Forestry & Forest Sciences · Silviculture · also Regeneration Methods, Silviculture II, Silvicultural Systems and Management
The planned sequences of regeneration felling and tending that produce a forest of a particular form: clear felling, shelterwood, selection, coppice and their variants and conversions.
In the exams: IFoS Forestry Paper I Section A (clear felling, uniform shelterwood, selection, coppice and conversion systems); ICAR AICE-JRF 59 Unit 2 (high forest and coppice systems); SAF Certified Forester (silviculture)
A silvicultural system is the planned programme by which the trees of a forest are tended, harvested and replaced, so that the forest takes on a particular, recognisable form. R. S. Troup's classic definition calls it the process by which the crops constituting a forest are tended, removed and replaced by new crops, resulting in the production of woods of a distinctive form. The system is chosen once and then governs decades of work: where and how much is felled each year, how the next crop arises, what the stand looks like at every stage, and what goods and services the forest can supply.
The subject sits between silviculture principles (how trees regenerate and grow) and forest management (how much to cut and when). A forester who understands the systems can read a forest: a block of even-aged teak in rows tells of clear felling and planting; a mixed stand of fir with trees of every size tells of selection felling; sal stools sprouting multiple shoots tell of coppice. The same knowledge lets a forester choose a system for a new objective, such as soil protection on a steep slope or habitat for a threatened species, and plan the conversion of a forest from one form to another.
The subject is examined in three main ways. The UPSC Indian Forest Service Forestry optional and state forest service papers ask for descriptive answers on clear felling, the shelterwood systems, selection, coppice and conversion, usually with Indian examples and a comparison of advantages and drawbacks. ICAR's postgraduate and research-fellowship entrance papers ask recall and short-reasoning questions on the same systems and on terms such as periodic block, regeneration period and felling cycle. Professional credentials such as the Society of American Foresters' Certified Forester examination ask about even-aged and uneven-aged regeneration methods, seed-tree and shelterwood cuts, group selection and retention harvesting. This manual covers all three, with examples from temperate, subtropical and tropical forests, and states where terms or practice differ between countries.
Every silvicultural system answers four questions. First, how is the old crop removed: all at once, in a series of fellings, or tree by tree? Second, how does the new crop arise: from seed falling naturally, from planting or sowing, or from shoots of cut stumps and roots? Third, how are the fellings arranged in space and time: concentrated in one part of the forest, or spread over the whole area? Fourth, what form does the resulting crop take: even-aged, where all trees are of nearly the same age, or uneven-aged, where trees of many ages grow together?
A few terms recur throughout the subject. The rotation is the planned number of years between the formation of a crop and its final felling. The regeneration period is the time taken to establish the new crop on a given area, from the first regeneration felling to the final removal of the old crop. A regeneration felling is any felling made to start or help the new crop; a tending operation (weeding, cleaning, thinning) improves the crop between regeneration and harvest. High forest is forest grown mainly from seed and normally managed on long rotations; coppice is forest grown from stool shoots or root suckers and normally managed on short rotations. An even-aged crop is one in which the difference in age between trees is small relative to the rotation, commonly taken as not more than about a quarter of the rotation, though textbooks differ on the exact limit.
The classification most used in South Asian and British teaching follows Troup's book Silvicultural Systems. It divides systems into three groups.
High forest systems produce crops of seedling origin. They include the clear-felling systems, in which the whole crop on an area is removed in one operation; the shelterwood systems, in which the old crop is removed in a series of fellings over a regeneration period so that the young crop starts under partial shelter (the uniform, group, irregular, strip and wedge systems); and the selection systems, in which single trees or small groups are removed throughout the forest, so that regeneration is continuous and the crop is uneven-aged (the selection and group selection systems).
Coppice systems produce crops mainly of vegetative origin: simple coppice, coppice with standards, coppice of two rotations, coppice selection and the pollard system.
Accessory systems are those that do not fit neatly into the other groups or that are applied for a period to change a forest's condition: two-storied high forest, high forest with reserves, and, in Indian practice, improvement fellings and the selection-cum-improvement system. Conversion, the change of a forest from one system to another, is treated separately because it is a process rather than a stable form.
Indian textbooks also group high forest systems by how concentrated the regeneration is. In systems of concentrated regeneration (clear felling and the uniform system) regeneration is confined to a definite part of the forest at any time. In systems of spread regeneration (selection) it occurs over the whole forest at once. The group and irregular shelterwood systems lie between.
