A short version of Mr Marsden’s report on Laman Street

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The day when council revisit the issue of the Laman Street Civic Park precinct is fast approaching.

Most of the community seem unaware that the fate of the trees has not been decided and they are comfortable in the mistaken belief that the trees are there to stay. I have lost count of the number of people who have expressed relief to me that the tree are staying and who are surprised when I tell them this hasn’t been decided.

As safety and the failure of other large trees in the precinct is where this all began I thought it was important to try to summarise last year’s arborist report on the health of the trees. 

I’ve abridged Mr Marsden’s report down to a page and a half. I’ve directly quoted from the report in all of the following except where square brackets show I’ve put in a word. The emphasis and italics are mine.

Mr Marsden did’nt have access to the ground-penetrating radar report (see link on home page) which showed that 8 of the trees have radial root systems, three have possible root systems and three have no apparent root systems or the peer review (see earlier post)  of the radar report which supported the investigators’ demonstration that what look like roots are indeed roots.

 Council believe that, based on trenching done by their teams,  the radar report is incorrect. There is a report on their website to this effect.

To me the important points are that

  •  Mr Marsden’s prediction is that something needs to be done about the trees some time in the next fifteen years 
  • the trees that may have inadequate roots have stood in this state for decades
  • all the trees that have failed have done so in storms.
  • root severance has been a factor in some tree failures.

Council close the street in storms now and have reduced the number of car parks in the street as well as the length of times cars can stay there. Because of these measures the street now rates as being better than ‘acceptably’ safe.

Here is my abridged version of the report. The whole report is available to read on council’s website on the page that has many key documents relating to Laman Street. It’s a very interesting read where you can learn a lot about Hill’s figs. I’ve left out the pages on included bark and notch defects because Mr Marsden says the trees don’t suffer from these to a worrying degree.

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An earlier study into the whole-tree failure of two Hill’s Figs on Tyrrell Street in 2004 concluded that …the trees had developed restricted, lineal root-plates through a combination of inhospitable edaphic conditions, constriction by nearby infrastructure, and root severance in infrastructure repair and road works.

 

All of the subject trees presented as being in acceptable health at the time of inspection. There were no signs or symptoms of major pests or diseases. There were no major fungus fruiting bodies on the stems or scaffolds or in the soil near the base of the trees. There were no stem lesions associated with major woody-root and butt rot diseases such as armillaria and ganoderma. Foliage colour and density plus shoot elongation appeared normal.

The foliage displayed no chlorosis nor did the crowns display dieback or carry any deadwood of note. Several of the trees displayed epicormic shoot production on scaffolds that are growing in areas which have been suddenly opened up to sunlight following the removal of adjacent trees, a reaction considered normal.

All of the subject trees have varying degrees of included bark at the main unions, although the extent of included bark is not such that it matches or exceeds the parameters adopted by Council for assessing included bark.

 

None of the trees displayed the multi-planted stem arrangement that has lead to the failure of Hill’s Figs elsewhere in Newcastle

Hence, the root-plates are the main structural weakness of the subject trees. 

In assessing the subject trees, we are not dealing with trees that fit neatly within textbook examples of horticultural ideals and well defined defects, rather, we are dealing with a departure from the ideal and the departure takes us out of the textbooks and into grey areas that are neither perfect nor so far in the opposite direction to perfect that tree removal is instantly and unequivocally warranted.

The [asymmetric] scaffold arrangements are also problematic but not on the same scale as the root-plates. The problems of the scaffolds can be assessed to a degree by signs that accompany failure in the trees’ body language and by the adoption of parameters for assessing included bark.

Hence, the root-plates are the main structural weakness of the subject trees.

This is not to say that the trees are at imminent risk of failure. The historical evidence in Newcastle is that Hill’s Figs with lineal root-plates and a history of root severance are more likely to fail under storm conditions than Hill’s Figs with entire and radial root-plates.

 

The question of when the trees would be likely to fail or “how long have the trees got” cannot be answered with accuracy and can only be addressed in general terms. It is known that the trees have defective root-plates.

All the [previous] failures occurred under strong wind conditions.

Lonsdale [says] that “for the present, considerable subjectivity is involved in the assessment of trees with eccentric root systemsand in such cases, casebook experience of the tree species…may be valuable.”

Nine of the subject trees have been given a SULE rating of 3B, which is: “Trees that may live for more than 15 years but would be removed for safety or nuisance reasons”. This does not mean that the trees need to be removed now. This means that problems of safety are likely to manifest within the next 15 years. Future circumstances may arise which necessitate a reevaluation of the timeframe; the 15 years should not be viewed as fixed.

Three trees have been rated as SULE 4B “Dangerous trees though instability or recent loss of adjacent trees”. Category 4 trees are those that should be removed within the next five years. Assigning the trees as category 4B is not to say that the trees are at imminent risk of failure. The three trees that have been assigned to this category (trees 12020, 12021, and 12022) have been done so on the basis of a defective root-plate plus a crown configuration that makes the trees more prone to wind throw than the remaining trees, plus the history of failure of the trees that were adjacent to trees 12020 and 12021. The category is more of a way of prioritising tree works for the purposes of this report.

One tree…has been assigned category 4E “Trees that may live for more than five years but should be removed to prevent interference with more suitable individuals or provide space for new planting”. This tree is a different species to the rest of the group and is of very poor form, having been topped and left to regrow.

One tree has been assigned category 4G “Trees that will become dangerous after removal of other trees (for the reasons given in A to F)”. Tree 12014 has a pronounced bias to the north and would be at increased risk of failure due to severe crown imbalance if the trees to the windward orbuffering’ side were removed

While it is true that the trees have survived for many decades with defective root-plates, the assessment of the hazard potential of the defect is not an assessment that can be made solely by reference to arboricultural texts, as the texts themselves recommend assessment by casebook experience.

It cannot be stated with any degree of precision how much time is remaining for the trees; there are too many unknowns.

In other words (mine) Mr Marsden says

9 of the trees may become a problem in the next 15 years.

  • 3 trees are assumed to be problems simply because adjacent trees have been lost.
  • one’s a different species, has a lean and looks unfortunate.
  • and one is supposed to fail if the trees around it go.’

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At the charette it was very pleasing to hear the council’s arborist say there was no rush to take out the trees.

See you at the next 2 council meetings. Tuesdays 530pm, 2nd floor of the Town Hall.   Home       Index

 

 

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