The first known photo of the Black Gum tree, from 2016. The note in the database from this tree inspection reads: “Poor quality tree – recommend removal.” Photo from Google Street View.

One of the main goals of an arborist is to use skill to help trees and people live together in harmony. A professional arborist must balance the risks and benefits of keeping trees healthy, and one of the primary ways to achieve that balance is through pruning.

In theory, pruning is very simple. After all, trees are made of wood, and saws will easily cut wood. However, proper pruning is a process in which training, practice, observation and experience matter.

Over the past decade, in collaboration with the City of Fredericksburg, Virginia, and the nonprofit organization Tree Fredericksburg, I’ve had the privilege of being personally involved in a large tree-pruning project.

From 2010 to 2024, Tree Fredericksburg planted approximately 10,000 trees throughout the city. Each year, we pruned an average of 1,500 of these trees on a rotating schedule.

Through this annual pruning project, I had the opportunity to watch how each of these trees responded to the application of our pruning principles. I’m not aware of any other projects that have had the same scope, duration and continuity involving the same pruning arborists.

In January 2017, a noticeable central stem is starting to develop. Photo courtesy of the author.

Cause and effect

The importance of experience and observation cannot be overstated for those who work with trees. While it may not be necessary to have a master’s degree in biology to do the work, it is critical to follow fundamental pruning principles and observe trees to ensure they’re responding as expected over time.

In my opinion, this is one of the biggest challenges in practicing arboriculture today. Often, the workers who are doing the pruning are disconnected from the opportunity to return to a job site to follow up on how a tree responded to their work. Their concern is primarily the present moment, not how their actions will create long-term consequences for a tree. This disconnect is detrimental to the development and education of a professional, experienced arborist.

Through the Tree Fredericksburg pruning project, we were able to practice our craft, observe the natural consequences and then validate or adjust our technique on a large scale.

Trees in the built environment

Progress that the tree has made, prior to being pruned again in January 2024. Photo courtesy of the author.

While trees may have a significant amount of evolutionary experience in the forest environment, their experience in the built environment is relatively new. Trees chosen to be durable and resilient, such as many types of elms, also may have a supercharged growth rate that demands continual revisiting, or the tree will quickly get out of hand.

Through our experience, we were shown time and again that there are no real solutions, only trade-offs, in the practice of tree care in the built environment. There was much learning and adjusting. We learned how certain varieties perform well for the purpose for which they were developed, but do not fit well in the urban environment. We gained firsthand experience with the difficulties of tree location, using new and relatively unproven varieties and managing differing tree growth rates while also dealing with budget constraints and uncertainties in the pruning cycle.

Through this experience, I was able to directly observe and interact with the trees in my community and gain valuable experience in tree management. This experience and knowledge cannot be gained through books or seminars.

While theory is important, a true understanding of professional arboriculture requires direct practice and experience.

The cost of the cut

Michael Blashford (left) and Steve Rossi, the two principal arborists on the Tree Fredericksburg project, standing next to a tree they planted 10 years ago. Photo courtesy of Suzanne Rossi.

Where I live, there has recently been a noticeable shift toward a style of pruning that does not consider the natural form of the tree or the consequences of indiscriminate pruning. Perhaps this is due to an honest lack of understanding, or maybe it is an attempt to oversimplify the many complex considerations that must be made in a successful tree-pruning project. Possibly this trend is the result of trying to provide elementary guidelines to an increasingly inexperienced workforce. Whatever the reason, the result has been more broken trees and branches, copious suckering at the cuts and large areas of tree decay. With modern tools, what has taken years to grow can be destroyed in a few misguided moments.

I often ask the students in my pruning classes, “Is there a right or a wrong way to prune?” I ask this because I want students to recognize that the consequences of pruning decisions are real – and that some are less desirable than others.

Choosing the proper pruning system is the result of understanding the science behind the tree’s response and then making properly placed cuts that will lead to the desired outcome over time. A natural pruning system is the most common in the urban landscape, because it balances the function and aesthetics of the tree. Some pruning systems, such as pollarding and traditional orchard pruning, may be visually jarring at first; however, they are not as detrimental to the long-term health or function of the tree as they first appear.

