Common name: Rubber tree

Originating from the humid tropical forests of Brazil, Bolivia, Colombia and Peru, the Rubber tree is valued for its latex, the world's principal source of natural rubber. 

It is a tall, fast-growing tree reaching heights of up to 40 m (130 ft) in native forests, though is more typically 15 to 20 m (50 to 65 ft) tall. 

The trunk is usually straight, round, with smooth, light grey, and often mottled bark. It supports a moderately branched, narrow crown, the branches tending to angle upward in closely spaced forests and plantations. On open sites, the branches grow outward and form a rounded, compact crown.

Leaves are compound, consisting of three oval leaflets, dark green above and light green below. They fall from the tree in the dry season but are soon replaced by new leaflets, emerging at the start of the rainy season.

The flowers are small and insignificant, with hairy, pale yellow petals and either female or male, in clusters arising at the sides and ends of the branches. They bloom in the rainy season, coinciding with new leaf growth, and are soon followed by three-lobed seed capsules, green when young becoming dark brown and woody. Inside each lobe is a smooth, brown, egg-shaped seed patterned with black markings. When mature, the capsule bursts open with a popping sound and scatters its seed a considerable distance from the parent tree.

^{Image by Tracey Wong from Pixabay}

Use

A sticky, white latex is tapped from the trunk using a series of connected incisions that allows the latex to flow into a receptacle. After it is collected, the latex is coagulated, traditionally by warming it over a fire but nowadays by using a coagulant such as formic acid, making it a cleaner and more efficient coagulation process. The resulting coagulated mass is crude rubber which is then dried and readied for further processing into rubber products. 

Rubber is used to manufacture various products, including footwear components, rubber gloves, and condoms. In the early 1900s, manufacturing automobile tyres from rubber led to its mass commercialisation. And still today, it remains a major component of automobile tyres and those for aircraft.

Yields of fresh latex is influenced by various factors, including climate, soil and planting densities, which, among other things, affect trunk diameter. Annual yields in commercial plantations range from 1000 to 1500 kg of latex per hectare (900 to 1300 lbs per acre).

The flowers produce abundant nectar suitable for honey production, with flows lasting up to forty days over the flowering period. It is a major honey plant in India, with Kerala and Karnataka state the leading producers.

Each tree is estimated to produce enough nectar to yield 3 kg (6.6 lbs) of honey. Reported yields vary from 10 to 40 kg (22 to 88 lbs) of honey per colony per season. The honey is clear, water-white to pale yellow, very sweet and quick to granulate, with crystals starting to form after two months.

The seed kernel, which amounts to 50% of the seed, contains about 45% of a red-coloured drying oil known as 'Para seed oil'. It is used chiefly in manufacturing soap but, after refining, can also be used in paints. It has also reportedly been successfully engine-tested as a biodiesel. The leftover cake or meal can be used as a fertiliser or feeding stock.

^{Image by Abhilash Jacob from Pixabay}

Climate

Grows naturally and yields reasonable quantities of latex in humid to very humid tropical lowland climates, generally frost-free areas with annual lows of 19 to 25°C, annual highs of 27 to 36°C, annual rainfall of 1500 to 4000 mm and a winter dry season of 4 months or less.

Rubber trees do not thrive in areas with a long or pronounced dry season, where there is frost or where the average low of the warmest month is below 10°C (50°F).

Growing

New plants are usually grown from seed. It performs best on deep, rich, free-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 light shade to partial sun exposure. The trees are ready to be tapped for their latex when around five to six years old.

Problem features

The mature fruit eject their seed with force, propelling them up to 15 m (50 ft) away from the parent plant. It is reported as an invasive species, a serious weed class and as naturalised in Australia. It would appear it is a high weed risk under conditions optimal for germination and growth.

Books

• Adams, C. D. 1972, Flowering plants of Jamaica, University of the West Indies, Mona, Greater Kingston

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

• Bradbear, N. 2009, Bees and their role in forest livelihoods : a guide to the services provided by bees and the sustainable harvesting, processing and marketing of their products, Food and Agriculture Organization of the United Nations (FAO), Rome

• Crane, E., Walker, P. & Day, R. 1984, Directory of important world honey sources, International Bee Research Association, London

• Food and Agriculture Organization of the United Nations (FAO) 1986, Food and Fruit-bearing Forest Species, 3 : Examples from Latin America, FAO Forestry Paper no 44/3, Rome

• Hill, A. F. 1952, Economic botany : a textbook of useful plants and plant products, 2nd ed, McGraw-Hill, New York

• Jamieson, G. S. 1943, Vegetable fats and oils : their chemistry, production, and utilization for edible, medicinal and technical purposes, 2d ed, Reinhold, New York

• Jensen, M. 1999, Trees commonly cultivated in Southeast Asia : an illustrated field guide, 2nd ed., Food and Agricultural Organisation of the United Nations (FAO) Regional Office for Asia and the Pacific (RAP), Bangkok

• Lopez, C., et al. 2004, Riches of the forest: fruits, remedies and handicrafts in Latin America, Center for International Forestry Research (CIFOR), Bogor, Indonesia

• Lorenzi, H. 2002, Brazilian trees : a guide to the identification and cultivation of Brazilian native trees. Vol. 1, 4. ed, Instituto Plantarum de Estudos da Flora, Nova Odessa, Sao Paulo

• Luna, R. K 1996, Plantation trees, International Book Distributors, Dehradun, Uttarakhand

• Macmillan, H. F. 1943, Tropical planting and gardening : with special reference to Ceylon, 5th ed, Macmillan Publishing, London

• Marshall, E. (Elaine) & Schreckenberg, Kathrin & Newton, A. C & UNEP World Conservation Monitoring Centre 2006, Commercialization of non-timber forest products : factors influencing success : lessons learned from Mexico and Bolivia and policy implications for decision-makers, UNEP World Conservation Monitoring Centre, Cambridge

• McIlroy, R.J. 1963, An introduction to tropical cash crops, Ibadan University Press, Ibadan, Nigeria

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

• Randall, R. P. 2002, A global compendium of weeds, R.G. and F.J. Richardson Press, Melbourne