Silviculture and its Application in Pakistan

By 
(Divisional Forest Officer Balochistan Forest & Wildlife Department)

What is Silviculture?
Silviculture is the application of the principles of forest ecology to a stand of trees to help meet specified objectives. 
The term Silviculture in English commonly refers only to certain aspects of theory and practice of raising forest crops, their growth and care up to the time of the final harvesting. It is American practice to differentiate “ silvics from Silviculture, the former covering the basic information on which the latter depends in dealing with the practice: Silviculture is thus the applied aspects of silvics.

The Forester is called on to apply the Silviculture knowledge & experience to all the land included within certain legal boundaries, irrespective of the nature of growth they may carry. The legal meaning of “forest” may be very different from the ordinary or botanical concept and the forester will usually have in his charge not only the tree growth of varying density and quality but also shrubs and grassland, even wasteland more or less bare of vegetation and the hilltop above the altitude where tree growth is not possible.

The science/knowledge of forestry has been developed in the temperate forests of the northern hemisphere and many general principles remain valid under the most of varied conditions, the application of knowledge & experience obtained in these temperate forests to the tropical forest of Pakistan and even to the temperate forests also requires the greatest caution. Tropical forestry has, in fact, to build up its own silvicultural science, for the experience has already taught that the difference from temperate forestry is often not merely a difference in degree but liable to be the difference in kind.
The forests of Pakistan, whether considered in the wide sense of foregoing paragraph or in the usual sense, probably include as great a range of composition and appearance as can be found over a similar area in any other part of the globe. Their Silviculture is accordingly more complex than that of a relatively small range of types of conditions.

Some forests of the country, notably the tropical evergreen forests of the wetter portion, are possibly still in their natural state as they have developed in accordance with the local conditions of climate, topography, and soil. The greater part of these forests, however, have been influenced directly or indirectly by human activities. Recognition of this fact and an understanding of the ways in which these activities have affected and still affecting the forests are most important to Silviculture.

APPLICATION OF SILVICULTURAL KNOWLEDGE IN PAKISTAN

Pakistan being located between 24o and 37o N latitude and 61o and 75o E longitude has a diversified climatic, edaphic, topographic features. It has a vast coastal area in the south-west, world largest living fissile juniper forest at Ziarat, a large extended area having arid, and semi-arid conditions. It also has subtropical, temperate, subalpine and alpine pastures. Water shortage and desertification are the two main threats which may determine the future of the region. So silvicultural knowledge and its application in Pakistan is very complex and also important. It plays the pivotal role in the livelihood of the rural population of a hillside, coastal line, and lifespan of our huge water reservoirs.

The major applications of silvicultural knowledge are listed below:
1: locality factors;
2: Nursery raising.
3: Sand dunes stabilization. 
4: mangrove forest management.
5: watershed management.
6: tending operation
7: silvicultural systems.
8: natural regeneration.
9: Site maintenance.
10: wildlife conservation.

1: LOCALITY FACTORS
The locality factors such as climate, soil, and topography are responsible for distribution of different forest type in Pakistan. The potential productivity of forests is determined by the conditions prevailing in the site it occupies. An understanding of the reactions between forests and locality forms the essential foundations of Silviculture. The type of forest occurring naturally on any site is largely dependent on such factors which can hardly be altered by forester but can be significantly influenced by various silvicultural treatments.

It is due to these factors that Pakistan being close to the tropics has a wide strip of temperate and alpine zones in its northern parts. .Pakistan, due to these locality factors has numerous type of forests i.e. mangrove forest, scrub forest of central Punjab and large enough area of K.P.K, Subtropical broad evergreen, pure chir pine and temperate forests. So the knowledge of Silviculture is widely used in identifying the most suitable species for a particular area and helps in selection of the most suitable silvicultural system for its management on sustainable bases.

2: NURSER8IES RAISING:
Forest nurseries are playing very important and central role in the development of forestry and improvement of the environment of our country. The establishment of nursery requires the basic knowledge of Silviculture of the species to be raised in the nursery. While raising nursery the due care must be given to site selection, location, water availability and aspects on which the nursery is to be established beside adopting proper techniques.

• Site selection: the selection of nursery site is very significant and it should be looked carefully. The important consideration given to site selection for the nurseries are the physical aspects, namely terrain, the nature of the soil, the presence of perennial water source the likelihood of frost, sunlight, accessibility and the distance from the plantation area.

• Location: the first issue that needs to be sorted out in planning a nursery is the “general area” where it should be established. For example for agroforestry, the nursery should be located in an area where sufficient area for plantation is available.

• Water: the source of water should be perennial and at a higher point for irrigation by gravity. Efforts should be made to improve the local water holes, springs water by planting suitable species.

• Soil: nursery soil should have sandy loam to loamy texture, medium to small blocky structure, pH varying between 5.5 to 7.5, moderate fertility. the site should be well drained.

Aspects: In hills, the aspect of the site plays a significant role in the success of a nursery. In our condition, the most congenial aspects are south and south-west in higher hills and in the eastern and southeastern aspects in the lower hill. In the plains, the beds should have longer Sides in the east-west direction.

Preparation of beds:
The beds can be of four types.
(a) Seed flats or beds for germination, from which seedling are pricked out either to a container or to other kinds of beds.
(b) Ploy pot container with an individual seedling.
(c) Housing beds, in which individual containers with one or more seedlings in each are placed side by side.
(d) Transplanting beds, where the plants are grown in the beds its self for eventual planting out.

