Individual tree quality can be improved by pruning. It is time consuming and expensive, so undertake pruning with a careful eye on costs. Prune only 50 to 100 crop trees an acre that have the form and vigor to produce high quality sawtimber or veneer.
Perform corrective pruning only on high-quality hardwood seedlings or small saplings, (primarily black walnut) to encourage a single straight leader (Figure 5-4). Most trees will correct themselves. Those that don?ft are probably genetically inferior and no amount of pruning will correct their form.
Figure 5-4. Corrective pruning.
The purpose of clear-stem pruning is to remove lower branches on the stem to produce knot-free wood (Figure 5-5). Clear-stem pruning is justified when it raises the tree grade enough to increase its stumpage value beyond the pruning cost. Clear-stem pruning may be appropriate for red pine, white pine, black walnut, red oak, sugar maple, and yellow birch. Have a forester teach you appropriate pruning techniques, especially before you prune young hardwood trees.
You can begin clear-stem pruning when trees are just 10 feet tall, and should complete it before trees reach 8 inches DBH. Prune at least 9 feet high, but remove no more than one-third of the live crown at any one time. Additional pruning through the pole stage should increase the total clear stem up to 17 feet, if 16-foot logs are the objective.
Prune during the late dormant season just before spring growth begins. Pruning at this time helps prevent diseases from invading the pruning wounds before they dry out or glaze over with pitch. Do not prune oaks from mid-April through mid-July because oak wilt may enter the pruning cuts. The dormant season also is a comfortable time to work in the woods because it is cool, visibility is good, and there are few insect pests. If possible, time pruning to coincide with thinning so the accelerated tree growth quickly grows over pruning cuts and maximizes knot-free wood production.
Figure 5-5. Clear-stem pruning.
Cut branches close to the trunk, but do not cut into the branch collar?\a swelling of the main stem around the base of the branch. Cutting into the branch collar wounds the main stem and may lead to decay in the tree.
Tree paint and wound dressings do not promote healing. Use them only when an emergency such as storm damage requires that trees (particularly oaks) be pruned in May or June.
Work safely. Wear the appropriate personal protective equipment for the tool being used. At the very least, wear a hard hat, eye protection and gloves. Sharp tools cut cleanly and require less effort to use than dull ones. Tools commonly used for pruning include hand pruning saws, pole saws, shears, and pole pruners (shears). Using a chain saw is dangerous for pruning because you must hold it above shoulder level where it is difficult to control. A chain saw easily damages trees by cutting into the branch collar and by nicking bark on the main tree stem near the pruning cut.