Ailanthus (PROSEA Timbers)
- Protologue: Mém. Acad. Sci., Paris 1786: 265 (1788).
- Family: Simaroubaceae
- Chromosome number: x= unknown; A. altissima: 2n= 64, 80, A. integrifolia subsp.calycina: n= 31, 32
White siris: lightweight hardwood, Ailanthus integrifolia Lamk, A. triphysa (Dennst.) Alston.
The timber is sometimes traded together with similar timbers as "mixed light-coloured hardwood". Sometimes the wood of Albizia procera (Roxb.) Benth. is also traded as white siris.
- White siris (En)
- Indonesia: kayu langit.
Origin and geographic distribution
Ailanthus consists of 5 species and its natural distribution is from Turkestan and India to China, through Malesia towards the Solomon Islands and north-western Australia. Two species occur naturally within Malesia. They have large areas of distribution, but are rare in most regions; A. integrifolia is locally common in New Guinea and the Bismarck Archipelago.
White siris is used for parts of furniture, laminated wood, drawers, ceilings, wooden shoes, moulding, toys, shingles, matchsticks, matchboxes, core of plywood, weatherboards, interior trim, brush stocks, pattern making, paper pulp, fuel and charcoal.
The leaves, bark, roots and resin have medicinal properties; they are used to prepare tonics, as febrifuge and against indigestion. In Vietnam, the leaves are used to dye silk black. The resin is burned for its pleasant fragrance (gaharu).
Production and international trade
Japan imports small amounts of white siris timber, mainly from Papua New Guinea, little from other areas. White siris accounts for about 1% of the total amount of timber imported in Japan from Papua New Guinea. In Papua New Guinea the wood is ranked in MEP (Minimum Export Price) group 4; logs fetched a minimum price of US$ 43/m3 in 1992.
White siris is a lightweight and comparatively soft wood. The heartwood is yellowish-white to pale brown and not distinctly demarcated from the sapwood. The density is 330-435 kg/m3at 12% moisture content. The grain is straight to shallowly interlocked, texture moderately coarse.
At 12% moisture content, the wood of A. integrifolia has the following mechanical properties: the modulus of rupture 54.5-62 N/mm2, modulus of elasticity c. 9175 N/mm2, compression parallel to grain 36 N/mm2, shear 5.5 N/mm2, cleavage 29.5 N/mm radial and 23 N/mm tangential, and Janka side hardness 1715 N.
The rates of shrinkage are fairly low to moderate: from green to 15% moisture content 1.0-1.5% radial and 2.3-4.0% tangential, from green to 12% moisture content c. 2.1% radial and 3.7-4.7% tangential, and from green to oven dry 2.8-4.2% radial and 5.2-8.1% tangential. The wood is easy to air dry and kiln dry, although sometimes liable to develop fine long surface cracks.
White siris wood is difficult to split but easy to saw, work and polish. It holds nails well. Veneer made from white siris may have a very fuzzy surface.
The wood is non-durable. It is often liable to staining. However, white siris is easy to treat with preservatives. The retention by the pressure treating method is 600 kg/m3 in the heartwood, and 665 kg/m3 in the sapwood of A. integrifolia.
Wood of A. integrifolia contains 74% holocellulose and 51%α-cellulose (calculated on an ash- and lignin-free basis), 31% lignin and 0.8% ash. The solubility is 0.9% in alcohol-benzene, 0.8% in cold water, 1.5% in hot water and 10.5% in a 1% NaOH solution. The inner bark tastes very bitter.
- Large, dioecious, evergreen or sometimes deciduous trees up to 60 m tall; bole cylindrical, up to 85(-175) cm in diameter, buttresses absent; bark surface smooth or with irregular fissures, grey-white to pale brown or greenish-brown, outer bark 1.5-2 cm thick, inner bark fibrous, grey-white or grey-brown; branches thick, with large leaf scars.
- Leaves more or less tufted at the end of twigs, arranged spirally, paripinnate or imparipinnate; stipules absent; leaflets opposite or subopposite, stalked, generally with some glands below or at the base.
- Inflorescence an axillary panicle.
- Flowers unisexual, 5(-6)-merous, zygomorphic; calyx small, 5(-6)-lobed or closed in bud and later irregularly splitting to the base (often in two parts), rarely cupular; petals 5(-6), free, induplicate-valvate in bud, concave, oblong or narrowly oblong;stamens 10, in female flowers either subnormal but without pollen, or vestigial, or absent; carpels 2-5, free, flat, in male flowers vestigial or absent, ovule 1 per locule, styles 2-5, free or united.
- Fruit a linear or oblong-lanceolate samara. Seed flat, orbicular or obovate or somewhat triangular, without endosperm, with a thin testa.
- Seedling with epigeal germination.
- Macroscopic characters:
- Heartwood yellowish-white to pale brown-yellow, not clearly demarcated from the pale yellow sapwood.
- Grain straight to shallowly interlocked.
- Texture moderately coarse; fiddleback figure sometimes present.
- Growth rings indistinct.
- Vessels visible to the naked eye, tyloses sparse to rather frequent.
- Parenchyma usually not distinct without a lens.
- Rays conspicuous.
- Ripple marks absent.
- Microscopic characters:
- Growth ring boundaries indistinct.
