Case Studies

Page hero image

Tree failure

As was the practice of the day all Hills Figs in Newcastle streets were routinely lopped to form a stout short trunk with a multi-stemmed branch habit that could be kept neat and rounded. Lopping ceased in the late 1970’s and many of these Figs now exceed 22m in height and 30m width despite extreme root space limitations from buildings, pavement and utilities.

Newcastle CIty Council has collated an 11 year photographic record of tree failures to inform decisions regarding the useful life and relative safety of large mature trees in the public domain with specific application to the Hills Weeping Fig.

It is important that Council have regard for this case history in assessing risk and likelihood of failure. This information informed Councils management decisions in relation to the Laman Street Figs.

Tree root mapping

Newcastle Council is committed to a sustainable urban forest. As part of that commitment Council invests in gaining knowledge to better inform tree management decisions. The Laman Street Exploratory Excavation and Root Mapping report is one such example and provides a rare look at the structure of the Hills Fig root systems within footway and road pavement. It is of particular interest as the opportunity and cost of such investigation means they are rarely undertaken. These types of investigation are valuable as there is significant variability in the way root systems develop within an urban environment.

Conditions of use

The Laman Street Exploratory Excavation and Root Mapping Report (PDF) is a detailed and professional document that needs to be interpreted and considered in its entirety for any purpose. This work is copyright.  Apart from any use permitted under the Copyright Act 1968, no part may be reproduced by any process, nor may any other exclusive right be exercised without the permission of Newcastle City Council 2016.
 

Gregson, Wallsend, Richardson, National & Islington Parks

In 2011, Council inspected 250 large trees located in high use areas within these five parks. The result was that 235 trees were retained with mulch areas increased around them to extend their useful life expectancy. Only 15 trees were considered for further investigation.

One of the 15 trees considered for further investigation was a Moreton Bay Fig which was located in the north east corner of Gregson Park, Hamilton, and was removed on the weekend of 2-3 June 2012. Renewal planting will proceed in accordance with the Gregson Park tree planting plan.

Possible causes

Inappropriate pruning practices in the past and misunderstanding about the consequences of repeated tree injury initiated the decay that led to the hollowness, cavities and root instability in the Gregson Park Fig.
 

Trunk hollowness exceeded the acceptable threshold

The internal condition of this tree, as outlined in the May 2011 technical investigations, found that the trunk hollowness exceeded the acceptable threshold. Open cavities at the root buttresses and within the trunk compounded the hazard and the tree was considered an unacceptable risk due to how close the tree was to power lines, pedestrian pathways and a traffic intersection. Alternatives to tree removal such as isolating the tree, or crown reduction pruning were found to be impractical and unacceptable.
 
Tree cut at the line shown in the photo The extent of trunk hollowness

The tree showed strong signs of subsidence

The tree’s major scaffold branches had been intermingled with similar branches from an adjacent tree for many years, and the branches had separated which indicates subsidence. When the tree was being removed, staff observed that as the crane lifted the last trunk section off the stump, the entire root plate moved confirming why the rubbing branches had separated ie. the hollow tree’s root system had subsided.
 
Crossing branches at 15 metres above the ground Old branch contact wound suggested the hollow tree had subsided