Tools and Resources
Silviculture is the care and cultivation of woodlands (as opposed to arboriculture which is the care and cultivation of individual trees). There is a wide range of different silvicultural systems which are, broadly speaking, management prescriptions for particular types and areas of woodland. Forestry, at its most basic level, is the interaction between tree species, site characteristics and a silvicultural system. There are a number of different silvicultural systems described here:
There are many variations on silvicultural systems which are usually tailored to a site and the tree species to be grown. There are, however, categories (which have broad similarities) and a number of variables, which allow you to describe a system in detail.
There are a number of silviculture systems which include a proportion of coppice
Coppicing consists of cutting back the stem of certain broadleaf species to near the ground and allowing the growth of multiple stems from the stool. Not all species coppice, and some coppice unreliably. Coniferous species do not coppice
| Silvicultural system | Rotation length | Regeneration method | Thinning | Felling | Notes |
|---|---|---|---|---|---|
| Short rotation coppice (SRC) | 3 years | Coppice regrowth until around year 20; then replant | None | Field by field. | Usually grown as an agricultural crop rather than forestry |
| Coppice | 12 – 20 years | Coppice regrowth | None | Clear fell to stool at end of rotation. Usually a small area felled annually. | Only used with specific broadleaved species. Coniferous species do not coppice, and some broadleaves coppice unreliably |
| Coppice selection system | 12 – 20 years | Coppice regrowth | Weaker or undesirable stems thinned (e.g. coppice restricted to 5 stems per stool) | Clear fell to stool at end of rotation. Usually a small area felled annually. | Only used with specific broadleaved species. Coniferous species do not coppice, and some broadleaves coppice unreliably |
| A proportion of coppice stems cut at each rotation allowing the remaining stems to grow on | Ongoing cutting of growth. | ||||
| Coppice with standards | 12-20 years for coppice. Full high forest rotation for standards (minimum 40-60 years, may be longer than 160 years for slow growing species such as oak). | A combination of coppice under layer and single large trees allowed to grow on for seed and/or a timber crop | Thinning may be carried out by coppicing poorer trees and allowing standards to grow on | Coppice felled on a regular rotation with standards allowed to grow on a much longer rotation. | Only used with specific broadleaved species. Coniferous species do not coppice and some broadleaves coppice unreliably. Standards may be any forestry species |
| Short rotation forestry (SRF) | 15 – 20 years | Usually replanted | Usually none | Clear fell at the end of rotation. | Not a true coppice system as there is no initial cutback to produce multiple stems from the stool |
Conventional silviculture consisting of even aged stands of trees.
| Silvicultural system | Rotation length | Regeneration method | Thinning | Felling | Notes |
|---|---|---|---|---|---|
| Clear fell/clearcut | Depends on species; a minimum of 40-60 years, but may be longer than 160 years for slow growing species such as oak | Usually planting on larger areas, may use natural regeneration from seed on smaller areas | May take place throughout the lifetime of the crop. Thinning may be systematic (e.g., every third tree) or selective (e.g., the 20% of trees with the poorest form) | The crop is cleared by a single felling at the end of the rotation | There is a grey area between a heavy thinning of a forest stand, and some of the systematic regeneration methods described below |
Conventional forestry with irregular felling patterns.
| Silvicultural system | Notes |
|---|---|
| Selection systems | Selection systems are different to other silvicultural systems because they do not restrict felling and regeneration to a specific area. Felling is carried out throughout the whole woodland area based on tree form, age and size. This method leads to a woodland with an uneven age structure which can closely resemble natural woodland. This method regulates yield throughout the woodland, while maintaining a continuous canopy cover and reducing environmental impact on specific locations. While a standard selection system removes single trees, a group selection system will remove trees from small areas, this is commonly used to favour light-demanding species which would otherwise struggle to regenerate |
Conventional forestry with different felling patterns performed at regular intervals
| Silvicultural system | Rotation length | Regeneration method | Thinning | Felling | Notes |
|---|---|---|---|---|---|
| Uniform system | As with a Clear Fell system, except the old crop is cleared by two or more successive regeneration fellings | May be planted on larger areas or if the species composition of the wood is being changed. Otherwise, will often use natural regeneration from seed (“Shelterwood” systems) | May take place throughout the lifetime of the crop. Thinning may be systematic (e.g., every third tree) or selective (e.g., the 20% of trees with the poorest form) | Even opening of the canopy (e.g., fell every other tree) | Similar to a progressively heavy thinning. Allows the natural regeneration of the woodland from seed from the remaining trees (rather than planting) where possible |
| Group system | Opening of the canopy in scattered gaps | Gaps are expanded in successive fellings. Allows the natural regeneration of the woodland from seed from the remaining trees (rather than planting) where possible | |||
| Irregular shelterwood system | Opening of the canopy irregular and gradual | A system of successive regeneration fellings similar to a group system with particular emphasis on the sustained output of good quality timber, and regeneration of native species mixtures | |||
| Strip and wedge system | A systematic series of fellings in narrow strips (often towards the prevailing wind direction) | Reduces the risk of wind damage to a crop, and allows natural regeneration |
In many cases, one of the primary objectives of forestry is to provide a sustained yield of timber. The yield of a woodland is determined by its area, the species planted, site conditions, rotation length and silvicultural system. In the UK yield is usually described in terms of “yield class”; this is a measurement of increment (the amount of solid stem wood added to an area of woodland) in cubic meters per hectare per year (m3/ha/yr) expressed in intervals of 2 (i.e. 4, 6, 8 etc.)
Unfortunately, trees don’t grow in an easy to measure shape, or at a constant rate over their lifespan. Ideally to estimate the yield class you need to measure the standing volume of a woodland (the amount of timber per ha) on more than one occasion, to establish the rate of growth. However, the yield class can be estimated for a species by measuring the top height of the stand of trees and using this measurement and the age of the tree to look up the yield class on a table. These tables are currently being revised by the Forestry Commission, and we expect them to be published soon. Please note that 1) these tables are only available for commercially grown species (mainly conifers) and 2) They only include stem wood, and may underestimate material available from trees with substantial branches. Once you know the Yield Class, you will then be able to predict the standing volume in later years and determine what the yield of the woodland is likely to be in the future.
You can assess the standing volume of timber by using the Estimating woodfuel potential – Measurement protocol devised by Forest Research
Once you know the current standing volume of timber and yield class, it is relatively straightforward to determine how much timber will result from a felling (based on the silvicultural system.)
To maintain a sustainable yield from a block of woodland, you either need to make sure that you are felling less than the annual increment (in the case of uneven aged stands and coppice) or that you are replanting or allowing the site to regenerate effectively after an even aged management felling or clear fell.
Remember that fuel is only one of a number of different product streams to come from forestry. You should find that higher quality of timber will fetch a better price when sold into different markets (such as building timber, furniture making etc.)
This can be an extremely complicated subject and you may need professional support for this stage of woodland management. If you need further information, the Forestry Commission publish the Forest Mensuration Handbook which covers the whole subject of timber measurement in more detail. The current edition was published in 2006, but the 1975 edition can be downloaded as a PDF.