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.
A excellent USDA pamphlet can be found and
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How to Prune Trees