In addition to the bed preparation due care/attention should be given to;
• Seed collection from plus trees.
• Proper Seed storage to keep the viability of seed intact.
• Pretreatment of seed for obtaining good germination.
• Pricking out of seedling.
• Watering, weeding, pest control and mulching.
• The uprooting of bare rooted and shifting of potted plants.

3: Sand dune stabilization
Pakistan Desertification Monitoring Unit (PADMU) under Pakistan Council of Research in Water Resources (PCRWR) conducted field surveys from 1982 to 1985 to assess and monitor the desertification processes in the Cholistan desert by involving ground truth investigations, Landsat data and computer analysis of satellite imageries etc. It was estimated that out of 2.6 million hectares total area of Cholistan, about 1.13 million hectares comprise stable as well as non-stable sand dunes and 0.95 million hectares are sandy soils. These coarse-textured soils of about 2.08 million hectares have been affected by wind erosion.

Vegetation and moisture are two factors which can bind the sand dunes. These two factors are interrelated and the best method to bind these would be to utilize the moisture present in the dunes for raising vegetation otherwise the moisture will disappear in no time leaving the sand dunes at the mercy of severe gales. For this purpose, various sand binding species are being tried. Usually, the grasses have served this purpose. the tough binding grasses with their harsh tufts check the wind, trap oncoming supplies of sand and continue to grow onwards as the entangled sand accumulates leaving behind them an intricate network of long roots. Such protective dunes become leveled up and tufted over. some tree species have also been tried for this purpose. however, stress should be laid down local species than introducing exotic ones. Since dunes have three locations and process different water content, therefore different species are planted according to the location.

The top of the dunes should be planted with Calligonum polygonoides, H.salicornicum, Salsola foetida, Capparis aphylla, Kochia indicia, Acacia arabica, Prosopis spicgera etc.
The middle of dunes with Lasiurus hirsutism, Eleusine compressa, panicum antiotale, Cymbopogan jwarancusa, Cenchrus spp and Aristida depressa.
While the bottom of dunes with Haloxvlon recurvu, Zizyphus nummularia, Peganum harmala, Fagonia cretica etc.

It will be feasible if the seeds, tufts, cutting or the entire plants as the case may be, of the above species are planted immediately after the rains in July and August. The species like Datura alba and Calotropis procera etc are unpalatable and posses no economic importance. The introduction of economically important and palatable species after eradication of the latter species will not increase the potential wealth of the area but also help boost up the economy of the locals of the area.

4: MANGROVE FOREST MANAGEMENT
Mangroves forests of Pakistan in Indus delta and along Arabian Sea coastal areas, as per estimates, are some 129,000 hectors and over 3,000 hectors in Miani Hor, Kalmat Khor and Gwadar bay areas.

Mangroves are one of the most familiar forms of vegetation occurring in the intertidal zones along sheltered coasts and river banks in coastal areas in tropical and subtropical countries of the world. Mangrove forests are highly productive ecosystems and are a natural, renewable resource. They provide essential goods and services and play a very important role in the lives of coastal communities. Through adaptations such as viviparous germination, the separation of fresh water from salt water and the conservation of freshwater, the ability to strike roots soon after coming into contact with soil and the ability to exchange gases through specialized root systems, mangrove species have been able to deal with a very adverse environment where few other plants would have survived.

Mangrove vegetation primarily comprises trees and shrubs, with a limited number of palms and lianas. Major mangrove species belong to less than 15 families but the most frequently occurring mangroves belong to the Rhizophoraceae, Sonneratiaceae, and Avicenniaceae.

Mangroves grow in conditions where few other plant species can survive. The occurrence of mangroves is contingent on a number of factors and important physiological adaptations which enable the flora to thrive in the exacting environment and which also have silvicultural implications.

Mangrove seeds and propagates are dispersed exclusively by water and their distribution is therefore greatly influenced by tides which carry them both upstream and downstream. The tidal range, together with the topography, of an area, regulates the lateral extent of mangrove development. The greater the tidal range, the greater the vertical range available for mangrove communities Tides also bring about changes in the salinity concentration of water in mangrove areas.

In most areas of the world, mangrove formations have simply been exploited with little or no attempt to manage the resource on a sustainable basis. The management of mangrove forests under selection and clear-felling silvicultural systems is practiced in a limited number of countries, mostly in Asia, although in recent years several countries have seriously taken up mangrove plantation establishment and the rehabilitation of degraded mangrove formation
To stop degradation and for the improvement of mangroves areas, the knowledge of Silviculture is extensively being used for establishment of mangroves nurseries, their conservation, preservation and for natural regeneration.

5: SILVICULTURE IN WATERSHED MANAGEMENT:
The implication of Silviculture to the watershed can be summarized very simply. Acting on these implications is the hard part. Firstly one must know what type of forest occurs, wherein the watershed, why, and what has caused them to be there and in their current form and condition, and how they are evolving. The forest as they exist, are a result of past management and mismanagement. Some forest due to the past history is not the most appropriate forest for the site on which they occur. Underlying the history of management is the history of glaciations and the surficial geology of the watershed that has resulted in the current soil and drainage.

