16

4: Forages

Albizia lebbeck (L.) Benth.

Lond. Journ. Bot. 3: 87 (1844).

LEGUMINOSAE

2n = 26

Mimosa lebbeck L. (1753), Mimosa sirissa Roxb. (1832), Albizia latifolia Boivin (1838).

Siris, koko, East Indian walnut (En). Indonesia: tekik (Javanese), kitoke, tarisi (Sundanese). Philippines: aninapla, langil (Tagalog). Cambodia: chreh. Thailand: kampu (general), chamchuri (central). Vietnam: bô kêt tây, lim xanh, trât.

Siris is indigenous to the Indian subcontinent and to those areas of South-East Asia with a marked dry season (e.g. north-east Thailand, the eastern islands of Indonesia) and to the monsoon areas of northern Australia. It has been introduced widely throughout the tropics and has become naturalized in many places.

The green leaf is a valued forage for ruminants and it should be useful in extensive grazing systems because of the feed value of the natural drop of leaves, flowers and pods. Free-standing trees appear to enhance pasture production and quality beneath the canopy due to increased N status of the soil. In India plantation-grown siris yields a high quality hardwood traded in Europe as 'Indian walnut' or 'koko'. More generally it is useful for fuelwood because of its high productivity. It is a valued honey tree because of its production of both nectar and pollen. It is a popular amenity tree throughout the dry tropics because of its shady spreading habit, although the copious litter is often regarded as a disadvantage.

In feeding experiments with sheep, DM digestibility and N concentration, respectively, were as follows: green leaf fed fresh: 64% and 3.5%; mature green leaf fed dry: 48% and 3.0%; fallen leaf: 42% and 1.6%; fallen flower: 57% and 3.8%; fallen pods: 44% and 3.0%. Leaf is notable for the absence of antinutritional factors such as phenolics, but pods contain saponins. There are 7-8 seeds/g.
The wood is dense (specific gravity 0.5-0.6), easily worked, yellow-brown, with a very distinct boundary between heartwood and pale sapwood. A range of uses such as cabinet timber have been listed, including the doors of Chinese temples. The massic energy of air-dried wood is 21 840 kJ/kg (5200 kcal/kg).

Deciduous tree, in plantations 3-15 m tall, bole length 3 m with diameter 45 cm; when grown in the open, often much larger, up to 25 m tall, often multi-stemmed and widely spreading (up to 30 m diameter); bark rough, grey, somewhat flaky; inner bark reddish; branches terete, puberulous or pubescent when young. Leaves bipinnate with 1-5 pairs of pinnae on a rachis of 8-9 cm length; leaflets in 3-11 pairs, oblong to elliptical-oblong, 1.5-6.5 cm x 0.5-3.5 cm, somewhat asymmetrical with midrib nearer upper margin, subglabrous, initially bright green and folding at night, maturing to a duller glaucous green with position fixed on rachis. Inflorescence a terminal and axillary globular cluster of 15-40 pedicellate flowers, often 2 or more together per axil; peduncle up to 10 cm long, pedicel 1.5-5(-7.5) mm long; calyx tubular, 2-5 mm long, ending in 5 triangular teeth; corolla tubular, 5-11 mm long, ending in 5 triangular lobes which are hairy at the apex; stamens at base united in a tube, free filaments numerous, 1.5-3 cm long. Pod flat-oblongoid, 12-35 cm x 3-6 cm, much swollen on the seeds, subglabrous, glossy, veined, pale yellowish, dehiscent. Seeds 3-12 per pod, flattened ellipsoidal, 7-11 mm x 6-9 mm x 1-1.5 mm, brown.

Siris has a strongly seasonally-dependent growth pattern with a leafless period of 1-2 months in the middle of the dry season. Production of new season growth commences in the dry season, shortly followed by abundant flowering which produces very little seed. Further growth and fruiting occur as the wet season develops. Flowers are insect pollinated. Pods mature in the early dry season but remain on the tree for 3-4 months.
Seed dispersal seems to occur mainly due to strong wind, when intact pods can be carried hundreds of metres. Some seed passes through the digestive tract of cattle but not of smaller ruminants. Light transmission through the canopy of free-standing trees is 40-50%. 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.
Growth stops in the early dry season, 2-3 months before leaf drop. New growth may be induced by fire damage, grazing or lopping.

Albizia Durazz. is a large genus and in parts of its range non-fertile material of siris may be quite similar to other local species. There is little problem with identification when both flowers and pods can be examined. Use of 'albizia' as a vernacular name should be avoided as some workers apply it also to Paraserianthes falcataria (L.) I. Nielsen, a very important species in South-East Asia and quite different from siris. Albizia is often misspelt as Albizzia and lebbeck as lebbek.

