Introduction to Silviculture and Silvicultural System
THE FOREST
DEFINITION
Forest is defined as ‘an area set aside for the production of timber and other forest product, or maintained under woody vegetation for certain indirect benefits which it provides.’ This is the general definition of the term and lays emphasis on the direct and indirect benefits that the forests provide.
But in ecology, it is defined as ‘a plant community predominantly of trees and other woody vegetation, usually with a closed canopy '. This definition describes the forest as a kind of vegetation in which trees constitute the predominant part, to distinguish it from vegetation in which grasses or shrubs may be predominant, and are fairly dense so that their crowns touch each other.
In legal terminology, forest is defined as ‘an area of land proclaimed to be forest under a forest law’. This definition describes the forest not as a biological unit but as property having an owner and with rights of certain people. This definition is useful only in law courts, where cases pertaining to offences committed are tried.
CLASSIFICATION OF FORESTS
Forests can be classified on the basis of:
( i ) Method of regeneration;
( ii ) Age;
( iii ) Composition ;
( iv ) Objects of management ;
( v ) Ownership and legal status and
( vi ) Growing stock
(vii) Climatic and edaphic factors, geographical location and condition
( i ) Classification based on method of regeneration - Forest can be regenerated either from seed or from vegetative parts; those which are regenerated from seed are called high forests and those regenerated by some vegetative method are called coppice forests.
( ii ) Classification based on age - Even in plantations raised in a particular year, all the trees are not of the same year because casualties are replaced in the second and third years. Thus forests having all trees of the same age are usually not found. Therefore forests are classified on the basis of age into even aged or regular forest and uneven aged or irregular forest.
( iii ) Classification based on composition - A forest may have only one species or more than one species. On the basis of the number of species present, the forest is classified into pure or mixed forest. Pure forest is defined as a forest ‘composed of almost entirely of one species, usually to the extent of not less than 80%’. It is also called pure crop or pure stand. Mixed forest, on the other hand, is defined as ‘a forest composed of trees of two or more species intermingled in the same canopy; in practice, and by convention, at least 20% of the canopy must consist of species other than the principal one. The species composing the mixture may be distinguished as principal, accessory and auxiliary’.
Principal species is defined as ‘ the species first in importance in a mixed stand either by frequency, volume or silvicultural value’ or ‘the species to which the silviculture of a mixed forest is primarily directed’. Accessory species is defined as ‘a useful species of less value than the principal species, which assists in the growth of the latter and influences to a smaller degree the method of treatment'. Auxiliary species is defined as ‘a species of inferior quality or size, of relatively little silvicultural value or importance, associated with the principal species’. It is also referred to as secondary species or subsidiary species.
( iv ) Classification based on objects of management - On the basis of objects of management, forests are classified as production forest, protection forest, recreational forest, etc. Production forest is ‘a forest managed primarily for its produce'. Protection forest is defined as 'an area wholly or partly covered with woody growth, managed primarily to regulate stream flow, prevent erosion, hold shifting sand. Recreational forest is a forest, which is managed only to meet the recreational needs of the urban and rural population.
(v) Classification based on ownership and legal status - On the basis of ownership, forests are classified into National forest, Private forest. National forest is a forest owned by state’ while Private forest is a forest owned by an individual person. National forests are further divided as Government managed forest, Community forest, Leasehold forest, and Religious forest.
Government managed forest are managed by the government. Community forest means a national forest handed over to a community forest users’ group for its development, conservation and utilization for collective benefit. Leasehold forest means a national forest handed over as a leasehold forest to any institution established under current law, industry based on forest products or communities. Religious forest means a national forest handed over to any religious body, group or community for its development, conservation and utilization.
(vi) Classification on the basis of growing stock - On the basis of growing stock, the forests are classified into normal and abnormal forest. Normal forest is defined as ‘a forest which for a given site and given objects of management, is ideally constituted as regards growing stock, age class distribution, and increment, and from which the annual or periodic removal of produce equal to the increment can be continued indefinitely without endangering future yields’. Abnormal forest is ‘a forest in which, as compared to an acceptable standard, the quantity of material in the growing stock is in deficit or in excess of in which the relative proportions of the age or size classes are defective’.
Growing stock is the sum (by number or volume) of all the trees growing in the forest or a specified part of it.
(vii) Climatic and edaphic factors, geographical location and condition
Forest types based on Climatic and edaphic factors, geographical location and condition are as following.
Tropical forest – below 1000m e.g., Shorea robusta forest, Acacia catechu-Dalbergia sissoo forest.
Sub-tropical broad-leaved forest – 1,000-2,000m e.g., Shima-Castonopsis forest, Alnus nepalensis forest
Sub-tropical pine forest – 1,000 – 2,000 m e.g., Pinus roxburghii forest
Lower temperate broad-leaved forest – 1700-2700m e.g., Quercus floribunda and Q. lamellose forest, Castonopsis tribuloides forest.