This physical and social history has resulted in broad forest types that occur on the features. Past history, including the topography and the disturbance, has resulted in the forests of the watershed as we see them today. We must see where our forests have been and where they are going, in order to determine our most appropriate actions. The natural tendency to a replacement of shade intolerants and mid-tolerant by shade-tolerant must be recognized as a natural phenomenon, often misguided by management practices. By understanding the history and underlying soil strata, and the normal process of succession, silvicultural systems must be chosen carefully to meet the management objectives that will not result in deterioration of their quality and quantity of the forests of the watershed. In some cases, what is currently needed are the silvicultural programmes that will result in forest restoration and one must not make the mistake of discounting the quality of forest based on the current degraded condition if the site and species are conducive to natural or man-made restoration. Forests have been intentionally degraded by excessive harvesting and mismanagement, in order to remove barriers to the residential development of these forests. This artificially degraded condition, which would only be temporary, facilitates the permanent loss of the forest.

Based on this assessment of forests and forest sites of the watershed, management objectives could be developed in a forest plan, which would identify targets for the representation of various forest types as well as for the forest cover as a whole. This would include identifying where in the watershed these forest types are normally found and what pressure exists in the area that affects their quality and quantity. Potential could be identified for various management regimes in terms of economics and environmental quality. Goals for maintenance, replacement, and management could be set for the watershed as a whole, which could be recognized and incorporated into local plans.

6: TENDING
Tending are operations carried out for the benefit of forest crop at any stage of its life between seedling and mature stage. It covers operations on the crop its self and on the competing vegetation. Tending include all the operation which provide conducive condition for the development of forest crop i.e. weeding, thinning, pruning, cleaning, cutting of climbers and removal of unwanted growth. Tending does not include any type of soil work.

In our country, the tending operations are actually carried out in irrigated plantations. For healthy development, tree crop requires protection from insects and disease. Furthermore, the individual tree must have adequate room to grow. All the infected, weak and damaged plants must be removed besides removing the host plants of insects. Such type of operation is also termed as sanitary felling. The primary concern of tending is to reduce the competition for food/nutrients amongst the forest crop and to ensure the development of crop as a whole.

Thinning is a felling made in an immature stand for the purpose of improving the growth and form of the tree that remains, without permanently breaking the canopy {ANON 1953c}. Thinning is chiefly concerned with promoting good growth of the stems that are retained.

Thinning is required/needed both in plantations, artificial and natural regeneration. Plantations are raised with the sole objective of producing maximum quantity of quality timber in a comparatively shorter period. so the thinning not only help and ensure the obtaining of straight and clean bole trees but also bring some early financial return from the very costly practice of raising plantation. Similarly thinning is also required in chir pine where the regeneration usually comes so profusely that they compete/strive for nutrients which hinder their vigorous growth. Though these are thinned by nature its self on the bases of natural rule” THE FETEST HAS THE RIGHT TO SURVIVE (Khattak) but it takes time and delays early development of diameter growth so to provide conducive condition and to reduce the intra competition and to provide adequate space , thinning is always advisable in chir pine regeneration. The main objectives of any sort of thinning are listed as under.

• Improvement of the existing stand.
• Regulation of tree & stand growth.
• Early financial returns.
• Reduction of conditions favorable to insects & disease.
• To create conditions favorable to reproduction.

Thinning is generally carried out on the following techniques:
Low thinning: taking out overtopped & small trees in the understory.

Crown thinning: removing trees from the middle & upper levels, opening the canopy for maximum growth of dominant & co-dominant trees in the stand.

Selection thinning: removes the dominant trees to concentrate on the growth of the lower crown classes. Not recommended unless the immediate income is the top priority.

Mechanical thinning: based on spacing with little or no regard for tree vigor, form or position in the canopy. in mechanical thinning 50% of the crop is removed of the original planting lines reducing the number of plants from 1210 to 605 and then 302 per acre and increasing the spacing from 6*6 to 12*12.such procedure is only practicable in areas where growth is good and even put it out of question in poor or uneven plantations. Such operation may also be done in the mixed plantation where one species is introduced to cover the ground quickly and draw up the major species, so its removal is necessary for the interest of main major species.

Generally, two methods most often used are row thinning & fixed intervals.
Row thinning-taking out complete rows of trees at a time and thus space is created and sufficient ground area is provided to tree crop and the intra competition is reduced which enhance the growth of tree both in diameter and height. (Example: every 3rd or 5th row)
Fixed interval-strips cut throughout the stand for providing adequate space for the retained crop.

TYPES OF THINNING:

1: ORDINARY THINNING:
The standard grades of ordinary thinning are as under:
I: LIHGT THINNING {A-GARDE}
in this type of thinning only dead, dying, diseased and suppressed trees are removed. Grade A thinning is of no practical use but forms a convenient stage, especially in research on the effects of thinning on increment.

II: MODRATE (B-GRADE)THINNING: in this type of thinning further removal of a defective dominated stem, branchy advance growth which is otherwise impracticable to prune are removed. This type is also of little importance in general practice as it has a little influence on increments of the remaining tree crop.

III: HEAVY(GRADE –C)THINNING: this consists in the further removal of the remaining dominated trees and much of the defective dominants as can be removed without making lasting gapes in the canopy.

IV: VERY HEAVY(GRADE –D)THINNING: in this type of thinning too, some good dominants are removed in such a way that lasting gapes are not created in the canopy. The trees selected for removal are such that the remaining crop consists of as for as possible of trees with good boles and crown, well and evenly distributed over the area and with a space for further development.

This type of thinning is best suited to light demanders such chir pine in which the dominants requires more room and the trees which comes under the lower canopy practically cease the growth and die. Shisham and eucalyptus must be well thinned from early youth whereas the mulberry and many shade bearers must be kept close to eliminate side branches and to give clear bole.

