UKTC Archive

Re: stability of surviving stem of a split co-dominant tree.

Subject: Re: stability of surviving stem of a split co-dominant tree.
From: Jerry Ross
Date: Jan 18 2022 11:39:34
You say that with a co-dominant stem, there is minimal or zero connectivity of wood fibres between the two stems. That may be a bit true with some forks, but unless the division is at ground level (when the contribution of buttress roots comes in) there is going to be some structural connectivity. It's much easier to split a tight V-shaped fork as compared to a more open one, but it still needs /some /force to break it apart, and the force needed to initiate that split gets greater with larger diameter stems.
I don't think one can disregard that linkage entirely.
There's also the question of the strength of a single stem with a circular cross section as compared to one that's flattened on one side as a result of having developed appressed to its do-dominant neighbour; and the section that actually split is likely to be nearer D-shaped, so the business of "coping with loadings on cylindrical stems by pre-stressing the wood in cylindrical section" cannot be assumed to apply. Especially at the tear, where there is no bark or outer tissues present to hold it all together. Also, of course, the stem that's left is likely to be leaning with nearly all the branches on one side. OK as long as it was sheltered by its other half, but... Every situation is different but my instinct would be to be rather suspicious of your imaginary tree.



On 18/01/2022 10:52, "Rupert Baker" (rupert_baker@xxxxxxxx.co.uk) wrote:
Dear Dave et al,
Thanks for the responses so far; the link to treecalc is useful; many thanks. 
I do however have reservations about using it in this situation.
As I said in my original post, the x-sectional area supporting the remaining 
stem has not changed; on the hypothetical tree -
  (and it is hypothetical! - I do not have a particular specimen in mind at 
present; it is just something I've come across many times over the years)
- there were once two stems each connected to the main trunk below; by 
definition with a codominant stem, there is minimal or zero connectivity of 
wood fibres between the two stems.

Each stem is therefore being supported by its own cross sectional area of 
wood. If there is no defect or decay within this wood, what is the difference 
between a single stem with the other one broken out and a pair of such 
co-dominant stems on a whole, undamaged tree.

  I understand the effect of an open cavity on a circular cross section of 
wood - one only has to split logs to realise that once one has made the 
initial split the others are all easier. Trees have evolved to cope with 
loadings on cylindrical stems by pre-stressing the wood in cylindrical 
section (Wessolly et al amongst many others).

        The key thing I don’t know is: does the presence of the other stem in 
a pair of whole co-dominant stems act in any way to assist in the pre-stressing of 
its neighbour? Or does each stem behave as -in effect - a cylinder with a section 
missing; and thus be prone to failure through bending stresses.

Rupert

-----Original Message-----
From:uktc-request@xxxxxx.tree-care.info  On Behalf Of David Evans
Sent: 17 January 2022 17:10
To: UK Tree Care<uktc@xxxxxx.tree-care.info>
Subject: RE: stability of surviving stem of a split co-dominant tree.

<<I've been musing about this for some time; if one has a tree which was 
double-leadered, with a pair of codominant stems and a tight compression fork between 
them>>

Hi Rupert

Put your remaining stem through TreeCalc.

https://www.treecalc.com/?lang=2

It'll give you a starting point Safety Factor.  You'll then have a 
conservative measured assessment, that'll be free of all hidden noise, bias, 
and error that are endemic to qualitative opinions about what is difficult 
and complicated decision.

Cheers

Acer Ventura




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