Some questions about the pulling tests and VTA

[Peter Sterken]

The (second version, as the first had somo paragraphs repeated) article is attached here as a pdf-file

The abstract is: Current methods such as the Visual Tree Assessment (VTA) of Mattheck and the pulling tests of Wessolly (SIM) and others will be analysed here. A number of authors have asserted since 1998 that their “generalised tipping curve” (GTC) would predict the uprooting of trees by extrapolating small values of stembase tilt angle under a static pull, and that 100% of the maximum or critical uprooting moment (Mcrit) would be reached at 2.5º. However, evidence elucidated from literature and pulling tests strongly suggest that a very different tipping curve (similar to a curve published in 1965 by a comparatively unknown researcher) has been used instead for the pulling tests, where 1º = 100% Mcrit. That curve will be called the SIM curve herein. A number of related researchers report contradictory findings, by showing either uprooted trees that had obeyed the GTC (0.25º) or trees that had perfectly obeyed the SIM curve (1º) which is confusing. This paper also analyses highly-cited and influential proclamations regarding the GTC and the “dynamic” versus “quasi-static” WLA, that may have, quite simply, sprouted from unconscious research bias.

 

[moss]

Pardon my ignorance on basic methods used by "certified tree assessors" or others that use the commercial software tools that you mentioned to evaluate stem or root failure risk. A couple of questions:

Do the risk evaluators take measurements like DBH (or CBH), tree height, average crown spread, species, general condition assessment (hollowing, defects etc.), context variables (forest grown, open grown, proximity to water table, healthy root zone, etc.) and enter these values and variables into the software tool to calculate the failure risk value?

Is it correct that the failure curves are used for software modeling only, that assessors are not actually pulling on trees as part of the assessment?

And a comment on the commonly held (by researchers) codominant structure ideas that you mentioned, something to the effect of: "bark inclusion separates and weakens limb and stem unions". It seems obvious to arborist practitioners that it is the lack of "holding structure" and pervasive and increasing rot between the two codominant parts that causes failure potential, not some incremental wedging effect from bark inclusion and new layers of wood added over time. Or is it that researchers internalized the entire pathology around included structures and are shorthanding it to what sounds like a description of an incremental wedging effect?

Thx for sharing your work n this subject!
-AJ

 

[Peter Sterken]

Pardon my ignorance on basic methods used by "certified tree assessors" or others that use the commercial software tools that you mentioned to evaluate stem or root failure risk. A couple of questions:

Do the risk evaluators take measurements like DBH (or CBH), tree height, average crown spread, species, general condition assessment (hollowing, defects etc.), context variables (forest grown, open grown, proximity to water table, healthy root zone, etc.) and enter these values and variables into the software tool to calculate the failure risk value?

Is it correct that the failure curves are used for software modeling only, that assessors are not actually pulling on trees as part of the assessment?

And a comment on the commonly held (by researchers) codominant structure ideas that you mentioned, something to the effect of: "bark inclusion separates and weakens limb and stem unions". It seems obvious to arborist practitioners that it is the lack of "holding structure" and pervasive and increasing rot between the two codominant parts that causes failure potential, not some incremental wedging effect from bark inclusion and new layers of wood added over time. Or is it that researchers internalized the entire pathology around included structures and are shorthanding it to what sounds like a description of an incremental wedging effect?

Thx for sharing your work n this subject!
-AJ

Hey Moss,

On "Do the risk evaluators take measurements like...": you should ask them But not all the necessary variables are taken into account, by which considerable deviations from reality may surge.

On the uprooting curves: some curves have been used to actually pull on trees as part of commercial assessments by assessors. Besides that, related researchers/assessors have published questionable, contradictory or even entirely wrong information regarding those tipping curves.

On co-dominant branches and included bark: there is some literature out there. But, that fairytale has been very influential and can still be heard among assessors and arborists. Nevertheless, I included my analysis on that fairytale, as nobody else had ever published my perspective, from which it can be suggested that VTA has self-invalidating foundations.
I hope this helps Greetings

 

[moss]

Hey Moss,

On "Do the risk evaluators take measurements like...": you should ask them But not all the necessary variables are taken into account, by which considerable deviations from reality may surge.

On the uprooting curves: some curves have been used to actually pull on trees as part of commercial assessments by assessors. Besides that, related researchers/assessors have published questionable, contradictory or even entirely wrong information regarding those tipping curves.

On co-dominant branches and included bark: there is some literature out there. But, that fairytale has been very influential and can still be heard among assessors and arborists. Nevertheless, I included my analysis on that fairytale, as nobody else had ever published my perspective, from which it can be suggested that VTA has self-invalidating foundations.
I hope this helps Greetings

Yes, perfect, thx!

 

[Bart_]

In a Joe Pesci voice, "You mean to tell me that grits boil different on your stove. The laws of physics cease to exist in your kitchen.... " Or use a Neil DeGrasse Tyson voice when he analyzes a space movie for "liberties" taken with astrophysics.

Very in depth. Seems like it ought to see some light of day and be addressed.


In a substantive vein, Smarter every Day had a video shaking pecans off for harvest with unidirectional back and forth vibration; he high speed camera'ed the distal twigs and for two 90 degree orthogonal directions of vibration application the twigs ended up wiggling the same, in their own directions. Tells you something about tree crown dynamics.