CROWN THINNING:
IN this type of thinning dominants are considered for removal, beginning with the least promising individuals which are hindering the development of the best individuals. Due attention is given to obtain as even distribution of good dominants over the area as possible. Crown thinning should be started as soon as crown differentiation has progressed for enough to permit it. One should switch to crown thinning from ordinary thinning as the lower canopy will have been removed in ordinary thinning. The removal of some of the dominants gives space and light for some of the dominated trees and a certain number of these may later take their place among the dominants. Crown thinning particularly does well in markedly or moderately shade tolerant species where the retention of lower canopy poses no difficulty. It is well suited to Sal, deodar but does not suite shisham or chir pine. 

IMPROVEMENT FELLINGS
Improvement felling is the removal or destruction of the less valuable trees in a crop in the interest of the better growth of the more valuable individuals. This operation is not meant for getting regeneration though it encourages the filling blanks. Similarly, revenue is not considered as objective. Any return from the material removed is purely incidental.

Improvement felling is usually prescribed for the inferior forest, especially those which are in poor condition due to felling, excessive grazing or burning for bringing back the forest to a regular production. Such fellings are prescribed in working plans and exclusive working circle “improvement working circle” is allotted for operations. In improvement working circle the following practices are prescribed.

• Felling of utilizable dry trees.
• Removal of unsound over mature trees which are unlikely to survive till next felling.
• Removal of badly shaped mature or immature tree where their removal will be beneficial to other better crop.
• Thinning of crowded groups of trees. this is to be done in the early stage with special provision for the exclusion of larger trees which should be retained to contribute to main revenue felling to be made latter on.
• Cutting back badly shaped/injured sapling and advance growth from which better coppice shoot could be obtained.
• Removal of undesirable undergrowth.
• Cutting of climbers..
• Removal of diseased, fig and infected trees.

7: SILVICULTU RAL SYSTEM
A silvicultural system is a planned program of treatments during the whole life of a stand designed to achieve specific stand structural objectives. This program of treatments integrates specific harvesting, regeneration, and stand tending methods to achieve a predictable yield of benefits from the stand over time.

The general aim of Silviculture is to ensure that most available growing space is filled with useful plants for as much of the stand’s life as is practical. “Useful plants” often include timber species, but increasingly include forage and other forest vegetation. Silviculture also strives to ensure that the dynamic structure of the stand, meets the needs of the landowner at any given point.

In the past, silvicultural systems have been designed to maximize the production of timber crops. However, more recently additional ecological considerations and resource objectives have been included. A silvicultural system generally has the following basic goals:

• meets the goals and objectives of the landowner 
• provides for the timely availability of many forest resources (not just timber) 
• produces predictable harvests over the long term 
• balances biological/ecological and economic concerns to ensure renewability of resources 
• ensure regeneration 
• effectively uses growing space and site productivity 
• Considers forest health issues.

In designing a planned program of treatments to achieve these basic objectives, a practitioner will generally create a detailed stand level plan or long-term prescription. However, these prescriptions can be grouped into readily recognizable types of programs called silvicultural systems.

The silvicultural system differ from each other in the method of regeneration, natural{seed, coppice} or artificial , the type of crop produced whether even aged or un even aged, the time of felling and the distribution of felled and unfilled area.{khattak}. When the regeneration is of seedling origin, the systems are called high forest systems as contrasted with coppice system. a compartment or sub compartment of a forest may contain tree of all age classes and regeneration operation dispersed through out the whole area. In such condition the system will be called as selection system, alternatively the forest may contain trees of restricted age range so that the regeneration practice will be limited to a certain area in which the trees are near to end of rotation , this system is one of the concentrated regeneration systems. the detail classification is as under:

Index to the Silvicultural Systems
1. High Forest Systems
Systems of Concentrated regeneration Selection Systems Accessory Systems
Clear Felling Systems Shelterwood Systems 1. The selection system. 
2. The group selection system. 1. Two storied high forest system. 
2. High forest with reserves systems. 
3. Improvement fellings.
1. The clear felling systems. 
2. The clear strip system. 
3. The alternate strip system. 1. The uniform system. 
2. The group system. 
3. The shelterwood strip system. 
4. Wagner’s Blender-saumcschlag. 
5. Eberhard’s wedge system. 
6. The strip and group systems. 
7. The irregular shelterwood system. 
8. The India irregular shelterwood system.
2. Coppice Systems.
1. The simple coppice system. 
2. The shelterwood coppice system. 
3. The coppice with standards system. 
4. The coppice with reserves system. 1. The coppice of two rotations system. 
2. The selection coppice system. 
3. The pollard system.

In concentrated regeneration system when the mature crop is removed in single operation resulting in more or less even aged crop, the system is known as clear fell felling system. When the mature crop is removed in more then one operation, resulting in roughly even aged regeneration, then the system is known as shelter wood system. If the canopy is opened evenly in making the regeneration felling, the system is known as the uniform system. If the canopy is opened by creating scattered gapes, subsequently extended over a large area, the system is known as group system and if the canopy is opened irregularly but gradually with long regeneration period, resulting in an uneven-aged crop, the system is called irregular shelterwood system.

CLEAR FELLING SYSTEM:
In clear felling system, a part of the area is felled and regenerated either naturally or artificially. Ideally, the area to be regenerated is divided by a number of years in which the work has to be completed. The area is mainly divided in to felling and regeneration area. Where regeneration is difficult to obtain, promising groups of sapling may be retained provided they are large enough to form a separate crop, however retention of scattered trees are not advisable As it interferes excessively the development of future crop and themselves by becoming too branchy.

This system is not practicable in the high forest due to their long regeneration period and similarly, the artificial regeneration cannot be ensured due to various reasons like funds availability and adverse climatic conditions.

