Common name: Balsam of tolu

Balsam of tolu is a tree legume highly prized for its resin and timber. There are two forms, over which there has been much discussion about whether they are different varieties of the same species or different species. Here they are treated as different varieties, var. balsamum from Central America and var. pereirae from South America.

Both varieties are slow-growing and reach up to 30 m (98 ft) tall under closely spaced forest conditions but are typically 15 to 20 m (50 to 65 ft) with straight trunks, smooth grey-brown bark and dense rounded crowns.

The leaves are large and feathery, comprised of five to ten pairs of medium green leaflets, each leaf-like on its own and arranged sub-opposite to alternate along the length.  In areas with low rainfall and a long dry season, they fall from the tree to conserve water but remain on the tree where the dry season is short and humid conditions prevail.

From spring to summer, white, fragrant flowers bloom on erect flowering spikes near the ends of the branches. The fertilised flowers develop into single-seeded, winged, brown seedpods that mature in autumn to winter and then fall and float to the ground.

Use

A dark brown resin tapped from the trunk is distilled into a vanilla or benzoin scented essential oil. The distilled oil has a long history of use in the perfume and food industries as a fragrance and flavour additive. It is considered an excellent fixative in perfumery and is used in oriental and chypre perfumes such as 'Youth Dew' and 'Chamade' and in soaps and toilet waters. The resin is also used in its pure form to make incense.

The tree of var. pereirae does not yield its resin freely. Traditional harvesting methods first involve wounding the trunk, then heating the wound with a lit torch before wrapping it with cloth rags to soak up the resin. After the rags have become saturated, they are boiled and pressed to release the resin. Mature trees yield about 2 to 3 kg (4.4 to 6.6 lbs) of resin per year.

The wood is heavy, averaging around 760 kgs per cubic meter (47 lbs per cubic ft). And, because of its high resin content, it has a high natural resistance to rot and decay, placing it in the durable hardwood class, fit for indoor and outdoor use. It is sawn into boards and planks to make furniture, cabinets and flooring, and beams for railway crossties or sleepers. The roundwood is used in turnery.

It is sometimes planted with shade-loving crops such as coffee (Coffea arabica) to shade the plant against full sun exposure, which can scorch the leaves. Its nitrogen-fixing abilities also help enrich the soil.

Climate

It grows naturally in humid, seasonally dry tropical lowland climates, generally best in areas with annual lows of 19 to 25°C, annual highs of 28 to 35°C, annual rainfall of 1300 to 4500 mm and a dry season of 2 to 6 months. In El Salvador, the trees of the indigenous variety, var. balsamum, thrives in coastal areas, from near sea level to elevations up to 300 meters (980 feet).

Growing

New plants usually start from seed taken from seedpods that have been pre-treated by soaking them in water. Seedlings and young trees perform best on free- to slow-draining clay and loam soils of an acid to neutral nature, generally with a pH of 4.5 to 7.0 and on sites with full sun exposure. Established trees have good tolerance to drought conditions.

Problem features

It has been introduced into countries outside its native range and has become naturalised in some. The thin paper-like seed are designed for dispersal by wind, potentially over long distances, which has contributed to its spread outside of cultivation. The Hawaii Pacific Weed Risk Assessment project (HPWRA) assessed it as a high weed risk species.

Books

• Allen, O. N. & Allen, E. K. 1981, The Leguminosae : a source book of characteristics, uses, and nodulation, University of Wisconsin Press, Madison, Wisconsin

• Barwick, M., et al. 2004, Tropical & subtropical trees : a worldwide encyclopaedic guide, Thames and Hudson, London

• Berni, C. A & Bolza, E. & Christensen, F. J. 1979, South American timbers - the characteristics, properties and uses of 190 species, Commonwealth Scientific and Industrial Research Organization (CSIRO), Division of Building Research, Highett, Victoria, Australia

• Chevallier, A. 2000, Encyclopedia of herbal medicine, 2nd American ed., Dorling Kindersley, New York

• Chudnoff, M. 1984, Tropical timbers of the world, Forest Service, U.S. Department of Agriculture (USDA), Washington, D.C.

• Coppen, J. J. W. 1995, Gums, resins and latexes of plant origin, Food and Agriculture Organization of the United Nations (FAO), Rome

• Croat, T. B. 1978, Flora of Barro Colorado Island, Stanford University Press, Stanford, California

• Culbreth, D. M. R. 1927, A manual of materia medica and pharmacology : comprising the organic and inorganic drugs which are or have been recognized by the United States pharmacopeia, 7th ed., Febiger, Philadelphia

• Francis, J. K. and Liogier, H. A. 1991, Naturalized exotic tree species in Puerto Rico, General technical report SO-82, USDA Forest Service, Southern Forest Experiment Station, New Orleans

• Groom, N. 1997, The new perfume handbook, 2nd ed., Blackie Academic & Professional, London

• Howes, F. N. 1949, Vegetable gums and resins, Chronica Botanica Company, Waltham, Massachusetts

• Jones, M. 2011, The complete guide to creating oils, soaps, creams, and herbal gels for your mind and body : 101 natural body care recipes, Atlantic Publishing Group, Ocala, Florida

• Khan, I. A. & Abourashed, E. A. 2010, Leung's encyclopedia of common natural ingredients : used in food, drugs and cosmetics, 3rd edition, Wiley Publishing, Hoboken, New Jersey

• Mors, W. B & Rizzini, C. T. 1966, Useful plants of Brazil, Holden-Day Publishing, San Francisco, California

• Randall, R. P. 2007, The introduced flora of Australia and its weed status, Cooperative Research Centre for Australian Weed Management, Glen Osmond, South Australia

• Record, S. J. & Hess, R. W., 1972, Timbers of the New World, Yale University Press, New Haven, Connecticut & Arno Press, New York

• Reyes, G. 1992, Wood densities of tropical tree species, U.S. Department of Agriculture, Forest Service, Southern Forest Experiment Station, New Orleans, Louisiana

• Scheffer, T. C & Morrell, J. J. 1998, Natural durability of wood : a worldwide checklist of species, Forest Research Laboratory, Oregon State University, Corvallis, Oregon

• Seidemann, J. 2005, World spice plants: economic usage botany taxonomy, Springer-Verlag, Berlin

• Vázquez, Y. C. 1999, Potentially valuable Mexican trees for ecological restoration and reforestation, Institute of Ecology, Database SNIB-REMIB-CONABIO, Project J084, Mexico

• Vozzo, J. A 2002, Tropical tree seed manual, U.S. Department of Agriculture (USDA), Forest Service, Washington D.C.