Lower temperate mixed broad-leaved forest – 1700-2700m e.g. forest of Lauraceae family
Upper temperate broad-leaved forest – 2200-3000m e.g. Quercus semicarpifolia forest
Upper temperate mixed broad-leaved forest – 2500-3500m e.g., Acer and Rhododendron forest
Temperate conifer forest - 2000-3000m e.g., Pinus wallichiana, Cedrus deodara, Tsuga demosa and Abies pindrow forests.
Sub-alpine forest – 3000-4100m e.g., Abies spectabilis, Betula utilis forest.
Alpine scrub- above 4100m e.g., Juniperus-Rhododendron forest, Hippophae tibetana forest.
Growth and Development of Trees
The tree starts its life as a small seedling, which grows by increase in length and diameter of its shoot and root. As the shoot grows upwards, it develops branches and foliage. The root grows downwards and develops lateral roots and its branches. Thus the seedling grows not only by increase in size of its shoot and root but also formation of new organs. The increase in size is commonly referred to as growth or increment and the formation of new organs is referred to as development. Thus both growth and development are responsible for the change that takes place in a small seedling growing into a tree.
Various stages of growth and development of a plant are designated as follows:
Seedling- Seedling is a plant grown from a seed till it attains a height of about 1 meter, i.e., before it reaches the sapling stage.
Sapling- Sapling is defined as a young tree from the time when it reaches about one meter (3feet) in height till the lower branches begin to fall. A sapling is characterized by the absence of dead bark and its vigorous height grows.
Pole –Pole is defined as a young tree from the time when the lower branches begin to fall off to the time when the rate of height growth begins to slow down and crown expansion becomes marked.
Tree- Tree is the stage of the growth beyond the pole stage when the rate of height growth begins to slow down and crown expansion becomes marked.
Tree is essentially a plant. Plants may be classified into the following categories:
I) Herb- it is defined a plant whose stem is always green and tender and height is usually not more than one meter.
II) Shrub – it is defined as a woody perennial plant differing from a perennial herb in its persistent and woody stem and less definitely from a tree in its low stature and its habit of branching from the base. A shrub is usually not more than 6 meters in height.
III) Tree- it is defined as large woody perennial plant having a single well defined stem (bole or trunk) and a more or less definite crown. A tree is usually more than 6 meters height, which can, according to species, be up to 127 meters.
Tree Classification
Standard tree classification adopted for regular crops is follows:
· Dominant trees (D): All trees, which form the upper most leaf canopy and have their leading shoots free. These may be sub-divided according to the position and relative freedom of their crown into;
1. Predominant trees: comprising of all the tallest trees, which determine the general top level of the canopy and are free from vertical composition.
2. Co dominant trees: comprising of the rest of the dominants falling short of and averaging about 5/6 of the average height of predominant trees.
· Dominated trees (d): Trees which do not form part of the upper most leaf canopy, but the leading shoots of which are not definitely over topped by the neighboring trees. Their height is about ¾ that of the tallest trees.
· Suppressed trees (s): Trees, which reach only about ½ to 5/8 of the height of the best trees, with leading shoots, definitely over topped by their neighbors or at least shaded on all sides by them.
· Dead and moribund trees (m): This class also includes bent over or badly leaning trees usually of the whip type.
· Diseased trees (k): Trees, which are infected with parasites to such an extent that their growth is seriously affected or they are a danger to their neighbors.
Crown cover
Dense canopy – There is strong competition between the crowns of the trees.
Normal canopy – Crowns slightly touch each other.
Light canopy – Crowns don’t touch each other but there is not enough space for an additional
tree.
Open canopy- There is sufficient space for an additional tree between two crowns.
Gaps – There is enough space for several trees between two crowns.
Forestry Terms
Stem-The principal axis of plant from which buds and shoots are developed. Stem, trunk and bole are synonymous.
Crown-Upper branchy part of a tree above the bole.
Canopy – The cover of branches and foliage formed by the crowns of trees in a forest.
Taproot – Primary root formed by direct prolongation of the radical of the embryo.
Lateral roots – Arise from the taproot and spread laterally.
Adventitious Roots – Produced from the parts of the plants other than the radicle or its sub-division.
Evergreen plant- Perennial plant that is never entirely without green foliage, the old leaves persisting until a new set has appeared.
Deciduous plant - Perennial plant, which normally remains leafless for sometime during the year.
Taper - The decrease in diameter of the stem of a tree or of a log from the base upward.
Conifer – A tree belonging to the order Coniferales of the group Gymnosperm, bearing cones and generally needle shaped or scale like leaves, usually evergreen and producing timber known as softwoods.
Broad-leaved – A tree belonging to the group Dicotyledons, and producing timber usually known as hardwood.
Rotation – The planned number of years between the formation or regeneration of a crop and its final felling.
Indigenous – Native to a specified area or region, not introduced.
Exotic – Not native to the area in question, introduced from outside.
Growing stock - It is the sum (by number or volume) of all the trees growing in the forest or a specified part of it.