This system can only be used in Pakistan for management of irrigated plantation where clear felling is followed by removal of all merchantable produce and burning of debris. Sowing or planting of forest crop is carried.

SHELTER WOOD SYSTEMS:
Except, where the conditions are exceptionally favorable for seeding and the seedling are enough hard, do not require protection from the sun or frost, the crop can not be removed in single operation then the crop is opened up gradually to an extent and at rate which permits the regeneration and early growth of the seeding from the natural seed fall. as the seedling grows, their light demand is met by removing more trees from the over head canopy. The system where the natural regeneration is obtained through one or two successive felling is known as shelterwood system.

Uniform system:
In this system, the canopy is opened uniformly over the entire area and the regeneration so obtained will be more or less uniform and even aged.

For the successful application of this system, it is essential that the crop is properly thinned throughout its life and ready for exploitation and regeneration. The successive thinning provides an opportunity for the development of the future crop and the best phenotypes having straight, most cylindrical bole and slenderest branched are retained. The crown should be well developed for abundant seed production.

In an irregular forest like in Pakistan where the forests are being converted to a uniform system, the crop is prepared by heavy preparatory thinning for crown development.

Various stages of implementation of this system are listed below.
Regeneration felling: in the mature crop, seeding felling is carried out and prescribed numbers of seed bearer uniformly distributed over the area are retained. The seed bearer should of the best stem of the original crop, uniformly developed crown and good bole form. The object is to have best parents for the future crop. In shelterwood system, it must be ensured that all felling will improve the genetic quality of the crop.

the number of seed bearer depends upon several factors like, site quality, the seed production capacity of the species, dispersal behavior and the site quality,e.g.5-8 seed bearer are sufficient in case of chir pine while 12-14 are considered sufficient for blue pine and the number is increased to 20 for deodar. on the other hand, a large number of seed bearer are required on hot, dry aspect than on cooler aspects and less seed bearer will be for light demander than with shade bearer.

The seedling felling allows the light and heat to the ground and stimulates the germination of any seed lying on the ground. Adequate seed germination will only take place if the supply of the seed is sufficient and crop before felling was reasonably dense and has succeeded in keeping down the weed growth. In case the forest floor is covered with dense shrubby growth then it have to be cut before the regeneration is expected and in case of chir pine, the thick layer of undecomposed needles is burnt. Since the object of the uniform system is to get even aged crop so all the advance growth has to be felled however large patches of advance growth below a certain size are usually retained.

Secondary felling: 
Once the regeneration appears on the forest floor, the over wood is removed in one or more felling to assist the development of the new crop. if the species is strong light demander and regenerates with ease e.g. chir pine the seed bearer may be removed in one felling though it will only apply to the parts of the area under regeneration. If the species is regenerated with difficult or requires protection against frost or draught then the over wood is removed in one or two felling. The rate of removal is determined by the progress of regeneration and it also affects the proportion of other species’ regeneration in the mixed forest. The first light felling will result in appearance and establishment of more shade bearer species and subsequent felling will result in the regeneration of light demander and disappearance of shade bearer species.

Regeneration(Reproduction)Period 
The time between the initial regeneration cutting and the successful re establishment of a new age class by natural means, planting, or direct seeding. Unlike the clear felling system in which an area is clear felled and regenerated every year, 20-30 years may elapse under the uniform system between seedling felling and the final felling in which the remaining over wood is removed. The length of regeneration period depends upon a number of factors i.e. seeding, locality factors, hardiness of species and natural hazards like fire etc. when these factors are favorable the period for establishment will less and if unfavorable the regeneration period will longer. The prescribed regeneration period is the only rough indication.

PERIODIC BLOCK:
According to the length of regeneration period, the area of forest is divided in to periodic blocks[P.B]in order to systemize the execution of various operations, e.g. if the rotation is 100 years and the regeneration period is 25 years, the rotation and the area can be divided into four P.B.

PERIODIC BLOCK CROP AGE{in years}
PB I 75-100
PB II 50-75
PB III 25-50
PB IV 0-25

All the stages of regeneration are carried out in PB I & PB II where the crop is prepared for regeneration and to increase the diameter of trees below exploitable size. No tree of good size is felled provided It can be retained for 25 years. Thinnings are carried out in an area having low diameter especially where the crown needs development for production of good seed crop. PB III is comprised of pole crop varying between 25-50 years while PB II is consists of young regeneration. In this PB mainly cleaning and thinning are carried out and mature trees which are so for retained are removed.

HOW P.B ARE ALLOTED:
The working plan officer, during the preparation of the working plan, allots compartments and sub compartments on the basis of age and condition of the crop to various periodic blocks. The PB is therefore not a concentrated area but usually scattered in different localities. Full allotment of all stands to several PB in the rotation is only possible where there are fair chances of obtaining good regeneration.

GROUP SYSTEM:
When a species are poor seed bearer and regeneration can not be obtained when & where desired, and where sensitive shade bearer forms an important part of the crop. The adaptation of group system result in adequate regeneration. Generally, small groups occur in the forest due to wind falls or lightning and regeneration may already be present in form of advance growth. These gaps are extended in a centrifugal manner to remove the over head cover from the established regeneration and to create further space for obtaining regeneration.

