Shelterwood System – A Detailed Note
Table of Contents
SHELTERWOOD SYSTEMS
· Shelterwood systems are those high forests system in which the young crop is established under the shelter (overhead or lateral) of the old one, the later at the same time affords protection to the soil.
· Shelterwood system includes the various systems of successive regeneration felling together with the selection system.
· Old crop is felled over the demarcated area in Block (Uniform), Wedge, Group, Strip, Group-strip or irregular method in successive operations, through:-
a. Uniform System
b. Selection System
UNIFORM SYSTEM
· In this system the canopy is opened up uniformly over the entire compartment to get more or less even aged crop.
· The old crop is removed in succession felling and the regeneration is obtained from seeds shed by the seed bearers which are retained in the area for this purpose.
· Sometimes Natural Regeneration is supplemented with artificial planting.
· The old trees are removed in successive felling known as regeneration or seedling felling which extended over a period of years.
· The period during which regeneration gets established is known as regeneration period.
· According to the length of regeneration period, the total rotation period is divided into 4 blocks technically known as PERIODIC BLOCKS.
· Regeneration period is allotted to PB IV.
· If rotation age of Chir (Pinus roxburgii) is 120 years then:
i. PB IV contains crop ranging from 0 – 30 years.
ii. PB III from 30 – 60 years.
iii. PB II from 60 – 90 years.
iv. PB I from 90 – 120 years.
· This system is used in case of Chir Pine forests.
· Stand of less than a specified diameter are retained as ADVANCE GROWTH.
· Sometimes, the regeneration in the form of “Advance growth” is also retained as in the Chir forests of Murree Hills and parts of Azad Kashmir. This modified system is known as “Punjab Shelterwood system”.
· Number of seed-bearers are mother trees are retained depends upon species, seed dispersal habits, site-conditions etc.
· These trees provide Shelter to the young regeneration specially in those areas where natural regeneration may not come up due to adverse locality factor.
· This system has certain advantages specially for those sites which are liable to deterioration because of sudden exposures.
SELECTION SYSTEM
· In this system, felling are done over a unit of forest area by fixing the number of trees of exploitable diameter to be removed annually which is known as the annual coupe, if they are silviculturally available.
· The forest is divided into felling cycle according to the requirements and nature of forest.
· The felling cycles are sub-divided into felling series with emphasis on the local conditions of market, labour, supply etc.
· Under this system, all age gradations are represented through Natural Regeneration.
· Annual increment put up by the forest is harvested keeping growing stock or the capital intact.
· Only trees of exploitable diameter are removed ensuring the establishment of regeneration and maintaining ecological equilibrium/ Balance.
· Care is taken for the removal of trees with consideration to the growth rate of trees, their distribution according to the different size, classes and the number of trees just below the exploitable diameter class.
· This is necessary so that proper representation of different diameter classes is ensured and removal is affected on sustained yield basis with optimum utilization of the site.
· This is an ideal system from forest management of view.
GROUP SELECTION SYSTEM
· In this system trees in groups are felled to create gap of for establishment of regeneration.
· This system is applied in slopy/ undulating areas to protect the soil from deterioration.
· In this system dependency wholly on natural regeneration and have to work on a large area at one time.
· Therefore the locality factors both Biotic and Abiotic play an important role in natural regeneration process out of these two important factors are accidental fire and grazing pressure in addition to frost and drought. These all factors affect adversely the natural regeneration process.
· The forests which cannot be regenerated under clearfelling or uniform systems are treated under this group selection system. e.g.
i. The forest of Dir, Swat, Chitral, Kaghan, Murree hills, A.K. of Deodar, Kail, Fir and Spruce forests.
ii. Deteriorated and open Chir forests of Murree hills, Azad Kashmir, Hazara, Bunari, and Swat.
· In some forests, a modified selection system is usually practiced as:-
a. Single trees are felled from the forest growing on steep slopes, southern aspects, degraded soils and under heavy pressure of grazing.
b. In other areas, where the slopes are gentle and mature trees are found in groups, concentrated felling as recommended in uniform systems are applied. The system applied is known as, group SELECTION SYSTEM.
