Many people appreciate the parklike appearance of a stand of trees in which the lower branches have been removed. Trails lined by pruned trees invite us to take a walk, and for some of us sawing off dead branches seems to satisfy a primordial impulse.
Pruning for profit is a different matter. People have been pruning fruit trees and rose bushes for centuries, but few take the time to prune crop trees in order to produce clear, knot-free wood. It will take years to realize a profit, but in some cases clear boards are so much more valuable than knotty ones that the cost of pruning is repaid with interest when the trees are harvested and sold.
A recent study by researchers at the Yale School of Forestry confirmed that the cost of pruning white pine could yield a compound interest return of as much as 13%, even when the trees were not harvested until 30 years after pruning.
Making money on your pruning investment depends on starting with reasonably good trees. You will also need to have a loooong time horizon (for some of us, it might fall into the category of estate planning), for it takes at least a couple of decades for a tree to cover the cut branch stubs with enough wood to yield clear lumber.
It is no use pruning unless you are willing to free the pruned trees from competition, so thinning the stand enough to promote consistent good diameter growth goes hand in hand with pruning. Otherwise your grandchildren will be in rocking chairs by the time your pruned trees reach maturity.
It has often been said that the wood from rapidly grown trees is inferior to more slowly grown wood, but the Yale study found no evidence for this belief. The wood from pruned trees that they grew as fast as they could, including one that had an average diameter increase of over 0.6 inches per year, was fine.
The trees to be pruned must be chosen carefully and pruned properly because pruning the wrong tree will not repay your investment, and pruning the right tree improperly can do more harm than good.
What Species To Prune
Good white pine, if you have it, is the best place to invest your pruning hours. White pine lumber ranges from magnificent clear cabinetmaking wood to ratty boards with loose knots. Pine is quite rot resistant and the dead branches (it is these that make loose knots) stay on the tree for a long time. Pruning can't cure all a pine's ills, but it can turn good into wonderful.
Only if the crowns of your pruned pines have room to expand in diameter at the rate of about one foot per year can you get the rapid stem diameter growth needed to maximize the pruning investment. Most other softwoods don't respond to thinning as well as white pine and, the difference in price between knotty and clear for other softwood lumber is not as dramatic.
Hardwoods, when grown densely as saplings and adolescents, will not develop thick side branches. The small branches rot quickly after they die and the trees usually self prune quite nicely. White ash is reliably self pruning but it is worthwhile to prune small branches from red oak, paper birch, yellow birch, black cherry or sugar maple.
Choosing Your Tree
Prune only crop trees. These are the healthiest, most vigorous and straightest trees of species that make good sawtimber. In hardwoods, prune between 25 and 40 of the best trees per acre. This will leave an average spacing of 33 to 42 feet between crop trees. Don't by any means remove all the non-crop trees early in the life of the stand. These may be thinned out later, but when just getting started they provide structure and force each other to grow straight and up, rather than sprawl outwards.
In softwoods prune between 35 and 60 beautiful trees per acre. This corresponds to a spacing of 27 to 35 feet between pruned trees.
A good time to prune pine is after the first thinning. This way there will be no logging damage to newly pruned trees and the pruned trees will grow fast. By the time the trees are thinned they may be about six inches in diameter. You may wish to start earlier in other kinds of trees. An initial pruning when the trees are about three inches in diameter, provided you leave plenty of greenery, gives the tree plenty of time to acquire a good thick shell of knot free wood. Pruning trees over nine inches in diameter is economically dicey.
How To Prune
Trees may be pruned any time of year but late in the dormant season is the best. They have a good spurt of growth in the spring and part of this effort will be directed towards growing over any injury.
When a branch dies it is highly vulnerable to decay organisms. Since dead branches are routine for almost all trees, they have evolved ways of dealing with this. In the process of shedding a branch the tree summons defensive chemicals to the base of the branch which limit the spread of decay. The living branch-bark ridge or collar is part of the process of walling off decay. Cutting into this collar when you prune disrupts the process. Furthermore, you are inflicting a new wound which is a new opening for infection.
It used to be thought that injuring the branch-bark collar stimulated "healing." Thanks to the work of Alex Shigo, formerly chief scientist at the Durham, NH, office of the U.S. Forest Service, "healing" is out. Plants don't have this ability; they only can wall off or compartmentalize, limiting decay to tissues formed prior to the injury.
Cutting small live branches outside of the branch-bark collar is acceptable. The branch shedding system will work to wall out rot-causing fungi, but you are courting infection and decay if you cut off live branches more than two inches in diameter, even in a healthy, fast growing tree. Besides, pruning large branches is time consuming.
Chances are you will mostly be cutting off dead branches. Cut as close as you can to the collar without injuring it. Long branch stubs will take many extra years to cover with clear wood.
Applying a wound dressing rarely, if ever, does any good because bacteria and the spores of disease causing fungi are very small and no wound dressing can tightly seal a wound over a period of years. Spores are released by the million and the cut tree surface you cover with dressing may already be covered with spores.
Axe The Axe (And The Chain Saw)
Never use an axe. It leaves a messy stub which the tree cannot close over easily. And, let's face it, sooner or later you will injure the tree trunk. Chain saws are almost as bad. Put a hand pruning saw between 18 inches and 26 inches long with four to eight teeth per inch on your Christmas list.
How Much To Prune?
If possible, prune as high as 17 feet above ground level in order to have a standard 16-foot log on a one-foot stump. However, any pruning over nine feet will result in a knot-free merchantable log. Twelve feet is a common log length in New England and pruning to 13 feet will allow for a one-foot squirrel platform. Pruning can be done in stages, perhaps first with a saw on a short handle and later with a pole saw.
Remove all dead branches that you can reach safely. When pruning live branches, don't remove more than one third of them. And always leave one third to one half of the tree's height in live branches when you are done. Remember, live branches hold the tree's green leaves. If too many are cut, diameter growth will slowdown. You need to balance tree growth against tree quality.
It may be prudent to delay pruning white pines until they are at least 16 feet tall. If the white pine weevil injures the leader after that, you at least will have one good full-sized sawlog.
If your forest ends at a field or road, don't prune the outside trees. The lower branches keep the sun and hot drying winds from penetrating into the stand.
A Good Investment
Even though you will have to wait from 25 to 50 years to recoup your 10- or 15-minute per tree investment, this effort can produce some of the highest long term returns available in timber production. And sometimes having an excuse to snowshoe into the woods on a sunny February or March day with your pruning saw can yield a pretty good return immediately.