I'm going to share an email I wrote to Ed Gilman, professor at The University of Florida, and a very researched voice in the arboriculture community.
This is me reaching out:
"Ed,
My name is T.C. Mazar. I am a contract climber working in Pennsylvania (ISA Arborist/Climber Specialist). I'd like to say I've had the pleasure of listening to you lecture at our symposium before, and I think your work on pruning is really fantastic. I admire your research and philosophy. Also, I hope this email finds you well.
I've been doing some deep thinking lately into my own pruning practices, meditating recently on "percentages"; specifically when it comes to removing a portion of live crown. As arborists we're quick to give a presecription of removing a certain live portion of the crown during pruning practices, say 30% or 20%. A third, a quarter and so on and so forth.
As of late though, I've been wondering how to truly quantify these percentages, how can we look at a crown prior to pruning, and then look at our finished product and give even a remotely accurate estimate of what we removed. My 20% would be someone else's 30%, for example.
I made this point in a Facebook discussion in one of the climber forums that I follow, and a shitstorm seemed to ensue. I do understand that these percentages are rough estimates, guidelines if you will for homeowners and contractors alike to meet expectations. But how relevant are these percentages in the fact that they can be interpreted so differently? I know that you use these percentages in your literature, and in your research to convery certain points on pruning.
My point is that the crown of a tree is so complex, so very busy in the live biology that's taking place, I feel we can never look at a crown and see it in it's own entirety to really understand accurately what we're removing. We just know that it's somehow right...right?
It always comes back to this: "well I know exactly what the tree should look like when it's pruned properly". Like a magician who never reveals the secret behind his magic.
My concern is that I'm sounding more intelligent than I really am, giving the homeowner the impression that I'm able to somehow accurately quantify their tree's live crown and than be able to accurately remove a portion of that crown.
I'm big on recording specific sizes of collar cuts for my own personal journals, objectives and rough estimates on tree size. The percentages though, I've been having a really hard time of as late, because I hear so many of my colleagues saying 30% and 40%, but what is that really? It seems like its just conceptual, and it never really pans out in the real world.
Can you shed some light on this? Can you, in a short breath or so, give some meaning to these percentages? I would love to be able to share this with the community. I know you are busy, and so anything at all to put my mind at rest would be greatly appreciated!
Best,
T.C. Mazar"
This is Ed's response:
"Fantastic questions. I have found in the several hundred pruning workshops I have done all over the us and overseas that as you say people's perception of what was removed varies widely. I don't think it is a good way to express what is to be done. We have gone recently to expressing the diameter of cuts, number of cuts, type of cuts ( reduction, branch removal), location in crown ( typically the largest diameter primary branches). This is the approach presented in the current draft of ANSI a300 which will be out for another public comment period this fall. Also, you will notice that the 25 percent guideline has been removed from the draft document.
That's for all those thoughts!
Ed Gilman, professor"
Ed Gilman, professor"
It puts my mind at rest to know that these percentages are misleading, and they are inaccurate to certain degree in the sense of how much they vary from individual to individual. This, of course, can be interpreted however you see fit. For me though, the percentage myth has been busted.
