Silvicultural Systems

Foresters, in charge of forest estates covering large areas, are often faced with situations in which areas with mature forest have to be harvested and replaced by new crop. In such situations, they have to decide, on the basis of their silvicultural knowledge and experience the method of

• (i) harvesting old crop,
• (ii) regenerating the harvested area  &
• (iii) tending the new crop to develop into a mature forest of good quality.

These methods vary with:

1. species in question and the forest type in which they occur in the area,
2. climatic, topographic and the edaphic factors of locality and
3. pressure of biotic factors in the environment of the harvested area,

 

The best combination of below under the hard realities of factors of locality, are considered for execution

• pattern of felling to obtain the crop of desired form,
• methods of regenerating the area with desired species and
• methods of tending for most of the life of the crop.

 

This best technique or procedure is called a Silvicultural System which is defined as

“a method of silvicultural procedure which is  prepared as per with accepted sets of silvicultural principles by which crops containing mature forests are:- harvested, regenerated, tended and replaced by new crops of distinct forms.”

 

Scope of Silvicultural Systems

As stated earlier, a silvicultural system is a silvicultural procedure adopted for renewal of a forest crop in a given set of conditions. Thus, it is just a technique perfected on the basis of knowledge of silviculture but its application is governed by requirements of forest management which prescribes the time and place where silvicultural technique or some part of it may be carried out so that the objects of management are achieved. Forest management aims at producing sustained yields of forest produce regularly and in order to achieve this, forest management prescribes a scheme of work after dividing the area into blocks and compartments in which felling or some other operation will be carried out. While the preparation of scheme is the concern of forest management, the technique referred to above is the silvicultural system which is concerned with the conduct of felling, method of obtaining regeneration and its tending. thus, Silvicultural System is a specialized tool or technique for achieving the objects of forest management.

 

Classification of Silvicultural Systems

Silvicultural systems are classified in India primarily on the method of regeneration and they are further classified according to the pattern of felling carried out in the crop. According to the method of regeneration, Silvicultural Systems are classified into following two groups :

• (I) High Forest Systems and
• (II) Coppice Systems.

 

(I) High Forest Systems

Silvicultural Systems in which the regeneration takes place from seedling, which could be natural or artificial or a mixture of both are called High Forest Systems. In these systems, rotation period is generally long. They are further classified on the basis of pattern of felling affecting the concentration or diffusion of regeneration.

On the basis of concentration or diffusion of regeneration, High Forest Systems are classified into three main groups:

 

The Systems of concentrated regeneration are those silvicultural systems in which regeneration fellings are, for the time being concentrated on part of felling series. As stated earlier, they are further sub-divided into two main sub-groups :

(A)  Clear-felling Systems

Those silvicultural systems in which the mature crop is harvested in a single  operation are called clear-felling systems.

 

 

 

 

 

(B) Shelterwood Systems

The Shelterwood 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. Other fellings, if any, are called secondary fellings3. The interval between the seeding felling and the final felling on a particular area, such as a compartment, is called regeneration interval and determines the degree of uniformity in the new crop. Systems of diffused regeneration are those silvicultural systems in which the regeneration fellings are distributed over the whole felling series (except in so far as felling cycles introduces a modification)

Accessory Systems

Accessory Systems are those silvicultural systems which result in irregular or two storeyed high forest.

(II) Coppice Systems

Coppice Systems are those Silvicultural Systems in which the new crop originates mainly in the from of coppice shoots of stools of trees of the old crop felled and where the rotation of coppice is short. This main group is further differentiated into following silvicultural systems on the basis of pattern of felling:

 

 

Even aged and Uneven aged forests & their crown classes:

Even in plantation 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.

Even-aged or regular forests are forests composed of even-aged trees.  The term even-aged used in this definition is 'applied to a stand consisting of trees of approximately the same age. Differences upto 25% of the rotation age may be allowed in cases where a stand is not harvested for 100 years or more.

Uneven-aged or irregular forests are those forests which are composed of trees that are of significantly different ages. The term uneven-aged is 'applied to crops in which individual stems vary widely in age, the range of difference being usually more than 20 years and, in the case of long rotation crops, more than 25% of the rotation'. Such a forest is called 'selection forest" Wien all or nearly all age gradations or age classes are present.

 

 

The Crown classes are generally met with in an even-aged forest and un-even aged forest:

(i) Dominant trees: All trees which form the upper most leaf canopy and have their leading shoots free. These may be subdivided according to the position and relative freedom of their crowns into pre-dominants, i.e., the tallest trees determining the general top level of the canopy and the co-dominants, i.e., the slightly shorter dominants or to be more precise, 5/6 of the pre-dominants.

(ii) Dominated—Trees which do not form part of the upper most leaf canopy but the leading shoots of which are not definitely overtopped by the neighboring trees. Their height is about 3/4 of the tallest trees.

(iii) Suppressed—Trees which reach only about 1/2 to 5/8 of the height of pre-dominants, with their leading shoots definitely over-topped by their neighbors or at least shaded on all sides by them.

Crown classes in an uneven-aged forest:

Crown classes in uneven-aged forests have not been studied in great detail so far but even on a superficial look, it is clear that it does not follow the same pattern as that of the even-aged forest. For, example, in the uneven-aged forest, the developmental stages such as seedling crop, sapling crop, pole crop, etc., are not found because the uneven-aged forest has a large number of age classes at the same place.

On the other hand, it has distinct and well-defined canopy classes which
are defined as 'the classes into which canopies found in a storeyed high forest are divided on the basis of their relative heights, e.g., top canopy, middle canopy, etc. Canopy classes are sometimes found in even-aged forest also but they are not so well-defined and clear cut as in the uneven-aged forest.

The canopy classes are usually described as top canopy or overwood, middle storey, lower canopy, undergrowth and ground cover. Mixtures of different species with varying light requirement make the canopy classes still more complex.

 

Over-wood: The uppermost storey of a storied high forest or any crop in which two or more distinct crown layers occur, either temporarily or permanently; for example, standards over coppice , crop of trees over bamboos seed bearers over regeneration.

Under growth: The lowest stratum of woody and other vegetation above the ground cover. Syn. Low cover

Ground-Cover : The carpet of herbaceous plant and low shrubs, which covers the soil. Syn. ground vegetation.