Increment – The increase in girth, diameter, basal area, height, volume, quality, price or value of individual tree or crops during a given period.
Forestry Statistics of Nepal
Total land area = 14,718,100 Ha
Forest area = 4,268,800 Ha
Forest % of total land area = 29
Shrub area = 1,559,200 Ha
Shrub % of total land area = 10.6
Forest and shrub total = 39.6%
Total volume = 387.5 million cubic meter
Mean stem volume = 178 cubic meter/Ha
Average number of stems/Ha = 408
Main tree species in terms of proportion of total stem volume = Sal (28.2% of total volume)
From 1978/79 to 1994, rate of decrease in forest area = 1.7%
(Source: Forest Resources of Nepal (1987-98), Department of Forest Research and Survey, Nepal, 1999)
SILVICULTURE
DEFINITION
Silviculture has been defined variously by various authors. According to Toumey and Korstian, ‘silviculture is that branch of forestry which deals with the establishment, development, care, and reproduction of stands of tmber’. Indian Forest and Forest Products Terminology (IFFPT), published by the Forest Research Institute and Colleges, Dehradun, defines silviculture as, ‘the art and science of cultivating forest crops’. According to Champion and Seth, “the term silviculture in English commonly refers only to certain aspects of the theory and practice of raising forest crops’.
Silviculture is the science and art of growing and tending forest crops. More particularly, the term silviculture means the theory and practice of controlling the establishment, composition, character and growth of forest stands to satisfy specific objectives (Broun; Kostler; Ford-Robertson; Smith, Daniel et al). According to Webster’s Dictionary, 'silviculture is a branch of forestry dealing with development and care of forest’.
According to the Society of American Foresters, 'silviculture is the art of producing and tending forest stand by applying scientifically acquired knowledge to control forest stand establishment, composition and growth; applying different treatments to make forests more productive and more useful to a land owner and integrating biologic and economic concepts to devise and carry out treatments most appropriate in satisfying the objectives of an owner'.
Though from the above definitions, there appears to be some diversity in views about the scope of silviculture, yet, in a broad sense, silviculture may be taken to include both silvics and its practical application.
Silvics deals with the biologic characteristics of individual trees and communities of them. It studies how trees grow and reproduce, as well as the ways that the physical environment influences their physiology (Ford-Robertson; smith Daniel et al;). According to Indian Forest and Forest Products Terminology (IFFPT), “silvics is the study of life history and general characteristics of forest trees and crops with particular reference to environmental factors, as the basis for the practice of silviculture’. Thus silvics implies the study of trees and forests as biological units, the laws of their growth and development and the effect of environment on them. It explains the natural laws of their growth and development and their behavior in a given set of environmental conditions. Silvics also includes the study of ways that the physical environment tempers the make up and character of a forest community, and the interaction of biologic components in those communities.
The knowledge gathered in silvics is applied to the production and care of forest crops. Thus the practice of silviculture is applied silvics. It deals with the procedure of obtaining natural regeneration under the various silvicultural systems, artificial regeneration of various species and methods of tending young crops, whether natural or artificial, to help them to grow into forests of quality timbers and great economic value.
Silviculture is not a purely biological science, which has no relation with economics. The foresters raise the forests and tend them for the service of the people, but this is not to be done at a prohibitive cost. If forests are to be grown for the public good, the methods of raising and tending them, developed on the basis of knowledge of silvics, will have to be modified in practice by economic considerations.
There have been foresters who have advocated that, in case of doubt, the trees should be approached for answer. Even today, the local flora is regarded to be the best guide about the suitability of a species for a particular site. This is so because in nature there are so many complex factors at play that it is only the vegetation that can give an indication of the possible solution. But in order to understand the indication of the vegetation or answer of the trees, it is necessary for the forester to be conversant with their language and proficiency in this art comes by close continuous observation and experience.
OBJECTS OF STUDY OF SILVICULTURE
The forests are as old as the universe; naturally they must have been growing and renewing themselves. It is a well-known fact that forest preceded civilization in every part to the world. Management of the forests by the Forest Department is a very recent phenomenon. Even today, there are virgin forests. The question naturally arises as to what use is the study and practice of silviculture and why should a forester take upon himself the work that the nature had been doing all these years? The answer to this question is purely economic. The object of study and practice of silviculture is to produce more useful and valuable forests to meet our multifarious requirements, than nature would do and that too, in a shorter time. The objects with which nature produces vegetation are not identical with that of man. The former produces a jungle the latter a forest. The study of silviculture helps in:
(1) Production of species of economic value - In the virgin forests, many of the species are generally neither very valuable nor useful. Therefore, the production of timber of species of economic value per unit area is low. If the forests have to produce timber of industrial and economic importance, it is necessary to study and practice silviculture so that we can produce only the desired species.
