UKTC Archive

Re: Tree Valuation systems

Subject: Re: Tree Valuation systems
From: Scott Cullen
Date: Dec 23 2010 12:01:10

  ----- Original Message ----- 
  From: Rupert Baker 
  To: UK Tree Care 
  Sent: Thursday, December 23, 2010 6:20 AM
  Subject: RE: Tree Valuation systems


  Dear Scott, et al,
  After my initial post, I re-read the paper, and it seems to me that the
  method advocated is much more soundly based than others I have used;
  especially, it uses an additive formula rather than a multiplicative one
  like Helliwell. (multiplicative ones increase errors form subjectivity to a
  much greater extent than additive systems).  

  SC True enough.  Simply maths at work.  And at work internally in any 
particular method.  A bigger concern is the foundation or underpinning of the 
method.  For instance what exactly is the Helliwell basic unit supposed to 
represent?  Is it a benefits unit (some sort of revenue)?  Is it a market 
price unit?  

  SC  In any particular method, the adjustments can be upward from some basis 
or downward from some basis.  If you have a basis of X per unit size and Y 
units of size then multiplication is sound.  (That might actually be 
development of total basis subject to adjustments).  So say 20X is the basis 
you can add points or whatever or multiply to get higher (as in CAVAT going 
higher for population density).  In CTLA methods the adjustment is from 20X 
downward.  The 20X represents to cost to replace or reproduce.  The 
adjustment addresses whetter the tree is worth it or less.  That is 
frequently done by multiplication by a %age<1.0.  Say the tree is 50% dead.  
It could also be done by simple subtractions of a known amount.  Using the 
known amount is better, but we don't often know the amount but we do know the 
tree is half dead or that it is 1/5 of a group and won't be missed as much as 
if it stood alone.  Some of this is by its very nature subjective and 
subjective judgments (error potential and all) are better than none when 
adjustment is obviously required.  

  SC Additive or subtractive adjustments from some table indeed reduce the 
variations among valuers.  But what do we know about how the methods 
developer selected the table adjustments?  

  SC So it is not as simple as additive vs multiplicative.

  RB The results for heritage trees
  in Hong Kong are skewed to give very high prices because of the
  extraordinary real-estate value in HK; a similar system used in US or UK,
  adjusted for local property valuation, would work rather well, I think

  SC Could well do.  Another basic question is what particular type (flavor) 
of value the problem requires.  When the market for property values the 
development potential of the land area and the space above it than it does 
the tree, the market value of the tree does nothing to protect it.  When the 
community wants to protect those trees and the law puts teeth in it something 
that elevates the tree to the level of the market land value can be 
effective.  This no doubt horrifies market valuers.  The recent RICS GN on 
Amenity Tree Valuation pretty much speaks to that horror.  The point is that 
valuations address some problem.  And may not fit other problems.
  SC And there will never be a one size fits all valuation method.  So no one 
attribute of a method makes it universally more or less sound.


  Have a good Christmas everyone!

  SC Indeed!

  All the best

  Rupert

  -----Original Message-----
  From: Scott Cullen [mailto:dscottcul@xxxx.net] 
  Sent: 21 December 2010 21:43
  To: UK Tree Care
  Subject: Re: CAVAT .....not really....climate change, peer review,
  bristlecones, hockey sticks, PCA......


    ----- Original Message ----- 
    From: Rupert Baker 
    To: UK Tree Care 
    Sent: Tuesday, December 21, 2010 4:11 PM
    Subject: RE: CAVAT .....not really....climate change, peer review,
  bristlecones, hockey sticks, PCA......


    If you want to have a look at Prof Jim's article, here is the link:

    http://www.springerlink.com/content/l03207w075150645/fulltext.pdf

    and the reference:
    Journal of Environmental Monitoring & Assessment: Vol 116; No's 1-3,
    PPs 58-80

    SC Ha!  No wonder I couldn't recall which journal.  Thanks for the ref.

    The bit that interested me was:  on average, the method gave values 66
  times
    higher than the CTLA method........... largely because of property values
  in
    Hong Kong - I'd never be able to afford to live there!

