cm in 1-2 months. Stumps of 8-10 months, however, can also be successfully used, but are more costly. In India direct seeding is done at a spacing of 2 m x 3 m and plantations require weeding for 2 years. In Vietnam and Laos direct seeding in enrichment plantings failed. Natural regeneration is enhanced by slightly opening the canopy around seed-bearing individuals and burning the debris; seedling establishment is favoured on loose, bare, well-drained soils under shade. The young seedlings must be protected from fire. A gradual opening of the canopy is necessary for further development of the established seedlings; weeds only become a problem when the canopy is opened too fast. X. xylocarpa coppices and pollards well and can produce abundant root suckers. Well-established trees resprout from burnt stumps. Trees of 26 years produced about 10 t/ha of litter annually. In Bangladesh a 10-15-year rotation for the production of power transmission poles has been suggested. X. xylocarpa is fire-resistant.

In many regions within its natural area of distribution X. xylocarpa is common, and large supplies of timber are available. However, many stands are already much depleted provoking genetic erosion.
In Cambodia two forms are distinguished which differ in wood colour: one is red-brown, the other pale red-brown.

The wood of X. xylocarpa is of excellent quality. The tree has a high potential to be grown in plantations as it grows fairly fast. However, techniques of establishment and the management of the light regime during the first years need to be further investigated. X. xylocarpa has been proposed in taungya systems to be interplanted with teak (Tectona grandis L. f.) as it has good soil-improving properties.

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Nguyen Ba

Ba, N., 1998. Xylia Benth.. In: Sosef, M.S.M., Hong, L.T. and Prawirohatmodjo, S. (Editors): Plant Resources of South-East Asia No 5(3): Timber trees; Lesser-known timbers. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea