Managing ageing trees
Many of our significant trees are under threat from different urban impacts.
Because a vast number of trees were planted around the same time during the latter part of the nineteenth century, many giants specimens – particularly Moreton Bay Figs – are rapidly approaching old age (senescence). The increased stress they experience in urban environments can accelerate their decline.
These typically ageing trees are located in a rapidly changing urban context. With building and infrastructure development and property consolidation, they often have less than ideal space to survive and grow.
As development continues, the processes of incremental loss intensifies. Each development proposal in isolation may not seem significant. However, the cumulative impacts of these actions over time can shift the balance and damage trees.
Developments, such as multiple off-street and underground parking areas, driveways, drainage retention devices, expansive outdoor paved living areas and swimming pools have all substantially increased the building footprint on blocks of land.
Intensive building leads to dramatic changes in existing soil profiles, with earth often compacted around the root systems of trees. Developments can greatly alter water-tables, modify soil nutrient and pH levels, change salinity, affect drainage and introduce new pathogens. All of this impacts on ageing trees in varying ways.
Even in established open spaces, our significant street and park trees are under enormous pressure. More people and traffic compact the root zones of trees, taking a heavy toll on the long-term viability of these specimens.
The space for these often large, remnant trees is diminishing as services increase.
Many significant trees are close to roadways – a legacy of nineteenth-century row planting. These trees may be affected by overhead and underground services and the requirements for access, maintenance and renewal of this infrastructure.
As a result, the city’s sylvan heritage is gradually diminishing. Individual specimens are being lost from ever smaller groups of trees. At the broader level, the visual integrity and historical connections trees have in particular landscapes are being greatly altered.
Replacing dying trees
Throughout much of the Post-War period and the latter part of the twentieth century, there was little systematic approach to ensure staged replacements to address these losses. As a result, ageing cultural landscapes are now in peril.
It is increasingly hard to find space for large specimen broad-leaf trees that have created Sydney’s outstanding landscapes. Replacement strategies often emphasise the use of smaller alternate species that require less space. For example, massive Moreton Bay Fig trees tend to be replaced by the smaller Port Jackson Fig, that was often a component within the palette of larger growing figs.
The City recognises the need to maintain our cultural heritage and landscapes. In many locations we have begun the process of succession planting, utilising the same species where appropriate and sensible.
The overall integrity and scale of historic schemes needs to be carefully considered and balanced within new management realities. It is important that we are flexible in selecting suitable replacement species and ensure that site-specific opportunities and constraints are properly addressed.
Find out more about the City’s policy of planting replacement trees.