Acacia leucophloea (PROSEA)

Plant Resources of South-East Asia Introduction

List of species

Acacia leucophloea (Roxb.) Willd.

Protologue: Sp. Pl. 4th ed., Vol. 4(2): 1083 (1806).

Family: Leguminosae

Chromosome number: 2n= unknown

Synonyms

• Acacia melanochaetes Zoll. (1846),
• Delaportea ferox Gagnep. (1852),
• Delaportea microphylla Gagnep. (1852).
• Mimosa leucophloea Roxb. (1800).

Vernacular names

• Indonesia: pilang (Javanese, Sundanese), opilan (Madura), pelang (Madura, Bali)
• Burma: ta-noung
• Thailand: chalaep-daeng (central), phayamai (Kanchanaburi)
• Vietnam: a bu, a kawa (Thuân Hai).

Origin and geographic distribution

A. leucophloea is native to large parts of South and South-East Asia, where it is found in India, Nepal, Pakistan, Sri Lanka, Burma, Thailand, Vietnam, Indonesia (Java, Timor, Sumbawa).

Uses

The tannin-containing bark was used in the leather industry in Indonesia, and less so in India, until the 1950s. Until the 1940s the tree was cultivated in commercial plantations in Indonesia mainly for this purpose. The bark is also used to prepare fine beverages (arak); its strong fibres are used locally to make fishing nets. The wood of A. leucophloea is used for indoor construction, flooring and, although a little hard to work, for furniture. It is also highly appreciated as firewood and is very suitable for making charcoal.

The consumption of cooked, germinated seeds as vegetable (hale) is reported from Java. Stem and roots produce a gum which is used for medicinal purposes. The pods and foliage are a protein-rich fodder source. In Tamil Nadu (India) farmers cultivate A. leucophloea for soil improvement. The trees are also planted around timber plantations as fire protection.

Production and international trade

In former times A. leucophloea was grown commercially for tannin production. Nowadays, the species is no longer considered commercially interesting and production figures are difficult to obtain. There is no international trade.

Properties

The bark contains 11-20% tannin, with an average of 15%; the tannin content is highest in older trees. The tannin is difficult to extract, and so the tanning process is slow. Because of its small content of sugar-like components, the tannin has hardly any acid-forming properties. The tannin is of the proanthocyanidin type, and colours leather red; the red colour darkens easily in light. In tanneries pilang bark was often used mixed with trengguli bark (Cassia fistula L.). In Indonesia pilang bark was replaced by the better tanning bark of Acacia mearnsii De Wild. (black wattle) after the Second World War.

The fodder (leaves and pods) contains 1.9% digestible fats, 7.1% digestible proteins and 12.4% digestible carbohydrates. Its hydrocyanic acid content varies during the year. In India, values ranging from zero (December) to 240 mg/kg hydrocyanic acid (May/June) have been measured in the leaves, and values over 400 mg/kg in the pods from October to April (with a maximum of almost 1000 mg/kg in November). Whenever the hydrocyanic acid content exceeds 200 mg/kg, the fodder should not be used as the sole source of animal feed.

The roots bear nodules with nitrogen-fixing microorganisms. Seed weight is small, about 37 000 seeds weighing 1 kg.

The heartwood is beautifully red, the sapwood is grey white. The wood is strong (class II in Indonesia) and durable (class III in Indonesia) when used indoors. In contact with moist soil, it decays quickly. The density of the wood is 710-890 kg/m³ at 15% moisture content. See also the table on wood properties.

Description

• Deciduous tree or erect shrub, 10-35 m tall, with deep taproot, few secondary roots, pale bark and broadly umbelliform crown. Young trees are often densely beset with thorny suckers; lower branches armed with paired straight or faintly curved stipular thorns, usually dark brown or black, less often white, up to 2.5 cm long.
• Leaves bipinnate, pinnae 4-13 pairs, rachis 3.5-8.5 cm long; leaflets in 6-30 pairs, linear, 3-11 mm × 0.5-1.7 mm. Inflorescences yellowish-white subglobose heads, ca. 1 cm in diameter, in large terminal densely hairy panicles up to 30 cm long; peduncles 0.4-1.3 cm long.
• Flowers sessile, calyx 0.8-1.2 mm, corolla 1.2-2 mm long; stamens 20-25.
• Fruit a linear, slightly curved or straight pod, 6-15(-20) cm × 7-11 mm × 3 mm, woody, glabrescent, dark brown, 5-12(-20)-seeded, indehiscent.
• Seeds very variable, orbicular, ellipsoid or trapezoid, 5.5-6.5 mm × 4-5 mm, compressed, greyish-brown.

