Shear Genius: Investigating How Hand Pruner Type Impacts Wounding Response (Journal Club 1)

In our last post, we questioned whether the widely repeated adage that anvil pruners cause more damage to plants than bypass pruners holds any merit. As we noted, data on this topic are scarce. However, one study surfaced in our Google Scholar search:

Marchi, E., F. Neri, M. Fioravanti, R. Picchio, G. Goli, and G. Di Giulio 2013. Effects of cutting patterns of shears on occlusion processes in pruning of high-quality wood plantations. Croatian Journal of Forest Engineering 34(2):295-304.

Given its relevance to our current research interests and its publication in a regional journal that may not be widely known, we thought it would be a great choice to feature in our first Tree Research Journal Club. Below is our take on the study and its relevance to our question, “Do anvil pruners deserve their reputation for being more damaging than bypass pruners?”

What Was Done?

In this study, the authors used three different types of pruners to make 36 removal cuts on young English oak (Quercus robur) trees. The pruners tested were double-bladed, anvil, and bypass. Image analysis was used to measure the extent of cambial damage at the time of pruning, and woundwood closure was assessed after 15 months. Five years after pruning, long-term damage was assessed based on the proportion of wound closure and the depth of woundwood.

What was Discovered?

A bar graph showing damaged associated with pruning cuts made with three different pruners. Double bladed pruners had an injury rating of approximately 15%. Anvil pruners had an injury rating of 33% and bypass pruners had an injury rating of 66%. — Figure 4 from Marchi et al. (2013). “DC” is the abbreviation for “draw cut shear,” the term used in the article for what we refer to as “anvil pruners” in this post. “BP” stands for “bypass shear,” which we call “bypass pruners.” “DB” denotes a “double-bladed pruner.”

Looking at Figure 4, we see that the amount of cambium damage varied between the three pruners. The different letters above each bar indicate that each pruner caused a distinct level of injury. The authors measured damage by calculating how much of the pruning wound (a 360-degree, circular shape) had damaged cambium.

Bypass pruners caused about 67 degrees of damage (roughly 18% of the cut’s outer edge). This was twice the damage of anvil pruners (about 9%) and four times the damage of double-bladed pruners (about 4.5%).

A bar graph showing percent wound closure for pruning wounds caused by three different pruners. Double bladed pruners had a healing index of approximately 93%. Anvil pruners and bypass pruners had healing indexes of around 65%. — Figure 5 from Marchi et al. (2013). “DC” is the abbreviation for “draw cut shear,” the term used in the article for what we refer to as “anvil pruners” in this post. “BP” stands for “bypass shear,” which we call “bypass pruners.” “DB” denotes a “double-bladed pruner.”

Looking at the 15-month data, this higher cambium damage at the time of pruning appeared to slow wound closure. Figure 5 shows the opposite trend of Figure 4: the double-bladed pruner, which caused the least initial damage, had the most wound closure. One year after pruning, anvil and bypass pruners had nearly identical wound closure rates of about 65%.

Five years later, all wounds made with double-bladed pruners had fully closed. In comparison, 90.6% of bypass pruner wounds and 71.9% of anvil pruner wounds had closed. However, the average wound closure rates for bypass and anvil pruners were not significantly different. This suggests that the remaining open bypass pruner wounds, while less common, may have been more severe. Additionally, wounds from bypass pruners developed thicker woundwood than those from anvil pruners.

Conclusion

The clear winner in this study is the double-bladed pruner. It was consistent throughout, minimizing visible damage from the onset, which translated to more rapid and complete wound closure both 15 months and 5 years later. For our question (bypass pruners vs. anvil pruners), the results are less clear. Initially, there was more visible damage with the bypass pruner, but over time, it appeared that the less obvious damage from the anvil pruner was slowing recovery. At the end of the study, variability in the data (and possibly low power given sample size) limited the researchers’ ability to detect differences for several of their wound response metrics. While we hesitate to draw conclusions from non-significant findings, those on “Team Bypass” might find the five-year trends encouraging.

Why We Like This Article

This study is reminiscent of the work Shigo and others conducted for the USDA Forest Service while investigating how to remove branches without degrading wood quality, making it highly approachable. The writing is clear and accessible, the analysis is straightforward, and there are plenty of relevant figures that effectively explain their methods, display their data, and provide visual context for what they observed when classifying damage (Figure 7). Finally, we applaud the researchers for extending this project for 5 years. You can see how the story evolves from initial pruning to 15 months later, to 5 years later. There are tremendous pressures to get results out quickly or craft a project that can be completed by a student in 2-4 years. Moreover, land set aside for a trial is land that could be producing trees for profit, supporting other projects, etc. While 5 years may not seem like much from the perspective of a tree, it was a significant investment of time and resources that allowed for a more thorough and meaningful evaluation of the long-term impacts.

A figure of three pruning wounds showing the initial damage and the regrowth 15 months later — Figure 7 from Marchi et al. (2013). “Draw cut shear” refers to what we call “anvil pruners” in this post, while “bypass shear” corresponds to “bypass pruners.” “DB” denotes a double-bladed pruner.

What are double-bladed pruners?

That is a very good question. The term was not immediately recognizable when we encountered it in the paper. However, searching for ‘double-bladed pruners’ will bring up several options from reputable online horticultural supply companies. You can bet we ordered a pair for trialling after reading this paper.

Acknowledgements

A special thanks to the Croatian Journal of Forest Engineering for granting permission to reprint the three figures featured in this post.

About this Blog

Rooted in Tree Research is a joint effort by Andrew Koeser and Alyssa Vinson. Andrew is a research and extension professor at the University of Florida Gulf Coast Research and Education Center near Tampa, Florida. Alyssa Vinson is the Urban Forestry Extension Specialist for Hillsborough County, Florida.

The mission of this blog is to highlight new, exciting, and overlooked research findings (tagged Tree Research Journal Club) while also examining many arboricultural and horticultural “truths” that have never been empirically studied—until now (tagged Show Us the Data!).

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