Pruning on tree time

Pruning is a game played on tree time, which means a tree must be given the appropriate amount of time between pruning cycles to respond to the dose, but not so much time that it outgrows the next stage. This means the tree will require several planned visits over multiple years to develop the final product.

According to Ed Gilman in “An Illustrated Guide to Pruning,” the full cycle may take as long as 25 years, with scheduled pruning spaced over a minimum of seven visits. If a pruning cycle is missed or improperly administered, all the progress may be lost, or the tree may never reach its full potential. For pruning to be effective, it must reach a short-term goal at each stage while simultaneously moving closer to the final long-term goal.

Overmanaged and “improved” trees often look aesthetically unpleasing and become structurally less sound over time. Improper pruning cuts can have the same appearance and detrimental consequences as topping. These include excessive sprouting, larger decay pockets and a higher likelihood of limb failure.

Sadly, rather than extending a tree’s useful life, improper pruning will shorten it. Where trees should be an inheritance, they instead become a quickly consumed commodity.

Training, pruning and trimming

In Gerald Beranek’s book “The Fundamentals of General Tree Work,” he makes a distinction between training, pruning and trimming. Training and pruning typically follow specific guidelines and are tree focused. Trimming is the indiscriminate cutting of a tree to fulfill a client’s goal without regard for the tree.

An example would be trimming trees for miles along a power line using the most expedient method and making cuts to a set distance from the utility, rather than to a specific place on the tree. Even in residential tree work, arborists sometimes simply need to satisfy the client. However, it is dangerous to step into the tree-trimming world without acknowledging this shift and having a clear vision of the goal and the consequences of coloring outside the lines. If the negative consequences outweigh the proposed solution, then a different tree-
management approach is necessary.

Conclusion

“The CODIT Principle: Implications for Best Practices,” by Dirk Dujesiefken and Walter Liese, highlights the many considerations and questions that need to be answered to prune correctly. (I use the term “correctly” to mean results that are both predictable and sustainable over time.)

As a tree climber and working arborist, I’ve found that there are several basic guiding principles that work the majority of the time. First, always prune the tree as though you will climb it again. This means leaving branches along the entire length of each branch or stem. If the branches are too close or too far apart, it will be hard to climb. If the pruning negatively affects the structure or strength of the tree, the tree will eventually no longer be safe to climb.

Second, it’s good to stay within the form of the tree and maintain a natural appearance. Landscape trees have many benefits, and being aesthetically pleasing is one of them. A naturally pruned tree will typically need less maintenance and pruning input. A tree that is forced into a different form will constantly need to be artificially controlled.

Finally, in pruning, sometimes less is more. Not all problems can be solved at one time. The tree needs leaves to make food, so when in doubt, leave a little more. The true cost or value of tree pruning becomes more apparent over time.

Michael Blashford is an ISA Board Certified Master Arborist with Arbor Care Complete Tree Service, serving the Fredericksburg, Tappahannock and Northern Neck regions of Virginia.

References

Beranek, G.F. “The Fundamentals of General Tree Work.” Beranek, 1998, Chapter 36.

Dujesiefken, D., and W. Liese. “The CODIT Principle and Arboriculture: Implications for Best Practice.” International Society of Arboriculture, 2015.

Gilman, E.F. “An Illustrated Guide to Pruning,” 3rd ed. Delmar, 2012.

Lilly, S., E.F. Gilman and E.T. Smiley. “Pruning,” 3rd ed. International Society of Arboriculture, 2019, p. 1.

Shigo, A.L. “Modern Arboriculture: A Systems Approach to the Care of Trees and Their Associates.” Shigo and Trees, 1991.

Shigo, A.L. “100 Tree Myths.” Shigo and Trees Associates, 2013, p. 37.

Hirons, A.D., and P.A. Thomas. “Applied Tree Biology.” John Wiley & Sons Ltd., 2018, pp. 131-132.