Soil Vault a Must-Have for Urban Trees in the City of Swan
By Kristyn Maslog-Levis
The efficiency of the Citygreen® modular Stratacell™ system is on full display at the Vale development in the suburb of Aveley, Western Australia.
Several years after the first stage of the project was completed in 2008, the trees that were planted using the Stratacell soil vault system are looking much healthier compared to the ones that were planted not using the system.
For all three stages of the project, Arborgreen supplied the Citygreen Structural Soil Modules as requested by the City of Swan council. The first stage used Citygreen’s previous model of structural soil cell, the RC120 RootCell. The second and third stages were done in 2011 and 2012 respectively, both using the Stratacell structural soil cell.
Rod Gooden, Arborgreen area sales manager, says each installation was beneath the parking lanes, between the tree out-stands on the main connecting road, Millhouse Road, of the new Vale development in Ellenbrook, surrounded by the Swan Valley.
“The Council wanted to achieve healthy tree specimens to provide quality shade in summer and avoid costly infrastructure damage in the years to come,” Rod says.
He added that the main reason why the Citygreen system was chosen was to provide the trees with larger volume of quality soil, whilst not sacrificing the carpark spaces in the parking lane.
“The Citygreen structural soil cells provided the structural load bearing aspect to support the pavement for car parks, whilst enabling a huge amount of quality soil for the root system of the adjacent trees,” Rod says.
City of Swan Mayor, Charlie Zannino, says the City picked the Citygreen system as the developers wanted to put trees and car parking embankments in the verge.
“We needed a treatment that meant trees wouldn’t damage engineering and infrastructure but would still be able to grow. We had used different treatments around the City but had never tried this one before. We wanted to see which system would be more successful. With this system, the trees have plenty of room to grow and the surrounding infrastructure is protected,” Mayor Zannino says.
The only issue they faced was with the initial installation as none of the contractors have previous experience with the system. Mayor Zannino also said the staff experienced difficulties creating the design using the system because they had never used it before.
“We contacted CityGreen and they came up with the design. The contractors also talked to the company for guidance on the installation,” Mayor Zannino says.
Several years after the first stage was finished, Mayor Zannino says the trees that used the Stratacell system are a lot more advanced compared to the ones that didn’t.
Rod observed the same thing after his visit to the site in 2011 and 2012. He says the trees from stage one that were installed with the Citygreen system are clearly looking visibly healthier than the median trees not planted with the Stratacells.
The difference between the treatments and planting of the two areas was that the trees installed within the median were installed directly into the native sand/soil and the surface remained un-sealed with understory planting. Whereas the roadside trees are installed with more than six cubic metres of imported quality soil within the Structural Soil Cells and the primary treepit void.
“This provides ideal growing circumstances for the tree during its early formative years. The canopies of these roadside trees were clearly more densely foliated than the trees in the median area,” Rod says.
“Everything seems to be going alright. The system works well with the design. We’re still using it with the continuation of the road. I’d recommend it to others,” Tim says.
The project is still ongoing and this year they constructed a Neighborhood Connector boulevard road that “facilitated the upfront installation of large mature deciduous trees in verge nib areas adjacent to onstreet carparking embayments”.
James Westh from Stockland says they engaged a civil contractor to install the soil vault Stratacell modules and root directors for trees to be planted in Millhouse Road in Aveley.
“The trees are yet to be planted but the previous developers of the property installed the same product on an earlier section of the road where trees have also been installed,” James says.
James revealed that the City of Swan council made it a condition of the Civil and Landscape approvals to use the Citygreen system.
“The system provides a medium into which the trees’ roots can grow that promotes the roots using the soil provided in the cells in designated locations under the paving in the carbays as opposed to inflicting long term structural damage on asphalt, kerbs, paths, parking bay brick paving etc by having the roots create their own growth locations,” James says.
Although this is their first encounter with the soil vault system, James reveals they did not have any major issues with it.
“In the appropriate location and application in relation to the cost expenditure, we see no issue why this product couldn’t be used again,” James says.