Albizia saman: pasture improvement, shade, timber and more

Albizia saman (Jacq.) F. Muell. (Leguminosae, Subfamily Mimosoideae) is a fast growing tree which obtains a large size. It is most common as a pasture, shade or ornamental tree, but has numerous uses. This New World tree is so widely cultivated and used in Southeast and South Asia it is often mistaken as native to that area. It was formerly classified as Samanea saman, Pithecellobium saman and Enterolobium saman. Common names include saman, monkey pod, raintree, cow tamarind, algarrabo and guango.

Albizia saman

Botany

Albizias are related to and often mistaken for Acacias-in the Philippines acacia is a common name for A. saman. Albizia saman can obtain a height of 3045 m and diameter breast height (DBH) of 150-250 cm. Open-grown specimens have short stems and stout wide-spreading nearly horizontal branches. The umbrella-shaped crown may be wider than the height of the tree. The brown gray bark is rough and furrowed into ridges and plates (Little and Wadsworth 1989). Limb bark is lighter in color. Twigs are stout and green. The bipinnately compound leaves are 2540 cm long dark green above and light green below. The stalkless leaflets are arranged in pairs numbering from 12 to 32 (Little and Wadsworth 1989). Leaflets are wider towards the apex. Both leaves and leaflets are progressively larger towards their terminal ends.

The showy flower heads, composed of many narrow pink flowers, are found near the end of twigs and appear from March to September (Hensleigh and Holaway 1988). The dark-brown to black pods are hard and thick with a raised seam. They are 8-20 cm long and about 2 cm wide. The pods do not readily open and remain on trees for long periods. Seeds are red-brown oblong and squarish. There are 5000-8000 seed/kg.

Ecology

Albizia saman is found in the tropics from sea-level to 1000 meters where the temperature is 20-35° Celsius. It is a common component of dry forests and grass savannas. Annual rainfall in these areas is 600-3000 mm/year. Albizia saman easily survives dry seasons of 24 months. While more common on drier sites, this species grows best in moist, well-drained fertile soils (Hensleigh and Holaway 1988). It tolerates heavy clays and infertile or waterlogged soils. Although normally found in neutral to moderately acid soils, it will grow in soil with pH as low as 4.6 (Franco et al. 1995).

Distribution

This species is native from Southern Mexico and Guatemala south to Peru, Bolivia and Brazil. It is naturalized throughout the tropics and has been introduced to sub-tropical areas.

Uses

Shade and ornamental.

Albizia saman is planted along roads throughout the tropics. In parks and commons, its high arching branches provide welcome protection from the heat of the tropical sun. Having crowns of great diameter, trees furnish ample shade. Trees serve as windbreaks and are cultivated for their beautiful pink flowers.

Wood.

The wood of Albizia saman is highly valued for the manufacture of furniture, cabinets, decorative veneers, bowls and other handicrafts. The chocolate heartwood and yellow sapwood form a beautiful contrast. The light-weight wood (specific gravity 0.48) is strong, durable, works easily and takes a good finish (Chudnoff 1984). It shrinks so little that products made from green wood dry without warping (NAS 1979). Albizia saman is a good quality fuel and charcoal, producing 5200-5600 kcal/kg (F/FRED 1994). Other uses of the wood include fencing, construction timbers, plywood and the manufacture of crates, wheels and boats.

Pasture and fodder.

Albizia saman is a valuable component of pasture systems. Its shade protects livestock from the hot tropical sun. Its nutritious pods contain 12-18% crude protein and are 40% digestible (F/FRED 1994). Relished by livestock, pods are an important dry-season fodder. Tree leaves are also nutritious, but are not an important fodder. The shade and nitrogen-rich leaf-litter of A. saman improve the nutritional value of understory grass (Allen and Allen 1981). During the dryseason, grass beneath trees remains green and succulent while exposed grass becomes dry and unpalatable. Leaves fold inward at night which may increase the amount of moisture, rain and dew, reaching the understory. In the morning leaves unfold giving full shade and conserving soil moisture.

Agroforestry.

This species is used as shade for tea, coffee, cacao, nutmeg and vanilla. Performance has been fair in alley-and hedgerow-cropping studies. Initial growth is slower than other woody perennials, but A. saman coppices well and yields nitrogen-rich green manure. However, shallow roots and large branch size compete heavily with companion crops, especially in dry areas. In these systems, A. saman must be heavily pruned. In most areas, other species will be more appropriate for alley-and hedgerow-cropping studies. Albizia saman is appropriate in home gardens where it provides a service role and multiple products simultaneously.

