Informing best practice in designing and maintaining engineered spaces for tree growth in paved areas in Australian cities

This work is copyright. Apart from any use permitted under the Copyright Act 1968, no part may be reproduced by any process, nor may any other exclusive right be exercised, without the permission of TREENET Incorporated, University of Adelaide – Waite Campus, PMB 1 GLEN OSMOND SA 5064




Expressions of Interest (EOI) are invited from organisations wishing to partner with TREENET in preparations for the delivery of a proposed national research project.

TREENET is seeking to refine the scope and methodology of the project, develop cost estimates, source funding opportunities and engage with key stakeholder groups in order to progress best practice in designing and maintaining engineered spaces for tree growth in paved areas in Australian cities.

Interest is therefore sought, at this stage, from research organisations, industry associations, product manufacturers/distributors, product user groups (eg. local government, landscape architects, urban designers, construction companies) and potential trial site stakeholders.

TREENET, as a reputable, independent non-profit organisation, dedicated to improving the urban forest, sees facilitating this research as critical to building home-grown evidence to support those designing our cities for trees.



2.1      Background

Urban trees and tree canopy cover are increasingly recognised as essential components of the cities and neighbourhoods where more than 90% of Australia’s forecast population of 35 million will live by 2050.  International research and practice, to date, has responded to the challenge of sustaining multi-functional, large, long lived trees within compact forms of development, amongst paved plazas, and alongside roads and streets.

A range of techniques have been advanced that are capable of delivering adequate quality and quantity of space for tree root growth while maintaining pavement functionality; including structural soil, soil filled load bearing cells, suspended slab pavement along with permeable pavements.

Applications of these engineered surface and subsurface tree spaces in Australian cities has occurred over the last 20 years, yet has been limited, rarely monitored and often perceived by developers, infrastructure authorities and local governments as a high cost, high risk approach.

Yet these same stakeholders are increasingly attentive to the opportunities that green infrastructure components offer to community health and well-being, tourism, business vitality, property value improvement, place making, buffering urban microclimate, managing local stormwater, air quality improvement, and so much more.

This study proposes a range of monitored, long term trials in Australian cities to advance best practices and build knowledge sharing. Complementary qualitative research is also proposed to explore the barriers to implementation and to collate the learnings from existing installations of surface and subsurface tree spaces.

2.2      Project objectives

  • To explore the gaps in technical knowledge that would inform best practice in engineered tree root growth spaces and surfaces in paved urban environments, for long term tree and pavement performance.
  • To identify non-technical barriers* to the uptake of such techniques/practices by government and industry
  • To utilise the independent, well respected role of TREENET to facilitate a collaborative, high quality research and knowledge sharing project
  • To involve/engage with TREENET membership in the development and implementation of the research


* non-technical barriers are barriers to uptake of techniques/practices that are not about the science of what makes things works best for trees in these engineered spaces, but about non-technical components that make or break uptake,

– business cases – benefit/cost, return on investment,
– level of awareness, understanding and perceptions of decision-makers like local government asset managers, engineers, development assessment officers, developers, etc.


2.3      Key information needed from the project

  • Comparable performance of the trees, pavement and the root growth environment across a limited range of engineered surface and subsurface tree space treatments (see Appendix A), including monitoring of factors which favour and limit tree health, stability and root growth within spaces and at interfaces of spaces, including,
    • Soil properties (chemistry and structure/aeration)
    • Soil quantity
    • Water availability, movement/infiltration and drainage,

in response to: rainfall, temperature, species choice (limited).

  • Comparable installation and maintenance requirements and costs
  • Levels of awareness, perceptions and factors which favour or limit the uptake of surface and subsurface tree spaces amongst: local government asset managers, engineers, development assessment officers, developers, urban planners, designers and landscape architects, arboricultural consultants and construction stakeholders.
  • Details about existing installations across Australia, their specifications, locations, cost, performance, owners and drivers for installation


2.4      Who is the target audience for the project?

  • Australian decision-makers (predominantly local government, developers and construction companies), product manufacturers, installers, advisors (arborists etc.), advocates and community.
  • International research audience
  • TREENET members who both invest in the organisation and are advocates for improving Australian urban forest


2.5      What are the potential research questions?

  • What are the barriers to the uptake of engineered spaces and pervious surfaces for trees by a) government and b) developers? (in Australian cities)
  • How do engineered soil spaces for tree root growth perform in situ over time? in both soil properties, root growth behaviour and tree growth
  • Are engineered tree spaces in paved environments cost-effective?
  • What techniques/specifications/modifications are required to optimise stormwater management benefits of engineered root growth spaces, without compromising tree health/longevity?