(2) Production of larger volume per unit area- In the virgin forests, the crop is generally either very dense or very open. Both these extremes are unsuitable for quantitative production. If the crop is very dense, the growth of the individual trees is adversely affected resulting in lesser timber volume production per unit area. On the other hand, if the crop were very open, the number of trees, and consequently volume, per unit area would be less. Besides this, a large number of trees die out as a result of competition before reaching maturity. In the unmanaged forest, they are not utilized and that volume of timber is lost. The study and practice of silviculture helps in raising sufficient trees per unit area right from the beginning to fully utilize the soil and as they grow up, gradually reduce their number so that the requirement of light and food of the remaining trees is met. In this way, while by raising sufficient number of trees, the volume production per unit area is increased, the utilization of the excess trees as the crop grows in age, prevents the loss and consequently further increases that volume.
(3) Production of quality timber - In the unmanaged forests, because of intense competition, a large number of trees become crooked, malformed, diseased and defective. This results in the deterioration of the quality of timber produced. If the production of quality timber is to be ensured, knowledge of silviculture will be essential so that the trees can be grown in disease-free condition without adverse competition.
(4) Reduction of rotation - In the virgin forests because of intense competition in the dense parts, the rate of growth of the individual tree is retarded with the result that it takes longer time to reach the size at which it can be exploited. This increases the cost of production of timber. With the knowledge and practical application of silviculture, the density of the crop can be properly regulated and consequently the rate of growth increased and rotation reduced.
Rotation is the planned number of years between the formation or regeneration of a crop and its final felling. In other words, average age at which a tree is considered mature for felling.
(5) Raising forests in blank areas - In nature, a large number of areas, potentially suitable for tree growth, occasionally remain blank due to certain adverse factors inhibiting growth of trees. Silvicultural skills and techniques help in raising forests in such areas.
(6) Creation of man-made forests in place of natural forests - There may be areas in natural forests which may not regenerate or reproduce themselves naturally or where natural regeneration may be extremely slow and uncertain. In such areas, it becomes necessary for the forester to take up the work of nature in his/her hand and raise man-made forests in such areas. Success in this endeavor can be achieved only when he/she has a good knowledge of the science and art of raising forest crops artificially.
(7) Introduction of exotics - The indigenous species may not be able to meet the commercial and/or industrial demands. In such areas, efforts are made to introduce exotics, which can grow in that particular locality and can supply the timber required by industries etc in time.
FORESTRY, ITS SCOPE AND RELATIONSHIP
Forestry is defined as ‘the theory and practice of all that constitutes the creation, conservation and scientific management of forests and the utilization of their resources.’ It is an applied science, which is concerned with not only the raising or cultivation of forest crops but their protection, perpetuation, mensuration, management, valuation and finance as well as utilization of the forest products.
Forestry encompasses the science, business, art and practice of purposefully organizing and managing forest resources to provide continuing benefits for people. Historically, forestry throughout the world has focused primarily upon organizing and managing lands to grow and utilize wood products and other commodities that forest ecosystem can provide in perpetuity.
RELATION OF SILVICULTURE WITH FORESTRY AND ITS BRANCHES
1. SILVICULTURE AND FOREST PROTECTION
Forest protection is defined as that branch of forestry which is concerned with ‘the activities directed towards the prevention and control of damage to forests by man, animals, fire, insects, disease or other injurious and destructive agencies. Knowledge of the injuries caused to forests by the local human and animal population, both domestic and wild, insects, fungi and other adverse climatic factors and the preventive and remedial measures to counteract them, is essential for effective protection of the forests. Thus while silviculture is concerned with the raising of forest crop, forest protection is concerned with its protection against various sources of damage.
2. SILVICULTURE AND FOREST MENSURATION
Forest mensuration is defined as 'that branch of forestry which deals with the determination of dimensions, form, volume, age and increment of logs, single trees, stands or whole woods.’ Thus while silviculture deals with raising of forest crop, Forest Mensuration deals with measurement of diameter and heights of crop so produced, calculation of its volume, age etc for sale and research to decide the best treatment to be given to the crop while it is being raised .
3. SILVICULTURE AND FOREST UTILIZATION
Forest utilization is defined as ‘the branch of forestry concerned with the harvesting, conversion, disposal and use of the forest produce’. Thus, while silviculture is concerned with the cultivation of forest crops, forest utilization is concerned with the harvesting and disposal of crops so produced.
4. SILVICULTURE AND FOREST ECONOMICS
Forest Economics is defined as those aspects of forestry that deal with the forest as a productive asset, subject to economic laws’. Thus while silviculture is concerned with the cultivation of forest crop, forest economics works out the cost of production including rental of land and compound interest on capital spent in raising the crop, and compares it with the sale proceeds to decide whether raising of the crop is economically profitable or not. It is also the function of the Forest Economist to compare the cost of production of a particular crop by different methods and then decide the most profitable method of raising that crop.
5. SILVICULTURE AND FOREST MANAGEMENT
Forest management has been defined as ‘the practical application of the scientific, technical and economic principles of forestry.’ Thus while silviculture deals with the cultivation of forest crop, forest management manages that crop according to the dictates of the forest policy. Silviculture deals with the techniques and operations, which result in the development of a forest. Forest Management prescribes the time and place where the silvicultural techniques and operations should be carried out so that the objects of management are achieved.
