What are Soil Vaults and How Do they Benefit City Trees?

Soil vaults like Citygreen’s Stratavault are underground structures that provide a natural rooting environment for trees in urban areas where soil is often compacted to handle the stress and weight of the above urban infrastructure. They are a modular matrix designed to support all of the tree’s mineral, nutrient, and root spaces requirements ensuring ideal underground growth conditions, while taking the weight of the above infrastructure off from the tree.

Trees planting in a continuous stratavault soil vaults in redeveloped Macquarie mall in Sydney Australia

Are Soil Vaults a Cost-Effective Solution for Urban Landscaping?”

Yes, soil vaults can be considered a cost-effective solution for urban landscaping in the long run. While the initial investment in installing soil vaults may be higher compared to traditional methods, their long-term benefits often outweigh the upfront costs.

Here’s why soil vaults can be cost-effective:

  1. Reduced Tree Replacement Costs: Soil vaults provide an optimal environment for tree root growth, leading to healthier and more resilient trees. This reduces the need for frequent tree replacements, which can be expensive in terms of tree purchase, planting, and labor.
  2. Enhanced Tree Growth: Soil vaults offer trees the necessary space, nutrients, and oxygen for robust growth. Well-established trees require less maintenance over time, leading to lower ongoing maintenance costs.
  3. Prevention of Infrastructure Damage: Urban trees with strong root systems supported by soil vaults are less likely to disrupt sidewalks, roads, and other infrastructure, reducing the need for costly repairs.
  4. Environmental Benefits: Healthy trees provide various environmental advantages, such as improved air quality, reduced energy costs through shading, and stormwater management. These benefits can lead to long-term savings for municipalities and property owners.
  5. Increased Property Value: Green spaces and healthy trees contribute to the aesthetic appeal of urban areas, increasing property values and attracting businesses and residents. This positive economic impact can indirectly contribute to the cost-effectiveness of soil vaults.

While soil vaults may have higher initial installation costs, their ability to accelerate healthy tree growth, minimize maintenance, prevent infrastructure damage, and provide numerous environmental and economic benefits make them a viable long-term investment for urban landscaping projects, and this is where having a asset register of your trees is invaluable to seeing the lifetime value green infrastructure can have.

All city councils have an asset register detailing the value of assets like roads, parks, street furniture, and so on. Increasingly – and rightly so – trees are now being included as quantifiable assets. In the past, it has been hard to quantify the value of trees, but today there are a number of methodologies for doing so. One such method, the Burnley Method – developed by Dr Greg Moore at the Victorian College of Agriculture and Horticulture Limited, Burnley Campus – is now being widely used and accepted. Available for download here.

comparison of stratavault soil cells and the end result of the tree installed in urban environment

The Burnley Method For Valuing Trees

The Burnley Method is a way to determine the value of trees in a straightforward manner. It involves looking at different aspects of a tree, such as its type, size, health, and where it’s located. By considering these factors, we can figure out how valuable the tree is both in terms of its natural qualities and its surroundings. The Burnley Method helps provide a clear and organized approach to assessing the worth of trees.


VALUE ($) = TREE VOLUME x BASE VALUE x (E) x (V) x (FV) x (L)

The modifiers to be used are: 

  1. TREE SIZE (V) : With large trees, the values determined by the formula were unrealistically high. Accordingly, a modifier was developed (Table 1) to reduce the value.
  2. USEFUL LIFE EXPECTANCY (E) : This modifier took into account the projected useful life expectancy of the specimen (Table 2).
  3. FORM AND VIGOUR (FV) : This factor was used to assess the form and vigour of the tree (Table 3)
  4. LOCATION (L) : This modifier was used to assess the tree’s suitability for its particular location (Table 4).

tables located here.

Why Cities Need To Value Trees

The City of Melbourne are pioneers in valuing their trees and looking after them accordingly. In fact, residents can even email local trees to raise concerns about their health or express their appreciation and affection for the tree. By putting a value on trees, councils are able to protect them in new and quantifiable ways.

For example, if a developer is building near a valuable tree, the council may require them to pay a bond – refunded provided the tree is unharmed post construction. If a developer destroys or removes a tree without permission, the council is able to sue that developer for the value of the tree per their register. All of this is effective and much-needed motivation to keep our valuable urban trees safe.

A council’s asset register forms a key part of their balance sheet. As the assets degrade over time, there is depreciation. Spend money on their assets, and there is growth. Naturally, councils want to spend money wisely in order to generate the greatest return on investment.

Internationally, providing enough shade in carparks is a big issue. Not only does shade drastically improve the shopping experience, it also prolongs the life of the pavement.

Results of using Soil Vaults for City Trees

In the City of Belmont, Perth, Citygreen’s Stratacell soil vault system had a massive impact on the council’s bottom line.

In an asphalt carpark next to an oval, five London Plane trees were planted in quite narrow islands, with adequate space and soil volume provided using the Stratacell system beneath the carpark pavement. The cost for the five trees (including the Stratacell soil vault system) was $50,000 at time of initial planting.

Four years later, as reported by Council, the trees have grown at an unprecedented rate – from a 75mm/3” trunk diameter at time of planting, to 250mm/10”. According to the Burnley method, these trees are valued by Council at $17,500 each – an amazing return on investment in just four years, with so much growth (literally and financially) still to come.

As a comparison, the same council planted the same species 15 years ago in a nearby carpark using the conventional method. The carpark was laid, a square cut in the pavement, some curbing placed around the edges, road base dug out, and a 80/20 structural soil loaded into the hole.

Planted 15 years ago (versus only four), these trees are valued at only $510 each. Of course, the initial outlay was much less ($250 per tree), but the return on investment monetarily, aesthetically and environmentally does not compare.

Related: Structural Soil VS Soil Cells: What’s The Better Choice?

tree comparison showing insane growth of the same tree species using soil vaults

Essentially, using the Citygreen soil vault system, this innovative Council was able to grow trees worth 34 times as much – in one quarter of the time!. As more emphasis is placed on generating ROI in relation to the value of trees, adopting innovative technology which enables trees to thrive in urban environments must be a priority.

Of course, this is not just about improving councils’ bottom lines, but also improving the health and wellbeing of the communities they serve.

Speak to our team to explore how soil vaults can maximise the value of your trees and generate an ROI faster.