analysis of resistograph results

[John Shutler]

as above ive got some resistograph printouts from an Oak ive been to look at, ive little experience with the resistograph and im trying to work out what the results are really saying. ive contacted the company who undertook the survey, who have so far been less than helpfull. the trees owners put in at app to fell the tree on the basis of the results ,but the LA responded that there was insufficient explanation of the results to warrant felling

 

does anybody have any information regarding interpretation of resistograph results

Edited April 15, 2012 by John Shutler

[David Humphries]

What was the dbh of the tree at measurement height & how long was the drill depth?

 

 

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[John Shutler]

measurement height was 10 cm, dbh was 105cmmm and depth was 39.8cm

[David Humphries]

Out of interest John, can you say what type of decay the resistograph was measuring for ?

 

 

In essence the drill is reading the resistance against the wood (sound or decayed) along that 40cm test drill.

 

 

Are there any major drop offs along the length of the test?

 

 

 

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[martwizz]

Im not sure how much you do/dont understand, but basically if the drill is 40cm into 105 dbh, lets just say its 40% of the DBH. (80% radius)

 

The graph measures the resistance of the wood as you bore in. So the start of the graph would probably be quite high as you would be drilling through newer live wood and healthy hartwood etc. If the graph starts to drop as the depth increases (or more time passes), it means that there is less resistance against the drill, so the wood is likely to be rotten.

 

Say the graph was high for the first half, then bottoms out because there is no resistance. Drilling 40% of the way in with those results would suggest you have a rotten cavity approxmately 60% of the DBH of the tree. Thats assuming its the same from all directions.

 

The only thing im not sure about is what the graph plots against. I think its depth right? Time wouldnt make much sense.

 

There are probably standardised readings for healthy trees somewhere, i guess the resistance should change naturally between the cambium, and layers of heartwood. Im not really too sure about that part.

 

Does that help at all? =/

[ScottF]

If you can scan them and post them I'm sure a few of us could give you some thoughts. Has the consultant given you a diagram or photos to indicate where each reading was taken?

[martwizz]

 

Like this. The first drill has ressitance for 60% of the depth then hits a cavity so drops

 

The second drill would only have resistance for 20% of the depth, then drops because it hits the cavity

 

thats why you drill from different directions, as it allows you to map out where cavities or rot may occurr in the trunk

[John Shutler]

there are various peaks and dropoffs. drop offs indicating decay and high peaks indicating areas of very hard deadwood. the tree was drilled at 4 points n,s,e,w, and all at a height of 10cm

personally im dubious of the intensions of the survey

[ScottF]

John, what you're describing is a typical resistograph reading, with peaks and troughs and gradients of higher and lower density. Depending on the settings you can even detect the growth things and other pretty discrete features.

 

I'm not sure about the "very hard deadwood"; it's very hard to tell that any increased or decreased density it down to. It could be reaction wood, included bark, decay etc etc and decaying wood inside the stem wouldn't be likely to harden in the way that dessicated dead wood on the outside of the tree would. The example that Martwizz has shown gives some idea how to interpret the readings, although it sounds like it's a more simple case than the one you're describing.

 

In terms of the intentions, possibly dubious or otherwise, it's often hard to be sure. Are there possible benefits to getting the tree down? Is the resisto reading the only evidence in support of felling? How's the crown/rest of the tree looking?

[Amelanchier]

as above ive got some resistograph printouts from an Oak ive been to look at, ive little experience with the resistograph and im trying to work out what the results are really saying. ive contacted the company who undertook the survey, who have so far been less than helpfull. the trees owners put in at app to fell the tree on the basis of the results ,but the LA responded that there was insufficient explanation of the results to warrant felling

 

Why is this your problem John? The previous complany were presumably engaged to undertake a resistograph test with the intention of providing some useful information. They appear to have failed and your client should be raining endless grief upon them rather than passing the results onto you for a second opinion!?!