· In this system, the exploitable diameter is fixed according to the market produce demand. Usually trees of 24″ DBH (60 cm) or more are felled provided they are standing over well established regeneration.
· The felling cycle usually extends 20 to 30 years.
KAGHAN INTENSIVE MANAGEMENT SYSTEM
· It is modified system introduced in Kaghan valley, Hazara, KPK.
· Under this system, natural regeneration is supplemented by artificial planting after clearfelling the undergrowth when selection felling are over.
· The results are encouraging.
· Extra expenditure is involved for artificial planting to supplement natural regeneration, yet the success of regeneration is ensured thus reducing the period of natural regeneration.
CLASSIFICATION:-
i. The uniform system.
ii. The group system.
iii. The irregular shelterwood system.
iv. Strip systems.
v. The wedge systems.
NATURAL REGENERATION UNDER SHELTERWOOD SYSTEM:-
· The shelterwood system is the system in which the mature crop is removed in a series of operations.
· The first operation is called seeding felling and the last is the final felling. The other felling if any, are known as secondary fellings.
· The shelterwood system is also called “Seed Tree Method” shelterwood compartment system or system of successive regeneration fellings.
· The regeneration occurs under a shelterwood which is removed in a final felling only after the natural regeneration has got established. The regeneration interval which is the interval between the seeding felling and the final felling in a particular area determines the degree of uniformity of the resulting crop.
· The mature crop is in different forms and accordingly the name is given to the shelterwood system. e.g
· In shelterwood uniform system the seeding felling is done so as to create the small gaps over the whole compartment.
· Whereas in shelterwood group system seeding felling is done in groups and therefore, Regeneration also comes up in groups.
· If the advance growth (saplings and poles) are retained for compensating deficiency of natural regeneration, the resulting irregular crop is called irregular shelterwood system.
· In all these shelterwood systems some mature trees are retained to supply seeds whereas other are felled to provide light for facilitating regeneration .the regeneration coming up in the openings is able to grow under shelter of the trees .
· After the regeneration has grown up the rest of the over wood is removed in one or two operations. The various operations in a shelterwood system are
· i. Retaining enough mature trees which may include advance growth also seed supply.
· The retained trees should be middle-aged.
· ii. Manipulating canopy for adequate light reaching on the forest floor. The young regeneration needs less light but as it goes in size the light requirement increases and therefore secondary fellings are carried out.
i. The soil conditions are improved by control of grazing, digging of compact soil and encouraging decomposition of leaf litters for better humus formation. The excess or shortages of moisture is not good for natural regeneration.
ii. Control burning for better regeneration in Chir pine.
iii. Disposal of slash for reducing fire incidence, insect and pathogens attack.
iv. Weeding and cleaning operation.
v. Protection against biotic interference.
ADVANTAGES OF SHELTERWOOD SYSTEM:-
i. Natural regeneration is more frequently obtained under the shelterwood system than under the clearfelling system.
ii. They afford protection to species sensitive in youth to frost, drought and cold wind as compare to the clear felling system.
iii. The soil is more effectively protected than under the clear felling system, particularly where the canopy is often gradually and continuously there is less risk of desiccation and the invasion of noxious weeds.
iv. There is less risk of multiplication of insects.
v. On steep slopes or unstable hillsides there is less risk of erosion or the rapid runoff of rainwater than under the clear-cutting system.
vi. Effective measure against damage by storms and snow.
vii. An opportunity is given to the best trees to put on enhanced increment when opened out in regeneration felling.
viii. From the aesthetic point of view shelterwood system are usually preferable.
DISADVANTAGES OF SHELTERWOOD SYSTEM:-
i. Shelterwood system require more skills (marking a tree) than the clear felling systems.
ii. Work is less concentrated and felling and extraction cannot be carried out so economically than under the clear felling.
iii. Damage is done to greater or less extent by felling of trees over young growth and dragging or sliding timber through it and prevention must be taken by suitable precautions.
iv. Serious economic loss as the young crop takes more time to establish that under the clear felling system.
v. The rate of cutting and regeneration are more difficult to control than the clear felling system.
vi. When mature crop is removed in two or more felling resulting crop more or less even-aged or somewhat uneven-aged is called shelterwood system.
