The Sal – Silviculture of Shorea robusta, Know your trees

Shorea robusta

(Family : Dipterocarpaceae)

Local Names : Assamese : sal, borsal; Bengali : shal Hindi : sakhu, sal; Oriya : ,sakwa, soringhi; Telugu : gugul.

(Family : Dipterocarpaceae)

Local Names : Assamese : sal, borsal; Bengali : shal Hindi : sakhu, sal; Oriya : ,sakwa, soringhi; Telugu : gugul.

Trade/Common Name : Sal

Sal, along with teak, is one of the two main commercial timbers of India. It is the most widely distributed and economically by far the most important species of North India. Sal forest occupy about about 14.2% of the total forest area in India (1971-72 figures). It occupies two main regions, the Northern and the Central Indian regions. separated by Gangetic plain. The main and almost continuous stretch of Sal forests in the northern region commences with Kalesar forest in Ambala District of Haryana on the right bank of Yamuna and stretches eastwards, along the sub-Himalayan tract as far as Darang district in Assam-through Uttar Pradesh, Bihar, Assam, Meghalaya and Tripura. Sal is at its northern and western limits in two small out-lying pockets  of Himachal Pradesh.

In the Central region, sal occurs in Bihar, West Bengal, Orissa. Madhya Peadesh, with isolated pockets in Andhra Pradesh. Sal forests occur in several forest types and sub-types of Northern Tropical Moist Deciduous and Dry Deciduous Forests, as classified by Champion and Seth (1969), occupying region with wide variations in climate ( rainfall and temperature), soil and topography.

Particular About Seed:

Flowers appear from late February' to April, depending on locality and season; fruits ripen May to July and fall soon after (late May to mid June in West Bengal; May to early June in Assam; June in Bihar and Dehra Dun; May to July in M.P.); fruits weigh 530 - 1060/kg (Sen Gupta), 575 - 1000/kg as reported in F.R.I. An average seed year may be expected after every two years, and a good seed year after every 3 - 5 years. Sound fresh seed has high germinative capacity of 80-96% and plant percent upto 86. seed loses viability rapidly; it may be sotred for about 7 days only alter collection in loose backets, in shade out of doors and packed in lime or saw dust. Seeds germinate soon after falling; in some cases even on the trees. seeds do not require any pre treatment. For seed ( fruits) collection. ground under the healthy, mature and well-shaped trees is cleared, and the fallen seed carefully selected and collected every morning.

Methods of Propagation:

Natural Reproduction : Natural regeneration of sal has been a subject which has engaged the attention of Foresters, Scientists and Researchers for more than 60 years. Soil, climatic and biotic conditions being widely variable, response to various Silvicultural Systems in various types and sub-types, such as Uniform, Selection, Irregular Shelterwood and Coppice Systems, in obtaining natural regeneration has also been variable. Volumes of reports have been presented and discussed at various Conferences and Symposia; it is not possible to give even the summary thereof, except to recapitulate barely that, by and large, out attempts at obtaining natural regeneration, at our will, when and where required by manipulation of various factors, have not been successful, at any rate not commensurate with our efforts and expenses involved. This is particulary true of moist and dry decuduous Sal forest types. The problem is not the recruitment of regeneration but its establishment. Early and well distributed rains synchronizing with seed fall, absence of frost and suitable soil conditions being the main favorable factors.

Some of the Sal forests of U.P., M.P., Bihar and Orissa are being worked under Simple Coppice, Coppice-with-Standards or Coppice-with-Reserves in several cases the Coppice Systems have been replaced by Clear-felling followed by taungya cultivation.

Artificial Regeneration:

The method very largely used in the field is by direct sowing. Stump planting, pre-sprouted-stump planting, entire Container plants, plants with ball of earth and air layering are among the methods tried, but all these are of limited application, confined to special situations and localities only. Sal has been successfully raised by sowing in clearfell led areas by departmental plantations in Tripura, by taungya in Uttar Pradesh, Assam and West Bengal. Techniques of taungya cultivation in respect of extent of area allotment, period of cultivation, nature of agricultural crops raised, spacing between the lines, method of beating up failures, mixture of species if any, methods of sowing (one, two or three rows) and depth of sowing, vary from State to State, sometimes within the State, depending on local considerations.

Planting : Planting of 22 or 34 months old basket plants in 60 cm' pits, 3 m apart in continuous strips, spaced 6 m apart, both in clear-felled areas and under Shelterwood, gave 80% survival, in Haldwani Division. U.P.

Transplants in dona containers have proved successful in dry Sal forests of Southern West Bengal; more successful than sowings in heavy clayey and lateritic soil. Dona planting is done in partly-filled trenches at a spacing of 1 to 1.25 m throughout to supplement sowings in plantations; it has given 75% survival and at a reasonable cost in West Bengal. Stumps Planting of Sal is also possible; is sometimes done to beat up failed lines. Stumps prepared from one or two year old nursery stock were successfully planted in West Bengal and Uttar Pradesh. Possibility of vegetative propagation of Sal by air-layering, with the help of hormone Seradix B-3, has been demonstrated at the F.R.I., Dehra Dun.

