UKTC Archive

Re: Non invasive cable brace[Scanned]

Subject: Re: Non invasive cable brace[Scanned]
From: Scott Cullen
Date: Dec 21 2006 14:30:10
SC: insertions
  ----- Original Message ----- 
  From: John Hearne 
  To: UK Tree Care 
  Sent: Thursday, December 21, 2006 8:41 AM
  Subject: RE: Non invasive cable brace[Scanned]


  Ian wrote:

  > If the focus of the applicant's justification for losing the tree is
  >down to the cost of maintaining the cable then surely the argument
  >doesn't stack up against the vastly more significant cost of felling
  the
  >tree, even if this financial decision was based on a projection of
  >cabling maintenance visits throughout the remaining life expectancy of
  >the tree.

  Not necessarily. And anyway, if the owner's preference is to fell, he
  could appeal and could make a very strong case. How confident would you
  feel in defending a cable brace against robust questioning as to its
  effect on adaptive growth and load transferences?

  SC:  As noted following where are the data either way?  How robust is the 
questioning if it is based on conjecture or occassional occurences.  
Experience fairly srongly shows - my experience anyway - that cables are 
pretty effective at managing risks wothout demonstrably increasing other 
risks.

  I believe the worst storm damage at Kew Gardens has been to cabled and
  braced trees. 

  SC:  might be.  But what where are the data?  And why.  Sorry to be cynical 
but this too is like the elastic crowd claiming all sort of "karate cop" or 
"paradontos effect" failuers above steel cables.  OK.  Where are the data?  I 
have just not seen it in my environment with properly installed cables.  
There is good, sound literature that suggests that crotch failures or even 
twig failuers are a "safety valve" that prevent whole tree failure.  Could 
be.  There are high profile cases where lots of cables were installed in the 
crown and the tree failed at the base.  We can argue that by keeping the 
crown together, the intercepted load and the base bending monet are 
increased, leading to failure.  If there are base wealnesses that needs to be 
considerd in the first instance.  But again that is not a really compelling 
argument to avoid all cabling and either remove tres or tolerate risks.

  SC:  We also have to ask what loading led to the increased damage in cabled 
trees.  And compar that to the risk that was being mitigated.  Did the cabled 
leader fall on the structure below or not?  Did the cable leave the tree in 
place to deliver benefits for x years before the storm rather than removing 
the tree in the first instance?


  You may provide the necessary strength to a perceived
  weakness, but understanding the changes to the distribution of stresses
  that you may introduce is a far more complex matter.

  SC:  The growing science on this (Ken James and others) is a good thing.  
But we can overthink it.  Gotta go back to experience.  On the whole are 
cable braces doing their intended job without casuing other failuers?

  I suspect that, in many cases, braced trees are more vulnerable to
  failure in stormy conditions, and not necessarily at the point you
  expected and had attempted to guard against. If there are unanswerable
  uncertainties - you simply cannot enforce.

  SC:  doesn't that cut both ways?  Is it an inanswerable uncertainty whether 
the tree will live past tomorrow?  Next week?  Next year?  We make certain 
assumptions and make management decisons in the face of uncertainty.  It is 
what we do.  Is it really likely the cable brace will preserve the tree from 
failure of that weal fork? Is it sort or marginally likely that the cable 
brace might increase the failuer risk of other tree parts?  Os ot a 100% 
certainty that if we cut the tree down it's gone?

  On the other hand, TPO powers should allow enforcement of other
  essential works such as painting wounds, concreting holes, draining
  water pockets, excising the slightest whiff of diseased tissue - and
  sticking dead cats in cavities.

  SC:  The dead cat thing might be effective but if perodic cable inspection 
and maintenance are a cost issue at say every two year frequency, it pales 
compared to the cat replacement.  What with maggot activity, bacterial action 
and scavengers the carcass is not likley to last more than a month... maybe 
more in Winter.

  John Hearne
   
  Tree Officer
  New Forest National Park Authority
  South Efford House
  Milford Road
  Everton
  Hampshire
  SO41 0JD
   
  Telephone 01590 XXXXXX
  Fax          01590 XXXXXX

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