- Vessels diffuse, 2-3/mm2, solitary and in radial multiples of 2-3(-4), rarely in clusters, generally oval, average tangential diameter 100-270μm; perforation plates simple; intervessel pits numerous, alternate, polygonal, c. 6μm, often with coalescent apertures; vessel-ray and vessel-parenchyma pits half-bordered, c. 6μm; pronounced reticulate thickenings sometimes present on the inner face of vessel walls; tyloses sparse to rather frequent.
- Fibres 600-2000μm long, non-septate, very thin-walled, with rather numerous, minutely bordered pits with vertical slit-like inner apertures, entirely confined to the radial walls.
- Axial parenchyma winged-aliform to confluent; paratracheal parenchyma rather abundant, on the radial sides of the vessels usually passing into short, sometimes long, tangential bands 1-4 cells wide; parenchyma strands 2-4(-8)-celled.
- Rays 3-4/mm, 1-8-seriate (mostly 5-6-seriate), uniseriate rays few, 4-60 cells high, almost entirely composed of square or procumbent cells, only 1(-2) rows of marginal cells regularly shorter in radial direction or composed of upright cells in narrow rays.
- Prismatic crystals rarely present in upright ray parenchyma cells and axial parenchyma cells, usually one large crystal per cell; yellowish-brown deposits sometimes present in axial and ray parenchyma cells.
- Axial intercellular canals of the traumatic type present in long tangential bands, 160μm in average diameter.
Species studied: A. integrifolia, A. triphysa.
Growth and development
A. integrifolia is a fast-growing tree. In Java, the mean height of planted A. integrifolia was 1.8 m 2 years after planting and 4.0 m 3 years after planting, and the corresponding mean diameters were 2.9 cm and 5.3 cm, respectively. In India, 10- and 50-year-old trees of A. integrifolia were 5 m and 39 m high, respectively, and their corresponding diameters at breast height were 18 cm and 60 cm, respectively.
Pollination is probably by insects. The fruits are dispersed by wind. Natural regeneration of planted trees of A. integrifolia has been observed after only four years, but annual seed production varies greatly and seems unpredictable. Early flowering and early profuse production of seed is reported for A. triphysa too, although there are reports from India that every other year is a good seed year.
Other botanical information
The genus Ailanthus belongs to the subfamily Simarouboideae, which is by far the largest subfamily within the family; it is the only genus of importance concerning timber within this subfamily in New Guinea.
A. altissima (Miller) Swingle (synonym: A. glandulosa Desf.), a native of China known as "tree of heaven", is widely planted as an ornamental and for shade, in shelterbelts and for erosion control in subtropical and temperate countries. The wood is ring-porous and is heavier (up to 650 kg/m3 at 12% moisture content) and more durable than white siris; it is especially used for furniture and utensils. The wood of A. excelsa Roxb. is used locally in India and Sri Lanka.
White siris occurs in humid rain forest and in monsoon forest, and in Bengal (India) even in dry mixed forest. The individual species are fairly uncommon and occur scattered, but never gregariously, in valleys, along streams and in open locations below 1000 m altitude. The observed variation in mean annual rainfall is large and ranges from 1600 mm to 4560 mm. White siris is most often found on well-drained deep soils like fertile sandy loams, and usually in association with Duabanga, Chukrasia, Erythrina, Garuga, Gmelina, Terminalia and Tetrameles.
Propagation and planting
A. integrifolia is propagated by seed; it has about 1800 wingless seeds per kg and germination of fresh seed is about 60% but varies greatly. No pretreatment is required. Germination starts 3-6 weeks after sowing. Seeds of A. triphysa remain viable for three months and germination takes place within 1-3 weeks; up to 100% germination has been observed. Seeds are broadcast and need only sparse watering, as they are susceptible to rot and damping-off. Seedlings of A. triphysa develop better when provided with partial shade, although the species is light demanding. When 8-10(-30) cm tall they are planted in fertile, well-drained sites at spacings of 1-2 m × 1-2 m. Seedlings are susceptible to damage by transplanting; the root system is especially vulnerable. In Papua New Guinea there are no plantations of white siris and it is harvested only from natural forest.
Silviculture and management
In Java, a stand of A. integrifolia planted at 1 m × 3 m was thinned three years after planting. Natural pruning of this species stimulates the development of a long (up to 35 m in Papua New Guinea) branchless bole. Natural regeneration is poor in the shade of the natural forest, but is reasonably successful in open weed-free locations where mineral soil is exposed. The establishment of a plantation of A. integrifolia may benefit from a taungya system, in which a low annual crop, such as chili or eggplant, may be planted the first year.
Diseases and pests
No serious diseases and pests have been reported for white siris, although A. triphysa seedlings are liable to attack by a fungus and a defoliator.
On suitable sites, A. integrifolia may be harvested at the age of 35-40 years.
White siris is considered to grow very fast. The mean annual increment in the first ten years of a plantation of A. integrifolia in Java was 15 m3/ha, and on favourable sites in India even 20 m3/ha. A. integrifolia tree yields about 8.5 m3 of timber.
Handling after harvest
The wood should be sawn as soon as possible after harvest as it is susceptible to blue stain (Ceratocystis sp.).
In India A. integrifolia has been taken up in a germplasm bank.
White siris grows very fast and shows several desirable characters in habit and behaviour (long straight bole, restricted crown, natural pruning etc.). It may, therefore, become more important for wood production in plantations. In Papua New Guinea it is classified as a minor hardwood, but with plantation potential. However, further studies on mechanisms controlling seed output are needed as a basis for further development.
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