Risk management quotes


The quotes and thoughts that follow entirely suit my purpose, which is letting people know there’s more to veteran trees than the risk they supposedly pose and less science than you think to tree risk assessment. People who believe QTRA (Quantified Tree Risk Assessment) – the method used to assess the safety of the trees in Laman Street – is infallible, for example, won’t find anything here to spruik about. The quotes are , of course, out of context but I have not tried to be misleading.The italics and emphasis are mine.  

That death or even serious injury by trees is rare fails to mitigate the widely held view that large trees are ‘dangerous’. The myth that trees are sentient beings that have intentions such as ‘seeking’ and ‘invading’ pipes is deeply ingrained. Some utilities and commercial enterprises reinforce these myths in order to gain work or support for the policies that remove trees and prevent replanting as a cost cutting exercise.    

  This first quote is from Phil Hewett, the Newcastle city Council chief arborist in his 2009 article at http://www.treenet.com.au/  ‘Urban Forest:Risk Started the Ball Rolling – So What Will Sustain it?’ Of course, Mr Hewett is absolutely to be congratulated for having been deeply involved in Newcastle’s Urban Forest Policy, something our city can be proud of.  

  In the Newcastle Herald ‘Bogey Hole Debate’ , 26 12 2009 (see ‘Not a Tree but another Newcastle Icon’) Newcastle  City councillor Aaron Buman said he supported many suggestions in the plan [to ‘revitalise’ the coastline of Newcastle] but it was unrealistic to close the Bogey Hole and was indicative of a council that wanted to remove all risk from amenities. “There is a tendency to just close something down to reduce cost or liability instead if deal with it.”     

  Substitute trees for amenities and you have the approach to remove all the trees from Laman Street.  Of course, Mr Buman voted in favour of the rescission motion.

treenet.com.au is an interesting website and has quite a lot of information about tree hazards and management. Mike Ellison has a 2007 article that says  

Whether in the public, corporate or private sectors, land managers have a legal duty to take reasonable care in managing the risks associated with trees in their control. But tree safety management goes beyond simply reducing the risks from trees, and requires consideration and optimisation of the benefits conferred by trees.    


  Mike Ellison, I believe, formulated one of the many ways to assess tree risk. In the same article he says     

‘It is usual to consider risks in two parts. Firstly, how likely is it that an adverse event will occur and secondly, what is the likely consequence of the adverse event. The likelihood of the event is considered in terms of both potential for tree failure and the likelihood that something of significance (target) will be present at the time of failure. ‘    

  This is significant when discussing trees like Hill’s figs which seem most likely to fail in ‘weather events’ when there are unlikely to be ‘targets’ (that’s us) in the vicinity.  

Elsewhere in this blog I have quoted Tony Blair from 2005 (I found this in a presentation on treelogic‘s website):  

 Britain… “is in danger of having a wholly disproportionate attitude to the risk that we should expect to run as a normal part of life.The result is a plethora of rules,guidelines,responses to “scandals” of one nature or another that ends up having utterly perverse consequences.My introduction to the world of tree risk management leads me to the conclusion that it is disproportionately risk adverse [sic]and is having utterly perverse consequences.”    


Mike Ellison’s already quoted 2007 article talks about risk assessment methods:  

There are several methods of tree risk assessment, the majority of which provide a ranking of risks on a simple scale … Norris(2007) reviewed fifteen of these methods including Quantified Tree Risk Assessment …    

Norris (op. cit) concluded “The 12 experienced arborists who assessed eight trees using eight different methods, produced the most interesting results. The hypothesis was that experienced arborists would apply similar values in similar circumstances … However, it appears that the differences in [their] assessment values…was… diverse …[and] the variation produced by the arborists [rather than the method itself]…influence[s]…the risk… values created by each method.” When the 12 arborists were asked how well they thought each of the methods worked, one of the simplest methods scored the highest but the range of results…was highly variable and it is clear that … tree-failure risk assessment[s] are highly assessor dependent.    

 This is the thing that concerns me about trying to predict tree failure. No matter how eminent or well-known arborists are, there is likely to be someone who disagrees with their opinion.   

  There was a street tree case in South Australia in 2007 called Goode vs City of Burnside which hinged on the opposing opinions of two tree assessors. In his judgement Commissioner Hodgson cited a QTRA journal paper saying,

    “Having read that paper and carefully considered Mr Lodge’s evidence, I have significant reservations about the utility of the Quantified Tree Risk Assessment System … The precise nature of the way in which “Risk of Harm” is expressed suggests a level of accuracy and reliability not borne out by a close examination of the inputs to the calculation of that risk.For example, as Ellison himself notes in his paper, with reference to the criterion “Probability of Failure’: Accurately assessing the probability that a tree or branch will fail is highly dependant [sic] upon the skill and experience of the assessor.” Environment, Resources and Development Court of South Australia. GOODE v CITY OF BURNSIDE. [2007] SAERDC 5 Judgment of Commissioner Hodgson 14 February 2007  

Jeff Corbett, in his blog on 14 12 2009 had this to say:  

Most of Newcastle’s councillors say they’ve got to go, the 14 magnificent fig trees that form the iconic Laman Street boulevard in Cooks Hill. The councillors have been spooked by a consulting arborist’s report and a “quantified tree risk assessment” that states that the public risk posed by each of the trees is 500 times the upper limit of acceptable risk.  

In my column in The Herald today I question this. What is acceptable risk and its upper limit? Five hundred times that risk means, presumably, that I’m 500 times more likely to be injured when I walk under each tree than I should be.  

A great many more trees in Newcastle’s many suburbs will, presumably, have a risk rating 250 times the acceptable limit. Phew, they’ll have to go too. Thousands will be just 100 times the acceptable risk, and they’re for the mincer too. Twenty times the risk is 20 times too high. Even double the risk should doom a tree. I see the campaign to remove Newcastle’s trees as the denuding of Newcastle, a new buzz industry that when it expires will leave us with saplings.  

  “As arborists it is possible to locate faults and to predict tree failure, what is particularly difficult to predict is: ‘When will the failure occur?’ If we are accurate to within a ten-year period in predicting tree failure then in terms of tree time, that is pretty good… There are very few references to techniques or methods to determine tree stability.’  

Phil Kenyon, Reducing Tree hazards in Urban Horticulture; treenet Symposium 2002   

We know that all trees are potentially hazardous. The last quote is from Mike Ellison:  

If absolute safety from tree failure were achievable, society would almost certainly find the cost in terms of tree losses unacceptable.















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