North American teaching, reflected in the Society of American Foresters' terminology, groups regeneration methods into even-aged methods (clearcutting, seed-tree and shelterwood), two-aged methods (clearcutting, seed-tree or shelterwood with reserves, where some trees are kept through the next rotation) and uneven-aged methods (single-tree selection and group selection). Coppice methods are listed separately. European writers often contrast age-class forest (Altersklassenwald), managed by clear felling or shelterwood, with continuous-cover or close-to-nature forest, managed by selection and target-diameter harvesting. These schemes describe the same practices with different emphasis; a student should be able to translate between them, for example recognising that the American seed-tree method is the European clear felling with seed bearers, and that two-aged management is close to Troup's high forest with reserves.
Systems can also be classified by how regeneration is obtained. Natural regeneration relies on seed from the old crop or neighbouring stands, or on advance growth already on the ground. Artificial regeneration uses sowing or planting. Vegetative regeneration uses coppice shoots or root suckers. Most systems can be run with any of these, though some, such as the uniform and selection systems, are designed around natural regeneration.
In the clear-felling system the whole crop on an area, the coupe, is removed in a single felling, and a new even-aged crop is raised on the cleared ground. In its commonest modern form the new crop is planted or sown, so the system is often called clear felling with artificial regeneration. Most industrial plantations of teak, eucalypts, pines, poplars and acacias in the tropics, and of spruces and pines in temperate and boreal regions, are managed this way.
Where the forest is in a normal state, with age classes equally represented, the annual coupe is found by dividing the area by the rotation. A working circle of 1,200 hectares of teak on a 60-year rotation has an annual coupe of 1,200 ÷ 60 = 20 hectares. In practice coupes vary with markets and age-class imbalances, and are regulated by the working plan.
The main advantages are simplicity of planning and supervision, concentration of felling and extraction (which lowers cost and suits mechanisation), the chance to introduce improved planting stock or a different species, and uniform even-aged crops that are easy to tend, thin and measure. The disadvantages follow from exposing the site: risk of soil erosion and nutrient loss on slopes, a flush of weeds, frost or drought damage to young plants in the open, loss of habitat and landscape value, and, where natural regeneration is attempted, dependence on a good seed year. Large clear fellings are restricted by law or certification standards in many countries, which set maximum coupe sizes, retention requirements or adjacency rules.
Natural regeneration after clear felling can come from four sources. Seed from the adjoining uncut stand can reach the coupe if the cleared area is narrow, which leads to the strip systems below. Seed from a few seed bearers left on the coupe gives the seed-tree method: the stand is clear-felled except for a small number of well-formed, wind-firm, seed-producing trees left scattered over the area, and these are removed once the new crop is established. Seed already on the ground, or held in closed cones on the felled trees, can be released by felling and site preparation; serotinous pines such as lodgepole pine and jack pine regenerate in this way after fire or after slash is scattered. Advance growth, seedlings already established under the old canopy, can be released by felling if it survives the logging.
The seed-tree method is widely used for light-demanding, wind-firm pines, for example Scots pine in Fennoscandia and several southern pines in the United States. It is unsuitable for shallow-rooted species, such as many spruces on wet soils, because isolated seed trees blow over.
Clear strip felling removes the crop in strips narrow enough to be seeded from the standing forest beside them. Strips are usually laid out across the direction of the prevailing wind so that seed is carried onto the cleared ground and so that the exposed edge of the standing crop faces away from storms. In the alternate-strip system every second strip is felled first; when those strips have regenerated, the remaining strips are felled and regenerated from the young crop's neighbours or by planting. In progressive strip felling, each new strip is cut next to the last regenerated one, so the felling front advances steadily across the compartment.
Patch clear felling removes small patches, often a hectare or less, scattered through the forest; it reduces visual impact and spreads risk but raises extraction cost.
Taungya, a Burmese word for hill cultivation, is a method of establishing plantations after clear felling in which farmers raise food crops between the rows of young trees for the first year or two in return for planting and weeding. It was developed in Burma in the nineteenth century under Dietrich Brandis for teak, and was later used widely in India, Indonesia, Nigeria and elsewhere. It is a means of regeneration within the clear-felling system, not a separate system, and is a forerunner of modern agroforestry.
In a shelterwood system the old crop is removed in a series of regeneration fellings spread over a regeneration period, so that the new crop starts under the partial shelter of the old trees. In the uniform system, also called the regular shelterwood system, these fellings open the canopy evenly over the whole regeneration area, and the result is an even-aged or nearly even-aged crop.