2.6      Potential elements of scope

  • That the baseline treatment specifications and construction process be easily replicated, such that they can be used to measure and interpret variations between sites/cities and between treatments;
  • That the baseline specifications include means by which to measure factors such as soil chemistry, moisture, drainage and aeration throughout the treatment space profile, in a manner that is able to be electronically recorded and ‘desktop’ monitored for a decade or more.
  • The trial has the flexibility to include variations that can be useful for future assessment, or that reflect local conditions or circumstances (e.g.  Tree species, interfaces with surrounding soils or infrastructure, or other aspects that are considered important by the city or funders ) i.e. Targeting the concerns of the city that are beyond the baseline specifications that need to apply to all installations;
  • That the prime locations for treatment trials be car parks or select streets;
  • That qualitative research be undertaken by survey and semi-structured interviews with a representative sample of Australia wide stakeholders.
  • Collation of a selection of local government case studies to showcase on the TREENET website. Case studies could also be requested in conjunction with the qualitative survey


2.7      Desired outcomes of the project

  • Use of collated existing case studies by local authorities and project managers as a catalyst to sharing experiences with installations, maintenance, costs and tree performance, reviewing and comparing aspects of how it was done; appreciate the pros and cons; etc


  • TREENET and/or partners, “publish” a best practice guide to engineered spaces for trees in Australian cities (that includes a standard drawing set and specifications that can be easily adopted by Local Government Areas, project engineers, plus cost/benefit examples) and is recognised as a significant step forward in mainstreaming green infrastructure for liveable cities


  • Best practice surface and subsurface tree spaces in paved areas of Australian cities becomes a standard practice and requirement


  • TREENET Trials are recognised as a drawcard for existing and new members.



A. Existing Data/case study contributions, and or

B. Research scope, methodology and costing for:-

B.1.          In situ trial site establishment, monitoring and reporting, and/or

B.2.          Qualitative research to identify non-technical barriers to the uptake of such techniques/practices by government and industry, and or

C. Funding ideas/ opportunities



Responses to Type A interest should indicate the:

  • Number of existing sites/installations
  • Location of existing sites/installations
  • Treatment types
  • Type of available monitoring, measurement data, photos etc.
  • Who owns the data/ case study site
  • Any conditions on sharing the data/ information

Note: specific details of existing data and case studies are NOT required at this stage, simply an indication of what type of information is available.


Responses to Type B 1 or B 2 interest should provide:

  • Summary of proposed/revised scope, methodology, duration and cost estimate
  • List of proposed researchers and their relevant experience in this field


Responses to Type C interest should provide:

  • Specific sources of funding
  • Indication of the level of funding
  • Any known conditions of funding, eg. ARC Linkage Grant timeframes, co-funding requirements, etc.


All responses should provide details of the respondent, their organisation/institution, which type of interest they are responding to, and contact details.


Responses Are Required By Friday 6th October 2017



Evaluation of responses will be undertaken by a TREENET project team, comprising a selected subset of TREENET management committee members. The project team will treat all responses confidentially.

A shortlist of proposed project partners will be selected based on the extent to which responses meet the project objectives and desired outcomes.

TREENET will arrange meetings with shortlisted respondents to gather further information to inform a final selection of one or more project partners.



Respondents to this EOI will be evaluated to enable TREENET (project owner) to develop a final project scope and structure, collaborative research partnership and funding strategy, aiming to commence in 2018.



Glenn Williams,

Director, TREENET

University of Adelaide – Waite Campus


Office:   (08) 8313 7078

Fax:   (08) 8 313 7079

Mob:   0448 599 955

Email:   [email protected]



Appendix A


“Potential Trial Configurations” – developed by Arbor Centre

Proposed TREENET Trials

TREENET is seeking sites where one or all three of the below sub-terrain systems can be installed and replicated within a car park &/or road in your city precinct……. Contact TREENET, email [email protected]


Presentation Slide No 2 – Structural Cells

Presentation Slide No 2 – Structural Cells


Presentation Slide No 3 – Structural Soil

Presentation Slide No 3 – Structural Soil


Presentation Slide No 4 – Pervious Paving

Presentation Slide No 4 – Pervious Paving


Presentation Slide No 6 – Potential Trial Configuration – Plan View

Presentation Slide No 6 – Potential Trial Configuration – Plan View


Presentation Slide No 7 – Potential Trial Configurations – Cross Sections

Presentation Slide No 7 – Potential Trial Configurations – Cross Sections