Silvicultural systems
Silvicultural systems explained: clear felling, shelterwood (uniform, group, irregular), selection and coppice, how each works and when to use it.
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A forest that supplies timber for centuries has to be harvested in a way that lets it grow back. A silvicultural system is the planned process by which the trees of a forest are tended, harvested and replaced, producing a forest of a distinctive form. The definition goes back to R. S. Troup's classic 1928 text on silvicultural systems, written from experience in Indian and British forests. The system decides whether the forest will be even-aged or uneven-aged, whether new trees come from seed or from shoots, and how open the canopy will be after each harvest.
Choosing a system depends on the species' light requirement and regeneration habit, the site and its risks (erosion, frost, fire, weeds), and the management goals: timber, fuelwood, fodder, watershed protection or biodiversity.
High forest systems
High forest systems regenerate the crop mainly from seed, whether natural or planted, and grow it on relatively long rotations to produce large timber.
Clear felling system
The whole crop on an area, called a coupe, is felled in one operation and then regenerated, usually by planting or sowing, sometimes from natural seed. The result is an even-aged stand.
- Advantages: it is simple to plan, harvest and supervise; harvesting is cheap; fast-growing species and improved planting stock can be introduced; and light-demanding species do well.
- Disadvantages: the soil is exposed to erosion and weeds, the landscape and wildlife habitat are disrupted, and the site faces frost and drought.
Teak and eucalyptus plantations in India are usually managed by clear felling with artificial regeneration. Variants such as the clear strip system and alternate strip system fell narrow strips so that the neighbouring stand provides seed and shelter.
Shelterwood systems
The old crop is removed in a series of regeneration fellings spread over a regeneration period. Young trees establish under the shelter of the remaining canopy, which protects them from frost, sun and weeds. A typical sequence has four stages:
- A preparatory felling opens the canopy slightly, to encourage seed production and prepare the seedbed.
- A seeding felling opens the canopy further in a good seed year, leaving seed bearers evenly spaced.
- Secondary fellings gradually remove more overwood as the seedlings need more light.
- A final felling removes the last old trees once regeneration is secure.
There are several variants:
- The uniform system opens the canopy evenly across the compartment. It has been used for sal (Shorea robusta) and chir pine in northern India.
- The group system opens gaps around existing groups of seedlings and enlarges them over time.
- The Indian irregular shelterwood system has a long and flexible regeneration period that produces a somewhat uneven-aged crop. It has been used for Himalayan conifers such as deodar, blue pine and spruce.
Selection system
Selection fellings remove single trees or small groups scattered through the forest, usually those above an exploitable girth, along with defective trees. The forest stays uneven-aged, with trees of all ages and sizes mixed together on every hectare, and is never cleared.
The forest is divided into blocks that are worked in turn. Each block is revisited after a felling cycle, often 10 to 30 years.
- Advantages: there is continuous cover, the best soil protection and the most natural forest structure, with high aesthetic and biodiversity value. It suits shade-tolerant species and steep or fragile sites.
- Disadvantages: it is complex to plan and supervise, harvesting is expensive and can damage remaining trees, and light-demanding species may fail to regenerate.
Selection working has been used in Himalayan fir and spruce, in hill forests on steep slopes, and in tropical evergreen and moist deciduous forests, often in modified forms.
Coppice systems
Coppice systems rely on vegetative regeneration: shoots from cut stumps (stools), or root suckers. Rotations are short, and the systems produce small timber, fuelwood, poles and fodder. Only species that coppice well are suitable. Examples are eucalyptus, sal, teak (when young), Acacia, Prosopis, Dalbergia sissoo, Albizia and many fuelwood species.
- Simple coppice: the whole crop is clear-felled at short intervals, often 8–15 years. Stumps are cut low and sloping so water runs off. Eucalyptus pulpwood plantations are typically coppiced for two or three rotations before replanting.
