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(Bengali) : sakhu, sal, shal
(French) : damar de l’Inde
(German) : salbaum
(Hindi) : borsal, hal, sakhu, sakhwa, sal, shal
(Nepali) : agrakh, sakhua, sakwa, sal
(Tamil) : kungiliyam (resin)
(Trade name) : sal
Shorea robusta is a large, deciduous tree up to 50 m tall and with a dbh of 5 m; these are exceptional sizes, and under normal conditions S. robusta trees attain a height of about 18-32 m and girths of 1.5-2 m; bole is clean, straight and cylindrical, but often bearing epicormic branches; crown is spreading and spherical. Bark dark brown and thick, with longitudinal fissures deep in poles, becoming shallow in mature trees; provides effective protection against fire. The tree develops a long taproot at a very young age. Leaves simple, shiny, glabrous, about 10-25 cm long and broadly oval at the base, with the apex tapering into a long point; new leaves reddish, soon becoming delicate green. Flowers yellowish-white, arranged in large terminal or axillary racemose panicles. Fruit at full size about 1.3-1.5 cm long and 1 cm in diameter; it is surrounded by segments of the calyx enlarged into 5 rather unequal wings about 5-7.5 cm long.
Ecology and distributionHistory of cultivation
In economic terms, S. robusta is the most important timber genus in the Asian humid tropics.
Of the 2 factors of habitat, climate and soil, the former decides the general distribution of S. robusta; among the climatic factors, rainfall is by far the most important. Annual precipitation normally comes with a dry season lasting 4-8 months (monsoon climate). At higher elevations, S. robusta can be damaged by frost. S. robusta occurs in both deciduous dry and moist forests and in evergreen moist forest. It accounts for about 14% of the total forest area in India. For example, southwest Bengal harbours luxuriant S. robusta forests. Fire is normally responsible for its frequent occurrence in pure stands or as the dominant species of mixed stands, as S. robusta is better equipped to survive conflagrations than other tree species.
Native : India, Myanmar, Nepal
Biophysical limitsAltitude: 100-1500 m, Mean annual temperature: (min. 1-7) 22-27 (max. 34-47) deg. C, Mean annual rainfall: 1000-3000 (max. 6600) mm Soil type: S. robusta flourishes best in deep, well-drained, moist, slightly acid sandy to clayey soils. It does not tolerate waterlogging. The most favourable soil is a moist sandy loam with good subsoil drainage. Availability of soil moisture is an important factor determining the occurrence of S. robusta.
S. robusta is a hermaphroditic, self-incompatible species. Pollen vectors in its natural habitat are insects from the family Thysanoptera. Heavy flowering of the tropical timber genus Shorea has is usually correlated with the previous drought period. Beginning at about age 15, S. robusta bears fruit regularly every 2 years or so, and a good seed-bearing year can be expected every 3-5 years. Major seed dispersal agents include wind and water.
Propagation and managementPropagation methodsS. robusta regenerates naturally through seed and coppice. Direct sowing is the cheapest and best method of artificial propagation, although stump plantings, planting out entire plants with balls of earth, and planting out container-grown seedlings are also employed. Air-layering is also physiologically possible. Artificial regeneration of S. robusta is practised to a major extent primarily within its native habitat. The seed germinates soon after falling off the tree if moisture conditions are favourable. The germination percentage of fresh seeds is 90-100%, but their viability falls to zero after just a few weeks. Germination is hypogeous. Generally, a seed produces a single seedling, but cases of polyembryony have also been reported. The primary root of the seedling is long, thick, terete, tapering and woody, and the stem is erect, wiry, very finely pubescent or glabrescent. Most commonly the seeds are planted 10-20 cm apart in rows with a spacing of 3-7 m.