6. SILVICULTURE AND FORESTRY
From the definition of forestry given earlier, it is clear that forestry has a very wide scope and silviculture is only one of its branches. It has the same relation with forestry as agronomy has with agriculture. While agronomy and silviculure deal with cultivation of crops, agriculture and forestry deal not only with the cultivation of crops but also with their protection, management, mensuration, marketing etc. In short, forestry is an applied science, which has many branches. It may be compared to a wheel. Silviculture is the hub of the wheel; it is neither the whole wheel nor is it the only essential part. But, just as a cart wheel composed of several sections is supported on its hub (central part); similarly forestry and its other branches are supported on silviculture without which there would be neither forestry not its branches.
Figure - Relation of Silviculture with Forestry and its branches.
R E
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SIVICULTURAL SYSTEMS
DEFINITION
Silviculture is ‘the art and science of cultivating forest crops’. It deals, in a general way, with the natural laws of growth and development of trees and forests, the effect of environment on them, techniques of regenerating them naturally or artificially and the methods of tending them. Since the techniques of regenerating forest crops vary with types and sub-types of forests, and physical conditions in which they exist, it becomes necessary to identify different methods or techniques for different sub-types in different localities. These methods or techniques are called silvicultural systems. Thus a silvicultural system may be defined as a method of silvicultural procedure worked out in accordance with accepted sets of silvicultural principles, by which crops constituting forests are tended, harvested and replaced by new crops of distinctive forms. In other words, it is a planned silvicultural treatment, which is applied to a forest crop, throughout its life, so that it assumes a distinctive form. It begins with regeneration felling and includes adoption of some suitable method of regeneration and tending of the new crop, not only in its early stages but also throughout its life.
SCOPE
As already stated, a silvicultural system is a silvicultural procedure adopted for renewal of a forest crop in a given set of conditions. Thus a silvicultural system is a specialized tool or technique for achieving the objects of forest management
Silvicultural System as a Plan for Management - Any review of silvicultural must recognize at least four basic concepts or premises that underlay its practice.
1. Foresters can change the character of tree community by manipulating its composition and density, and often to better serve the special interests of a landowner.
2. They can affect the results by applying different kinds and intensities of treatments at varying stages of stand or age class development, and arranging them in a unique sequence.
3. The treatments must fit characteristics of the species of interest and the physical site conditions within the stand under management, and prove ecologically acceptable.
4. To adequately control stand or age class establishment, composition, and development (growth), silviculturists must plan both an appropriate intensity and an optimal time for applying each treatment to insure the sought after effects.
Conceptually, both the type of manipulation and time of its use influence how a stand or age class will develop afterward. For that reason, timing and sequence may prove as important as the actual kind of treatment applied at any juncture. Time in this sense means the stage of development, rather than season of year or even the chronological age of the trees.
To integrate these concerns and guarantee the appropriate timing, sequence and kind of treatments that will produce the desired outcomes, foresters need a conceptual framework for their management. The silvicultural system serves this role. It describes the long-term plan for managing an individual stand to sustain a particular set of values of interest. It reflects the silviculturist’s concept of how to control, facilitate, protect and salvage within a stand.
Conceptually, foresters develop a unique silvicultural system for each forest stand. Yet all silvicultural systems include three basic component treatments or functions.
( 1 ) Regeneration
( 2 ) Tending
( 3 ) Harvest
All systems for all stands will give due attention to all components in some form or another, and arrange them to fit the needs of a particular stand and a particular ownership. A silvicultural system describes the means for effectively regenerating, tending, and harvesting in a timely and economically viable manner.
Regeneration Phase Component Treatment
Treatments Natural
Artificial
Tending Pruning
Thinning
Harvest Clear felling Method
Shelter wood Method
Selection Method
Fig 1. Components and Character of Sivicultural System (After Nyland et. al. 1983)
Sivicultural System
Regenerate Tend
Harvest
Fig 2.
Silvicultural S
Regenerate Tend
Harvest Fig 3.
Fig2, Fig 3. Alternate views of the sivicultural system emphasizing its continuous nature
and the interdependence of its component treatments
Figure 1, indicates that silvicultural systems commonly incorporate harvesting techniques to implement both the intermediate treatments and the methods for regenerating a new age class at appropriate time. Figure 2, highlights the cyclic nature of silvicultural systems. Normally, events move from regeneration of an age class to the tending of it during intermediate ages, and finally to its regeneration again at maturity. Figure 3, suggests the interdependence of these components and the necessary linkages of different parts to ensure a system approach to management. Skipping one part makes the program incomplete, just as taking away one leg of a tripod lets it collapse. In fact, an appropriate silvicultural system should,
Optimize the yields - capitalize upon the full productive potential of a site to serve a landowner’s interest;
Improve the quality - provide the kind of stand and trees best suited to a landowner’s needs, and to the fullest extent possible;
Shorten the investment period - bring a crop or tree community to the desired condition or stage of usefulness without needless delay;
Contain the costs - minimize the investments to optimize those sought-after values; and
Sustain ecosystem health and productivity - limit practices to those that appear ecologically and biologically appropriate.
