Crack monitoring gauge applied to arboriculture

joshuarov

joshuarov

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Olympia
This codom Elm was reduced heavily by another arborist a couple years ago, was a harder reduction that I think I would have done, but I can understand the reasoning given the situation. Also, very much in line with the reduction work that appears to be commonplace in the EU/UK, as well as what I have started to see recommended in consulting arborist recommendations here in the PNW.
PXL_20250724_223152642.jpgHere's where I enter the picture: The property owner is committed to retaining it, given that what kicked off their desire to have the tree assessed several years ago was that the union was "opening up" (and then apparently closed up once the reduction work was done), I wanted to establish a more rigorous approach to monitor the separation of the stems, as part of the calculation to inform weight reduction pruning intervals.

I was discussing this issue with a structural engineer friend of mine and he suggested I use a "crack monitor", primarily used to assess cracks in stone/concrete construction over time.
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I came up with a mounting system for this tree.
PXL_20250724_223114933.jpg
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Curious to hear any thoughts or if anyone has tried something like this?
 
I’ve played around with two separate methods for getting an idea. What I came up with is that it isn’t conclusive. The tree is going to grow and put on wood, so if the crack measures the same it’s actually slowly opening at the same rate of the new ring.
I’ve placed a rebar rod flush in the ground and found a place to place a nail. A simple tape measurement can give you an indication of movement. Similar you can hang and leave a plumb bob, (use a throwline made of dyneema or very low stretch and already broken in).

A digital level on two nail heads driven in the tree as a fixed reference location.

Two nails on each stem on opposing stems as measurement reference points.
 
I propose that reference or anchor nails be placed on a trunk radius line so as to be perpendicular to the advancement of growth rings and thus not be affected by that.

Having the calibrated scale right there to read is neat and convenient but susceptible to nature, critters and weather.

The coolest nerd solution would be a small data logger device that could capture seasonal and wind trunk movements. That might cross over into gathering info for cabling efficacy. Logging could also be wifi to a base station (web page program etc) which could add real time alerts and analysis. A technical issue is measuring separation of two points as shown vs measuring the position of a single point when no easy pair of reference points/"nails" are possible. It would be like a very low frequency high sensitivity seismometer. One could potentially spot a weak stem in codoms. I acknowledge this is a whole different level of cost and complexity. I ramble :)
 
joshuarov said:
This codom Elm was reduced heavily by another arborist a couple years ago, was a harder reduction that I think I would have done, but I can understand the reasoning given the situation. Also, very much in line with the reduction work that appears to be commonplace in the EU/UK, as well as what I have started to see recommended in consulting arborist recommendations here in the PNW.
View attachment 99176Here's where I enter the picture: The property owner is committed to retaining it, given that what kicked off their desire to have the tree assessed several years ago was that the union was "opening up" (and then apparently closed up once the reduction work was done), I wanted to establish a more rigorous approach to monitor the separation of the stems, as part of the calculation to inform weight reduction pruning intervals.

I was discussing this issue with a structural engineer friend of mine and he suggested I use a "crack monitor", primarily used to assess cracks in stone/concrete construction over time.
View attachment 99177
I came up with a mounting system for this tree.
View attachment 99178
View attachment 99179
Curious to hear any thoughts or if anyone has tried something like this?
Click to expand...
I have been looking for this very thing. May I ask where you got the monitor?
 
Y'all noticed that the gauge gives an X and a Y value from the grid, so it can register shifting of the two sides in addition to width of the crack? Otherwise crack width is just two nails and a tape measure.
 
So when are you supposed to be concerned with movement? They have to move some. How much is too much??? And how do you know that? If you observe "X" mm of movement and think that is normal, but the tree fails next week does that put liability on you? Or, if you observe "X" mm of movement but see no other signs of concern, do you remove the tree? Seems like a good idea to gather data...but I think you need to gather data on hundreds, if not thousands, of trees to see how much they are moving before failure to have any useful information. But I'd like to hear thoughts on that! Maybe I'm overthinking it.

If the trunks move forward and backwards (as I'm looking at them in the last pic) at opposite times as opposed to left and right, that will still show up on the meter, right? A couple more meters could help log those movements.

I like the idea...I'm just questioning the usefulness of the data.
 
ATH you're bang on correct. Interpretation of the numbers is its own whole thing. The most basic start point is "summer sag/droop" vs "it hasn't measurably changed" vs "every time I check it it's opened more so it's not holding stable". Based on armchair thought statistics :)

Accumulated data could allow software to be written to monitor the data logging. Dragon's Den anyone?
 
ATH said:
So when are you supposed to be concerned with movement? They have to move some. How much is too much??? And how do you know that? If you observe "X" mm of movement and think that is normal, but the tree fails next week does that put liability on you? Or, if you observe "X" mm of movement but see no other signs of concern, do you remove the tree? Seems like a good idea to gather data...but I think you need to gather data on hundreds, if not thousands, of trees to see how much they are moving before failure to have any useful information. But I'd like to hear thoughts on that! Maybe I'm overthinking it.

If the trunks move forward and backwards (as I'm looking at them in the last pic) at opposite times as opposed to left and right, that will still show up on the meter, right? A couple more meters could help log those movements.

I like the idea...I'm just questioning the usefulness of the data.
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I don't think you are overthinking at all, and you raise all valid and excellent questions.

I'm trying to get at something somewhere in between true "data" and an experience based hunch (the latter is honestly the best we've got most of the time). Or rather, the ability to inform our experience based hunch with a slightly more rigorous benchmark than the naked eye.

My primary goal in this application is to be able to visualize/quantify an effect of a future canopy reduction prune. I see a whole tree canopy reduction prune as a whole stem weight reduction. What I'm hoping for is, just as a branch lifting when end weight work is done, to see a couple mm of inward movement on the gauge after a reduction prune is done.

I of course did not bill this to the client as a "solution to keep the tree from falling" but as a way to look at the rate of change over time.
 
that's all good stuff @joshuarov I like the plan to monitor (I assume over time - is it close enough you can drive by after heavy storms?), then continue monitoring after reduction. That might not help inform the "how much movement until failure?" question, but it will certainly give some real solid data about benefits of reduction.
 
Does this device record movement? Or does it only indicate static separation? I could see it being really cool if it drew a squiggly line which could record peak movements
 
ATH said:
that's all good stuff @joshuarov I like the plan to monitor (I assume over time - is it close enough you can drive by after heavy storms?), then continue monitoring after reduction. That might not help inform the "how much movement until failure?" question, but it will certainly give some real solid data about benefits of reduction.
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The tree is a little less than a mile from where I live, so I'll absolutely be able to check in on it easily. Additionally, I like how intuitive it is to read, this allows the property owner to be able to directly engage with it.

Yah, it leaves the likelihood of imminent failure question unanswered.

I'm theorizing that this is an imperfect proxy for static load, but, at least in my region, storms (dynamic load) are the primary cause of tree/limb failure...
 
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evo said:
Does this device record movement? Or does it only indicate static separation? I could see it being really cool if it drew a squiggly line which could record peak movements
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Afraid not, just some pieces of plastic.

Probably the easiest/cheapest way to pull that off would be to work with someone who is competent with some coding and a raspberry pi or similar to make a battery powered unit that could give a plot of movement through a storm. Then again, we might just be left with even more inconclusive data at that point.

Still would be hard to pull actionable info out (and would require massive amounts of data). Imagine we had the "plot" for a union that fails in a storm, how could you generalize that to another union in question on another tree, even of the same species? Let alone a more general use case than that.

Interesting thought experiment for sure though.
 
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