Grand Drive Trial Remediation

The Grand Drive Trial Remediation is a project that the Centennial Park and Moore Park Trust (Trust) is undertaking to try to extend the life of some of the most significant trees within Centennial Parklands.

Grand Drive, the main loop road around Centennial Park, is a magnificent late 19th century landscape design feature comprising the riding track, footpath, road, trees, embankments and fences.

The most significant element of the Grand Drive landscape is undoubtedly the two avenues of trees. These avenues incorporate 466 trees, comprising three main species: the Port Jackson fig (Ficus rubiginosa), the Holm Oak (Quercus ilex) and the Norfolk Island Pine (Araucaria heterophylla).

The majority of these trees are considered to be in declining condition due to a combination of age and sustained soil compaction caused by the use of road base around the trees and vehicles parking over tree root zones.

Expert assessments indicate that replacement of most of these trees will be required over the next 20 years. A method of removing and replacing the Grand Drive Tree avenue in segments (block removal) is considered the most appropriate process to enable the future re-establishment of the formal avenue landscape (Centennial Parklands Tree Master Plan, 2002).

There are, however, a number of issues that have led the Trust to look for alternatives to block removal at this stage, including:

• total loss of tree canopy and heritage vistas that would result from this 'scorched earth' approach
• prohibitive cost of block removal - being in the millions of dollars
• changing community attitudes to the significance of these tree avenues and their retention

The Trust believes that it would be negligent in its care of the Parklands if it did not look at alternatives aiming to extend the life and existence of these trees before getting to the point of removal, and as a result has decided to implement this trial remediation project.

Much of the trial is about soil and soil improvement because trees depend on soil for water, air and nutrients.

The Grand Drive Remediation Trial will take approximately six months to complete, with work commencing on Monday 10 November 2008.

The trial site contains 13 trees (7 x Port Jackson figs, 4 x Holm Oaks, 2 x Norfolk Island Pines) and the parking bays between them located between the Robertson Road entry to Centennial Park to the Dickens Drive intersection (see map).

The Trust will be fencing off these trees and the 23 car parking spaces usually occupying this space for the trial period, to determine what effect car parking over the rootzone may be having on the health of the trees.

The trial activities will consist of installation of barricades, mulching, fertilizing, and aerating the existing soil profile using specialised equipment that injects shots of high pressure air into the soil profile up to 500mm deep to reduce the effects of soil compaction, without damaging the tree roots. The Trust has engaged an independent arborist and soil scientist to oversee this part of the project.

It is hoped that the trial will provide information about how the differing tree species in varied condition respond to the maintenance at this late stage in their life cycle.

These soil remediation works have proved successful for other parks and are considered ‘best practice’ arboricultural techniques for maintaining and improving the health of mature trees. The consultant Arborist who has been engaged will monitor and report on the trial to assess tree health and longevity benefits, in conjunction with the Trust's Arborist.

If successful the trees would be expected to show signs of recovery and improved health such as new root growth, denser leaf coverage in the canopy. branch-tip extension growth and renewed vigour.

This trial will determine whether an integrated maintenance strategy may be required to improve and prolong the life of other groups of trees along Grand Drive.

Each of the Grand Drive tree species - Port Jackons Fig, Holm Oak, Norfolk Island Pine - can be found growing in other parts of Centennial Park, where they are not subjected to the same environmental stresses. Their health and condition are very different for trees of approximately the same age.

Consider the following two images of Holm Oaks in Centennial Park. The first image is on Grand Drive within the trial project zone, the second is a Holm Oak of similar age elsewhere in the north east corner of Centennial Park.

The notable differences are the reduced canopy density, the thinning crown, the prevalence of epicormic or lower branch shoots and the lack of new extension growth at the branch tips of the Grand Drive trees.

Holm Oak (Quercus ilex) is a tree from the Mediterranean region that thrives in poor soil and dry climates. These two trees in Centennial Park appear remarkably different even though they are only a few hundred metres apart.

The Grand Drive Trial Remediation will take approximately six months to complete, with work commencing on Monday 10 November 2008.

The trial project zone is immediately adjacent to the Robertson Road entry gates to Centennial Park.

• Download an aerial map of this zone
• Find the Robertson Road Gates on the interactive map

The Trust has a qualified and experienced team of arborists and horticulturalists, working in conjunction with external specialists in the field of urban tree management and soil management.

The Trust has also invited recognised experts in urban tree management to provide independent validation of the process being carried out on the trees. They are:

• Ms Karen Sweeney, City of Sydney
• Ms Judy Fakes, Ryde TAFE, School of Horticulture
• Mr Bruce Rann, Woollahra Municipal Council

This trial will not result in pedestrian or cyclist access restrictions in Centennial Park.

Establishing the trial site will, however, result in the temporary loss of 23 car parking spaces (of 1880 spaces in the Park) for the six month period.

There will be minimal impact upon horse riding within Centennial Park.

During the initial two weeks of the project, the section of the horse track adjacent to the trial project site will not be open. The Trust is taking this step to ensure there is no danger of the equipment being used affecting the horses.

No other impacts are anticipated.

Centennial Parklands has a magnificent legacy of some 15,000 trees planted over the 120 years of its existence. The Parklands' trees enhance its aesthetic and cultural value and reflect changes in these values over time.

The Tree Master Plan for Centennial Parklands sets out principles and strategies for conserving the existing tree population. It also provides a framework for sensitively integrating new plantings into the Parklands' historic fabric, taking into account the plant performance, environmental constraints of the site, and aesthetic and design aspects.

The Plan defines management approaches to strengthen and sustain the ageing tree population, and ultimately the Parklands itself, into the next millennium. It puts forward a structured approach to phased removal and replanting of poorly performing trees, as well as guidelines for tree preservation.

It acknowledges the importance of the trees in defining the character, spaces and role of the Parklands throughout its history, and the part they play in enhancing its recreational, aesthetic and cultural value.

• Read or download the Centennial Parklands' Tree Master Plan

For more information on trees and tree management practices, please visit:

• Botanic Gardens Trust (Sydney)
• Department of Environment and Climate Change (NSW)
• Australian Institute of Landscape Architects