----- Original Message -----
From: Luke Steer
To: UK Tree Care
Sent: Saturday, June 30, 2012 4:14 AM
Subject: Re: BS 5837 (2012) annex D
Hi Jon,
We assess structural condition separately and also life expectancy which is
based on a combination of both.
We developed this system for our own use and it works well. Each health
class and structural condition class is described within the report.
SC Some arbs shy away from life expectancy (generally or in a more formal
SULE construction) because estimates are imprecise or uncertain. IMO I don't
know how you select trees for retention or management w/o considering life
expectancy...based on health, structure, extent of construction impact and
another variable: species construction (root disturbance) tolerance.
SC The tolerance variable is in the Matheny and Clark text and was I think
based on an earlier BS5837. I not through this thread somewhat
interchangable use of vigour and vitality and I think that is common among
arbs and the public, notwithstanding that some purists (including I think
Shigo) insist vigour is genetic potential and vitality is specimen expression
or condition. So a purist might suggest tolerance is vigour and health is
vitality. I like Matheny & Clark's use of tolerance that is plainly
meanigful and avoids the potential confusion.
SC Looping back to life expectancy, what you do with the estimate can be
variable. It can be very useful on occasion to retain a tree with a short
life expectancy (and structurally acceptable): to provide scale or screen
while new plantings grow into the site; or to be a place holder, a piece of
ground that will accept a replacement later... may be easier to battle over
that space for an existing tree than a replacement; or as part of the tree
protection... that tree can serve as a traffic bollard, less likely to be
removed than the fence as soon as you turn your back, may take some abuse but
protect better retained trees beyond. But I digress...
Scott
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