CLASSIFICATION of SILVICULTURAL SYSTEM
Silvicultural systems have been classified in a variety of ways but the most commonly used classification is based primarily on the mode of regeneration, and this is further classified according to the pattern of felling carried out in the crop. According to the mode of regeneration, silvicultural systems are classified into following two main categories or groups:
( I ) High Forest System and
( II ) Coppice System
( I ) HIGH FOREST SYSTEMS
High Forest Systems are those silvicultural systems in which the regeneration is normally of seedling origin, either natural or artificial (or a combination of both) and where the rotation is generally long. These are further classified on the basis of pattern of felling, which, in turn, affects the concentration, or diffusion of regeneration and the form or character of the new crop so produced.
(1) System of concentrated regeneration - These are those silvicultural systems in which regeneration fellings¹ are for the time being concentrated on part of the felling series. These are further subdivided into two main categories:
(A) Clear-felling systems
(B) Shelter wood systems
(A) Clear-felling systems - Clear-felling systems are those silvicultural systems in which the mature crop is removed in one operation to be regenerated, most frequently, artificially but sometimes naturally also. The area to be clear-felled each year in uniformly productive sites is 1/n of the total area allotted to this system, where n is the number of years in the rotation, and is usually referred to as the annual coupe. But where due to variations in site and crop, the yield per unit area is likely to vary considerably from year to year, the coupes to be felled each year are made equi-productive, i.e., on poorer sites with inferior patchy crop larger areas are clear-felled so that the annual yield is nearly the same.
Application:
This system should not be applied in the areas, which are geologically unstable.
This system is most suited to light demanders.
It is the only system by which forests composed of slow growing species of little economic value can be replaced by new crops of fast growing and valuable species for industrial and other uses.
It is the simplest of all high forest systems as it does not require a high degree of skill in carrying out its marking. Therefore it is easy to practice.
As the soil remains exposed till the canopy closes, there is great danger of deterioration of soil and the possibility of soil erosion increases. So, this system should not be applied in sloppy and erosion prone areas.
(B) Shelter wood system - Shelter wood systems are those silvicultural systems in which the mature crop is removed in a series of operations, the first of which is the seeding felling and the last is the final felling. This method is used where an inadequate seed supply or a sharp change of environmental conditions might prevent success following clear cutting. Shelter wood method also allows them to temper visual characteristics within regenerating stands, and to maintain essential habitat conditions for selected animals.
This system differs form clear felling in three principal respects.
(1) Relatively low density residual of vigorous seed-bearing trees of good phenotypic character as seed source, and for protective cover.
(2) The residual overstay trees provides sufficient canopy cover to mitigate sensitive environmental conditions.
(3) Reserve trees are removed once new generation of adequate size and density forms, and no longer needs protection.
(2) Systems of diffused regeneration - These are those silvicultural systems in which regeneration fellings are distributed over the whole felling series. These are further subdivided into two main categories:
( A ) Selection System
( B ) The Group Selection System
(A) The Selection System
The Selection System is defined as a silvicultural system in which felling and regeneration are distributed over the whole of the area and the resultant crop is so uneven aged that trees of all ages are found mixed together over every part of the area. Thus, the Selection System differs from other systems mainly in the following respects:
(i) The felling and regeneration in the systems so far described are concentrated, i.e., these are confined to a certain part of the whole area, whereas in selection system, these are distributed over the whole area.
(ii) The resultant crop in all the systems so far described, is even aged and the constituent age-classes are found in different areas, whereas, in the Selection System it is completely uneven aged so much so that all age classes are mixed together on every unit of area.
(iii) In the systems so far described, the regeneration operations are carried out only during a part of the life of the crop, after which only thinning are done to improve the growth and form of the remaining trees, whereas in Selection System, regeneration operations are carried out throughout the life of the crop and thinning are done simultaneously for improving the growth and form of trees.
Application:
This system is suitable where slope is steep and terrain is broken to serve the soil conservation and landslide protection,
It is favorable where continuous ground cover is necessary such as catchments areas and erosion prone areas.
In the areas where the product of particular size and species is in demand.
Sensitive shade bearer species are more suitable to work under this system.
It is suitable where objective of management is promotion of bio-diversity as regeneration of diverse species is possible under this system.
( B ) The Group Selection System
The Group Selection System is defined as a Selection System in which trees are felled in small groups and not as scattered single trees of the typical Selection System. These felling may be distributed over the whole area if it is small, otherwise these are carried out only on a part of the whole forest each year under a felling cycle. Consequently, the regeneration is also spread over the whole area.