It is further classified into
(A) Regeneration fellings distributed over whole compartments or sub-compartments:-
i. Uniform systems
ii. Group system
iii. Irregular shelterwood system
(B) Regeneration fellings confined to certain portions of compartments or sub-compartments.
· Strip system
· Wedge system
i. Uniform system or uniform shelterwood system
If the canopy is opened out evenly young crop more or less even-aged and uniform.
ii. Group shelterwood system
If the canopy is opened out by creating scattered gaps, young crop more or less even-aged.
iii. Irregular shelterwood system
If the canopy is opened out gradual and irregularly with along regeneration period, resulting in young crop uneven-aged.
Ø Strip system
Fellings in strips
Ø Wedge system
Fellings beginning in internal lines and advance outwards in a wedge formation.
THE UNIFORM SYSTEM
-
Definition:
· “The uniform opening of the canopy over the whole area of a compartment with a view to obtain more or less uniform regeneration, It has also been called shelterwood compartment system, the regular system, and the system of successive regeneration fallings.”
- General Description:
· Under the clear felling the final crop was removed in one operation and the new crop generally planted artificially with little assistance from nature.
· Clear felling follows the practices of agriculture where the kind of crop grown is entirely subject to man control, success or failure depending on the accuracy of his judgment of the capabilities of the soil and the suitability of the climate to the species selected for cultivation.
· In shelterwood system depending on natural as opposed to artificial regeneration , the forester obtain his regeneration by following the precepts of nature , by manipulating the mature crop in such a way as to obtain suitable soil condition and so as to afford the young crop condition of light and shed , protection and moisture suitable for germination and growth .
· In the process of natural regeneration the heart of silviculture reaches its zenith, without an inborn appreciation of the growth of trees, without an instinctive knowledge every detail of there silvicultural requirements, no one can become a master of this art and without a masters, skill no system of natural regeneration can reach perfection.
· Where in clear felling we plant what we require.
· Under all systems of natural regeneration, we try to obtain from nature new crops of such species and such mixture of species as we desire.
o THE METHOD OF OBTAINING REGENERATION:-
· The regeneration is affected by different operations according to the stage of the regeneration at which they are made.
· These are defined as
i. The preparatory felling
ii. The seeding felling
iii. The secondary and final fellings.
· In actual practice these successive fellings take a number of years, technically known as the regeneration period, to carry out over any particular area.
· The rotation is therefore divided into a number of periods and the age classes are allotted to there respective periods.
· Similarly the area allotted in working plan to each different age class is called periodic block .supposing that a period of 30 years has been prescribed in the working plan, this denotes that in theory this length of a time is allotted for the regeneration of each compartment. The age of regeneration may, therefore, is theory differ by as much as 30 years.
· In practice, it is immaterial how quickly any particular compartment is regenerated so long as regeneration of the whole block is spread over the prescribed period.
o ORGANIZATION OF THE REGENERATION:-
· Suppose a rotation of 120 years divided into four periods of 30 years, then, in theory, the age classes will be distributed as follows and the area allotted to each age class designated a periodic block numbered as below, the forest operations to be carried out in each block are also shown.
o PERIODIC BLOCK:
§ The periodic block is a sub-division of a felling series and is defined as: “The parts of a forest allocated for regeneration or other treatment during a specified period”. The regeneration period is decided arbitrarily as a sub-multiple the rotation taking into account the silviculture of the species, the climate, soil and biotic factors of the locality.
§ According to the length of the Regeneration period, to systematize the execution of various operations, Forest may be divided on the basis of age classes into blocks which is known as periodic blocks.
Area of period Block = A.P
(A)= R
Where P = Regeneration period
R = Rotation
A = Area
e.g. If the Rotation is 80 years and the Regeneration period 20 years.