Growth and development

Only a small proportion of the seeds germinates. Pretreatment of seeds with hot water improves germination. In Indonesia pretreated seeds have taken up to 75 days to germinate. Flowering is at the end of the rainy season/beginning of the dry season. Leaf fall occurs for a very short period at the beginning of the rainy season. There is some disagreement in the literature as to whether the trees bear fruit every year.

Ecology

The ecological range of A. leucophloea is wide: it occurs in areas with a pronounced East Monsoon, under semi-arid (rainfall 600 mm/year) to humid (2000 mm) conditions, at altitudes ranging from sea-level to 550 m, on sandy-marl to heavy clay-marl soils. The plants need much light and space to develop into mature trees. In the wild, the tree occurs individually and sometimes in groups in heterogeneous, deciduous forests on soils with a moderate to poor fertility. It is never found in evergreen, closed forests on fertile soil. A. leucophloea tolerates soils that are periodically very dry, and soils with compaction features, because of the adaptibility of its root system to poor oxygen availability. It does not survive on poorly drained sites.

Propagation and planting

Plantations of A. leucophloea are established by sowing seeds directly, using 10-12 seeds per hole, at 2 m × 1 m. If enough space and light are available, abundant natural regeneration has been observed in Tamil Nadu (India) with 1000 seedlings/ha. It is advisable to plant in combination with a creeper that gives effective soil cover, or to intercrop with other species that provide more shade in the youth phase. In mixed plantations, however, accompanying species should be carefully selected because A. leucophloea is easily suppressed on account of its slow growth when young. When combined with other species it should be planted in small groups.

Husbandry

In monoculture plantations, A. leucophloea needs intensive and expensive maintenance to suppress the heavy undergrowth that develops because the trees provide little shade.

Diseases and pests

Seedborne rust infections by Hapalophragmiopsis ponderosum cause amorphous, tumorous galls. The seed of A. leucophloea may be seriously infested by a small weevil of the genus Caryoborus and by a bruchid beetle. Caterpillar plagues have also been observed. The species is fire resistant and the bark recovers easily.

Harvesting

For tannin production, the bark is stripped at the beginning of the growing season because then the high water content facilitates the process. The bark is cut into pieces of 50 cm × 10 cm, and dried in the sun for 2-3 days. During drying the bark loses one-third of its original weight.

Yield

Production figures from plantations in Indonesia with a rotation of 12 years indicate an annual dry bark production ranging from 8 kg/tree for diameter class 10-14 cm to 81 kg/tree for diameter class 30-35. The annual wood production is ca. 15 m³/ha (whole tree), 11 m³/ha thick wood (diameter breast height > 7 cm) and 9 m³/ha clear bole. Under wide-spaced conditions in an agroforestry system in India (Tamil Nadu), an annual yield of 100 kg pods/tree and a 20-23% increase in height growth and dry-matter yield of fodder sorghum cultivated under the trees has been reported.

Handling after harvest

After the bark has been air-dried at the factory, it is chopped into small pieces and put in the tanning extraction vats. Only 3-4 days may elapse between harvesting and extraction, because fungal infections degrade the colour and quality of the extract. After continuous countercurrent extraction first with cold, then with warm water (below 60°C), the resulting extract is concentrated in a triple effect evaporator and finally in a copper vacuum evaporator until it has the desired moisture content. The extract is stored in containers.

Prospects

A. leucophloea is a promising species for agroforestry and especially for silvopastoral purposes. It can be used in sites that suffer from compaction as a result of overstocking. It produces good fodder that is rich in protein, and enriches soils by nitrogen fixation. Its open crown transmits enough light to permit crop cultivation under the trees. Nevertheless, A. leucophloea has not yet received much attention in agroforestry and silvopastoral research.

Literature

• Howell, J.H., 1987. Choice of species for afforestation in the mountains of Nepal. Banko Janakari 1(3): 7-14.
• Japing, H.W., 1936. Looibasten op Java [Tanning barks in Java]. Korte Mededelingen van het Boschbouw Proefstation No 57, Buitenzorg (Java). Archipel Drukkerij. pp. 808-836.
• Japing, H.W. & Oey Djoen Seng, 1936. Trial plantations of non-teak wood species in East Java. Short communications of the Forest Research Institute No 55, Buitenzorg. pp. 12-18. (English summary and introduction)
• ten Oever, H., 1908. De teelt van pilang (Acacia leucophloea) en trengguli (Cassia fistula) [The cultivation of pilang (Acacia leucophloea) and trengguli (Cassia fistula)]. Tectona 1: 9, 16, 92.

36, 162, 163, 261, 369, 474, 526, 575, 649. Timbers

Authors

• L.M. Berenschot