(3) The Accessory System-
The term Accessory Systems refers to those high forest systems, which originate from other even-aged systems by modification of technique, resulting in an irregular or two-storeyed high forest. The following accessory systems are commonly met with:
(A) Two-storeyed high forest system
(B) High forest with reserve system
( A ) Two-storeyed High Forest System
Two-storeyed High Forest System is an accessory silvicultural system which results in the formation of a two-storeyed forest, i.e., a crop of trees in which the canopy can be differentiated into two strata, in each of which the dominant species is usually different. The crop in each storey is approximately even-aged, and is of seedling origin.
( B ) High Forest- With Reserves System
High Forest-With-Reserves System is an accessory silvicultural system in which selected trees of the crop being regenerated are retained for part or whole of the second rotation, in order to produce large- sized timber.
( II ) COPPICE SYSTEM
Those silvicultural systems in which the new crop originates mainly from stool coppice and where the rotation of the coppice is short. Following are the different coppice systems.
( 1 ) The Simple Coppice system
It is defined as a silvicultural system based on stool coppice, in which the old crop is clear felled completely with no reservation for shelter wood, or any other purpose. The crop produced under this system is even-aged.
The best season for coppicing is a little before the growth starts in spring because, at this time, there is a large reserve of food material in roots, which is utilized by the coppice shoots. The stump should neither be too low nor high. Thus, the stumps are usually kept 15 to 25 cm. The trees are felled in such a away that the stumps does not split, the bark does not get detached from the wood and that it slopes slightly in one direction so that rain water may quickly drain off.
Application:
o This system is suitable for areas where the factors of locality are low and incapable of producing lager-sized timber.
o This system is applicable only to areas where there may be demand for fuel, poles and small sized timber only.
o It is very simple in application.
( 2 ) The coppice of Two Rotations System :
It is the modification of the simple coppice system in which at the end of the first rotation of coppice, a few, selected poles are left scattered singly over the coupe in the second rotation to attain bigger height. The main objective of the system is to produce some large-sized timber in addition to the poles of ordinary size.
( 3 ) The Shelter wood Coppice System :
In this system, even in the first clear felling, some shelter wood (125 to 150 per hectare) is retained for frost protection. The shelter wood is removed after the coppice shoots are fully established. This system is applicable in following special circumstances:
o Where frost is of common occurrence;
o Where the locality is good;
o Where in addition to small-sized timber, there is demand for some large-sized timber also; and
o Where a rotation longer than ordinary coppice rotation can be adopted.
( 4 ) The Coppice with Standard System :
In this system, an over wood of standards, usually of seedling origin and composed of trees of various ages, is kept over coppice for periods which may be multiples of coppice rotation and as a permanent feature of the crop throughout its life. The standards are kept in this system with the following objectives:
o Supply of large-sized timber;
o Protection against frost;
o Enrichment of coppice; and
o Increase in revenue
( 5 ) Coppice Selection System :
It is a silvicultural system is which felling is carried out on the principles of selection system but regeneration is obtained by coppice. In order to carry out fellings on principles of selection, an exploitable girth or diameter is fixed according to the size of material required and a felling cycle¹ is decided. The character of the crop produced under this system is uneven aged. This system has been applied in the Khair (Acacia catechu) forest.
( 6 ) The Pollard System : It is the simple coppice system but removal of exploitable material is done by periodical pollarding².
( 7 ) The Coppice With Reserve System :
Silvicultural system in which felling is done only in suitable areas likely to benefit, after reserving all financially immature growth of principal as well as other valuable miscellaneous species for protective reasons. This system is applicable with advantage only under the following conditions:
o When the crop varies greatly in density, composition and quality and proportion of the valuable species is low;
o When most of the species are good coppicers and coppicing power of the most valuable species is low; and
o When valuable species in the crop are light demanders.
Difference
Coppice of Two Rotations System
Shelter wood Coppice System
1. Complete clear felling is done at the beginning of the 1st rotation.
2. Some poles are retained at the beginning of 2nd rotation to remain through out the 2nd notation
3. Object of retention is production of large sized timber.
4. It is applied in ordinary areas where simple coppice system is applied.
1. Some shelter woods as standards are retained as frost protection.
2. Standards (shelter wood) are retained for forest protection only till no longer required.
3. Object is forest protection.
4. It is applied in frosty localities.
Coppice of Two Rotation System
Coppice With Standards
1. The crop in the 1st rotation does not have any standards which are selected at the beginning of the 2nd rotation
2. Standards are selected out of the coppice crop and retained only for one extra rotation
3. Object is to simply produce large sized timber.
1. Standards are kept from the very beginning; they are composed of trees preferably of seedling origin.
2. Standards are seedling origin and are maintained for periods, which are, multiply of coppice rotation, as a permanent feature throughout the life of the crop.