The rotation and the area can be divided into four period Blocks as follows:-
|
S.No.
|
Periodic Block
|
Age Range at the time of formation
|
Age Range at the end of Regeneration Period
|
|
|
|
(years)
|
(years)
|
|
1.
|
Periodic Block I
|
61-80
|
1-20
|
|
2.
|
Periodic Block II
|
41-60
|
61-80
|
|
3.
|
Periodic Block III
|
21-40
|
41-60
|
|
4.
|
Periodic Block IV
|
1-20
|
21-40
|
o OPERATIONS IN PERIODIC BLOCKS
i. All stages of Regeneration fellings are carried out in Periodic block I.
ii. In Periodic Block II, the object will be to prepare the crop for Regeneration and increase the diameter growth of trees below exploitable size.
No trees of good size is felled if it can be retained for a period of 20 years.
Thinnings are carried out in the trees of the dower diameters especially where the crowns need development to produce a good seed crop.
iii. The periodic block comprises pole crops varying from 21 years to 40 years of age.
The operation carried out here are thinnings and the Removal of any mature trees which may be present.
iv. Periodic block IV would bear young Regeneration and sapling crops in which cleanings and thinnings would be carried out and any mature trees which might have been retained so far, would be Removed.
o ALLOTMENT TO PERIODIC BLOCKS
Ø The working plant officer allots compartment and sub-compartments on the basis of the age and condition of the crop to various Periodic Blocks. A Period Block is not a concentrated ages but usually comprised of forests scattered in different localities.
o FLOATING/SINGLE PERIODIC BLOCK
Ø In this case compartments and sub-compartments needing Regeneration during the plan period is allocated to periodic Block I (PB I) and the rest of the compartments are kept un-allotted. Since fresh allotment of compartments is made to periodic Block I and Revision of working plan and Regeneration Block float around the felling series, so it is called as FLOATING PERIODIC BLOCKS.
o IN INDIA:
Ø Working plan officers have always designated the area under regeneration as PB1,
Ø In theory PB1 should be completely regenerated during the period and the over wood removed.
Ø In practice the final felling can differ to the last period. It is also permissible to commence preparatory felling and even to induce regeneration in PB.II.
Ø It will be therefore seen that although each periodic is according to the working plan a separate unity in practice of silvicultural operations follow each other in regular harmony through the preparatory felling. The seeding felling, secondary and final fellings, the cleaning and thinning of the young crop, until the completion of the rotation and renewal of the regeneration operations
Ø Periodic blocks may change with each revision of the plan, they are servants of the management not the master, they exist merely to facilitate order in the carrying out of forest operation and for assistance in calculating the yield.
o THE FLOATING PERIODIC BLOCK:-
Ø Under this system, regulation of yield depends on the allotment of compartments which need to be regenerated to the current period.
Ø The floating periodic block method is a development of the fixed or single periodic block method. This development takes place as under
Fixed self-contained P.Bs
Fixed scattered P.Bs
Ø Scattered P.Bs with boundaries subject to revision
Ø Compartment for obtaining regeneration by natural means in management maps such areas are generally colored BLUE.
Ø At each working plan revision two groups of the compartment may be allotted as under
- Group 1
· Those compartments which are already under regeneration during the current plan
- Group 2
· Those compartments which are to be regenerated under the revised working plan
o REGENERATION FELLING:-
i. Preparatory felling
ii. The seeding felling
iii. The secondary felling
iv. The final felling
o THE PREPARATORY FELLING:-
Ø Starting with more or less Even-aged crop of average maturity the preparatory felling would consist of opening out crowns of the mother trees of the future so as to get them ready for the production of seeds.
Ø They are carried out a little before the seeding fellings. The object of such felling is to promote the development of a good crown and to ensure the production of high-quality seeds.
Note: In India, this is of so little importance and Chir pine is not required.
o SEEDING FELLING:-
Ø The canopy is opened so as to provide enough light for the seedlings to come up and ensure their survival in the initial stages e.g.
Ø Chir pine is the classic example of seeding felling, where 8-10 selected mother trees per acre are left standing on the compartment to be regenerated, the rest of the crop remove, the slash burnt and the ground left bare and ready for the reception of the seeds.
Note: Regeneration fellings are nothing but an extension of thinnings.
o SECONDARY FELLING:-
Ø The mother trees are removed in a series of fellings that more and more light is gradually admitted for the growth of the seedlings on the forest floor.
Ø The object of the secondary fellings is gradually to uncover the regenerated crop in one or more operations depending on the progress of the regeneration.