Although siris will grow in the humid tropics, its natural range is in semi-arid to sub-humid areas with marked dry and reliable wet seasons. However, it may be established under conditions of low (400 mm/year) and irregular rainfall. Seedlings will not tolerate frost or waterlogging. Reserves in the root system enable young plants to survive total defoliation from fire or grazing, but with an obvious setback in growth. Siris is tolerant of salinity and can be established on most soils except cracking clays.

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; a proportion of seeds germinate immediately without any treatment. There is nothing published on preferred rhizobial strains but it appears to nodulate readily without inoculation. Plants can be direct-sown, container grown, or raised in a massed seed-bed and planted out as bare-rooted stems.

Siris is probably not productive under repeated cutting (more than 2 cuts per year). It does not develop a shrubby habit and is thus not suitable for direct browsing. However, larger trees can be lopped annually with removal of the entire green crown without loss of vigour.

Establishment can be adversely affected by grazing of young plants by mice, rabbits and other wildlife. Leaves are largely unaffected by insects, but young leaves may be subject to heavy predation by larvae of the grass yellow butterfly (Eurema hecoba); this appears to be a short-lived effect. The most serious pests are bark-feeding larvae of longicorn beetles. These do not affect small stems and have little effect on large stems, but through complete girdling can cause dieback in stems with diameters ranging from 4-10 cm. There is considerable variation in susceptibility of individual trees. Trees may be more susceptible under prolonged drought stress.

Branches may be lopped for fuel and forage. In extensive grazing systems, the free-standing tree itself provides feed. Production of sawn timber involves felling the whole tree, with concommittant production of fuelwood and forage.

Comprehensive yield data have not been published. Under best conditions plants can grow 5 m/year. Fuelwood plantations produce 5 m³/ha per year. Isolated mature trees produce edible DM at the rate of 100-120 kg/year. Roadside trees in the dry tropics show a crown diameter expansion of 2-2.2 m/year until mature.

The wide natural range suggests a broad genetic base, but there are no comprehensive germplasm collections.

There are no reported programmes in breeding, collection, or evaluation of existing accessions. The value of siris is critically dependent upon resistance to insect attack and this should be the first objective of development work on the species.

Siris offers excellent prospects for developing more productive agroforestry systems in areas in the semi-arid tropics. It would appear to have excellent multipurpose aspects, being potentially useful for cabinet timber, fuelwood, animal feed, and for enhancing crop production. Perhaps most remarkable is the prospect of obtaining enhanced pasture production in addition to the tree products. Despite its great economic importance on the Indian subcontinent and its widespread distribution in South-East Asia, its qualities are little known there. This may reflect a lack of research and development in the drier ('outer') areas in the region. Other species of Albizia are worth considering for the same purposes, in particular Albizia procera (Roxb.) Benth.

Lowry, J.B., 1989. Agronomy and forage quality of Albizia lebbeck in the semi-arid tropics. Tropical Grasslands 33: 84-91.
Lowry, J.B., 1991. Integrated production from Albizia lebbeck trees and tropical pastures. Journal of the Australian Institute of Agricultural Science 4: 36-38.
Lowry, J.B., Lowry, J.B.C., Jones, R.J., 1988. Enchanced grass growth below canopy of Albizia lebbeck. Nitrogen fixing Tree Research Reports 6: 45-46.
Murugan, M. & Kathaperumal, V., 1987. Nutritive evaluation of vagai (Albizia lebbeck) leaves for goats. Indian Journal of Animal Nutrition 4: 61-62.
Nielsen, I., 1981. Légumineuses-Mimosoïdées. Flore du Cambodge, du Laos et du Vietnam. Vol. 19. pp. 82-84.
Prinsen, J.H., 1987. Potential of Albizia lebbeck as a tropical fodder tree - a review of . Tropical Grasslands 29: 78-83.
Schlink, A.C., Lowry, J.B. & Gibson, D.S., 1990. Products from the tree legume Albizia lebbeck as supplements for sheep in dry tropics. Proceedings Australian Society for Animal Production 18: 546.

J.B. Lowry

Lowry, J.B., 1992. Albizia lebbeck (L.) Benth.. In: Mannetje, L.'t and Jones, R.M. (Editors): Plant Resources of South-East Asia No 4: Forages. PROSEA Foundation, Bogor, Indonesia. Database record: prota4u.org/prosea