    SC  As I recall there were some issues with the use of CTLA methods and
  his "CTLA" values were lower than might properly result.  But none the less,
  even corrected, the multiple from CTLA to FEM would be several times.  Also
  as I recall, the relulating FEM values were not necessarily based on market
  data (actual contributions of trees to property market values) but rather
  the inputs and adjustments were intended to result in values high enough
  that trees were not trivialised in comparison to property values.  No I
  suppose I should test my recollections by re-reading the paper.
    SC You and I could not afford to live in posh neighborhoods, but I imagine
  there are neighborhoods where we could pool our money and afford a closet.

    Cheers

    Scott


    Rupert

    -----Original Message-----
    From: Scott Cullen [mailto:dscottcul@xxxx.net] 
    Sent: 21 December 2010 18:16
    To: UK Tree Care
    Subject: Re: CAVAT .....not really....climate change, peer review,
    bristlecones, hockey sticks, PCA......


      ----- Original Message ----- 
      From: Jon Heuch 
      To: UK Tree Care 
      Sent: Tuesday, December 21, 2010 12:00 PM
      Subject: RE: CAVAT .....not really....climate change, peer review,
    bristlecones, hockey sticks, PCA......


      Peer review may have its flaws, but it does help an editor weed out
    problem papers - just that,
      help, not guarantee. However, just because it may have flaws shouldn't
  put
    you off it. On the other
      hand, having CAVAT "peer" reviewed by arborists would have its
  limitations
    - it needs to be reviewed
      by a wider group of professionals.

      SC Accepting the flaws, the question would be "peer review for what?"
  The
    peer review process is most applicable to research.  Was the experimental
    design acceptaable?  Were the data and analyses appropriate.  Were the
    properly arcane and symbol heavy statistical tests applied?  And so on.
    "Peers" are folks with some familiarity with the basics of research and
    statistics and the topic area.

      SC would CAVAT's peers be the LTOA?  Well this is keen, it does what we
    want and it can be learnt in a day.  Economists would not get it because
  it
    is not what normative economics tells them the world should be like.
    Chartered surveyors sort of get it and are bothered by the results not
  being
    tied to "market."  Nevermind that amenity trees, especially street and
  park
    trees, are not market goods... they should be.  CAVAT could be reviewed
  for
    its maths, that is the calculations. One of the biggest questions is the
    validity of the population density multiplier (or whatever it is called).
    Understand that the adjustment assumes that a tree in central London MUST
  be
    worth more than a tree in a country churchyard because more folks enjoy
  its
    benefits.  Intuitively appealing.  How is the resulting number tested?
  When
    we undertstand the mnethod was crafted to create eye catching numbers then
    it is what i claims to be.

      SC C.Y. Jim who is a professor in Hong Kong and fairly prolific in
    publishing developed a Formulaic Expert Method to Value Trees in a Compact
    City.  It was peer reviewed and published (not sure in in Arb Jour, Urban
    Forestry and Urban Greening, Journal of Arboriculture or Landscape and
    Regional Planning).  FEM's stated purpose was to arrive at figure
    sufficiently large to discourage tree loss in development in Hong Kong.
    Would CAVAT fair any differently in peer review?

      SC IMO part of the problem is that few - even in the various "peer"
    communities - really understand the range of meaning for "value."
    Economists want it to be one thing, surveyors another and perhaps arbs
    another.  And there is nothing essentially wrong with that.  The problem
  is
    when one concept is tested by the preconceptions of another.  Valuation is
    always an answer to a question or an aid to a decision.  A valuation
  method
    can only be judged by how well it addresses the question or the decision.
    And the decison maker might be aided by any number of questions, that is
    look through various lenses.

      Scott Cullen


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  The UKTC is supported by The Arbor Centre
  http://www.arborcentre.co.uk/




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  The UKTC is supported by The Arbor Centre
  http://www.arborcentre.co.uk/


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To unsubscribe send mailto:uktc-unsubscribe@xxxxxx.tree-care.info

The UKTC is supported by The Arbor Centre
http://www.arborcentre.co.uk/