Ø Some parts regenerate sooner than others and therefore demand the more rapid removal of the over wood.
Ø The right amount of light and shade required for the young trees must be provided and also the seed for the completion of the crop.
Ø The secondary fellings also permit the manipulation of the mixture of species is in the young crop. e.g.
Ø In the case of a mixed forest of spruce, fir, and blue pine regenerated the secondary fellings bore heavily on the spruce and fir mother trees so as to complete the regeneration with more valuable and light demanding pine.
Ø There may be one or more secondary fellings. The greater the shed demanding requirements of the crops the greater will be the number of mother trees and the greater the number of secondary felling e.g.
Ø Standard prescription of mother trees for fir and Chir pine 30-35 and 6-8 respectively.
o FINAL FELLING:-
Ø In final fellings all the remaining seed bearer are removed and the new regeneration is fully established. This is the final stage of regular fellings under the uniform system.
Ø After these fellings, all the blanks are restocked by the artificial means.
Ø Final fellings may not be needed for certain species which are light demander and are growing under ideal conditions of growth. In such cases, regeneration is abundant and establishes itself freely.
Ø In modern forestry, the trend of treating seeding, secondary and final fellings as separate stages is been fast discarded.
Ø For certain species the above felling stages are nothing more than a continuation of the thinning process which begins soon after the regeneration establishes itself.
Ø The modern concept distinguishes no felling stages and broadly speaking felling is only an intensity of thinning operations as follows.
- Note:
The process of felling and extraction has to be followed with the precautions mentioned below.
i. Before felling, the main branches should be lopped off so that damage caused as the tree falls is minimized.
ii. Dragging and sliding should be avoided as it causes damage to the regeneration and excessive soil erosion.
iii. In case there is a danger of damage by wind, felling should be carried out against it.
- General
· Generally speaking it may be said that where there are no severe climatic conditions with which to contend and where conditions of seeding and regeneration are favorable, the uniform system owing to its simplicity, as a special advantage for most of the other system.
· It is not so well adapted for regions where serious damage by storms or snow is to be feared or where seeding or soil conditions are unfavorable.
· The life of forest being treated under the uniform system (also to all shelterwood system in general) can be divided into two distinct stages as under
i. Education or preparation
ii. Regeneration stage.
1. EDUCATION OR PREPARATION:-
Ø The forest is subjected to early cleaning, this is followed by a period of thinning at fairly regular intervals right up to a few years before seeding fellings.
2. REGENERATION STAGE:-
Ø It commences from seeding felling and continues till the end of the final felling. In this stage, a new crop becomes established in the entire forest.
ADVANTAGES OF UNIFORM SYSTEM:-
i. The fellings are simpler in execution than compared to most of the high forest system.
ii. A more or less even aged crop is produced as the best economic returns due to the trees having clean, tall cylindrical wood.
iii. Superior to the selection system.
DISADVANTAGES OF THE UNIFORM SYSTEM:-
i. Damage to young growth by felling and extraction is far more intensive than that under the wedge and strip systems.
ii. The mother trees isolated in seeding or secondary felling are liable to be thrown by winds and shallow-rooted species e.g spruce (shallow roots) is susceptible.
iii. In hot situation, isolated seed-bearers of thin-barked species are liable to suffer sun-scorch e,g beech.
iv. In areas where damage by snow and storms is common, the even-aged crops produced under the uniform system is affected more severely than the more uneven-aged crops produced under other systems like the selection system or the group system or the irregular shelterwood system or the strip system etc.
v. In localities which are subject to severe frost and drought, the provision of an overhead cover is less helpful than aside cover as it is available in areas being treated under the strip system.
TREATMENT OF UNEVEN-AGED FORESTS UNDER THE UNIFORM SYSTEM:-
Ø The uniform system was first introduced for the treatment of uneven-aged forest in France in the Jura mountains before it was treated under the selection system.
Ø Now considerable attention has been paid towards the conversion of irregular forests into regulars ones by the treatment of under the uniform system.
Ø A manifold development of the system of concentrated treatment and regeneration based on the principles of the Uniform system, in tropical, sub-tropical and temperate areas the practice is vogue in many countries.