Troup named four kinds of felling. The preparatory felling, made a few years before regeneration is wanted, thins the stand moderately to let the crowns of future seed bearers develop, to speed the decay of raw humus and to make the trees wind-firm. It is omitted if the stand has already been well thinned. The seeding felling, timed for a good seed year, opens the canopy further and evenly, leaving the best seed bearers spaced so that seed falls over the whole area and the seedlings receive enough light to establish while still sheltered from frost, drought and weeds. Secondary fellings, one or more, gradually remove the overwood as the regeneration grows and needs more light. The final felling removes the last of the old crop once the new crop is fully established and no longer needs shelter. The regeneration period runs from the seeding felling to the final felling.
The uniform system suits species whose seedlings need some protection when young, such as many firs and beeches in Europe, and it was the standard system for European beech for much of the nineteenth and twentieth centuries. In South Asia it has been applied to chir pine in the subtropical Himalaya and to moist sal forests in northern India, where results depended heavily on fire control, weed control and seed years.
Because regeneration in the uniform system takes many years, the forest is divided into periodic blocks. A periodic block is the part of a working circle set aside to be regenerated, or otherwise treated, during a given period. The number of periodic blocks equals the rotation divided by the regeneration period. A forest of 1,200 hectares on a 120-year rotation with a 30-year regeneration period has 120 ÷ 30 = 4 periodic blocks of about 300 hectares each, numbered PB I to PB IV. PB I is under regeneration during the current period; PB IV holds the youngest crop.
Indian working plans distinguish several kinds of periodic block. A fixed or permanent periodic block keeps the same area through successive rotations. A revocable periodic block may be re-allotted when the working plan is revised. In a single periodic block arrangement only PB I is allotted and the rest of the forest is left unallotted. A floating periodic block is not fixed on the ground; areas ready for regeneration are chosen at each plan revision wherever they occur. Fixed blocks are simple but rigid; revocable and floating blocks allow the manager to regenerate the stands that are actually ready.
The main advantages of the uniform system are natural regeneration under shelter, protection of the site, even-aged crops that are easy to manage, and the chance to select seed bearers of good form. The drawbacks are dependence on seed years, damage to young regeneration during secondary and final fellings, exposure of seed bearers to windthrow, and the need for skilled marking and supervision.
In the group system, regeneration starts in scattered groups rather than evenly over the whole area. Fellings are made around existing groups of advance growth, or small gaps are opened where regeneration is wanted. These gaps are then enlarged by successive fellings around their edges until they merge and the whole area is regenerated. The resulting crop is even-aged in each group but slightly uneven-aged across the compartment, with a gentle undulation in canopy height that shows where the groups began.
The group system suits forests where advance growth occurs naturally in patches, or where some species need side shelter and others overhead light. Mixtures of a shade-tolerant and a light-demanding species can be handled by starting groups of the light demander in larger gaps. It is closely related to the German Femelschlag, a term that covers a range of group-based shelterwood methods; writers differ in where they draw the line between group shelterwood, irregular shelterwood and group selection.
The irregular shelterwood system has a long regeneration period, often a substantial fraction of the rotation, and regeneration fellings are made in a less regular pattern than in the uniform or group systems. The resulting crop is uneven-aged within a range of ages, irregular in structure and often mixed in species. It is a deliberate middle way between even-aged shelterwood and selection.
The system is used where continuous cover is valued for protection against erosion, avalanche or rockfall, where species with different light requirements are grown together, and where markets or terrain do not allow regular heavy fellings. Mountain forests of fir, spruce, beech and larch in central Europe have often been managed under irregular shelterwood, as have some Himalayan conifer forests. Its demands are high: the forester must judge each part of the stand separately, and yield regulation is more difficult than under a regular system.
In the shelterwood strip system the regeneration fellings are confined to a narrow strip at the edge of the stand. A strip passes through seeding, secondary and final fellings in turn, while the next strip begins its seeding felling, so the regeneration front advances across the compartment in a series of bands. The fellings usually move against the direction of the prevailing wind, so that the exposed edge of the old crop faces away from storms and the young crop is sheltered.
The strip system was developed in central Europe for wind-sensitive species, especially Norway spruce, on sites where large openings led to windthrow. Wagner's Blendersaumschlag, developed in Württemberg in southern Germany in the early twentieth century, is the best-known form; it used very narrow strips and close attention to the direction of fellings relative to the sun and the wind. The strip systems give good protection to the site and to regeneration but need careful layout of felling series and extraction routes, and a single compartment can take decades to traverse.
In the wedge system, associated with Eberhard in Bavaria, the regeneration front advances in the shape of a wedge, combining the protection of a strip edge with the ability to work the stand from more than one face. In the strip-and-group system, regeneration fellings start in groups inside the stand and along a strip at its edge at the same time, and the two advance until they meet.
