We recently pruned an ornamental Pear and a Norway Maple tree on the same property. Although the pruning objectives were similar in each tree (reduce risk and improve health), we utilized different methods in order to achieve those objectives.

And so this project has me thinking quite a bit about method, which is the process by which you achieve a certain pruning objective (ie. reducing risk, providing clearance, improving structure or health, controlling size, etc.). For example, utilizing a reduction cut at the end of a long scaffold limb would be one method by which to reduce the risk of that limb failing at the branch union, because the reduction cut removes weight from the end of leverage arm, in turn reducing stress on the branch attachment point or branch collar. Another method, in this same scenario to achieve the objective of reducing risk, is installing a supplemental support system on the limb. So methods can vary in the approach to accomplishing a single objective. 

By definition, a reduction cut shortens the terminal section of a branch back to a lateral branch that is equal or smaller in diameter than the section pruned (Gilman, 81). A removal cut, on the other hand, is made back to a branch collar on the stem of the tree or on a branch larger than the pruning cut.

Reduction cuts are more effective at shortening the overall length of the branch, removing more weight and apical growth potential, depending on the cut location and available branch contributors to cut back to. Although removal cuts can slow branch growth, reduction cuts are more effective at slowing growth and changing limb and tree architecture. But there is a physiological tradeoff between each cut. The reduction cut (unlike the removal cut) is not placed at a branch collar or natural barrier zone, so utilizing this pruning method on species that are poor compartmentalizers could be a poor method in some instances. Both of these methods (removal and reduction) are powerful tools when considering how to achieve specific pruning objectives. A combination of these cuts will most likely be an efficient way of achieving pruning objectives focused on structure and growth control.

Staying with the example of a long scaffold limb, a reduction cut would also be a way to provide clearance on say, an unmovable structure such as a roof or a utility line that the limb is encroaching towards or growing over. By comparison, a removal cut can also be utilized in this scenario, although one cut may be better suited for the objective than another. Limb architecture will ultimately be a major factor in determining which specific pruning method to utilize. For instance, the number and size of tertiary limbs or branch contributors that are available to cut back to, as well as their orientation, will be important factors for deciding to use the reduction cut over the removal cut. Also, we know that smaller cuts are a better option in most instances, because smaller pruning cuts expose less heartwood to exposure of fungi and bacteria, remove less sapwood which is a major energy storage site, and smaller cuts have the ability to callus over quicker than larger cuts. Considering tree species, smaller pruning cuts will be more beneficial on poor compartmentalizers and less vigorous characters as well. Ultimately, the pruning objective paired with tree species and architecture (bio-mechanics) will provide direction for arriving at a suitable method.

The Pear tree we worked on that sparked this contemplation had been pruned in the past, perhaps four to six years prior. Callus had developed around the smaller cuts since the last pruning cycle. There was a large lead about six or seven inches in diameter that was removed from what I assume was the space over the deck, given its orientation on the tree next to the deck. At that cut site there was significant sprouting, but not much callus development. Aside from that removal cut, the majority of the other removal cuts were in the upper half of the crown, sized approximately 3.5 inches and less. Very little reduction pruning was done in order to shorten limbs of the crown. Therefore, the crown was thinned with removal cuts, but it was not shortened, in essence leaving the tree exposed to the same amount of sail forces in the periphery of the crown.

There was also a clear indication of gaff marks throughout the interior of the crown on all the major scaffold limbs of the tree, most likely applied during the last pruning cycle. Ribs of callus were developing along the margins of the gaff scrapes, some on the interior of upright scaffolds and some on the top of horizontal scaffolds and secondary limbs. Climbing on gaffs is another example of a particular arboriculture method, although in this case it is a poor method if the objective is to improve the health of the tree. Those gaff wounds initiate the formation of what Alex Shigo referred to as a reaction zone and a barrier zone. “The barrier zone is a highly effective means for separating infected wood from healthy wood. However the barrier zone is a disruption in design of woody tissues. When loading occurs, the barrier zone may be the starting point for a fracture,” (Shigo, Tree Failure Risk Evaluations). Shigo’s insight illustrates how gaffing trees during preservation operations is a poor method. By continuously wounding the tree along a significant length of the stem, the potential for cracking at each of those barrier zone sites accumulates. Improving tree health should be a thread that connects all pruning objectives. Although in some hazardous situations wearing gaffs to prune may offer a safer work position for a climber, this method does not belong in most pruning scenarios because of the potential future risk of tree failure it introduces.

Our prescription on the Pear was to utilize the reduction cut as our primary method in order to achieve the main objective of reducing risk major branch unions, a very common objective given this particular species and its biomechanical tendencies to develop included bark and fail under load at those unions. On the largest horizontal scaffold limb, we applied a heavy dosage of reduction at the end of the limb, about 6 cuts in the 2-inch range. We then applied lighter dosages in the periphery of each successive major scaffold limb: One 2-inch cut per limb). Our objective was to shorten the crown in order to slow growth and also to slightly reduce the overall profile of the tree.

Back to the second phase of the job: removing dead branches from a mature Norway Maple. During this part of the project, we found ourselves mostly utilizing removal cuts located at the branch collars of the dead branches. The natural protection zone of the branch collar was highlighted by my ability in many cases to simply break dead limbs clean at the collar, reducing the need to even use a hand saw at many collar sites. By breaking smaller branches at the branch collar, this reduces the risk of cutting into the branch collar by accident and damaging the developing callus wood. The dead branches had simply been shaded out under the dense crown, and so the tree no longer allocated resources to those energy sinks. The tree cut its losses. We removed and chipped them. Here is a species that compartmentalizes poorly, and so by selecting this method for reducing risk, as opposed to something with a higher dosage like reduction pruning, we were able to achieve the objectives of improving the aesthetic of the tree and reducing the risk of those dead branches breaking off and potentially hitting a parked car in the driveway under the edge of the crown.

It would be helpful to briefly examine the concept of method under the light of the pruning system you are working within. Ultimately, the general pruning system itself will help determine the types of methods you utilize in achieving objectives. There is a wide variety of pruning systems, such as: natural, pollard, formal (topiary, espalier, pleached, etc.), bonsai, and orchard or fruit production. The overall pruning system an arborist works within on a specific tree really concerns itself with the main objectives of form and structure. The method though-the cuts and the tools utilized to make those cuts and the accuracy at which those cuts are made-is at the heart of working within a pruning system and achieving specific pruning objectives.

Annie Dillard wrote, “I never saw a tree that was no tree in particular.” I love that notion of individuality. It is true that no tree is alike, even the same species will be in a particular microenvironment with a particular phyllotaxy owned by a particular client that will have a very particular set of expectations. This is part of the challenge of being a good arborist: to look at a tree individually and think in terms of tree time, and attempt to translate the language in which trees speak. It is the methods we choose as arborists that make art and science bloom.