April 2013: Volume 6

Proper PruningWhen people think of forest managementequipment, they tend to focus on chainsaws,spacing saws, winches and large harvestingmachines. Yet one of the most effective (but oftenoverlooked) tools is a pruner. Pruners, either handheld or small saws on the end of long poles, areused to clip off unwanted branches and they can bevery useful when managing forest trees for highvalue wood products and maintaining tree health.

Why Prune?Go to a hardware store and compare the cost ofknot-free lumber and similar boards that contain atleast some knots. In many cases, the cost of theknot-free lumber will be significantly higherbecause it can be used to make high end furniture,flooring, cabinets and many other wood products.

Knots are defects which can tarnish the look of thewood and decrease its strength and load-bearingcapabilities. As a rule, the larger the knot, thebigger the defect in the wood and thus, the lowerthe value of the wood. This also applies to woodwith multiple small knots.

Many land owners realize that proper pruning cancreate higher value products that will often fetch apremium price. They understand that logs that lookthe same on the outside can have significantlydifferent values at the mill - particularly logs withmore years of post-pruning growth.

What are Knots? A knot is basically a section of side branchimbedded in the wood. As a tree grows, the trunk ofthe tree will often grow around the base of thelower branches. In many cases these branchessimply die and fall off. However in some cases, thetree will encase the remains of the old branch insidethe wood and this segment of old branch is called aknot.

Live branches can also form knots but in both cases,they create flaws in the wood that can reduce thestrength and look of the wood.

When should I start to Prune?As a rule, the smallerthe branch, the easierit is to remove andthe faster the treewill recover butstarting too soon canalso slow down thetree’s growth. Therefore, it isusually best to waituntil the tree crownsbegin to touch andthe lower branchesstart to die offnaturally. In aplantation or a youngnatural stand, treesusually reach this

stage when they are between 15 and 20 years oldbut the correct timing will be influenced by theoverall growth rate and development of the stand.As well, if possible it is best to try to prunebranches before they reach 2.5cm (1 in) in diameter.

However, this is often the time when the firstthinning is done in many young stands, so it is alsoadvisable to wait until after that thinning treatmenthas been finished before you start any pruning.

Where do I Start?After the first thinning has been completed, it ismuch easier to work in the stand and to identify theindividual trees with the highest potential. Thispotential depends on the owner’s goals and valuesbut it is usually a combination of factors such astree species and the straightness, diameter, heightand lack of other defects or damage on individualtrees. There is little to be gained by pruning a treethat will only produce low value material or doesnot otherwise meet your goals for the stand.

Before any pruningstarts, it is veryimportant to locatethe branch collar.This is a raisedring that surroundsthe branch where itextends out fromthe trunk. Thiscollar helps the treeto heal the pruningwound quickly andeffectively, so it isimportant to avoiddamaging orcutting into it.

Begin to prune when the lower 2 - 3m of branchesstart to die off naturally. Dead branches can bepruned at any time of year but live branches shouldonly be pruned when the tree is dormant for thewinter. Most land owners prune up at least 2m from the base of the tree during the first pruning. Asthe tree grows and develops additional pruning canreach 5m or more.

You don’t have to prune all of the trees inone area or one operation. Selecting only thebest trees and spreading the work out over anumber of seasons can be a much easierjob!

Larger branches may require an under cut toprevent the limb from breaking off andstripping bark off the trunk.

It is alsoimportant toremove no morethan 1/3 of thelive branches(crown) in anypruningoperation. Inorder tomaintain goodgrowth andhealth, the treemust have about2/3 of the livecrown intact.Many ownersalso keep a record of when the pruning was doneand the diameter (at a predetermined height abovethe ground - usually 1.4m) of each pruned tree at the time of pruning. This allows them to showpotential buyers that the tree has had 10, 20 or moreyears of knot-free growth and is now 2", 4", 6" orgreater in diameter.

Are There Other Benefits toPruning?Proper pruning can also help reduce problems withcertain diseases. For instance, Eastern White Pineoften suffers from a fungal disease known as WhitePine Blister Rust. Pruning dense branches permitsmore wind to circulate and increases the dryingeffects of sunlight. This reduces the chances that thefungus can become established and damage or killthe young white pine tree.

Corrective pruning can also help to repair damagecaused by insects and diseases or breakages fromsnow loads. In cases where the central branch (theleader) has died or was damaged, corrective pruningtechniques can be used to encourage a good qualityside branch to become the new leader.

Pruning also allows more sunlight to reach thefloor, helping to warm the soils in spring andpromote the growth of new plants and trees in theunderstory.

What Kind of Tools Should I Use?Never use an axe to prune a tree! An axe is difficultto accurately direct and will usually result in cuts inthe trunk and tearing to the bark surrounding thebranch. Both of these actions will damage thelumber potential of the tree.

The most common tool is a good quality handpruner or clipper. You can use one to carefullyremove unwanted branches up to head height.

For higher branches, you can use a telescopic polepruner. This unit usually has a small saw at the endof a long pole that can be used to cut off a branch,Many also have a small clipper component that willsnip off other high branches.

Other Factors: Sanitation:Pruning can provide many benefits but you have toensure you do now spread infectious agents fromtree to tree. Proper and regular cleaning of yourequipment are essential.

Begin by wiping the tools with a cotton cloth toremove any sap or gum that adheres to the bladesafter pruning. Dampen the cloth with paint thinnerto remove the pitch resin excreted by coniferoustrees such as pines.

Finally use rubbing alcohol or diluted bleach (10%solution) on an old cloth and wipe down the bladesof the pruning tools to kill fungi or other harmfulorganisms. Allow the tools to dry completely beforeusing them again or storing them.

Season:Dead branches may be pruned off at any time.

Conifers can be pruned in all seasons but manypeople prefer to prune when the tree is dormant inorder to minimize sap flow. This is also the periodwhen most infectious or harmful agents are alsodormant, reducing the risk of pruning relatedinfections.

Deciduous species are also left to the dormantmonths because sap flows can attract harmfulinsects. It is also often easier to see what you arepruning when the leaves are off for the winter.

Damaging the tree:For species such asWhite Spruce(Picea glauca), it isimportant to refrainfrom pruning untilthe unwantedbranches have diedoff naturally.Pruning live whitespruce branchescan cause the treeto react byincreasing sapflow, and as thissap hardens it can

stain and create other unwanted defects in the wood.

For all trees regardless of species it is important toavoid cutting or damaging the bark or the roots.Wounds allow fungi and insects to enter the wood,often ruining the economic value of the tree andshortening its lifespan.

Safety:Areas with high human traffic can benefit by theremoval of lower branches. This prevents accidentalinjuries caused by running into a sharp branch.

Conclusion:Each tree species has its own special pruningrequirements but with a little time andunderstanding you can improve the quantity andquality of solid wood growing on your land. TheForest Enhancement Program(www.gov.pe.ca/forestry/fep) provides informationand incentives tohelp land ownersmanage their landsfor any number ofvalues includingproducing highvalue woodproducts.