These systems are now taught mainly for their principles rather than as prescriptions to copy. Each solves a particular problem: how to regenerate a wind-sensitive or frost-sensitive species without exposing large areas, how to work steep ground in small units, and how to combine natural regeneration with continuous protection. Modern continuous-cover forestry in Europe draws on the same ideas.
A comparison is often asked in examinations. Clear felling exposes the whole coupe at once. The uniform system shelters regeneration evenly but opens the whole periodic block within a few decades. The group and strip systems confine the openings, the group system scattering them and the strip system arranging them in a line. Irregular shelterwood stretches regeneration over a long period. Selection keeps the canopy almost closed everywhere and regenerates in small gaps all the time.
In the selection system, also called single-tree selection or the Plenter system after its German name, trees are removed individually or in very small groups over the whole forest, and regeneration takes place continuously in the gaps. The crop is uneven-aged: trees of all ages and sizes are mixed together on every hectare, and the forest never loses its canopy cover.
Felling is organised by the felling cycle, the interval between successive selection fellings on the same area. The forest is divided into annual coupes, so that a working circle of 1,500 hectares on a 15-year felling cycle has an annual coupe of 1,500 ÷ 15 = 100 hectares. In each coupe the forester marks trees for removal: trees that have reached the exploitable size (a diameter or girth set in the working plan as the size at which a tree is ready to harvest), and trees that are dead, diseased, badly formed or suppressing better neighbours. This marking is the heart of the system and needs skill.
In a balanced selection forest the number of trees falls steadily from small to large diameter classes, giving the reverse-J curve described by de Liocourt in 1898. The ratio between the numbers of trees in successive diameter classes, q, is roughly constant. If the largest class holds 10 trees per hectare and q = 1.4, the next classes downward hold about 14, 19.6, 27.4 and 38.4 trees. The BDq method of uneven-aged regulation, widely taught in North America, sets a target residual basal area (B), a maximum diameter (D) and the q ratio, and marks trees so that the stand after cutting matches the target curve.
Selection suits shade-tolerant species that can regenerate and grow under partial cover, such as silver fir, Norway spruce and European beech in the mountain forests of Switzerland, France and Slovenia, and sugar maple and eastern hemlock in North America. It is also chosen where continuous cover is essential: protection forests on steep slopes, catchments supplying water, avalanche paths, recreation areas and forests valued for landscape.
In India the selection system has been used in the hill conifer forests and in tropical moist forests, but the dominant tropical form is the selection-cum-improvement system. In each coupe, mature trees above the exploitable size are removed (the selection component) and dead, dying, defective and unwanted trees are removed or girdled to help the remaining crop (the improvement component), with gaps planted or enriched where natural regeneration fails. It has been applied to the tropical evergreen and semi-evergreen forests of the Western Ghats, the north-east and the Andamans.
Advantages of selection are continuous cover and soil protection, resistance to wind and snow damage in well-structured stands, high landscape and habitat value, and production of large timber. Disadvantages are the skill and supervision needed, higher extraction cost because felling is dispersed, damage to young trees when large trees are felled and extracted, difficulty in regulating yield and measuring growing stock, and poor results for light-demanding species, which do not regenerate well in small gaps.
In group selection, trees are removed in small groups rather than singly, creating gaps in which regeneration establishes. The gaps are large enough to admit more light than single-tree gaps, which lets moderately light-demanding species regenerate, but small enough that the forest remains uneven-aged at the scale of the compartment. In North American practice group openings are often described as up to about two tree heights across; definitions vary between countries and authors.
Group selection is distinguished from the group shelterwood system by its intent and time scale. In group shelterwood the gaps are enlarged until the whole area has been regenerated within a regeneration period, giving an even-aged crop at the compartment scale. In group selection each group is a separate unit regenerated on its own, and the forest is never wholly regenerated at once; groups of every age are present permanently. The distinction matters in examinations and in planning, because it determines whether yield is regulated by area and age class or by the felling cycle and a target structure.
Coppice is regeneration from shoots that grow from the stool, the stump left after a tree is cut, or from root suckers. The ability to coppice is a property of the species and declines with age and size of the stool. Most broadleaved species coppice well when young: sal, teak, Dalbergia sissoo, eucalypts, acacias, oaks, sweet chestnut, hazel, alders, willows and many others. Most conifers do not; coast redwood and Chinese fir are well-known exceptions. Some species, such as poplars, aspens and Dalbergia sissoo, also regenerate strongly from root suckers.
