Council assessed the Laman Street trees according to the DCP element 4.10 Tree Management.

DCP element 4.10 Tree Management

During the last decade significant issues have arisen about the maintenance and safety of Hills figs used as street trees in a number of locations across the city.

In the case of the Laman Street-Civic Precinct Hills figs, road works and the subsequent installation and maintenance of underground public utilities including electricity, stormwater and water supply have created structurally compromised root plates resulting in greatly reduced ability to withstand wind loading.

The Hills figs trunk and branch structure along with pruning techniques used on these trees in their early development have weakened crown architecture leaving a canopy that is prone to rapid and unpredictable failure.

These defects and associated risks have been identified by Council and independent arborists. The results of the independent Quantified Tree Risk Assessment indicate the Laman Street figs pose a significant risk to public safety and Council must implement risk abatement strategies.

Risk management options

In response to these identified risks and to exercise its duty of care, Council's Infrastructure Management Services developed and implemented a range of risk management options.

This includes the restriction of public access to this area when mean wind speeds exceed 50 km/hr. Weather predictions for this mean wind speed trigger an automatic SMS message to designated Council staff who undertake Laman St road closure procedures, including the notifications to all relevant agencies and stakeholders.

This risk management regime has been in place since December 2009 and ensures Council actions are in keeping with State Wide Mutual Insurance obligations for managing risks associated with trees located in the public domain.

This obligation requires the risk abatement strategy to be continually reviewed and upgraded as required. This has happened with changing circumstances since Dec 2009

Maintaining the trees 

Pruning and soil/surface treatment.

Pruning to reduce crown weight has been undertaken to compensate for the annual increase in tree crown mass. The need for further pruning will be considered in view of potential impacts on tree health.

Removal of infrastructure

Removing current infrastructure such as kerb and gutter and road pavement risks increasing tree instability because the trees are gaining a degree of support from the bulk of existing infrastructure.

Asset Renewal

Council is committed to sustaining the public tree population by strategic replacement planting and by scheduled whole of life tree maintenance. Species planted in an earlier era may no longer be suitable selections for today. Tree planting and maintenance practices have changed and past practices are no longer acceptable.

Whole-of-street approach to Laman Street

The recommendation for adopting a whole-of-street tree replacement strategy responds to the identified increase in risks to remaining trees when some individuals are removed from within the street - eg removing the short usefeul life expectancy (ULE) trees and retaining the longer ULE trees.

Expert advice received by Council rejects engineering solutions such as cabling remaining trees in order to increase stability.

In order to reinstate a tall closed canopy character in Laman Street the new planting must have adequate below ground space for root development. This space is currently confined to the road due to existing utilities.

A redesign of the precinct may afford other opportunities that the current site constraints do not allow.