<b>Tree Care Guide:</b> Tree pruning made easy

Pruning cuts made too close to the trunk – flush cuts – make wound closure more difficult and can impact trees’ tissue and systems. Photo: ©iStockphoto.com/PhilAugustavoI clearly remember listening to a lecture by Alex Shigo in 1977 and being captivated with the “new” concepts and terminology such as CODIT, branch collar and branch bark ridge.

Our thinking about tree pruning, wound treatment and other arboriculture practices took on a paradigm shift. Shigo and his associates developed some beautiful illustrations to summarize these concepts.

I have been asked to give many talks about tree pruning to a variety of audiences. Over time, I have tried to develop simple analogies to help audiences grasp the concept of the importance of the location of the pruning cut on a limb in relation to systems associated with the branch and the trunk.

The goal was to easily convey to the audience how the location of the pruning cut could impact tissue/systems associated with the trunk and branch. Pruning cuts made too close to the trunk – flush cuts – make wound closure more difficult.

I developed a series of slides to visually capture the concepts of making a proper tree pruning cut, but I still saw sleepy eyes in the audience.

My next iteration was to ask the audience to visualize water-tight doors in a naval ship. It seemed like most folks had watched a movie with a boat being hit by a torpedo and sailors rushing to close doors to save the sinking ship. I mention that rushing to close the water-tight doors is analogous to a tree walling off, or compartmentalizing, wounded areas in a plant. Audiences seemed comfortable with that analogy.

It’s all about the ‘building’
In telling the story about proper tree pruning cuts, I recently developed the storyline that asks the audience to imagine the building they are in and the utility services (e.g., electrical, plumbing or heating and air). It’s easy for people to visualize that if you add a wing to a building, that the wing will have its own utility services, but at some critical, overlapping point, the utility services from the main building (trunk) and the new wing (branch) will make connections or interact.

It is then easy to ask the audience to imagine how cutting utilities in the wing should have minimal impact on the main building; however, if we cut utility systems in the overlapping area (branch collar) we can impact systems associated with the main building.

From that storyline, I started to develop visual aids to support the story. I was fortunate years ago to find a piece of wood in my woodpile that almost showed the concept without any graphics magic.

From that base piece of wood, graphic artist Chris Meux developed graphics overlays to accompany the building utilities story (see Figure 1).

The story and images may not clearly tell a person exactly where to make the proper pruning cut on their trees, but they at least make them pause to consider how the location of their cut may impact the tree overall.
 

 From left to right: 1) With the bark removed, underlying wood (xylem) patterns somewhat show areas for branch, branch collar and trunk tissues. 2) This overlay illustrates "utility pipes" associated with only trunk tissue (the main building). 3) This overlay illustrates "utility pipes" associated with only the branch tissue (a new wing of building). 4) This overlay shows combined "utility pipes" and an area in the branch collar region where interaction might occur. "Valves" can be used to represent compartmentalization. 5) This dashed red line outside of the branch collar (the shaded region) indicates the position for a proper pruning cut that will minimize impact on trunk tissues.

James Robbins is professor of horticulture at the University of Arkansas.