In simple coppice the whole crop is cut on a short rotation and regenerates from the stools. Rotations depend on the product: from a few years for willow biomass, through roughly 6 to 15 years for many fuelwood and pulpwood crops, to longer rotations for poles. Good practice is to cut low, close to the ground, with a clean sloping cut that sheds water, using a sharp tool that does not split the bark from the stool. Cutting is done in the dormant season or shortly before the growing season begins, so that the stool's food reserves feed vigorous shoots and the new shoots harden before frost or drought. Stools lose vigour after several cycles and some die, so gaps are filled by planting.
Eucalyptus plantations for pulpwood in India, Brazil and South Africa are often managed for one or two coppice rotations after the planted crop before being replanted with improved stock. Simple coppice is cheap and reliable, produces small material quickly and needs little skill, but it exhausts nutrients on short rotations, gives only small sizes, and exposes the site after each cut.
Coppice with standards is a two-storied system. The lower storey, the underwood or coppice, is cut on a short coppice rotation. The upper storey consists of standards, trees retained over several coppice rotations to produce large timber and seed. At each coppice felling some young stems are chosen as new standards, some existing standards are kept, and the oldest standards are felled. As a result the standards are of several age classes, each a multiple of the coppice rotation.
Take a coppice rotation of 20 years with standards kept for three coppice rotations. At each felling the standards present are about 20, 40 and 60 years old; the 60-year-old ones are felled, and a new set of 20-year-old stems is chosen. The number retained in each class is set so that, after mortality and thinning, enough reach the oldest class. The standards must be spaced so that their crowns do not suppress the coppice too much; too many standards reduce coppice yield.
The system was the classic management of oak and hazel woods in England and France, where it supplied both firewood and building timber, and it has been widely applied to dry deciduous forests in India, including drier sal and teak forests, where it supplies fuelwood and poles to local people while keeping some large trees for timber and seed.
In coppice of two rotations, a variant described by Troup, standards are retained for one extra coppice rotation only: at each felling all the old standards are removed and a fresh set is retained, so there is a single age class of standards. It is simpler than full coppice with standards.
In coppice selection, only shoots of exploitable size are cut from each stool at each felling, and smaller shoots are left. The stool always carries shoots of several ages, and the ground is never bare. It is used on steep slopes and in protection forests where clear coppice felling would expose the soil.
In the pollard system, trees are cut at a height of about two to three metres or more, above the reach of browsing animals, and new shoots grow from the top of the trunk. Pollarding is traditional for willows and poplars along rivers in Europe, and for fodder trees on farms and along roads in South Asia and Africa. Lopping, the cutting of branches from standing trees for fodder or fuel, is related but does not remove the crown entirely. Pollards often become very old and develop hollows, which gives them high habitat value.
Two-storied high forest has two distinct canopy layers, usually of different species and ages, managed together. The commonest way to create it is underplanting: a light-demanding species with a thin crown, such as oak, larch or Scots pine, is grown to mid-rotation and thinned, and a shade-tolerant species, such as beech, western red cedar or silver fir, is planted beneath it. The lower storey keeps the soil shaded, suppresses epicormic branching on the oak stems, improves litter and humus, and provides a second crop. The upper storey is felled at its rotation, and the lower storey may then be managed as the main crop or allowed to form a new two-storied stand.
The system raises the total productivity of a site and protects it, but it needs careful timing, because the upper storey must be open enough for the underplants to survive and the lower storey must not compete too strongly with it.
In high forest with reserves, a number of trees from the old crop are kept standing through the whole of the next rotation instead of being felled at the regeneration fellings. The reserves grow to very large sizes, supply seed, add structural diversity and habitat, and can command high prices for special timber. They are chosen for vigour, wind-firmness and good form. The system can be combined with clear felling (clear felling with reserves) or with shelterwood (shelterwood with reserves). In North American terminology the result is a two-aged stand. Too many reserves suppress the young crop beneath them; too few, or poorly chosen ones, blow over when isolated.
Some forests are too irregular or degraded for any regular system. In India these have often been worked under improvement fellings: fellings that remove dead, dying, diseased, malformed and unwanted trees, free promising young trees from competition and climbers, and so raise the quality and value of the crop without trying to impose a particular form. Improvement fellings are usually prescribed as a transitional measure until the forest can be brought under a regular system, and are often combined with selection as the selection-cum-improvement system described earlier.
Accessory systems also include the temporary regimes used during conversion. While a forest is being converted, for example from coppice to high forest, it is neither one nor the other, and the working plan prescribes a special conversion regime for the transition. Such regimes are discussed in the next chapter because they are defined by their purpose, which is change, rather than by a stable structure.