Ø During the conversion of an irregular forest to regular on under the uniform system the following stages of felling have been recognized.
i. Regeneration felling
ii. Selection and improvement fellings
Ø These are carried out in areas where which have been allotted for the purposes of obtaining and establishing regeneration.
Ø These occur in the form of thinning regeneration.
Ø During the process of conversion, regeneration felling can rarely be carried out with the precision which is characteristics of the uniform system.
Ø In case of many species growing in ideal conditions, such felling may comprise only of freeing the regeneration which is already occurring, while it may also become necessary to carry out supplementary artificial regeneration.
Ø The young crop produced as a result of these operations is somewhat irregular, but the irregularity disappears after a certain period (generally after the crop crosses the pole-stage).
Ø The second stage of felling ( Selection and improvement ) are aimed to utilize the mature timber and at the same time to remove the defective and desirable stems which interfere with the growth of the promising individuals. A definite felling cycle is followed during the extraction process.
APPLICATION IN PAKISTAN:-
i. The coniferous forest of Pakistan and Kashmir are under conversion from the selection type of uneven-aged crops to more or less even aged and a modified form of the uniform system known as the Punjab shelterwood system has been restored to in the Murree hills in parts of Kashmir.
ii. The limit adapted varies being 16-inch diameter breast height in Murree hills Chir forest and 18-24 inch in the Jhelum valley Kail and deodar forest.
iii. The regeneration period adapted for all conifers is usually 30 years. The rotation of Chir is 120 years .and for Kail and deodar is 150 years. Chir is divided into four periodic blocks and the deodar Kail into five P.Bs
iv. In the Jhelum valley forests of Kashmir, compartments which should be included in PB I & V are allotted to the regeneration block and the rest of the area is left un-allotted. The regeneration block has to be regenerated in a period of 60 years.
UNIFORM SYSTEM FOR CHIR PINE:-
Ø Chir regenerates prosuely and ideally suited simplicity of management, the ease of regeneration and the light demanding nature of Chir pine, the uniform system is by far the best system of management for this species and is the standard method applied through the Chir pine zone from Hazara.
Ø Fire is the only factor inhibiting the application of the system and the danger has overcome by departmental burning during the winter months thereby fireproofing them against a conflagration in the hot weather. No preparatory fellings are required.
Ø The seeding felling leaves 10-25 seed bearers per acre the rest is removed, and the slash burnt and regeneration commences.
Ø In selecting Chir seed-bearers large crown mother trees are most desirable and only trees free from twisted fiber should be retained.
Ø To restrict the retained advance growth to 12-inch diameter and control of grazing/browsing.
Ø The final felling should not be carried out until the regeneration is from 6-10 feet high. The final felling should be completed in the winter. The young crop is adequately protected till attaining the age of 7-8 years.
UNIFORM SYSTEM AS APPLIED FOR DEODAR AND KAIL FORESTS:-
Ø Sir Gerald TREVOR was the first to introduce the US for the management of deodar and Kail forest in 1912. Deodar, a shade bearer is often mixed with Kail which is light demander.
Ø Under the US seeding felling is first carried out so as to suit deodar and when it has regenerated adequately, the canopy is further opened so as to help in the regeneration of Kail, besides helping the young crop of deodar to grow.
Ø The canopy is so opened during seeding felling that one crown width is left between the seed bearers. Hence, in the case of Kail, about 25-30 seed bearers per acre are retained while for deodar the number is 45-50.
Ø Once the felling are over the slash is cut, collected in heaps away from the advance growth and the seed bearers are burnt during the months of October to November, in any case before the occurrence of snowfall.
Ø In localities, where a heavy weed growth and a thick layer of undecomposed humus occurs on the forest floor contour strips are required to be clear before the occurrence of a good seed year
Ø The over wood may be removed in2-3 stages.
Ø The width of the common of an average blue pine mother tree is 30-35 feet leaving a space of one crown width the acre.
Ø Deodar has a narrow crown than Kail and the standard distance for the mother trees is 55 feet. A distance which has given excellent results over a period of 20 years, this spacing will give 20 trees to the acre.
