 | Pruning Your Forest Trees Pruning is removing branches of a standing tree flush with the branch collar. Why to Prune: Pruning may be done for safety, to improve the health or appearance of a tree, or to increase its commercial value. Proper pruning is one the most profitable treatments you can perform on a stand of trees. It improves value by: reducing incidence of knots and increasing production of high grade clear wood reducing stem taper hastening maturity into healthy, high value trees reducing white pine blister rust.
When to Prune While conifers and dead branches may be pruned at any time of year, it is best to prune live branches during their dormancy in the fall and winter. This is particularly true for hardwoods, as their wounds may exude excessive sap or become vulnerable to disease causing insects or pathogens such as oak wilt or Dutch Elm disease. Even with conifers there are advantages both for the trees and for those pruning during the cooler, less busy, more insect-free months of fall and winter. It is best to begin pruning while the tree is young and the branches are small. This will allow the most clear timber to grow on the bole; since knots form as each year's new growth surrounds a branch, living or dead. Also, it is easier, more efficient and healthy for the tree to prune small branches regularly than to prune large limbs. Usually the tree should be pruned after it is at least 3 or 4" diameter. One should never remove more than 1/3 of the live crown of the tree. This operation may be repeated regularly until the lower 17' of the bole (more on very productive sites) has been pruned. Economic Benefits of Pruning: The commercial value of the timber crop can be greatly increased by pruning. Stumpage values can be increased 20 to 25% by pruning. The following table shows the ratio of clear and knotty lumber per 1,000 board feet grown on trees pruned at different diameter sizes.* Diameter of Board Feet of Board Feet of: Knotty Core Clear Lumber Knotty Lumber 3 inch 920 80 4 inch 835 165 5 inch 750 250 6 inch 660 340 7 inch 595 405 UNPRUNED NONE 1000 * Measured on logs 12" in diameter at the small end and 14' long. Harvard Forest Bulletin, "Pruning for Profit as Applied to Eastern White Pine." Other studies on small samples of white pine in Maine found, after adjusting for taxes and inflation, 13.5% and 13.65% increases in value of pruned as compared to unpruned trees. The advice of a professional forester can prove helpful with all phases of pruning your forest stands from selection of trees to the actual pruning. How to Prune Marking trees to be pruned before pruning will save time and labor costs. You or your forester can select and mark the best species and trees to prune. This is a good time to start to keep good records of which trees are pruned and when. These records will prove helpful in order to obtain your pruned logs increased value at the mill. Logs may look the same outside. However, the more years of post-pruned growth, the more clear lumber there will be on each pruned log. Your pruning records will alert the mill to their worth. Select only straight trees with small branches for pruning. Prune only dominant or codominant trees, with healthy crowns. Where necessary, selected crop trees should be released by thinning around them prior to pruning. On a commercial stand prune at least 100 trees per acre (approximately 20' x 20' spacing) where species and stem conditions permit. To maintain stocking, 50 extra trees, well distributed over an acre should be pruned. Crop trees should be pruned to a height of 17' (one 16' log, with a 1' stump) where tree form and quality permit. Dead branches should be pruned. However, do not prune more than one-third of the live crown at one time. Example: if 15' is the total length of live crown, do not prune more than 5' of live branches. Depending on the age of the trees when pruning is begun, they may be pruned in several operations or height increments. Pruning live branches near the ground on young white pine may decrease the incidence of blister rust. Low pruning of some pine species may also prevent snow damage. Never prune with an ax. Use a pruning saw or shears. Small dead branches may often be easily knocked off. A lightweight power saw in skilled hands is effective on lower branches, but care must be used to avoid damaging the tree. For safety, do not attempt to prune higher limbs with a power saw. Prune to the desired height with a pole pruning saw. A Forester can advise you on sizes, types and sources of equipment. For good equipment from a forestry supplier, a hand pruning saw may cost from $17 - $43; a pole pruner from $35-$160; and pruning shears in the $17-$110 range. Do not paint or treat the pruning cuts. A Forester can demonstrate for you correct pruning techniques: First, make an undercut to prevent bark from tearing further. Next, safely remove the branch. Last, cut flush with the ridge of the branch collar (ridge around where the branch joins the bole), as close as possible without cutting it. Cutting into the branch collar injures the tree.