3. Objects are- (i) Production of large sized timber (ii) Protection against frost (iii) Enrichment of coppice.
Shelter wood Coppice
Coppice With Standards
1. The standards are retained for only a part of each coppice rotation.
2. The standards are kept only for frost protection.
3. One rotation and that for coppice
1. The standards are retained as a permanent feature throughout the life of the crop.
2. The standards are kept for variety of reasons. As given above.
3. Two rotations - one for coppice
- other for standards
Coppice With Reserve
Coppice With Standard
1. The resultant crop can’t be differentiated into different storeys.
2. The crop is treated as a whole.
3. The reserves are selected both singly as well as in groups. Uniform spacing is not necessary.
4. The object of reserving tree is protection of soil, maintenance of soil fertility, supply of seed, fruit or any other economic forest produce.
5. The reserves are of several species.
1. The crop is composed of two storeys.
2. There are distinct treatments and rotations for under storey and upper storey .
3. The standards are selected individually and spaced uniformly over the area.
4. The object of retaining standards is production of large sized timber.
5. The standards are of one or two valuable species.
Choice of Silvicultural System
It has been observed that each system has some advantages and disadvantages. Therefore the choice of a system to be adopted for any species in any locality depends upon the relative advantages and disadvantages in these specific conditions. For a careful consideration of its choice, the question should be examined as under:
(i) Suitability of the system to the principal species - Only that system should be adopted which suits silvicultural requirements of the principal species. The most important factors that should be considered are light requirement, seeding and the ease of regeneration. If the principal species is a strong light demander, clear-felling system is suitable for it. On the other hand, shelter wood or selection system should be preferred for shade bearers.
( ii ) Topography and soil - Forests growing on rocky and precipitous slopes should be worked under Selection System as regeneration comes up only in limited pockets of soil. Similarly, slopes liable to erosion should not be worked under clear- felling system as clear- felling is liable to accelerate erosion.
( iii ) Resistance offered to external dangers. - Though resistance of forest crops to external dangers largely depends upon the species, the silvicultural system adopted may aggravate or reduce the danger. Where forest, drought or insect damage is considerable, shelter wood systems afford better protection than clear-felling systems; but in areas where the openings made in shelter wood systems are liable to induce dense weed growth, Selection System is the best.
( iv ) Object of management - If the object of management is production of fuel, small timber or even poles, any of the coppice systems may be applied with advantage for species which coppice. If, however, the object is to produce large sized quality timber, one of the high forest systems will be the choice, depending on other factors.
( v ) Economic considerations - Concentration of work reduces cost of felling, logging and extraction. From this point of view, systems based on concentrated felling and regeneration, offer a great advantage over selection system, which results in diffusion of work. Amongst the former, the clear-felling and simple coppice systems are the most advantageous, as the regeneration period is the shortest. The longer the regeneration period and greater the number of secondary fellings the lesser will be the advantage.
( vi ) Development of communications - Development of communications affects the choice of system as it affects the extraction costs. Forests situated in inaccessible areas with practically no roads, can only be worked under selection system, as extraction of smaller timber does not pay for the high extraction cost. Clear-felling System can be applied in areas that are well connected by roads.
( vii ) Availability of skilled staff and labor - Certain systems require greater skill in marking, felling and extraction than others. Therefore such systems can be adopted if adequate skilled staff is available. For instance, selection system if correctly applied, requires great skill not only in marking but also in felling and extraction of trees without damaging the immature crop growing under the trees being felled. Similarly, in the mixed forests, application of shelter wood system requires considerable skill in regenerating different species in proper or desired proportion. On the other hand, clear felling system does not require any considerable skill.
( viii ) Aesthetic considerations - From the point of view of aesthetic considerations, silvicultural systems which maintain a continuous cover such as the selection system, are the best. Clear felling system is the least desirable system from this point of view.
References
Amatya S.M & Nepal Forestry Handbook. Forestry Research Support Programme for
Shrestha K.R. (2002) Asia and Pacific, Bangkok.
HMG/N (1999) Forest Resources of Nepal (1987-1998). Department of Forest Research and Survey, Publication No. 74.
Khanna L. S. (1977) Principles and Practice of Silviculture. Khanna Bandhu, Dehradun,
India.
Nyland R. D. (1996) Silviculture concepts and Applications. The McGraw – Hill
Companies Inc.
Ram Prakash & Theory and Practice of Silvicultural Systems. International Book
Khanna L. S. (1979) Distributors, Dehradun, India.
Shrivastava M.B.(1998) Introduction to Forestry. Vikash Publishing house Pvt. Ltd.
¹ Regeneration Felling: A felling made with a view to inviting or assisting regeneration. It includes:
o Seeding Felling – Opening the canopy of a mature stand to provide conditions for securing regeneration from the seed of trees retained for that purpose. It is the first stage of regeneration felling.
o Secondary Felling- A regeneration felling carried out between the seeding felling and the final felling in order to gradually remove the shelter and admit increasing light to regenerated crop. It is also called intermediate felling.
o Final Felling – The removal of the last seed or shelter trees after regeneration has been established. The final stage in the regeneration felling.
¹ Felling Cycle – The time which elapses between successive main felling on the same area.
² Pollarding - Cutting of a stem in order to obtain a flush of shoots, usually above the height to which the browsing animals can reach. Example- Salix