In case where no natural gaps exist, they are created artificially for providing space and light for obtaining regeneration. The rotation period may be divided in to the number of PB as in uniform system or floating PB is selected for regeneration. The difference between the two systems lies only in a manner of regeneration felling. In uniform system seedling felling are carried out in the entire area and the seed bearer are left at more or less even spacing while in group system during seedling felling small gaps are created or the already existing gaps where the regeneration are present are extended over the compartment. As the regeneration comes up in the created gaps and fill up the extended area theses are extended further. The gaps then become larger and larger till they run together and all over wood are removed. While carrying out felling, the largest trees are removed first and moderately large trees are left to serve as seed bearer. The regeneration period varies with ease in which the species can be regenerated.

Generally long regeneration period is required due to the presence of sensitive shade bearer. Therefore the crop produce in this system is more uneven-aged as compared to even-aged, the difference, however, tends to disappear in pole stage.

Advantages
• Protect new regeneration that is sensitive to frost, drought, and cold winds. Such protection is not found in clearcuts except in small cuts. 
• May more efficiently use the productive growing space since the sheltering overstory will add growth as regeneration establishes. Generally, trees not capable of further increases in volume and value are cut first to make room for regeneration. 
• May provide some protection of soil from erosion and mass wasting since precipitation inputs to soil may be reduced via interception and evapotranspiration. This effect will depend on many factors including the amount of overhead cover, skid trail density and location, and the amount of site disturbance. 
• Usually preferred aesthetically to clear-cut and seed tree systems through the regeneration phase. 
• May be more beneficial for wildlife, recreation, or water objectives where a significant overhead cover is desired. However, this will depend on leave-tree characteristics and their duration on-site. 
Disadvantages
• Require more skill and time to secure regeneration than with clear cutting or seed tree systems. 
• Work is less concentrated, so harvesting and associated planning will be more costly. 
• Potential to damage young trees through the removal cut, although this risk can be reduced by careful planning and system design. 
• Cutting rates and regeneration establishment and growth may be more difficult to regulate and control than with clear-cutting and seed tree systems. This could complicate sustained yield goals. 
• Major problems can develop with some diseases (e.g., dwarf mistletoe) or insects (e.g., spruce budworm), which easily spread from the over the storey to the regeneration. 
o In the BC interior, some forest managers prescribe cutting mature trees that overtop regeneration to reduce budworm problems. 
o Trees to be harvested in known Armillaria infection centres have been “pushover logged” or roots have been extracted afterward in some parts of the interior. 
• Maybe more diff.

SELECTION SILVICULTURAL SYSTEM:
When individual trees or group of trees are removed from the forest, creating small gaps to stimulate or freeing the regeneration, an uneven aged crop results in which trees of all age class are distributed over the whole area. Such a system is called selection system.

The whole area is divided in to a number of blocks, one of which is worked each year. The number of blocks determines the period between two successive felling over the same block. This period is known as felling cycle. The numbers of blocks and felling cycle have to be so fixed to ensure sufficient material for economics removal and to permit a number of trees to reach the exploitable size and to encourage regeneration in the area where it is absent. In selection system, the thinning and removal of mature trees are carried simultaneously. There is no rotation, no size limit on felling and differentiation between regeneration and thinning operation. Principally dead, dying and diseased trees are removed and the desirable trees which are still growing vigorously are retained regardless of age or size.

This silvicultural system is characterized by the absence of both larger integral open area and larger compact young forest stand. Felling is evenly distributed across the whole area of forest stand with individual exploitable tree specimens or their small groups (up to 0.20 ha in size) being selected. This criterion divides selection system into the following methods:

• single tree selection method that results in uneven-aged stands having tree specimens of various diameter and age closely to each other and is suitable for regeneration of shade bearer. 
• Selection cum improvement??
• group selection method that in reality represents a very fine shelterwood system thus resulting in forest stands formed by several groups differing in age , is recommended for light demander where large gaps are created by removing groups of trees.

As this silvicultural system does not provide for open area formation nor does it lead to significant changes of biomass volume, it is very convenient from the point of view of ensuring permanent fulfillment of all forest functions. Equally, we can say that final forest stands are very stable. Selection silvicultural system almost exclusively rests on natural regeneration, underplanting is acceptable only in the case of new tree species introduction.

PROS AND CONS:
• Suitable for species which seed very irregularly and sporadically.
• Each seed year can be utilized over the whole area.
• The system does not involve the sacrifice of advance growth.
• It is ideal for soil and water conservation.
• Preferred for rough, broken, stony terrain and sites where regeneration cannot be obtained as and where desired.
• Produce un even aged crop which considered as best resistant to fire, wind and snow damage better then even aged.
• The greatest draw back of the system is that the regeneration is not concentrated over a limited area where it can be effectively looked after.
• In Pakistan, where grazing is one of the main factor determining the success or failure of regeneration, the selection has not resulted in acceptable regeneration due to unbridled grazing. 
• Due to the presence of all age class, there is always the danger of crown fire.
• Young crop is subjected to more damage during felling operations.
In Pakistan , the selection system is adopted for the forest which can not regenerated under clear felling or uniform system. These include kail, fir and deodar forests of K.P.K, AJK and MURREE hills.

In conifers forests, a modified selection system is usually in practice. This include carrying out single tree selective felling in forests growing over steep slopes or hot aspects or in poor crop and area where the incidence of grazing is heavy.

In mixed coniferous forest to which the selection is usually applied, more valuable species are favoured over less valuable one during thinning and main felling.

Deodar has the highest preference followed by kail and then fir. In mixed kail/chir forest kail preferred over chir. Broad leaved in high zone forest are preferred over all species due to their extreme shortage and desirability of their retention for soil improvement.