Other uses.

Children eat the pods which contain a sticky sweetflavored pulp. A fruit drink is also made from the pulp. Honey is produced from the flowers. The bark yields gums and resins. In Thailand, A. saman is an important host plant for lac production (Subansenee 1994).

Silviculture

Propagation.

Seeds of A. saman have hard, impermeable seedcoats. Two methods of seed scarification are recommended. For small quantities of seed, cut through the seedcoat opposite the micropyle, or pointed-end of the seed, taking care not to damage the seed embryo. For large quantities of seed, pour boiled water over the seeds, soak and stir for two minutes. Drain off the hot water. The hot water should equal five times the volume of seeds. With either method of scarification, the seed should be soaked in cool water overnight before sowing (NFTA 1989). Seed should be sown at a depth equal to its width in large nursery bags, 10cm x 20cm. The recommended nursery mixture is 3 parts soil: 1 part sand: 1 part compost. Seedlings should receive partial shade for 2-4 weeks and then be exposed to full sunlight. After 3-5 months seedlings will be 20-30 cm tall and ready for field planting. Direct sowing is possible, but success depends on rigorous weed control. Albizia saman can be propagated by cutting or stump cutting.

Management.

Open-grown A. saman have short trunks and spreading limbs which are considered poor form for timber production. Close spacing, 1.5-2 meters, does produce straighter trees with less branching, but boles retain a spiral form. For this reason, A. saman is not commonly planted in single-purpose timber plantations. In pastures, home gardens or other multiplepurpose plantings, tree spacing will depend on companion plants and management strategy.

A light-demanding species, A. saman grows fast and is tolerant of heavy weed competition. However, survival and growth can be improved through vigorous weed control until trees achieve dominance over competing vegetation. Wood production varies by site and management system. A good site can produce 10-25 m³/hectare/year under a 10-15 year rotation (F/FRED 1994).

Symbiosis

Albizia saman forms nitrogen fixing symbiosis with many strains of Rhizobium. In the field it readily forms root nodules.

Limitations

Heterophylla cabana, Psylla acacia-baileyanae and other defoliators are common pests (Braze 1990) but do not cause serious stress problems. Wide spreading branches and shallow roots make A. saman susceptible to damage during intense storms. The destruction of natural forests threatens the genetic diversity of this species. In response to this threat, the Oxford Forestry Institute has included A. saman in its gene conservation program (Hughes 1989).

References

Allen, O.N. and E.K. Allen. 1981. The Leguminosae: a source book of characteristics, uses and nodulation. Wisconsin Press. Madison, Wisconsin, USA. pp. 590-92.

Braza, R.D. 1990. Psyllids on nitrogen fixing trees in the Philippines. NFTRR 8:62-63.

Chudnoff, M. 1984. Tropical timbers of the world. Agriculture Handbook 607. USDA Forest Service. Washington, DC.p. 134.

F/FRED. 1994. Growing Multipurpose Trees on Small Farms (2nd ed.). Module 9. Species fact heets. Bangkok, Thailand. Winrock International, pp. 22-23.

Franco, A., E.F.C. Campello, LE. Dias and S.M. de Faria. 1995. Revegetation of acidic residues from bauxite mining using nodulated and mycorrhizal legume trees. In: D. Evans and L. Szott (eds.), Nitrogen fixing trees for acid soils. Nitrogen Fixing Tree Research Reports (Special Issue). Morrilton, Arkansas, USA. In press.

Hensleigh, T.E. and B.K. Holaway. 1988. Agroforestry species for the Philippines. US Peace Corps. Washington, DC. pp. 281-84.

Hughes, C.E. 1989. Intensive study of multipurpose tree genetic resources. Oxford Forestry Institute, University of Oxford, UK. pp. 66-79.

Little, E.L. and F.H. Wadsworth. 1989. Common trees of Puerto Rico and the Virgin Islands. Agriculture Handbook No. 249.USDA Forest Service. Washington, DC. pp. 164-66.

NAS. 1979. Tropical legumes: Resources for the future. National Academy of Sciences, National Research Council. Washington, DC. pp. 202-03.

Macklin, B., N. Glover, J. Chamberlain and M. Treacy. 1989. NFTA cooperative planting program establishment guide. Nitrogen Fixing Tree Association. Morrilton, Arkansas, USA. 36 p.

Subansenee, W. 1994. Economic value of Albizia saman. In: JB Raintree and HA Francisco (eds.). Marketing of Multipurpose Tree Products in Asia Bangkok, Thailand. Winrock International, pp. 229-35.

NFTA 90-04 July 1990