When did you stop beating your wife? 4.5.2011

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At yesterday’s meeting of the Laman Street  Poor-Bloody-Fig-Trees Working Party, members  were addressed by Council’s insurer’s solicitor (quel mouthful) and  Ken James, an engineer who is an expert in tree stability.

There was a sense of déjà vu for me about many of the issues that came up. I presume the minutes of the meeting will be public so I’ll write about what stood out for me.

The 25-words-or-less version is that the working party moved that cutting edge technology be used to monitor the stability of these beautiful and iconic trees – and the hope of course is that this will provide the evidence that these trees can be preserved for many years to come.

I liked the fact that the solicitor preferred to use the word ‘collapse‘ rather than ‘failure’ when talking about trees – if this straight talking were commonplace we wouldn’t have had experts confused about what happened to the trees in 2007.  

His talk was full of scary stuff . A huge issue for Council staff is that they can be held personally liable if something goes wrong and they have not taken appropriate action to prevent it. A community representative pointed out that there is action that can be taken by council to look after these trees so we can move forward, such as encouraging aerial roots and mulching [not replacing them with liquidambars].

The solicitor gave examples of public liability cases. He was asked how commonly trees come up and he said it’s usually only in relation to cars driven into  fallen trees. He said there has been no death from a street tree falling on a pedestrian, but gave the sad case of a major branch injuring a woman in Hyde Park.

Cr Osborn asked about balancing risk throughout the LGA – trip hazards versus rock platforms on the coast versus trees. [Skate parks – fully supported and indeed supplied by Council – must be a great example of risky places.]The solicitor said it could be argued that in the case of slippery rock platforms if you have provided steps down to a risky area, a ‘slippery when wet etc’ sign would not necessarily lessen your liability because you have led the person down there… [Do they teach that thinking at university?]

One of my favourite parts of the meeting was when the acting General Manager asked if there had been any tree collapses in Laman Street. He was toldNot yet’. And he asked if there had ever been any major branch failures and he was toldNot yet’. [Reminiscent of ‘When did you stop beating your wife?’]

What stood out from KenJames’ talk was that there is no structural info on Hill’s figs and very little info on urban trees, and that a lot of the work that has been done has been on northern hemisphere trees which may have no relevance to Australia.

In Europe there are examples of expensive and long-term measures that are saving trees that once would have been condemned. In the US he gave the example of the Liberty tree where no expense has been spared to save the tree.

He said it’s important to define failure (but if we did I missed it).

He explained dynamic testing ie monitoring movement of trees using gorgeous-looking devices.

He mentioned a device called an accelerometer which at the moment is expensive and experimental but in 5-10 years will probably be routine.

He gave a lovely example of a tree outside the Vice Chancellor’s office at Monash uni which is 25metres tall, towering over the building and exposed to winds; it looked very dodgy because the ground had been excavated nearby. He was asked to monitor it which he did; a major windstorm came and the tree survived but ironically a healthy-looking tree on the other side of the building fell down while the dodgy one survived and is still standing two years later.

He talked about the benefits of trees for example the difference in temperature under and around them: he gave an example of Swanson Street in Melbourne where there are two rows of trees that create a beautiful area for people to walk under [hello Laman Street].  He gave the example of Singapore where the policy is to cover all road surfaces with tree canopy [presumably to reduce the heat island effect and to prolong the life of bitumen].

He touched on carbon credits, aesthetic value, heritage importance, and how much a community values trees versus risk.

He was asked about planting new figs in the spaces where trees were removed and he said small tree shouldn’t be a problem from a structural point of view.

He said groups of trees do better than individual trees. He said removing branches can be bad from a tree stability point of view because branches tend to disperse energy in wind but he said that was a controversial statement. (It did make me wish such a controversial statement had been made when yet more major pruning took place in late 2009, early 2010 in Laman Street.)
.

He was asked whether road base can hold up a tree – since this has been asserted a number of times and my understanding was that he said this can be the case in the short term but not long term.

***

Wouldn’t it be great if we didn’t have to rely on visual tree assessment at all, ever again? I can dream. Home

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