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THE SELECTION SYSTEM
· When individual trees or small groups of trees are removed from all over the forest, creating the small gaps to stimulate or free regeneration, an uneven-aged forest results in which trees of all age classes distributed over the whole area of the forest such a system is known as a selection system.
o DESCRIPTION AND EXECUTION:-
· As the whole area cannot in practice gone over every year, it is divided into number blocks, one of which is worked over each year.
· The number of blocks determines the period of years elapsing between two successive fellings over the same block. This period is known as felling cycle.
· The number of blocks and consequently the felling cycle have to be so fixed as to ensure that the block to be gone over provides sufficient material for economic removal and the period intervening between two successive fellings is sufficient to permit the requisite number of trees to reach the exploitable size and to stimulate regeneration in areas where it is absent or deficit.
· Incorrectly executed selection working, thinnings among the smaller trees are carried out simultaneously with the removal of mature trees.
· Strictly speaking there is no rotation, no size limit on felling and no differentiation between regeneration and thinning operations. Dead, Dying, Diseased trees are removed and so are trees which are defective or are not putting on much increment. Trees which are of vigorously may be retained for further periods regardless of age or size.
· The selection system of removing single tree is suitable only for the regeneration of shade bearers.
· Where light demanders are concerned to get regeneration layer gaps must be created by removing groups of trees.
· In its most intensive form under the name of control method
· Full enumerations are carried out at short intervals-usually six years so that with due allowance for fellings , the volume of the growing stock , the increment over the period , and the size class distribution all are precisely known and the first and the last of these quantities can be compared with the best estimate available for optimum growth.
· At each felling, the markings are concentrated as far as possible on those size classes which appear to be in excess, the total volume felled being decided on a comparison between actual standing volume and the assumed ideal.
· For each felling cycle the increment can be determined and comparison with previous increments provides the necessary indication for deciding on the volume to be cut in the next cycle.
· Higher sustained yield can be obtained under the selection system than under the even-aged system.
o GROUP SELECTION SYSTEM:-
· This is an accessory of the selection system. If selection system is to be applied for the treatment of light demanders, it becomes essential to fell trees in groups, so as to create gaps of sufficient size for the successful establishment of regeneration. Fellings of this type are known as group selection felling and this system is termed as the group selection system.
· A more even-aged forest results from the group selection system. This system has been employed for the treatment of certain coniferous forests of the western Himalaya.
o ADVANTAGES OF SELECTION SYSTEM:-
i. If affords considerable protection against soil erosion, landslides and snow slides.
ii. A constant forest cover is maintained at all times and at different levels.
iii. All seeds year can be made use of for establishing the regeneration and the young seedlings are scattered well.
iv. Extraction work is not affected due to continuous forest cover.
v. This system is the local forester with high degree flexibility and silvicultural considerations prevail over prescribed yield.
vi. It is possible to retain tree as long as they are putting on valuable increment as in uniform system increment tends to go down.
vii. A larger portion of the total growing stock and the yield is available for removal from the trees of large sizes while in uniform forest there must be equal or near equal areas of each age class.
viii. Selection forest has been considered to be more attractive from an aesthetic point of view.
o DISADVANTAGES OF SELECTION SYSTEM:-
i. A fair degree of silvicultural knowledge is needed on the part of the marking officer for successful implementation of this system.
ii. The selection system is largely applicable for the treatment of shade bearers while the group selection system has to be adopted for light-demanding species .but the selection system results in the forest losing many of its characters of a selection forest.
iii. Felling and extraction operations need to be carried with skill and caution.
iv. The selection system is not suitable for areas where grazing is to be carried out.
v. Under this system, there is no thinning period during which efforts may be made towards improving the stand.
o FELLING CYCLE:-
· It has become customary to divide the entire area into a number of more or less, equal blocks in selection system.
· One block is brought under regeneration each year and the entire forest is worked during the period of a year, which is equal to the number of blocks into which the area is divided.
· This period is known as felling cycle. The blocks may be divided as under:
· The following are some silent features of felling cycles under the selection system.
I. The felling cycle is fixed according to the requirement of each case.
II. If felling cycle is kept too short, involving large coupes, then the cultural advantages of the selection system come into full play. However, the work proves to be fairly costly, growing to the scattered nature of fellings.
III. If the felling cycle is kept too long, involving the small coupes, felling over definite coupes, becomes intensive.
It will result
in a. Large quantity of timber, economic advantage.
b. Create favourable conditions for regeneration. recreation of large gaps
c. Cultural advantage is largely lost.
d. Upset the balance in the proportion of size classes.
e. The time character of selection forests is lost.
IV. Felling cycle in different parts of the world are as under
o THE SELECTION SYSTEM IN PAKISTAN:-
· The selection system is adopted in Pakistan are forest which can not be regenerated under the clear felling or uniform systems. These include the Deodar, Kail, Fir and Spruce forests of Kaghan, Murree hills, Dir, Swat and AJK. The open, deteriorated Chir forest of Murree hills and AJK, Hazara etc.
o THE SELECTION SYSTEM IN THE CONIFEROUS FORESTS:-
· In the coniferous forest, a modified selection system is usually in Vogue.
· This entails carrying out a single tree selective felling in forests growing in forests over steep slopes or hot aspects , or in poor crops and in areas where the incidence of grazing is heavy.
· On easiest slopes and mature trees occur in groups, regeneration is secured and tended by concentrated felling as under the uniform system.
· An exploitable size is fixed depending on the type of produce and demand the commonest exploitable size for all coniferous trees is 24 inch dbh .though 28 inch dbh is prescribed in Kaghan and 30 inch dbh in the Deodar, Kail, Fir forest of Muzaffarabad forest division.
· All trees over exploitable size, when occurring over established regeneration, are removed in addition to dead, dying, diseased, malformed and broken trees.
· In Kail, Deodar and Fir forest of AJK, groups of mature trees without regeneration under them are opened out uniformly, so that the trees are 35 feet for Kail, Deodar, and 20 feet for Fir.
· Things are carried out where required, together with the main felling. No green trees below the exploitable diameter for increasing the yield. a nominal rotation is specified which corresponds to the age at which trees reach the exploitable size it is usually 120 years but 150 years for Deodar , Kail and fir in the moist zone of AJK and Kaghan and 200 years for the dry zone of Kaghan . The rotation has no effect on the application of the system which is practiced on the basis of the exploitable size and felling cycle alone. The felling cycle is usually 20-30 years.
· In Murree hills Kail forests desirable trees above exploitable size can be retained if growing vigorously either among groups of middle-aged trees or in groups on an easy ground where the majority of trees are mature and regeneration felling will be made later under the uniform system. The yield is usually prescribed by volume or number of trees above the exploitable size.
· In Kaghan thinning also count against the prescribed yield. In mixed coniferous forests to which the selection system is applied, the more valuable species are favoured over the less valuable one during thinnings and main fellings.
i. Deodar has the highest reference followed by Kail and the Fir.
ii. In the mixed forests Kail – Chir forests Kail is preferred.
iii. Broad-leaved trees occur in high zone forests are usually preferred overall species, due to extreme scarcity and the desirability of there retention in the interest of soil improvement e.g In Murree they are ruthlessly lopped by the villagers having attenuated crowns, not damp regeneration.
iv. The selection system in tropical semi-evergreen forest is applied.
o THE SELECTION SYSTEM IN THE MANGROVE FOREST:-
· The regeneration appears to be keeping pace coming with felling at present, more concentrated methods of regeneration will be demanded in future by the past developing forest industries and research is needed to develop them.
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