Centennial Parklands’ Tree Master Plan recognises that estimating a tree’s life expectancy is quite difficult. Typical lifespans vary with different species as well as between individuals within a species. There are a number of factors that contribute to any estimation process.
Analysis of tree life expectancy must begin with a close look at the age and condition of the existing tree population. Before any prognosis about a tree’s lifespan can be made, consideration needs to be given to its growth rate and performance over time, taking into account the particular conditions in which the tree finds itself growing.
The environment is a major factor to be considered in this regard. In Centennial Parklands, trees have to contend with a range of problematic factors, including a fast draining and sandy soil, which is low in nutrients and poor in its water holding capacity, a degree of coastal-zone exposure. Growing in a Parkland has its own limiting factors and stress causing factors, such as a restricted cycle of nutrients that would usually be sustained within a plant community, compaction by vehicles or pruning required for public access such as roads.
Taking into account growth criteria and environmental measures, Centennial Parklands arborists are reluctantly forced to acknowledge that their most venerable tree assets are in gradual but inevitable decline.
Trees are living organisms that have definite lifespans. Trees all eventually reach a senescent phase where they are likely to have more health and disease problems, increasing their rate of decline and/ or structural stability. These may become likely safety concerns requiring increasingly intensive management. We can prolong the life of mature and even over-mature trees, however, good tree management also requires making pragmatic decisions based on maintaining a healthy tree population with all the associated benefits and plan for the future by getting new plantings underway now.
A tree replacement program
The Centennial Parklands Tree Master Plan promotes a proactive planting and replacement program for its ageing tree population – the majority of the Parklands’ trees were planted between the 1880s and 1920s.
This means that as the designed landscape comes to maturity, it has a beautiful, coherent appearance. A problem with this in is that as trees reach an age requiring replacement, a lot of individuals begin to decline and require removal simultaneously.
Staged and planned succession planting is the ideal. This means not waiting for a tree to die, but rather to take proactive and early steps to plan for its replacement.
In many cases, you can’t establish new trees until the mature ones are taken out. The growth habits of existing trees, and their dense proximity, would make it virtually impossible for new trees to grow and thrive.
Grand Drive is a good example where staged ‘block replacement’ will ultimately be required in combination with selective tree replacement in locations where conditions are suitable for establishment. With Port Jackson figs, Holm oaks and Norfolk Island pines growing together in such close proximity, competition for space (both underground for roots and above ground for canopy), sunlight and water is fierce. It would be extremely hard for the new trees to become established under these conditions.
We are currently underway with our Grand Drive succession planting, which aims to establish (and experiment with) a new generation of trees, paying tribute to the same species and planting sequence that was originally laid out by William Forsyth in 1897, which will fill some gaps and eventually replenish our iconic road avenue.
Retaining the identity of the Parklands
The Tree Master Plan’s uncompromising objective, however, is to retain the identity and character of the Parklands. This means conserving the design elements that its great early visionaries Charles Moore and Joseph Maiden, and their overseers created.
They translated an English ‘Public Park’ design idiom into the Sydney landscape through the use of Australian tree species, such as Moreton Bay figs, paperbarks and Norfolk Island pines, to provide a similar visual effect. They took a very visual image of the English ‘Public Park’ and remade it in an Australian setting with Australian species.
The Parklands has a mix of Australian natives and exotic species. Most people think of eucalypts and acacias when they think of Australian natives, but in the Parklands, there is a more quirky mix, including trees from rainforest habitats much admired in the nineteenth century but now less widely used.
A fascinating aspect of the Parklands’ history of tree planting (see A History of Tree Planting) is the way it reflects a philosophy of trialling and experimentation that still underpins the Parklands’ planting practice. It was a paramount philosophy at the time of Moore and Maiden, neither of whom could predict what would work and what wouldn’t.
Diversity is strength
It is nevertheless salutary to reflect that some over half (58%) of the 15,000 trees in the Parklands are represented by only a handful of species – Predominantly the Melaleuca quinquenervia (broad leaf paperbark), Pinus pinaster (maritime pine), Ficus rubiginosa (Port Jackson fig), Eucalyptus spp. (eucalypts), Casuarina cunninghamiana (river she-oak), Quercus ilex (holm oak) and Ficus macrophylla (Moreton Bay fig).
Having greater diversity in tree species will give greater protection to the Parklands in the long run. This was graphically demonstrated by the devastating impact of the Fusarium wilt (fungus) on the Canary Island date palms on the Avenue of Nations, Parkes Drive. If we can get greater diversity in trees, we will be building protection in depth from potentially catastrophic events such as this pathogen, that may affect all individuals within a species. The Parklands can benefit in many other ways by increasing our tree diversity in age and species such as, the introduction of more flowering trees that increase the diversity of pollinators or trees better suited to their environment, which is more appealing to the eye or provides more shade to sit in on a hot day.
The Tree Master Plan identifies a range of trees already planted in the Parklands which may be worthy of wider use, including Angophora costata (Sydney red gum), Flindersia australis (crow’s ash), Ficus virens (deciduous fig), Quercus suber (cork oak), Quercus virginiana (live oak), Metasequoia glyptostroboides (dawn redwood) and Brachychiton discolor (pink lace wood). The plan also recommends a range of trees that may be worthy of introduction to the Parklands, including Bauhinia spp. (orchid tree), Castanospermum australe ( Moreton Bay chestnut), Elaeocapus grandis (blue quandong) Jubea chilensis (Chilean wine palm) and Koelreuteria paniculata (golden rain tree).
The way forward
Tree management practices are continually developing and evolving in response to a greater understanding of the environment and ongoing monitoring of tree performance.
Trees are recorded and managed using our ‘Iris’ database, which assists the arborists in managing such a large and demanding collection of trees. It will also enable us to develop a state-of-the-art interactive visitor experience, which is currently in development where information about the Parkland trees you love so much will be accessible at the touch of a button through any smart device. The Parklands continues to be a leader in the documentation and prioritised management of trees.
The implementation of the Tree Master Plan will be incremental and occur over decades as we work with our dynamic and everchanging Parkland. Sometimes it can be daunting to imagine trees being cut down in such a beautiful landscape, but a far more frightening vision would be to do nothing.
Download the Tree Master Plan
The Centennial Parklands' Tree Master Plan is available to download. Please be aware these are large files and may take some time to download.
Tree Master Plan - Volume 1
Tree Master Plan - Volume 2
Download Executive Summary (PDF, 2.4MB)
Download Part 1 (PDF, 3.1MB)
Download Part 2 and 3 (PDF, 3.1MB)
Download Part 4a (PDF, 3.0MB)
Download Part 4b (PDF, 4.7MB)
Download Part 4c (PDF, 2.7MB)
Download Part 5a (PDF, 1.8MB)
Download Part 5b (PDF, 3.3MB)
Download Part 5c (PDF, 4.6MB)
Download Part 6 (PDF, 595kb)
Download Appendices (PDF, 434kb)