Common Name: Siris Tree

General Information

Albizia lebbeck is a very fast-growing deciduous tree with an open, large, spreading crown; it usually reaches a height of 15 - 20 metres, with exceptional specimens growing up to 30 metres[, ]. The straight, cylindrical bole can be 50 - 100cm in diameter, with exceptional specimens to 300cm[, , ].
In India plantation-grown siris yields a high quality hardwood that is traded in Europe as 'Indian walnut' or 'koko'[]. The tree has been widely planted in agro-forestry schemes in the drier parts of the Tropics[]. Plants are used to provide shade for coffee and cocoa plantations as well as to provide a valuable timber and fuel[]. It is a popular amenity tree throughout the dry tropics because of its shady spreading habit, although the copious litter produced beneath it is often regarded as a disadvantage[].

Known Hazards

The wood dust is aromatic and peppery. It may cause irritation to the nose and throat of sawmill workers[, ].
The bark is used as a fish poison[].
A red dye obtained from the bark has caused skin irritation[].
The pods contain saponin and are not eaten in large amounts by sheep, although cattle eat them readily[].

Botanical References

, ,

Range

E. Asia - drier areas of the Indian subcontinent and southeastern Asia to northern Australia.

Habitat

Tropical to subtropical sandy river beds and savannahs[].

Properties

Weed Potential	Yes
Medicinal Rating
Other Uses Rating
Habit	Deciduous Tree
Height	15.00 m
Growth Rate	Fast
Pollinators	Bees, Insects
Cultivation Status	Cultivated, Ornamental, Wild

Cultivation Details

Although siris will grow in the humid tropics, its natural range is in semi-arid to sub-humid areas of the tropics and subtropics that have marked dry and reliable wet seasons[, ]. However, it may be established under conditions of low (400 mm/year) and irregular rainfall[]. Plants can succeed at elevations from sea level to 1,800 metres in areas where annual daytime temperatures are within the range 26 - 36°c, but can tolerate 12 - 48°c[, ]. It prefers a mean annual rainfall in the range 600 - 2,000mm, but tolerates 500 - 2,500mm[, ]. Seedlings will not tolerate frost, but trees are moderately frost resistant when established[].
Prefers a well-drained, moisture-retentive soil and a position in full sun[]. Plants are able to succeed in most soil types, including saline but excluding cracking clay, so long as they are well drained[]. Tolerant of degraded or nutritionally poor soils[]. Prefers a pH in the range 6 - 7, tolerating 5.5 - 8.5[]. Established plants are very drought tolerant[]. Seedlings will not tolerate waterlogging[]. Requires a position sheltered from strong winds[].
Widely cultivated, the tree has become established in the wild in various areas outside its native range and is considered to be invasive in some of these areas[].
A fast-growing species, it can reach a height of 18 metres within 10 years from seed[].
When grown as a fuel crop on a coppice rotation of 10 - 15 years, it can produce about 5 cubic metres per hectare[].
Optimum annual wood production is 15 - 20 cubic metres per hectare[].
Plants have brittle limbs that can break off in high winds[]. They also have a shallow, though wide-spreading root system that does not support them well in windy positions[].
The dried seedpods hanging on the tree constantly rattle in the wind[].
Reserves in the root system enable young plants to survive total defoliation from fire or grazing, but with an obvious setback in growth[].
The tree coppices well, responds to pollarding, pruning and lopping, and will produce root suckers if the roots are exposed[]
The trees are killed by even light fires[].
This species has a symbiotic relationship with certain soil bacteria, these bacteria form nodules on the roots and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant but some can also be used by other plants growing nearby[]. The tree is not Rhizobium specific, and native strains are nearly always capable of producing an abundance of nodules[].

Edible Uses

None known

Medicinal

The leaves and seeds are used in the treatment of eye problems such as ophthalmia[, ].

The bark is astringent[] It is taken internally to treat diarrhoea, dysentery and piles[].
The bark is used externally to treat boils[].

The flowers are applied locally to maturate boils and alleviate skin eruptions[].

The powdered seeds are used to treat scrofula[].

Saponin from the pods and roots has spermicidal activity[].

Studies have shown that a methanol extraction of the plant is a very effective treatment for diabetes[]

Agroforestry Uses:

A fast-growing tree that fixes atmospheric nitrogen and succeeds in full sun, it is an excellent plant to use as a pioneer when establishing woodland or woodland gardens, though its ability to invade areas outside its native range means that it is best used only within its native area[].
Due to its extensive, fairly shallow root system, the tree is a good soil binder and is recommended for eroded lands and erosion control, for example along river embankments[, ]. The nitrogen-rich leaves are valuable as mulch and green manure[, ].
Light transmission through the canopy of free-standing trees is 40 - 50%[]. Free-standing trees appear to enhance pasture production and quality beneath the canopy due to the increased nitrogen status of the soil[]. In an open woodland environment it has been repeatedly observed that there is modification of the ground cover with enhancement of grass production and quality beneath the canopy[].
Seedlings and cuttings are used as an initial shade in coffee, cardamom, cocoa plantations etc[, , ]. The tree is also used in rehabilitating old cocoa farms or on improved fallows intended for cocoa cultivation due to its nitrogen-fixing abilities[].
Although not completely wind firm, the tree is tolerant of salt-laden winds and can be planted in moderately exposed coastal situations and as quick-growing shelter for less hardy plants[, ].
A valued honey tree because of its production of both nectar and pollen[].

Other Uses

It seems probable that the fruits can yield 10 barrels of ethanol per hectare per year[].

The trunk yields a reddish gum that is used as an adulterant of gum arabic[].
A red dye is obtained from the bark[]. It can cause skin irritation[].

The bark contains 7 - 11% tannin and is used locally in India for tanning fishing nets[, ].

When dried and pounded, the bark can be used for soap[, ].

The heartwood is golden brown when freshly cut, turning to a rich dark brown with black streaks; it is clearly demarcated from the paler sapwood. The texture is medium to coarse; the grain deeply interlocked; lustre is medium; there is no distinctive odour or taste The wood is moderately heavy and hard; strong and fairly durable. It seasons well, works and polishes easily. An excellent, very decorative timber, it has been compared to black walnut. The wood is suitable for turnery, carving, general construction, furniture, veneer, agricultural implements etc[, , , , ].
More generally the wood is useful for fuel wood because of its high productivity[, ]. It makes an excellent charcoal[, ].

Propagation

Seed. The species is not particularly hard-seeded and requires only mild treatment (e.g. in water at 50 °c for 3 minutes) to germinate successfully[]. Be careful, though, since some seeds are quite thin-skinned and can be damaged if the water is too hot[]. A proportion of the seeds germinate immediately without any treatment[]. Plants can be direct-sown, container grown, or raised in a massed seed-bed and planted out as bare-rooted stems[].
There is nothing published on preferred rhizobial strains but it appears to nodulate readily without inoculation[].
Cuttings.
Air layering.

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