Sal (Shorea robusta) is a tall handsome tree providing very good quality timber. Its botanical family is dipterocarpaceae. In local languages it is called salwa, sakhu, sakher, shal, kandar and sakwa. Sal is a gregarious species and it forms the dominant composition in the forests where it occurs. It grows well in a well-drained, moist, sandy loam soil. It is a moderate to slow growing species and can attain a height upto 35 m and a girth of about 2 to 2.5 m in about 100 years under favorable conditions.
Sal trees are found from Burma in the East, to Assam, Bengal, Nepal, the Deccan Plateau, going up to the foothills of the Shivaliks on the left bank of the Yamuna river. In Haryana, Sal can be found in the Morni Hills and the Kalesar forest. Sal grows well in low height plains to foothills viz. Shivaliks from 200 to 1200 meters above mean sea level. But Sal growing in Nepal and Singhbhum district of Bihar are considered to be the best variety.
The bole of Sal tree is erect and cylindrical. The crown tends to be linear and sharp topped in young trees and round to flat in older ones. The bark of the young tree is smooth with a few long deep and vertical furrows. Its thickness is 2 to 5 cm. and color dark brown. Its texture is rough with peculiar longitudinal furrows in mature trees.
Sal tree is seldom completely leafless. In dry regions, however, it tends to shed practically all leaves for a short period from February to April. Fresh leaves appear during April to May depending upon the local climate. These are ovate-oblong in shape and 10 to 25 cm x 5 to 15 cm in size. The texture is tough and coriaceous with a typical shine on upper surface when fully mature.
The sal flowers, whitish in color, appear in early summer. These come out in auxiliary racemos panicles covered with white pubescence. They fruit during summer and the seeds ripen from June to July. These tend to germinate even while on the tree and accordingly begin to fall soon after appearance. The sap wood in Sal is of small thickness. It is whitish in color and less durable. Heart wood is pale when freshly cut and tends to grow dark brown on exposure. It is coarse grained, hard and of fibrous structure. Annual rings are visible in young trees or on freshly cut wood. Its pores are of moderate size. These are filled with a kind of resin which makes the wood naturally durable.
Sal wood is one of the three naturally lasting timbers of the Asian subcontinent, the other two being Teak and Deodar. It weighs nearly 25 to 30 kg to a cubic foot. It is difficult to plane and more so to drive a nail in to it. It is accordingly considered most suitable for railway sleepers, piles, beams and other load bearing parts of bridge structures, wheels and bodies of carts and other similar load carriers, including motor trucks, super structure of house tops, etc. In fact Sal wood is most suitable for all such applications where strength and elasticity are foremost requirements, and where polishing is not so very essential. Sal wood being so much sought after for construction purposes, its demand is much more than the available supply. The states having good Sal forests earn a lot of revenue.
Sal tree when tapped, yields white opaline resin which is burnt as incense in Hindu homes during religious ceremonies. It is also used for caulking boats and ships. The seeds are used for fat extraction. The oilcake, though rich in tannins (5-8%), has been used in proportions of up to 20% in concentrates for cattle without detrimental effects. As the protein remains completely undigested, the oilcake yields energy only. Sal seed cake can constitute up to 10% of poultry and pig rations without changes in performance. A kind of oil is also obtained from sal fruit which is used for burning in earthen lamps. It is also misused for adulterating ghee. Further, during famine poor people grind the fruit into flour and eat it to ward off starvation.
The Sal tree worshipped among Buddhists and Hindus in India and the adjoining countries. The legend has it that the famous Lumbini tract where Lord Buddha had sat for meditation and acquired salvation constituted a thick forest of Sal trees.
The healthy forests of Sal in their original habitat like Singhbhum (Bihar) and Doon valley (Uttaranchal) regenerate on their own. In less favorable areas these need continuous assistance for regeneration. These causes and remedies for the difficulty of Sal regeneration are an important subject of research at the National Institute of Forestry and Environment, Dehra Dun. They are also conducting studies into the insects and bacteria afflicting the healthy growth of Sal trees.