Conversion is the change of a forest from one silvicultural system to another. Common reasons are a change in objectives (from fuelwood to timber, or from timber to protection and biodiversity), a change in markets, the failure of the existing system to regenerate the forest, the introduction of a more productive species, and changes in law or certification. Conversion is a long process; it usually takes at least one rotation and often more, and the working plan must prescribe a conversion period, the time over which the change is to be made, and a special regime of fellings for that period.
The commonest conversion in South Asia and Europe has been from coppice to high forest. It can be done in three main ways. In conversion by planting, the coppice is clear-felled and the area planted with seedlings of the same or a different species. In conversion by storing, the coppice is left uncut beyond its normal rotation; the best shoot on each stool is retained and the rest removed (singling), and the stored stems are thinned and grown on as high forest; seedlings that arise from their seed form the next crop. In conversion through shelterwood, the stored or overgrown coppice is treated as a shelterwood, with seeding and secondary fellings to obtain seedling regeneration beneath it. Coppice with standards can be converted by allowing the underwood to grow on, retaining more standards and treating the whole stand as high forest. In northern India many sal coppice forests were converted to high forest during the twentieth century to produce larger timber.
High forest can be converted from one high-forest system to another. Converting even-aged forest to selection or continuous-cover forest, often called transformation in European writing, is done gradually: thinnings favour the development of crowns and stability, small gaps are opened to start regeneration, and over decades the stand is brought towards an uneven-aged structure. The process is slow and must avoid opening wind-sensitive stands too quickly. The reverse, converting selection forest to even-aged clear felling, is technically easy but often restricted by law or certification on protection and biodiversity grounds.
Irregular, degraded or mixed forests have been converted to plantations of valuable species, such as teak in central and southern India, by clear felling and planting. Such conversions raise timber yield but reduce species diversity and may harm local people's access to non-timber products; many forest policies now discourage converting natural forest to plantation.
Conversion of high forest to coppice is rare, because few large trees coppice reliably, but it occurs where fuelwood or biomass becomes the main objective and the species coppices well.
A conversion plan sets out the objective, the target system, the conversion period, the treatment of each part of the forest during the transition, and how yield is to be regulated while the forest is irregular. A simple calculation often required is the area to be treated each year. If 900 hectares of coppice are to be converted to high forest over a conversion period of 30 years by planting, about 900 ÷ 30 = 30 hectares must be converted each year. In practice areas are chosen by condition, with the poorest or most overmature stands converted first.
During conversion, yield usually falls, because the forester gives up short-term coppice yield to build growing stock. This loss must be accepted by the owner, and in public forests by local users who depended on the fuelwood and small poles. Successful conversions therefore depend as much on agreement with users and on protection from grazing and fire as on the silviculture itself.
The silvics of the main species is the first consideration. Light demanders, which need full or nearly full light to establish and grow, such as teak, most pines, larches, eucalypts and sal, regenerate best under clear felling, the seed-tree method or uniform shelterwood with fairly quick removal of the overwood. Shade bearers, which can establish and survive under cover, such as silver fir, beech, hemlock and many tropical understorey species, can be managed under selection, group selection or long-period shelterwood. The frequency of seed years matters: species with infrequent good seed years are awkward under systems that depend on a single seeding felling. Coppicing ability decides whether coppice systems are possible at all. Rooting habit decides wind-firmness and therefore how much the canopy can be opened at once.
The young stages matter most. Seedlings of many species are damaged by frost in open hollows, by drought on exposed ground or by weed competition, and need shelter for a few years; for such species a shelterwood system is safer than clear felling.
Site conditions can rule systems in or out. On steep slopes, shallow or erodible soils, avalanche paths and catchments, continuous cover is usually needed, pointing to selection, irregular shelterwood or coppice selection. Exposure to wind favours small openings arranged against the prevailing wind, or systems that keep the canopy closed. Frost hollows favour shelter. Wet sites with a high water table can become waterlogged after clear felling because evapotranspiration falls, which hinders regeneration. Fire-prone forests, such as chir pine and dry deciduous forests, need systems that allow controlled burning or fire protection and that do not leave heavy fuel loads under regeneration. Heavy grazing or browsing pressure may make natural regeneration under any system impossible without fencing or the cooperation of local people.
Fertility matters too. Short-rotation coppice removes nutrients frequently; on poor soils this may be unsustainable without fertiliser.
The owner's objectives decide what the forest should produce: large timber, poles, pulpwood, fuelwood, fodder, water, soil protection, wildlife habitat, recreation or carbon storage. Large timber points to long-rotation high forest; fuelwood and small poles to coppice; protection and landscape to continuous cover. Most public forests now have several objectives, and the system is chosen to give an acceptable balance.