Pruning Cuts
Pruning cuts should be made so that only branch tissue is removed and stem tissue is not damaged. At the point where the branch attaches to the stem, branch and stem tissues remain separate, but are contiguous. If only branch tissues are cut when pruning, the stem tissues of the tree will probably not become decayed, and the wound will seal more effectively. |
| 1. Pruning living branches (Fig. 6)
To find the proper place to cut a branch, look for the branch collar that grows from the stem tissue at the underside of the base of the branch (Fig. 6A). On the upper surface, there is usually a branch bark ridge that runs (more or less) parallel to the branch angle, along the stem of the tree. A proper pruning cut does not damage either the branch bark ridge or the branch collar. | 
Figure 6A. Targeting the cut
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A proper cut begins just outside the branch bark ridge and angles down away from the stem of the tree, avoiding injury to the branch collar (Fig. 6B). Make the cut as close as possible to the stem in the branch axil, but outside the branch bark ridge, so that stem tissue is not injured and the wound can seal in the shortest time possible. If the cut is too far from the stem, leaving a branch stub, the branch tissue usually dies and woundwood forms from the stem tissue. Wound closure is delayed because the woundwood must seal over the stub that was left. | 
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The quality of pruning cuts can be evaluated by examining pruning wounds after one growing season. A concentric ring of woundwood will form from proper pruning cuts (Fig. 6B). Flush cuts made inside the branch bark ridge or branch collar, result in pronounced development of woundwood on the sides of the pruning wounds with very little woundwood forming on the top or bottom (Fig. 7D). As described above, stub cuts result in the death of the remaining branch and woundwood forms around the base from stem tissues. When pruning small branches with hand pruners, make sure the tools are sharp enough to cut the branches cleanly without tearing. Branches large enough to require saws should be supported with one hand while the cuts are made. If the branch is too large to support, make a three-step pruning cut to prevent bark ripping (Fig. 6C). | |
1. | The first cut is a shallow notch made on the underside of the branch, outside the branch collar. This cut will prevent a falling branch from tearing the stem tissue as it pulls away from the tree. | 2. | The second cut should be outside the first cut, all the way through the branch, leaving a short stub. | 3. | The stub is then cut just outside the branch bark ridge/branch collar, completing the operation. | | |
2. Pruning dead branches (Fig. 6)
Prune dead branches in much the same way as live branches. Making the correct cut is usually easy because the branch collar and the branch bark ridge can be distinguished from the dead branch because they continue to grow (Fig. 6A). Make the pruning cut just outside of the ring of woundwood tissue that has formed, being careful not to cause unnecessary injury (Fig. 6C). Large dead branches should be supported with one hand or cut with the three-step method, just as live branches. Cutting large living branches with the three step method is more critical because of the greater likelihood of bark ripping.
3. Drop Crotch Cuts
(Fig. 6D) A proper cut begins just above the branch bark ridge and extends through the stem parallel to the branch bark ridge. Usually, the stem being removed is too large to be supported with one hand, so the three cut method should be used. | |
1. | With the first cut, make a notch on the side of the stem away from the branch to be retained, well above the branch crotch. | 2. | Begin the second cut inside the branch crotch, staying well above the branch bark ridge, and cut through the stem above the notch. | 3. | Cut the remaining stub just inside the branch bark ridge through the stem parallel to the branch bark ridge. |
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D. Crown reduction
| | | Figure 6. Pruning cuts |
To prevent the abundant growth of epicormic sprouts on the stem below the cut, or dieback of the stem to a lower lateral branch, make the cut at a lateral branch that is at least one-third of the diameter of the stem at their union. Pruning Practices That Harm Trees | | | Topping and tipping (Fig. 7A, 7B) are pruning practices that harm trees and should not be used. Crown reduction pruning is the preferred method to reduce the size or height of the crown of a tree, but is rarely needed and should be used infrequently.
Topping, the pruning of large upright branches between nodes, is sometimes done to reduce the height of a tree (Fig. 7A). Tipping is the practice of cutting lateral branches between nodes (Fig. 7B) to reduce crown width. | 
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These practices invariably result in the development of epicormic sprouts, or in the death of the cut branch back to the next lateral branch below. These epicormic sprouts are weakly attached to the stem and eventually will be supported by a decaying branch.
Improper pruning cuts cause unnecessary injury and bark ripping (Fig. 7C). Flush cuts injure stem tissues and can result in decay (Fig. 7D). Stub cuts delay wound closure and can provide entry to canker fungi that kill the cambium, delaying or preventing woundwood formation (Fig. 7E). | 
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| | | Figure 7. Practices that harm trees |
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