COPPICE SYSTEM
The coppice system is an even-aged silvicultural system for which the main regeneration method is vegetative sprouting of either suckers (from the existing root systems of cut trees) or shoots (from cut stumps). This system is limited to hardwood when small wood is required for fire wood, basket manufacturing and small poles etc.this system is also adopted on arid eroded slopes subject to heavy grazing and natural regeneration is scanty and artificial regeneration is not economical.

Simple coppice system:
This system involves the clear felling of the annual coupe. Regeneration is obtained in form of coppice and root suckers. the coupe is clear felled and all the poles and brush wood are cut to within 1 foot. Of the ground level. Blanks of failed coppice area is regenerated artificially

Selection coppice system:
This system is applied to olea , Acacia modesta, and dodonaea viscosa scrub forest of Pakistan. an exploitable diameter is fixed for each species which is usually 6-8 inches for olea, 8 inches for modesta and 2-3 inches for Dodonaea. This size is attained by the former two in approximately 60 years and by the latter in less than 30 years. the rotation is usually divided into two felling cycles of 30 years each.

The felling rules prescribe the clear felling of all clumps which contain one or more shoots of exploitable size. While carrying out felling, olea is preferred over the other species. The stumps are cut as low as possible and dressed to reduce the chance of rot. At the same time cleaning is also carried out on the stocks to reduce the number of shoots and provide a better condition for the retained shoots.

The selection coppice is considered most suitable than simple coppice on arid slopes where these forests grows as the cover is maintained all the time and a large number of shoots in every stock is believed to offer protection against grazing to the main shoots which will be exploited in due course of time.

Coppice with standards:
Under this system, a limited number of coppice shoots or seedling plants which have come up among them either naturally or artificially , is retained at each coppice felling. In the following coppice felling, a proportion of standard so retained is felled and a new set is retained. At next coppicing, the oldest standard may be felled or a number of them be retained yet for another coppice rotation. There will be thus always upper storey of standards of 1, 2 or 3 age depending on the maximum size of the standard required (khattak)

The irrigated shisham were originally managed under this system, the standard being retained for three of 20 years coppice rotation (TROUP, 1921, VOL. I) but with spread of profitable mulberry and longer experience of growth of plantation, changes have been introduced leading to present two storey high forest with every prospect of further change to the clear felling system with replanting of industrial species.

NATURAL REGENERATION:
Definition
Natural regeneration relies on older pine trees left on the land to provide seed to regenerate the site. This practice can only be employed if the site has not yet been harvested. Plans are then made for harvesting the present forest stand and leaving some trees to provide the seed. ( Mary L.Duryea university of Florida ) 

Mostly pine stands grow best where all trees are of the same age and receive the same amount of sunlight. Therefore, once the seedlings are established the large seed trees must be removed.

Steps
1. Selecting the seed trees. Before the site is logged, seed trees must be selected and marked with paint. Selection means choosing the best-looking trees for seed which are the straightest and tallest and have large crowns (lots of green needles) and no disease. The number to leave on the site will vary according to species. The number of seed bearer depends on various environmental and silvicultural characteristics of the species, e.g. light demander like chir pine needs up to 8 trees /acre in normal condition while it requires up to 12-15 seed bearer/acre on northern aspects. similarly kail, deodar needs more seed bearer due to their seeding behavior and climatic condition.

2. Planning for a good seed crop. The frequency of good seed crops varies from year to year and species to species. To insure successful natural regeneration, the site should be logged just prior to a good seed crop so that sufficient quantity of seed is available for germination.

3. Logging. The logging operation should be closely supervised to insure that the seed trees are not damaged by the logging. Damaged trees may die or not produce a good seed crop.

4. Preparing the site. The site must be prepared to first incorporate the forest litter (organic matter) and then expose mineral soil — seeds need soil to germinate and grow. Some site preparation options are to burn, mechanically scarify, and/or spray with herbicides. The soil needs to be exposed prior to October, when most seeds fall from the trees. Sometimes the logging operation is enough of a disturbance to expose the soil. However, the completeness and intensity of the site preparation may improve seedling establishment especially during periods of poor seed crop or drought.

5. Logging the remaining trees. When an adequate seedling stand is established and about 1-2 years old, the seed trees should be harvested . If you wait too long, seed trees may affect the growth of the seedlings and logging may damage the seedlings. For Longleaf pine the seed trees may be left.

6. Controlling unwanted vegetation. Shrubs, small trees, and herbaceous vegetation will compete with small seedlings for nutrients, water, and sunlight causing mortality or slower growth. For the first few years, the planting site should be observed to see if this unwanted vegetation is affecting seedling growth and survival and measures should be taken to control the weeds. Chemical control, hand-cutting, and mowing are three possible methods of control.