Economics and administration complete the choice. Concentrated systems (clear felling, uniform) give cheaper harvesting and easier mechanisation; dispersed systems (selection) cost more to harvest and supervise. Systems that depend on skilled marking need trained staff. Local rights to fuelwood, fodder and grazing, markets and roads, the law and certification standards, and the risk tolerance of the owner all affect what is feasible. In examinations a choice of system should be justified under each heading: species, site, objectives, economics and administration, and protection.
Retention forestry, or variable retention harvesting, keeps selected parts of the original stand at the time of harvest and leaves them for at least the next rotation. The retained elements include live trees of various sizes, especially large old trees, standing dead trees (snags), fallen logs and other coarse woody debris, and patches of undisturbed vegetation and soil. The aim is ecological continuity: to carry organisms, structures and processes from the old forest into the new, to enrich the structure of the young stand, and to keep the landscape connected.
Retention can be dispersed, as single trees spread over the harvest area, or aggregated, as patches of intact forest. Aggregated retention protects interior conditions and is easier to harvest around; dispersed retention spreads structure over the whole area. The amount retained varies widely, from a few per cent of the original stand to more than half, depending on objectives, law and certification standards.
The approach was developed in the Pacific Northwest of North America in the late twentieth century, from research on how forests recover after natural disturbances such as fire and volcanic eruption, which leave many living and dead structures behind. It is now applied in boreal and temperate forests in North America, Fennoscandia, Australia and South America, and retention of trees and dead wood at harvest is required by several forest certification standards. Retention modifies other systems rather than replacing them; it is most often combined with clear felling.
Continuous-cover forestry (CCF) is management that maintains forest cover permanently and avoids clear felling. In Britain one widely used working definition excludes clear fells larger than about a quarter of a hectare. It includes selection, group selection, irregular shelterwood and other close-to-nature approaches. In German-speaking countries its roots lie in the Dauerwald (permanent forest) idea put forward by Alfred Möller in the 1920s, and the Pro Silva association, founded in Europe in 1989, promotes it today.
CCF management usually relies on natural regeneration, mixed species, structural diversity, and target-diameter harvesting, in which individual trees are felled when they reach a diameter chosen for their species and site rather than at a fixed rotation age. Thinning focuses on selected crop trees of good quality and stability. Stands are often managed towards an irregular or uneven-aged structure.
The claimed benefits of retention and continuous-cover forestry include better protection of soil and water, continuity of habitat for forest species, landscape quality, reduced risk from some disturbances in well-structured stands, and spreading of income over time. They also have limits. Retained trees isolated in the open may blow over. Light-demanding species regenerate poorly under continuous cover. Harvesting and marking cost more and need more skill. Growth and yield models built for even-aged stands do not apply directly. The economic and ecological results depend strongly on the site, species and management, and the evidence for some claimed benefits, such as greater resilience to storms or pests in all conditions, is mixed. A forester should present these systems as tools for particular objectives rather than as universally superior.
In boreal forests of Canada, Fennoscandia and Russia, clear felling with planting or natural regeneration is the dominant system, often with seed trees for Scots pine and with retention of trees and dead wood under certification. Shelterwood is used where seedlings need protection. In the temperate forests of central Europe, beech, fir and spruce have been managed under uniform, group, strip and irregular shelterwood and under selection, and there has been a broad move towards continuous-cover and mixed forests since the late twentieth century. In the Pacific Northwest, clear felling of Douglas-fir with planting became standard in the twentieth century, modified since the 1990s by retention.
In the Himalayan temperate conifer forests of deodar, blue pine, silver fir and spruce, Indian working plans have prescribed shelterwood systems of various kinds and selection fellings, with heavy emphasis on protection of steep slopes and catchments. Since the ban on green felling in several Himalayan states, commercial regeneration fellings have largely ceased in several of these forests, and management focuses on protection and salvage.
The subtropical pine forests of the Himalaya are dominated by chir pine, a light-demanding, fire-resistant species. They have been managed under the uniform shelterwood system, with seed bearers left at the seeding felling, protection from fire for some years after regeneration and controlled burning later to reduce fuel. The forests are also tapped for resin, which affects tree selection and rotation. In other subtropical regions, such as southern China and the south-eastern United States, plantations of pines, Chinese fir and eucalypts are generally managed by clear felling and planting, with coppice used for Chinese fir and eucalypts. Southern pines in the United States are also regenerated by seed-tree and shelterwood methods, often with prescribed fire.
Humid tropical forests are managed either by monocyclic systems, in which all merchantable trees are harvested in one operation and the next harvest comes after a full rotation, or by polycyclic systems, in which selected trees above a diameter limit are cut on a cutting cycle shorter than the rotation, relying on the growth of remaining trees for the next harvest.