Ø All seed-bearers must be well-developed trees of past middle age. The number of secondary fellings is never prescribed. The final fellings can be deferred.
Ø Virgin spruce and silver fir forest up to 9000 feet has also been regenerated under the US e.g (Kulu, kalga forest C4)
Under heavy grazing, advance growth is often entirely absent.
SUBSIDIARY OPERATIONS:-
Ø Under all circumstances certain silvicultural operations consisting of weeding, cleaning and early thinning are necessary.
Ø Frequently some artificial sowing or planting will be required to complete the area or to establish the mixture of species desired.
APPLICABILITY OF THE SYSTEM:-
Ø The system can be applied in the hills and plains under all conditions where natural regeneration can be obtained at the will of the forester.
THE GROUP SYSTEM:-
Ø The group system resemble the uniform system in the sequence of felling which is carried out i.e
Seeding=> secondary => final
Ø When the species under treatment are poorer seeders, regeneration cannot be obtained and where sensitive shade bearers from an important part of the crop, the adoption of the group system may result in adequate regeneration.
Ø Where small gaps occur in such forests due to windfalls or lightning, regeneration may already be present in the form of advance growth.
Ø The group system requires the extension of these gaps in a centrifugal manner to remove the overhead cover from established regeneration and to create further openings in which regeneration can take place. Where no natural gaps occur they are created artificially.
Ø The difference between uniform system and group system lies only in the manner in which regeneration felling is carried out e.g
Ø In the uniform system, the seeding fellings are carried out uniformly over the entire compartment or sub-compartment leaving seed bearer trees, scattered at more or less equal spacing all over the area, which
Ø In group system the object is to carry out fellings in such a manner as to create small gaps all over the compartments and sub-compartments under the regeneration and to extend existing gaps where regeneration is present.
Ø A longer regeneration period is required about 40 years for a slow-growing sunshine shade bearer such as silver fir.
Ø A crop produced under group system is more uneven-aged. The difference between US and GS tend to disappear during the pole stage
Ø The system is not successful for deodar and fir of the high hills and super seeded by the uniform system.
GAP FORMATION AND REGULATION OF MIXTURE:-
Ø The initial gaps which are created by wind, snow or other natural causes vary in extent.
Ø In case the natural regeneration is an uncertainty, then they should be regenerated by artificial means. The size of the gaps varies from species to species and area to area.
Ø The diameter of the gap in case of prominent shade-loving species may be
Ø When a crop, which is a mixture between shade loving and light demanding, is to be treated under this system, the size of the gaps depends upon which of these two are to be formed. The following condition may occur in such a mixture
a. In a mixture of fir and spruce, if fir is to be favored, smaller gaps are created initially but if spruce is to be favored, larger gaps are to be created.
b. Species tend to regenerated vigorously and other becomes dominant.
It is necessary to full up seedlings of that species in the gaps where they interfere with the seedlings of the other species.
c. In forests where individual strong light-demanding species occur all over the forest, they are left in the form of seed bearer, scattered all over for some time over the young the crop, till regeneration of other species becomes established, such measures help to fill up the blanks by seeding them effectively.
d. Under conditions where the proportion of a shade loving species is not up to the desired level , artificial means are resorted to
e. The procedure to plant up the gaps with certain grasses as a stop-gap arrangement is also followed in Europe to protect the soil against the erosion.
PROTECTIVE MEASURES:-
i. Fellings are generally carried out in a direction against the wind, e.g the direction of prevailing wind is from north, the compartment is divided into three gaps i.e north, south and central. The southern is worked first and the northern gap last. In such cases the distances between two gaps is not very large.
ii. In areas where there is danger of severe soil erosion , small gaps are created and to ensure establishment of a regeneration before enlargement
iii. On hillsides with the moderate slopes, regeneration operations are commenced from the top of the slope and progress is made in the down hill direction.
To ensure that no damage is caused to the young regeneration when the timber is slide down the hill slopes. Fall of trees is away from regeneration.
iv. In snow bound areas damage to the young regeneration is avoided by carrying out felling operation, where there is snow on the ground.
