I would suggest strongly that you stay at least 1/2" or more from the collar of the limb, as that will allow for less likelihood of critters getting into the bowl of the tree. On my tree farm I use a pneumatic trimmer the helps keep me back from the collar and from scarring the tree's main stem.
I'm in N.J. and get lots of trees from tree services that have been trimmed. Can't tell you how many times I got a nice looking log, only to find 5 or 6 inches deep a limb cut rotten or with insects. If it's taken care of right, the lumber is still no good! The tree heals over but does not reattach wood to the cut area and means you have to cut that part out of the board or plank. I don't believe you increase log grade by cutting small limbs off. There is still a knot or cat face there no matter how many years it grows over that area.
On the radiata pine farms in the southern hemisphere, they trim the lower branches as a matter of course, to increase the yield of clear lumber. Maybe it is specie specific.
Here in the Northeast, white pines are pruned when they're at 4-5" DBH. I've never heard of any other tree pruned on a large scale and I was always told "never prune a hardwood."
A couple years back a sawyer in the town next door paid top dollar for some clear pine that averaged 20" small end. These trees were pruned at 12-14" so they looked clear on the outside, butů
You prune hardwoods in the first 10 years to give them the ideal growth pattern, period. You prune softwoods in the first 15 years because of slow growth in the beginning, then picking up speed around 10 years. Any pruning of softwoods in mature trees will show up in sapwood even 20 years down the road.
I work in landscaping. What I have learned is that you never cut into the collar of the tree when you are pruning. Also, never leave a stub. It will promote rot and will not heal correctly. This is just a thought, but it seems to me it would be better to get rid of the lower limbs at an early age to have clearer wood in the end. Never remove more than 1/3 of the growth of a tree.
The labor would be cost prohibitive on a large scale and the size of the pruning would have to be under 3/4", some say up to 1", to not damage the cambium layer on small landscaping efforts and still allow for the tree to properly heal itself as it would when naturally shedding branches. I have, out of boredom and excess energy, pruned (flush to the bole) trees in my yard for 14 years to offset the openness of their planting and eliminate their excess limbs. It's endless because the light forces dormant buds to continue sprouting. But as the crown of the tree begins to shade the lower trunk, the buds cease to sprout. I have a crop of 20 pecans that are open grown, 40 feet tall, perfect looking boles with no scarring that now bear pecans and appear to have been forest grown and gone through natural shedding. They are twice the height of other trees that I purposely didn't prune. The trees responded to grow height. As to the soundness of the wood of the ones pruned, in 30 or 40 more years someone might harvest them and have an answer to that question.
Softwoods as a general rule will improve in saw log quality if they can be pruned in the early stages. Ideally it is great to get the first 16' of the stem pruned as soon as possible to maintain the maximum knot free log. Most conifers can stand to have up to 1/3 of their living crown removed without negatively affecting the tree's growth. I generally recommend that folks start pruning as soon as possible after planting - usually when the trees are just above 1 or 2 m.
Up here in Northwestern Ontario, it is the bunnies and deer that take care of pruning the white pines, unfortunately.
The key to successful pruning is: get them young, cut them clean, and cut them as close to the branch collar as possible *without* damaging the branch collar.
While at Purdue Forestry School 50 years ago, many of the textbook writers were people who had studied in Europe. They all seem to believe that conifers in plantations should be trimmed up to about 16 to 17 feet. Now with most of the conifers going into pulp wood and MDF, that is still true. Land taxes and short rotation trees will not have time to produce saw logs of high value, trimmed or not. As far as control of the deer and bunnies, the best solution is hasenpfeffer and venison.
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Comment from contributor B:
I don't prune much, but I think it is safest to use it to remove only dead branches. In small softwood, remove the branches that have died from being shaded out. The tree will grow over the (knot) and as the tree grows outward past the cut you will someday have knot free lumber. All you are doing is speeding up nature. Cutting off live branches will result it sap runs, etc. I think pruning works best on thick stands where branches have died off, remove them and thin your stand.
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