The Malayan Uniform System, introduced in lowland dipterocarp forest in Malaysia after the Second World War, was monocyclic: mature trees were felled in one operation, unwanted trees were poisoned or girdled, and the existing seedlings of dipterocarps were released to form a new, roughly even-aged crop. The Tropical Shelterwood System of Nigeria used a series of canopy openings and climber cutting to induce regeneration before felling. Both were largely abandoned as forests were converted to agriculture and as polycyclic systems became preferred. Malaysia's Selective Management System and Indonesia's selective cutting and planting system are polycyclic, with minimum felling diameters and cutting cycles set in national rules; the exact limits differ by country and forest type and have changed over time. Reduced-impact logging, with pre-harvest inventory, directional felling, planned skid trails and climber cutting, lowers damage to the remaining stand and is now standard guidance. Enrichment planting in lines or gaps adds valuable species where natural regeneration is poor. In India, tropical evergreen forests have been worked under the selection-cum-improvement system, and teak and other valuable species have been raised in plantations by clear felling and planting.
Dry tropical forests are dominated by species that coppice well and are under heavy pressure for fuelwood, fodder, grazing and small timber. Coppice and coppice with standards have been the main systems in the dry deciduous forests of India, Africa and Latin America, often combined with fire protection and control of grazing. Dry teak and drier sal forests in India have commonly been worked under coppice with standards. Thorn forests and degraded dry forests are often managed for protection and rehabilitation rather than timber.
Mangroves need systems that keep the shoreline protected and allow regeneration from the abundant propagules. The Matang mangroves in Malaysia are a well-known example of planned management by clear felling in small coupes, with thinnings and a rotation of about 30 years, and with replanting where natural regeneration fails. Elsewhere, including the Sundarbans of India and Bangladesh, selection-type fellings have been used, and protection now dominates management.
A student should be able to describe each system in Troup's classification, draw the sequence of fellings for clear felling, uniform shelterwood, selection and coppice with standards, and define rotation, regeneration period, periodic block, felling cycle and exploitable size precisely. In the field, the student should learn to recognise a system from the structure of a stand: even-aged rows, multi-aged mixtures, stools with several shoots, scattered seed bearers or retained trees. Practise the simple arithmetic of coupes, periodic blocks and conversion areas, and be ready to justify the choice of system for a named species and site under the headings of species, site, objectives, economics and protection.
A range or divisional officer five years into service applies the system prescribed in the working plan: laying out and demarcating coupes, marking seed bearers and trees for removal in shelterwood and selection fellings, choosing standards in coppice with standards, timing coppice cuts, supervising extraction to protect regeneration, and recording whether regeneration has succeeded. When regeneration fails, the officer must diagnose why (seed year, fire, grazing, weeds, felling damage) and recommend changes. In plantation companies the same forester manages clear felling and replanting or coppice rotations of eucalypts and other short-rotation crops.
A senior forester with twenty-five years' experience writes or approves working plans: deciding which system each working circle will follow, the rotation, regeneration period and felling cycle, whether a forest should be converted, and how retention or continuous cover will meet certification and biodiversity requirements. The decisions involve local communities' rights, markets, budgets and law. The senior forester judges proposals from staff and contractors, explains the long-term consequences of a system to ministers, boards and community committees, and reviews whether past prescriptions achieved their aims.
A researcher with long field experience studies how silvicultural systems affect regeneration, growth, biodiversity, carbon, soil and water, and resilience to wind, fire, pests and climate change. Typical work includes long-term experiments comparing clear felling, shelterwood, selection and retention; modelling uneven-aged stand dynamics and yield; testing conversion methods; and evaluating tropical selective logging rules. Such a researcher advises governments and certification bodies on standards and judges which claims about systems are supported by evidence and which are not.
This manual describes systems and their principles; it does not give stand-level marking rules, regeneration stocking standards or felling-cycle and diameter-limit values for particular countries, because these are set in national rules and working plans and change over time. Detailed silviculture of individual species belongs to the silviculture-of-species subject, and thinning regimes to stand-tending-thinning. Yield regulation under each system (area, volume and structure methods) is treated only briefly here and fully in forest-management-yield-regulation. The history of each system in particular Indian states and the outcomes of named working plans are not covered. Evidence comparing systems for carbon, biodiversity and climate resilience is summarised only in general terms because results differ widely by site and study.
Original practice questions written to the syllabus and pattern of the exams named in each question's examTags. They are not past papers and do not reproduce any board's questions.
These notes are free to read here, with no account.
What the Laisha app adds:
Free for ten days, then a subscription. We would rather write that here than have you find it later.