EXAMPLES OF THE GROUP SYSTEM:-
Ø In certain parts of France, Germany and Sweden the group system has been used for the management of Scots pine, fir and spruce
Ø In India this system was tried out for Deodar in Chamba and Chakrata (before 1970) and Kail in Paber but was not found to be very successful.
ADVANTAGES OF GROUP SYSTEM:-
i. Mixtures are easily regulated or created by regeneration or introduction of new species in groups.
ii. This system is best suited where years do not occur at regular and short intervals.
iii. The young crop is able to develop under more natural condition than in the case of the uniform system.
iv. The group system makes full used of the partial side, protection afforded to the young regeneration, together with the provision of complete overhead light.
v. In the initial stages of regeneration, there is less danger of damage from wind, than in the case of uniform system.
vi. There is adequate provision of protection of the seedlings against frost, drought or snow under the group system.
vii. There is avoidance of damage by felling in earlier stages of regeneration operation (by making the trees fall away from the young seedlings )
viii. The uneven aged condition of these forests is removed after the pole stage.
DISADVANTAGES OF GROUP SYSTEM:-
i. In hot exposed situations, desiccation of the soil is likely to occur, even if the gaps are small in extent.
ii. Heavy mortality amongst seedlings may occur when the soil is of dry and poor type.
iii. There is a risk of serious damage to the young regeneration by prevailing winds as the gaps becomes larger and larger , as the seed bearers becoming isolated .
iv. It is difficult to maintain a working balance in the face of yield (as per prescription) removal and the progress of regeneration.
v. On steeply sloping hillsides, it becomes difficult to protect the regeneration from the sliding timber.
vi. It is difficult to control a yield and regeneration, due to a large number of expanding gaps.
IRREGULAR SHELTERWOOD SYSTEM:-
Ø It is a system under which the crop to be regenerated is opened up in a irregular manner and the resulting forest is UNEVEN AGED.
Ø This system is not merely a modification of the uniform system but comprise between the uniform system and selection system.
Ø The term “Punjab shelterwood system” has also been applied to this system and there are no periodic blocks allotted to regeneration blocks and are adjusted at each revision of the working plan.
Ø The emphasis is on retaining a superior stems for putting on increment. Fellings are concentrated on defective trees. This system does not appear at present for Pakistan conditions. This avoids unnecessary sacrifice of the immature crop.
Ø It differs from the uniform system on the following two points.
i. It provides for both the retention of groups of pole size and also immature trees, to form a part of future crop.
ii. It provides for adaptation of selection system principles on steep and rugged terrain.
EXAMPLES
- Deodar forest J&K, HP, UP hills are generally worked under this system.
- The Chir pine forest of J&K , HP, UP hills
- The ever green and semi ever green tropical rain forests of Hassam and Andaman islands.
ADVANTAGES OF IRREGULAR SHELTERWOOD SYSTEM:-
i. Time is saved in the establishment of regeneration the young crop is between 40-50 years old when the rotation ends.
ii. This system is a fairly elastic one, it gives a free hand to the forest manager and is modified to suit local conditions.
iii. The adequate protective measures are available against wind and snow damage by individual stem and the production of uneven aged crop.
iv. Provision for an enhancement of increment on the best growing individuals.
v. The long period and a continuous opening help prevention of soil exposure and allow regeneration to come up adequately.
DISADVANTAGES OF IRREGULAR SHELTERWOOD SYSTEM:-
i. This system favours the growth of shade bearers as against light demanding species.
ii. The felling and logging is unpopular with the labourers as often carried out in very dense and wet under growth.
iii. The young crop is kept under the cover of over wood for a good number of years, the enhanced increment is nullified.
iv. Considerable damage is caused to the young crop during felling and extraction.
v. Supervision and control is difficult as a large area is brought under regeneration simultaneously adds confusion.
vi. A consider skill is required to forest manager to treat a forest under this system.
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Naeem Javid Muhammad Hassani is working as Conservator of Forests in Balochistan Forest & Wildlife Department (BFWD). He is the CEO of Tech Urdu (techurdu.net) Forestrypedia (forestrypedia.com), All Pak Notifications (allpaknotifications.com), Essayspedia, etc & their YouTube Channels). He is an Environmentalist, Blogger, YouTuber, Developer & Vlogger.