Advantages
• The initial costs of establishing a forest stand may be lower especially if site preparation is not necessary. 
• Less heavy equipment and labor is required. 
• The seedling has a naturally shaped root system, unlike seedlings which have been grown in a nursery. 
• Chance of tip moth damage is reduced (Beaufait and others 1984). 
Disadvantages
• A seed crop must be available and seed dispersal must be timed correctly with site preparation so that a suitable seedbed is available for the seed germination. 
• Moisture in the soil is necessary for the seeds to germinate; exceptionally dry years or sites may result in poor germination or seedling mortality. 
• Insects and other small seed-eating animals may consume all or most of the seed. 
• Competing vegetation may be a problem for survival and growth for a longer time period than with planting because seedlings are smaller or seed may not be disseminated in the first year. 
• If the seed is abundant and a dense stand results, a pre-commercial thinning may be necessary to decrease the number of trees per acre. For example, if there are more than 2000/acre pine seedlings at age three, growth may be inhibited and the site will require pre-commercial thinning 
• 700-1000 trees per acre. This thinning may be accomplished by hand-cutting or plowing up rows of seedlings and leaving the remaining rows about 10-12 feet apart. 
• Because the site is planted with seed versus 1-year-old seedlings, the rotation length (time until harvest) may be increased by one or more years. 
• The seed coming from the seed trees is not genetically improved as when the seed comes from a seed orchard. 
• Natural regeneration may be less expensive initially but more costly in the long run if it is necessary to prepare the site or pre commercially thin. 
• Open sites without trees such as clearcuts, abandoned fields, and stands after a wildfire or windstorm cannot be naturally regenerated. 
• There is no control over spacing between trees or stocking levels and so often these can be very uneven. 
• A successfully regenerated site may take longer to reach harvest than with direct seeding or planting.

SITE MAINTENANCE:
The are two phases required for the maintenance of productivity of forest site.
• Management of soil and water resources during regeneration.
• Proper management practices in relation to the standing crop.
In certain cases the two phases over lap each other, e.g. in shelter wood system but for the practical purpose, a silvicultural system involving clear felling may be equated with afforestation practices followed the restoration of tree cover on bare site, whereas other systems may be dealt with as site maintenance under existing stands.

Site maintenance during regeneration:
During operation, the soil becomes exposed and tends to deterioration during the period of establishment. A grass cover provides an effective check on surface erosion but also checks the tree growth often seriously. In dry condition, moisture conservation becomes a vital factor and dry farming method involving deep cultivation to encourage deep rooting and maximum absorption of rain fall, the maintenance of humus content and mulching all becomes desirable.
Clear felling result in a complete, if an only temporary change of soil climate, insulation, the condition being suddenly and fundamentally altered. If the cleaning is followed by burning, the change is even greater.

The immediate effects of clearing beneficial through a rapid mobilization of nitrogen under exposed condition, and the ash from the burn supplies soluble mineral salt and may increase nitrification but it also cause surface run off on sloping ground, if cover is not soon provided, a loss of fertility follows and it may be a considerable loss. Hence when clear felling is necessary as the only satisfactory method of regeneration, it is important to restore a plant cover to the soil as quickly as possible and then to restore the original forest condition.

In the management of soil during afforestation of cleared or bare sites two aspects must be kept in mind, structural management of the soil and regulation of the moisture condition, which can be done by different methods like soil working, mulching, cultivation, and weeding etc.

Proper soil working achieves the dual purpose of establishment of plant growth and conservation and moisture. Conservation structure which are solely meant for reducing the speed and amount of water flow. this generally achieved by a combination of ridges, furrows, ridges-ditches, bunds, trenches. in extensively cut up area, regained or hilly terrain, they may be supplemented by engineering structures such as plugs, dams, reservoirs, and diversion drains (Khattak).

Site maintenance in forest stand:
Proper silvicultural system provides protection to the soil. Selection felling provides an ideal condition for soil conservation while shelter wood systems are generally satisfactory from the point of view of soil management and offer the additional advantage of permitting temporary modification of surface condition to those suitable for regeneration of forest with out undue or sudden exposure. The clear-felled strip may also affect this if suitable in width and orientation.

Grazing has very determinantal effects on soil fertility in a variety of ways. The direct removal of carbon and proteins is probably of no special importance but the physical effects of trampling of the soil may be very for reaching both on soil and vegetation it carry. Trampling makes the soil harder and less aerated, resulting in the loss of porosity which has devastating effects on soil fertility (khattak)

There fore it is of utmost importance that a proper silvicultural system must ensured as per requirement of soil and stand condition elsewhere it will be the total loss of site and regeneration similarly stall feeding in forest area be encouraged and control grazing system is adapted.

Wild life conservation:
The forest provides habitat for wild life where they breed and flourish so the wild life is directly dependent on the wise application of the knowledge of Silviculture.for wild life conservation, preservation it is of great importance to know that which species is being used for food and shelter. A well established forest stand can support the wild life while it has been observed that denuded sites have lost its wild life. For rehabilitation of wild fauna, the lost forests have to restore for which Silvicultural knowledge is of utmost importance.

Conclusion:
The silviculturist in our country encounters numerous aspects of forestry in almost all branches of his work. He is called on to reclothe the denuded hillsides with vegetation, and so to stop the soil erosion and burying of agricultural lands down the valley with sterile sand & boulders. He is expected to stabilize the man made dunes, reclaim man made swamps and restore the exhausted supply of fuel wood, at the same time providing more grassy cover on the land that put out of production by over stocking and general misuse. He is also required so to tend and harvest the timber from the surviving forests that the protective functions of the tree cover are disturbed as little as possible. He must also tend, harvest and regenerate them satisfactorily while at the same time he supplied from them the many needs of the local population which is generally entitled by right to much forests produce and often most difficult of all, he must also provide grazing for a large number of cattle.

In order to achieve and confront the goals and challenges conferred upon the forestry sector, it is high time for the silviculturist to identify and prescribe proper silvicultural practices for the existing forest resources of the country as all have not been lost , but in fact a large part of the forest has already been destroyed and the last remnants are seen to be doomed to early disappearance unless some thing is done to protect them, the realization of the great benefits conferred by the forest is gradually dawning on those who are at the same time both the destroyers and among the first victims. So the time has come to manage the leftover natural forest resources on sustainable basis before it is too late.
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