Nursery Practice:

Artificial regeneration of Sal by planting out nursery-raised sal seedlings (dona, basket or polythene bag plants) or stumps has not been practised on a large scale; these methods were attempted on a small experimental scale in the recent past. Another method of raising sal container plants, successfully adopted in Southern West Bengal and Bihar, is in donas (leaf-cups), made of Sal leaves, 6-8 cm diameter and 22 - 23 cm deep. These are filled with tank silt, earth and cowdung mixed in 2:4: I proportion. Two seeds are sowning each as soon as ripe and collected; watered regularly and kept in shade in summer. When monsoon rains have well set in, dona seedlings with 4 leaves and 12 - 15 cm in height are fit for planting out, with containers.

Intensive tending of young crops of Sal, whether natural or artificial, is very important, for establishment of seedlings. These operations involve weedings, hoeing, selective shrub-cutting, fencing, fire-protection, and manipulation of cover at various levels and various stages.

Natural Crops:
In sapling and pole crops, cleanings and thinning, climber cutting, cutting back of malformed saplings, singling of stems, cutting down of all competing growth and inferior species, etc., are carried out. Subsequently, thinning are carried out, C/D grade or Light Crown thinning, on a 10-year cycle. In Coppice-with-Standards, 2 thinnings at the ages of 14 - 15 and 27 - 30 where 40 year rotation is adopted and 3 at the ages of 15, 30 and 45 years where 60 years rotation is in vogue.

Plantation Crops : In West Bengal taungyas, climber cutting is done almost annually upto 10 years age, and thereafter twice every five years till the crop reaches 30 years age; subsequently climber cuttings is done alongwith thinnings as per prescribed schedule. Thinning intensity experiments (Kalimpong, West Bengal) in high quality taungya plantations suggest a 5-year cycle upto 20 year age, and thereafter the thinning cycle should be increased. First two thinnings are mechanical, the third or sometimes the fourth is a C/D silvicultural one. However, in most of the forests, thinnings are done on a 5-year cycle upto about 30 years, and thereafter on a 10-year cycle.

Injuries, Pests and Diseases

Climatic - Sal crops, young and old, are liable to damage by thought; its extent and seriousness is aggravated by fire and grazing. Sal suffers badly from frost; seedlings and coppice shoots may be killed-back by frost, year after year, till they shoot up and escape frost ultimately. Severe frosts, however, cause injury to the crowns of poles, and even larger trees, killing the leading shoots and resulting in epicormic branches. Radiation frost in the plains and pool frost in the valley forests are common; Silvicultural Systems and methods of regeneration are also determined by the occurrence, or otherwise, of frost.

Fire : Sal is one of the most fife-resistant species of the region. In fire-prone areas, Sal may be burnt back year after year, but it recovers slowly but surely. Fires cause hollowness, and/or unsoundness in Sal crops, particularly in drier types, and resultant loss in quality and quantity of out-turn; complete fire protection is beneficial. However, in moist types, complete fire protection is seldom necessary; controlled and regulated burning is useful for inducing and establishing regeneration.
Parasitic Plants and Weeds: Obnoxious weeds and Mistletoes such as Lantana, Mikenia, Eupatorium and are serious problems in plantations in West Bengal, U.P. and Assam.

Animals : Wild animals, like elephants, bison, pigs, deer, monkeys and rats cause damage to Sal crops at various stages. Domestic cattle grazing are a source of mechanical injury to young crops and physical deterioration of soil. However, regulated grazing in time, place and intensity is beneficial in most types.

Insects : A large number of borers of bark and wood, defoliators, sap suckers, fruit and seed eaters have been recorded.

The most important primary borer and potentially the most destructive, in Sal heart-wood borer, Hoplocerambyx spinicornis. It is a beetle which emerges with the commencement of monsoon. Serious epidemic attacks have been reported from U.P., M.P., W. Bengal, Assam and Himachal Pradesh. It attacks dead and dying trees. There are a large number of secondary borers of minor importance which may affect Sal trees.

Fungi : A large number of fungi have been recorded on Sal causing fungal diseases. Fomes caryophylli causes heart-rot; Fomes fastuosus causes butt-rot and Polyporous shoreae causes root-rot.

(i) Sal is a large deciduous tree, seldom quite leafless; one of the most important timber trees of India. It is a light-demander; sensitive to drought ' and frost; fire-resistant. As a rule, it coppices well upto a moderate size.
(ii) Sal wood is very hard, tough and heavy; heart-wood is very durable naturally; sapwood requires treatment before use. Timber is difficult to saw and work with, due to interlocked fibres.
Main use of Sal timber is for railway sleepers. It is in great demand in the form of poles and ballies; after preservative treatment these are used for overhead electric transmission lines, telegraph and telephone circuits, scaffolding, mining timber, etc. Sawn timber is used for beams, columns, bridges, building construction, etc. Other uses of Sal timber are for agricultural implements, boat building, carts, cooperage, marine piles, bus and truck bodies, railway carriages and wagons, ship building, tent poles and pegs, rice pounders, tool handles, etc. Sal wood is excellent fuel.
(iii) Sal wood in admixture with other hardwoods, can be used for manufacture of wrapping, writing and printing paper.
(iv) Sal bark is a useful tanning material.
(v) Sal seeds yield a vegetable oil on extraction.

Management : Sal forests are being worked in various States under a variety of Silvicultural Systems, depending on the forest type, ecological factors (climatic, topographic, edaphic), governing conditions of regeneration, and objects of Management. These are : Uniform, Irregular-Shelterwood, Selection, Clearfelling with natural regeneration (as in South Raipur. M.P., and Saranda in Bihar), Clear-felling with arfiticial regeneration (taungyas of W. Bengal, Assam, U.P.), Simple Coppice, Coppice-with¬Standards, and Coppice-with-Reserves.