Young plants grow quickly, attaining top heights of up to 6 m after 6 years. The 1st thinning is usually performed after 5 years, and thereafter the trees are thinned every 5-10 years. Rotations of 30-40 years are used when coppice regeneration is practised, and 80-160 years for high forest regeneration. A species that requires a lot of light, S. robusta coppices well. Both coppice regeneration and planting of seedlings are used in plantation systems. It is also ideally used for growing under taungya systems.
Storage behaviour is recalcitrant; viability is lost within 2 weeks in open storage at room temperature; 10% germination on desiccation at 33-36 deg. C to 9.6% mc. There are about 400-1000 seeds/kg.
Functional usesProductsFood: In India seeds are boiled into a porridge with flowers of Bassia latifolia and fruits of Dolichos biflorus. In Madras, India, seeds are ground into a coarse flour used to make bread, and the plant is used as a famine food. The chemical composition of the seeds consists of 10.8% water, 8% protein, 62.7% carbohydrate, 14.8% oil, 1.4% fibre and 2.3% ash. S. robusta butter, used in cooking, is derived from the seeds. A de-fatted kernel powder, popularly known as sal seed cake, contains about 50% starch, in addition to proteins, tannins and minerals. The physico-chemical property of the starch can be exploited for preparing canned food products. Fodder: In India, S. robusta is lopped for fodder, but the leaf fodder is considered to be of medium to poor quality. The oil cake, though rich in tannins (5-8%), has been used without detrimental effects in concentrates for cattle in proportions of up to 20%. As the protein remains completely undigested, the oil cake yields only energy. Salseed cake can also constitute up to 10% of poultry and pig rations without affecting the performance of these animals. The leaves can be used as roughage for cattle and are fed to Antheraea mylitta, a tasar silk-producing worm. Lipids: S. robusta seed oil fat has become a significant foreign exchange earner for India. Timber: The dark, reddish brown, hard and heavy heartwood (specific gravity of 0.83-0.93 cm³) is very durable and highly resistant to termite attack; grain is strongly spiralled and rather coarsely structured; seasoning also presents problems. Wood is easy to saw, but because of its high resin content, it is difficult to plane and turn; it has a tendency to split when nails are driven into it. This important Indian hardwood is especially well suited for structures subject to heavy stress in house construction, hydraulic engineering, ships and railway cars. It is also used for poles, railway ties and posts, simple interior finishing such as window frames and floors, and many other applications. For making household or agricultural implements, S. robusta coppice shoots are used. Other products: S. robusta leaves are widely used for making leaf plates and cups for both home use and sale to sal plate factories.
Intercropping: In Assam, India, artificial regeneration of S. robusta is practised in combination with crops such as upland rice, maize, sesame and mustard. Good results have also been achieved with mixed plantations in which S. robusta is cultivated together with Tectona grandis.
Pests and diseasesS. robusta is beset by a number of pests and diseases. Among the insect pests in India, Hoplocerambyx spinicornis is the most destructive. Its larvae tunnel through the bark, sapwood and finally to the heartwood, causing death of the tree. The population of the pest keeps building up and if not checked may assume an epidemic level. Other insect pests include Diacavus furtivus and Xyleborus spp. The major fungal diseases include those caused by Polyporus shorea and Polyporus gilvus. The semi-parasite Loranthus scurrula can also cause increment losses.
BibliographyAnon. 1986. The useful plants of India. Publications & Information Directorate, CSIR, New Delhi, India.
Hong TD, Linington S, Ellis RH. 1996. Seed storage behaviour: a compendium. Handbooks for Genebanks: No. 4. IPGRI.
Kayastha BP. 1985. Silvics of the trees of Nepal. Community Forest Development Project, Kathmandu.
Lamprecht H. 1989. Silviculture in the tropics: tropical forest ecosystems and their tree species; possibilities and methods for their long-term utilization. Dt. Ges. für. Techn. Zusammenarbeit (GTZ) GmbH, Eschborn. (Translated by Brose J et. al.).
Singh RV. 1982. Fodder trees of India. Oxford & IBH Co. New Delhi, India.
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