Pruning for Clearwood Production
Note Number: AG0773
This Agriculture Note describes pruning of plantations for clearwood production.
What is it?
Pruning is a critical part of managing plantations for valuable clearwood, which has no knots. Knots degrade the strength and appearance of timber, and therefore its value. Pruning allows growers to manipulate tree development in order to produce clearwood sawlogs (see Agriculture Note AG0818: Growing trees for sawlogs),
Pruning requires considerable work spread over a several years. Pruning must be done in conjunction with appropriate thinning (see Agriculture Note AG0775: Thinning for sawlog production).
Pruning is often divided into form pruning and clear pruning.
Form pruning is the early removal of secondary stems and forks to ensure that trees have single straight stems, which are essential for good sawmilling and thus log value.
Clear (or stem or clearwood) pruning is the removal of tree branches in order to confine branch knots to the cores of logs. After pruning, as the trees grow and the stems thicken, clearwood is laid down over the pruned stem. The result is high quality clearwood logs containing narrow cores of low quality knotty wood (Figure 1).
How does it work?
- Ensures a final crop of clearwood sawlogs without excessive work, by timely pruning of an appropriate number of trees – often annual winter-early spring pruning of initially 400-500 trees/ha and less over time, as the stand is thinned to final stocking (annual pruning means several visits but relatively small branches and easy work).
- Allows greatly reduced rotation lengths, by allowing early thinning without excessive branch development.
- Promotes single straight stems, by removing secondary stems (where there are multiple stems, double leaders or forks) and keeping only the best stem, enabling it to grow straight up rather than bending out and away from secondary stems under competition for light.
- Results in clearwood logs of appropriate length, by clearing stems of branches to an appropriate height (often 6.5 m, possibly higher on very good sites or lower with more difficult sites or species).
- Ensures high recovery of sawn clearwood, by promoting narrow uniform defect cores, by way of removing branches when stems are of appropriate diameter and leaving minimal branch stubs.
- Promotes rapid healing and limits infection and decay, by pruning on time (ideally annually in winter-early spring), making clean cuts close to the stem without tearing bark, bruising the stem or damaging the “branch collar” (figure 2), and leaving only small clean wounds.
- Prevents defects caused by pruning of dead branches (Figure 3).
- Prevents large penalties to tree growth, by pruning on time (ideally annually) and not removing large proportions of foliage.
Simple pruning program (an example)
Timing and tree selection
- Before trees are 2 m tall, thoroughly check the plantation and form prune (this is quick and easy at this stage) where necessary, to ensure at least 400 trees/ha are vigorous, well formed and fairly evenly spaced (potential sawlogs).
- After that, prune all sawlog trees, except culls or thinnings, every winter-early spring until stems are clear to 6.5 m (easy form pruning is soon overtaken by clear pruning, but higher form pruning must also be continued to at least 6.5 m).
- Remove any forks (remember to look up!) to produce single straight stems (form pruning).
- Remove all branches attached below 6.5 m to stem 8 to 10 cm or more in diameter (clear pruning).
- Remove any other branches below 6.5 m that are heavy (thicker than 2.5 cm), dead or twisted around the stem.
Choice of equipment depends on the size of the job and the labour available. Good quality tools are usually well worth the expense. The most suitable pruning tools will cut very cleanly and close to the stem. Never prune with axes or machetes.
Good quality secateurs are essential for quick, clean, early form pruning.
Loppers (Figure 1) are the most used clear pruning tool and cut very cleanly. There are two basic styles: “bypass” (blade slides past opposing hook) and “anvil” (blade stops against opposing anvil). For forest pruning, either style should have some form of multi-pivot head for improved leverage. Holsters are also very useful.
When lopping a branch, loppers should be held so the cutting blade is above rather than below the branch to be cut. With bypass loppers, the cutting blade should also next to the stem and the hook away from the stem.
Some people prune with saws, and others carry a saw in reserve for cutting large branches. Curved pruning saws are good for steeply angled or closely spaced branches. Small tapering framed saws with replaceable blades are also excellent. However, saws cut less cleanly than loppers and careful undercutting is often required (Figure 2). Again, holsters are very useful.
Powered pruning tools
Powered tools can significantly improve pruning productivity, especially for those unused to physical labour. By reducing fatigue they can also improve safety. However, small amounts of work may not justify the relatively high cost of most powered tools.
Electric (battery), pneumatic or hydraulic loppers are available. Pneumatic and hydraulic loppers require vehicle access and a motor. Small pruning chainsaws are available but must be well maintained and used with great care. Battery powered saws are available at relatively low prices.
Aluminium ladders with a stem prop (Figure 4) are commonly used for high pruning, along with loppers and saws. Ladders must be fastened to trees by rope or chain and used in conjunction with an appropriate safety harness.
Pole saws or loppers mounted on extension poles can also be used, but can make it harder to see your work and to cut cleanly.
Ladder pruning is difficult work and use of lifts or elevating platforms should be considered as an alternative, especially for large jobs. Platforms can be set up with powered loppers (see Agriculture Note AG1014: Mechanical high pruning).
A diameter gauge (Figure 4) is a simple way to regulate branch removal according to stem diameter. All branches are removed where the stem is too thick to fit the gauge. This is most useful for learners and for ensuring contractors work to specification.
Good maintenance of pruning tools is important for several reasons:
- clean cutting
- ease of work, thus productivity, fatigue and safety
- longevity of tools.
Loppers and saws must always be kept clean, and free of rust, dirt and grit. Loppers need proper lubrication and sharpening. Blunt saw blades are better replaced than resharpened. Power tools need to be properly serviced.
A minimum kit includes helmet, eye protection, gloves and long clothing. Ladders must be secured to trees and appropriate safety harnesses used. First aid kits and communication devices should be available and more than one person should be present, in case of accidents.
Pruned Stand Certification
Pruning operations in a plantation can be independently audited and certified. Pruned stand certification may improve growers’ chances of negotiating premium returns from sale of clearwood logs. Keeping photographic records may also help.
Bird PR (2000) Farm Forestry in Southern Australia: a focus on clearwood production of specialty timbers, Agriculture Victoria, Hamilton, Victoria.
Montagu K, Kearney D, Smith G (2003) Pruning eucalypts: the biology and silviculture of clear wood production in planted eucalypts, Publication No. 02/152, Rural Industries Research and Development Corporation, Barton, ACT.
Reid R (2009) ‘Growing high-quality sawlogs’, in I Nuberg, B George, R Reid (eds), Agroforestry for natural resource management, CSIRO Publishing, Collingwood, pp. 161-182.
Reid R (2002) ‘The principles and practice of pruning’, Australian Forest Grower, Winter 2002, vol. 25 (2), Special Liftout No. 60.
Reid R, Stephen P (2001) The farmer’s forest: multipurpose forestry for Australian farmers, RIRDC Publication No. R01/33, Australian Master Tree Growers Program.
Contact/Services available from DPI
See the DPI website (www.dpi.vic.gov.au), under “Forestry”, for more information including the Notes series.
Customer Service Centre, telephone 136 186.
This agnote was developed by: Desmond Stackpole, Centre for Forest Tree Technology. December 2001.
It was reviewed by:
Tim Jackson, Farm Services Victoria. November 2009.
Published and Authorised by:
Department of Environment and Primary Industries
1 Spring Street
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