I recently walked a woodlot with a landowner who had pruned his younger trees according to instructions that he found online. The problem was that those instructions didn’t differentiate between pruning softwoods and hardwoods, nor did they discuss the importance of avoiding flush cuts, or conversely, the folly of leaving long branch stubs, which leave the wound susceptible to decay. The result was a woodlot where the conifers had long branch stubs and the deciduous trees were pruned too high, with major scaffolding limbs unnecessarily removed.
Before pruning, it’s important to consider just how different broadleaf deciduous trees are from conifers. For starters, conifers have an excurrent (pyramidal) form with a determined central leader and a series of obedient lateral branches that don’t typically compete for dominance unless the terminal leader is damaged. Deciduous trees, on the other hand, have a decurrent (spherical) form with many branches competing for dominance. Understanding these natural tendencies will aid you in pruning decisions.
Reasons for pruning include woods safety and timber economics, as well as tree health and aesthetics. Oftentimes these goals are mutually inclusive. In woodlot settings, two approaches to pruning are generally employed: crown thinning and crown raising.
Crown thinning is primarily used with hardwoods. The goals are to increase light penetration, promote air flow (which makes it harder for moisture-loving diseases to establish), and improve the tree’s structure and form. Branches with narrow V-shaped angles should be given special consideration for removal since the tight angle often results in included bark, which creates a weak, decay-prone union. Never remove more than one-quarter of the living crown at a time. In terms of the actual pruning cuts, employ this three-step method. The first cut is a shallow notch on the underside of the limb several inches from the branch collar (image 1). The objective of this cut is to prevent the bark from peeling away when the branch falls and damaging the stem tissue of the tree. The second cut should be above the first cut and result in a short branch stub (image 2). The final cut is made just outside the branch collar at a slight angle (image 3). Pruning a dead branch uses the same method, but in some ways is easier because the live branch collar will contrast with the dead limb, clearly indicating the proper cutting point.
Crown raising is the practice of symmetrically removing lower branches from a tree’s crown. This practice is commonly used on conifers to promote the development of knot-free wood. The lateral branches of conifers grow in whorls that are pruned to a height corresponding with the desired log length, plus a bit extra to compensate for the stump. I generally use a 10-foot pole pruner which allows me to reach a height of about 17 feet, which is adequate to produce a standard 16-foot sawlog (image 4). Pruning in late winter is not only physiologically preferred for the tree, but also allows you to use the snowpack to gain additional height with the pole saw.