- Coppice with standards: a two-storied forest in which a lower coppice layer is cut on a short rotation, while selected standards, usually of seedling origin, are kept through several coppice rotations to produce larger timber. It was used in sal forests of Uttar Pradesh and in European oak.
- Coppice with reserves: some trees are kept at each felling to protect the soil or provide seed, without the formal standards structure.
- Pollarding: stems are cut 2–3 m above ground, out of reach of browsing animals. It is common for fodder trees such as Ficus, Grewia and willow.
Stools gradually lose vigour, so coppice crops are eventually replanted.
Area allocation
Even-aged systems divide a forest into annual coupes, so that the same area is harvested each year.
Planning annual coupes
A teak working circle of 1,800 ha is managed by clear felling on a 60-year rotation. By the area method, the annual coupe is 1,800 ⁄ 60 = 30 ha. A coppice fuelwood working circle of 600 ha on a 12-year rotation would have coupes of 600 ⁄ 12 = 50 ha. In a selection forest with a 20-year felling cycle, the forest is divided into 20 blocks, and one block is worked each year.
Choosing a system
| Factor | Favours |
|---|---|
| Light-demanding species (teak, chir, eucalyptus) | Clear felling or uniform shelterwood |
| Shade-tolerant species (fir, spruce, many evergreens) | Selection or group systems |
| Steep slopes, watersheds | Selection or shelterwood; continuous cover |
| Fuelwood and pole demand near villages | Coppice systems |
| Plantations of improved stock | Clear felling with planting |
India's National Forest Policy of 1988 gave priority to conservation and the needs of local communities, which led to much less commercial clear felling of natural forests. Today systems are increasingly chosen for multiple goals, including carbon storage and biodiversity.
Key points
- A silvicultural system is the planned process of tending, harvesting and regenerating a forest (Troup, 1928).
- High forest systems use seed: clear felling (even-aged), shelterwood (regeneration fellings under a canopy: uniform, group, Indian irregular) and selection (single trees, uneven-aged).
- Shelterwood stages are preparatory, seeding, secondary and final fellings.
- Coppice systems use shoots: simple coppice, coppice with standards, coppice with reserves and pollarding.
- Selection gives continuous cover and suits shade-tolerant species and fragile sites; clear felling suits light-demanders and plantations.
- Annual coupe = area ⁄ rotation (area method).
What the exams ask
- Classify silvicultural systems and define each briefly.
- Describe the stages of the shelterwood system.
- Compare the clear felling and selection systems.
- Explain coppice with standards and pollarding.
- Calculate annual coupe area.
Described in general terms: the kind of examination, not a past paper. Laisha never reproduces exam questions.
Questions people ask
Is clear felling always bad for forests?
Not necessarily. For light-demanding species and plantations it can be ecologically appropriate, and it imitates natural disturbances such as fire. Problems arise when coupes are too large, slopes are steep, regeneration fails or natural forests are converted. Coupe size, buffer strips and retention of some trees reduce the impact.
Why does eucalyptus coppice so well?
Eucalyptus has dormant buds under the bark of the stump and lignotubers (woody swellings at the base) that store food and buds. After felling, many shoots sprout, and two or three are kept. This allows several harvests from one planting.
What is the difference between a felling cycle and a rotation?
A rotation is the planned age at which an even-aged crop is harvested. A felling cycle is the interval between successive selection fellings in the same part of an uneven-aged forest. Selection forests have felling cycles, but no single rotation.
Sources
- Troup, R. S. Silvicultural Systems, 2nd edition, edited by E. W. Jones. Oxford University Press, 1952.
- Matthews, J. D. Silvicultural Systems. Clarendon Press, Oxford, 1989.
- Khanna, L. S. Principles and Practice of Silviculture. Khanna Bandhu, Dehradun, revised edition 2015.
- Nyland, R. D. Silviculture: Concepts and Applications, 3rd edition. Waveland Press, 2016.
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