Welcome to the penultimate conclusion of the Anvil vs. Bypass Pruner saga.

If you have not been fully engrossed over the past year, take a moment to revisit our previous blogs (The Saga Continues, Part Two, Part One) describing our methods and initial findings.  

Why we did this:  

It is commonly accepted among the horticulture community that anvil pruners are less desirable than bypass pruners as they will supposedly ‘crush the cambium’ and ‘damage the plant’. When the Koeser lab team dug into the research behind this claim, we found minimal evidence in the literature to support this idea. (see this paper and this paper) So as any good group of questioning folks would do, we set up a test. 

What we did, a summary:  

We made 60 small pruning cuts on branches up to half an inch in diameter, using both small and large versions of each pruner type (check out the maps in previous blogs to see how we found the cuts later). To ensure fair comparisons, pruning was done by me, all on the same day, on the same species (live oak, Quercus virginiana) and following standard pruning techniques. Treatments were randomly assigned, with several cuts on each tree and environmental factors such as sunlight, soil conditions, and irrigation kept as consistent as possible. The goal was to isolate the effect of the pruning tool itself, rather than outside influences. 

After pruning, the trees were monitored over time to assess wound closure and whether sprouting impacts were observed. We recorded whether the cut tissue was crushed or torn, how much discoloration developed in the wood, whether new shoots formed, and whether the tree produced callus tissue to seal the wound. These observations were made shortly after pruning, again several months later, and finally at the end of the growing season one year later.

To make our final data collection adventure all the more exciting, we removed the entire branch from the tree, whittled away the bark (with only minimal blood loss, I assure you), and measured the depth of discoloration using ImageJ software. 

The results from anvil and bypass pruners were then compared using standard statistical methods to determine whether one tool caused more damage (influenced the depth of discoloration) or led to different healing outcomes (ANOVA allows us to compare average tree responses across multiple pruning tool groups at the same time while accounting for natural variation among cuts). 

What we found:  

Drumroll……we found no clear evidence that the type of hand pruner used affected how much discoloration developed in pruning wounds. Neither the depth of internal discoloration nor the visible severity of discoloration at the cut surface differed significantly between pruning treatments, although there was a wide range of responses among individual cuts. 

We did observe a trend showing that larger pruning cuts were more likely to result in observed bark splitting and delayed wound closure, which aligns with previous research showing that wound size can influence tree response, even though this pattern narrowly missed traditional levels of statistical significance (P=0.054). 

So, we found nothing. But in this case, nothing is something! We found nothing in this study to support the prevalent assertion that anvil pruners will result in damage and are not recommended for small pruning cuts.  

What this means (maybe):  

In our study, our coefficients of variation were pretty high, indicating substantial in-treatment variability. The coefficient of variability is a way to describe how much the results differ from one another, with higher values meaning there was more natural variation in how trees responded to the same treatment. But, overall, we found nothing that would suggest we should keep telling people not to use anvil pruners for small pruning cuts.  

What our limitations were:  

These outcomes were only observed for a single species, and a hardy one at that. Live oak is well known for its compartmentalization and resistance to decay. Also, damage can sometimes take longer than one growing season to develop. We were able to address some of the potential limitations related to tree quality, environmental conditions, and tool sharpness, but more studies are needed

What we want to do next:  

Cut more trees! We want to replicate this study with different tree species to better understand variability. Another important next step would be to examine the role of blade sharpness by intentionally comparing sharp versus dull pruners. Maybe timing of cuts, terminal branches versus not etc. etc. What would you like to know? If you have a thought regarding this study and where you would like to see it go next, drop us a line via email: alyvinson@ufl.edu or akoeser@ufl.edu. 

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!).

Want to see more? Visit our archive.

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