Eye-catching Japanese Elms, known for their leafy canopy in summer and colourful displays in autumn, and an Australian native Weeping Lilli Pilli will replace the failed spotted gums in the Crown Street Mall.

All up, 12 Elms and 4 Lilli Pillis will be planted in the top end of the Mall between Keira and Church Streets. The work will be phased across March and April to minimise disruption to retailers, businesses and shoppers.

The decision to replace the failed Spotted Gums with the Elm and Lilli Pilli species comes after a number of Spotted Gums were removed from the Mall in August last year. The trees had their limbs and/or trunks broken after days of high winds which reached more than 100 km/h.

“We are the first to acknowledge that this has been a challenging process and that people want to know what we are going to do about the trees in the Mall and to solve the issue of the spotted gums,’’ Wollongong City Lord Mayor Councillor Gordon Bradbery AM said.

“The Mall is a unique urban environment and we needed to understand why the trees didn’t work, so we could look to a long term solution. The working group looked at the causes, assessed the remaining trees, and recommended the replacement species. It was complex work and based on the information at hand this is the best solution.”

The group, which included Council representatives and an independent expert, found there wasn’t one single cause of the failure of the spotted gums as a result of last August’s wind storm. Rather, their evaluation of the trees, and the subsoil conditions found there were a number of contributing factors. These were:

• The growing conditions of the spotted gums with the strong summer reflective heat saw them grow at 2.5 times the rate they would in their normal habitat.
• The watering system provided water at the base of the tree which meant the roots didn’t need to spread out to reach a water supply.
• The tree grates on the ground restricted air flow to the soil and roots.
• The rich organic soil placed under the paved surface needed to be denser to provide a more solid foundation for the root development.

“Now that we know there wasn’t a single reason the gums failed, but series of factors has been so important,’’ Cr Bradbery said.

“This information has been used when we looked at options for replacement species, as well as what needs to happen below the surface of the Mall to make sure these plants have the best growing conditions we can provide.’’

Cr Bradbery said the species of Japanese Elm and Weeping Lilli Pilli were chosen because they complimented each other in the urban environment. The mix of evergreen (Lilli Pilli and the existing Illawarra Flame) and deciduous trees offered shade in summer and opening the Mall up to winter sunlight while retaining some green foliage.

“By using the Elms in the western end of the Mall, we’re able to minimise the risk they will be damaged by the strong winds we regularly get in August,’’ Cr Bradbery said. “This is because, being deciduous, they’ll have lost their leaves and this means, unlike the Spotted Gums, the wind should be able to pass through them with less resistance.’’

The Elms and Spotted Gums drop a roughly the same number of leaves within a year – the elms just concentrated across a season.

The new trees will be about four metres when planted, and will grow to between 6-10 metres tall. They take about 15 years to be fully mature.

Before the trees are planted, there will be a new irrigation system installed into each of the tree pits. The system will be able to phase watering close the root ball and then further away as the tree grows. In addition, the tree grates will be removed and a modified version will be replaced once the trees are established, and a new tree anchor system will be used to hold the root ball firmly in the ground. The tree guards will remain.

“By using this combination of techniques, along with a phased planting during the optimum growing season on March and April, we’re looking to take on the lessons learnt and build on them as part of Council’s commitment to activate this popular space,’’ Cr Bradbery said.