Melbourne, Australia: Urban Forestry

As part of the development of the strategy, the City of Melbourne’s 70,000 street trees were surveyed and mapped. The survey looked at species, size and condition to assess the useful life expectancy of each tree. All findings from this work were made available in an online map called the Urban Forest Visual, and each tree assigned an identification number and email address to facilitate tracking and reporting, an initiative that attracted unexpected worldwide interest. The associated database was also used to model how the canopy would evolve under different circumstances, including a “do nothing” scenario. The modelling showed that reaching the 40% canopy cover target would require planting at least 3,000 trees a year until 2040. The modelling did not focus exclusively on tree numbers but also considered how tree planting conditions would affect canopy size. Such analysis showed that achieving targeted increase in canopy cover would require footpath extensions, drainage reconfigurations and/or planting trees into carriageways beyond existing kerb lines, where there is adequate below and above space to accommodate root and crown development, and where it is much easier to give trees access to moisture.

Also supporting the strategy is a series of ten Urban Forest Precinct Plans that guide implementation in local neighbourhoods until 2022 (ie over the first 10 years of the strategy’s anticipated lifespan). These plans were subject to the same official adoption process as the main Urban Forest Strategy. Each of them shows on a street by street level the current state of the local urban forest and the changes that will take place – whether replacement or new plantings. It also defines tree species choices, as well as possible opportunities for wider street redesign work. The works identified are prioritised, with projects being allocated a timeframe for delivery either in year one to four, five to seven or eight to ten. This prioritisation was based on data collected on thermal hotspots, low canopy cover levels, concentrations of vulnerable residents, tree health and scale of opportunity. The Urban Forest Visual is updated on a live basis to reflect where projects identified in the precinct plans have been completed. As of July 2020, a vast majority of the projects identified have reached such completion stage.

Another important enabling factor in Melbourne’s success was its early focus on plant suitability and plant quality. Any large-scale urban greening programme, whether focused on trees or other vegetation types require resilient, responsive supply chains, delivering suitable plants.

Upstream of its procurement programme, the City of Melbourne’s Parks and City Greening department has worked with academics such as Dr Dave Kendall at the University of Melbourne’s School of Ecosystem and Forest Sciences to assist with identifying climate suitable trees under different climate scenarios anticipated for the city. This identified a wide range of suitable potential species from Australia or further afield, many of which, it turned out, were not being used or even commercially produced. This work was conducted with support from the Royal Botanic Gardens and Nursery and Garden Industry Victoria, the professional body representing plant growers – including tree nurseries  –  in the State of Victoria. The Royal Botanic Gardens assisted with the sourcing of seed and other plant materials identified in the study. This collaboration also involves the planting of some species on test sites along low-key Melbourne streets, where suitability for the street environment is being monitored and assessed prior to City committing to their wider use.

The City of Melbourne’s Parks and City Greening department works closely with tree nurseries, involving them in research projects involving the sourcing and testing of new species, as exemplified by the project described above. Nurseries are also brought into all industry events the City organises and solicited as part of team building exercises conducted for City staff. When procuring trees intended for high-profile projects or when new species are involved, the City enters into contract growing arrangements with the supplying nurseries. Tighter controls are being exercised with all tree suppliers to insist on compliance with the Australian standard for nursery-grown trees (AS 2303:2018 Tree stock for landscape use) and any other additional specification the City might have requested. Contract-grown stock is inspected on a quarterly basis, and all trees procured are subject to inspection by a City member of staff after reception in the contractor’s yard and prior to planting into the landscape. This collaborative approach between nurseries and local government means that trees planted in the city have great chances for long term success.

Where are the City of Melbourne’s greening initiatives headed next?

One direction is to place a greater emphasis on getting the private sector to make stronger contributions to the City’s urban greening effort, an area where the municipality’s performance is not as strong as some of its neighbours in the Greater Melbourne Area. Such comparisons have become easier now that a metropolitan scale initiative has been launched to align around common minimum standards the different urban forestry and greening initiatives undertaken by local city administrations. The City of Melbourne is looking to adopt a greening factor, comparable to that in use in Seattle, in the US or in Berlin, in Germany or London in the UK. In the associated calculation tool, tree canopy, especially from trees planted directly into the ground, is given the highest score.

Another key direction is an increased focus on urban ecology. Enhancing urban ecology was identified in the 2012 Urban Forest Strategy as the next logical development of the City’s urban forestry work. Trees are part of wider ecosystems, which need to be healthy for trees to thrive. This includes soils, companion vegetation, and the associated fauna – birds, insects and other species that can help control pests and diseases. Implementation of the actions identified in respect to urban ecology in the Urban Forest Strategy led to the publication of the Nature in the City Strategy in 2017 and the hiring of a dedicated urban ecologist to oversee its implementation. Daily collaboration between ecologists and tree experts is resulting in better ecosystem outcomes for the city.

One of the flagship projects undertaken as part of the Nature in the City Strategy has been the prototyping of streetscape plantings for biodiversity. This has been led in partnership with academics from the University of Melbourne’s Green Infrastructure Research Group specialising in urban ecology (Nick Williams) and horticulture (John Rayner). This collaboration aimed at developing and testing the impact of an understorey plant palette that would enhance biodiversity in city streets by providing resources for birds, bees and butterflies. As with other urban greening projects led by the City of Melbourne, a large amount of documentation is publicly available about this work, including a comprehensive case study documenting the circumstances and lessons learned from the first four pilot streetscapes as of Spring 2020. The available documentation also includes the plant palette the research team identified to meet the horticultural and biodiversity criteria defined for the project. The goal is to enable and encourage other professionals, including other city departments and private sector landscape designers, to use such plant palette.

From a horticultural standpoint, the plant selection focussed predominantly on native perennial herbs, grasses and shrubs that were aesthetically attractive, required little maintenance and had high environmental tolerances, including to drought, waterlogging and compaction. The plant selection was further narrowed down based on scientific evidence that they could provide resources for birds, bees or butterflies – such as nectar and pollen for pollinating insects and small non-aggressive birds; larval food resources for local butterflies; seed and fruit for birds; nesting material for birds and solitary bees; and protection for small birds, for example, plants with dense and prickly foliage. The four first trials showed encouraging results on an ecological level, with a notable increase in the total number and diversity of bees observed. The bird population didn’t show any significant change, however, this was expected given the short timeframe involved: some of the shrub that can provide bird habitat is likely to be still too small to become attractive. However, the project also revealed some challenges in plant procurement and management.

With short timeframes to implement the proposed designs, the contractors who carried out the implementation didn’t have time to consider contract growing the plant materials.  Many species proved impossible to procure in the amounts needed for the projects. Substitutions had to be made that weren’t always satisfactory. The streetscape created also proved difficult to look after for the private contractors in charge of maintenance. Most are not used to recognising native plants (easily assimilated with weeds) or with management practices allowing natural dynamics such as self-sowing. The City of Melbourne ended up dispatching to the biodiversity streetscape pilot sites the maintenance contractor in charge of Royal Park, Melbourne’s largest inner-city park and the richest in native plantings. The long-term efforts that were made on supply chain and contractor management in support of the City of Melbourne’s tree-focused work will need to be extended so that its urban ecology aspirations can be successfully scaled-up.

While the four streetscape biodiversity pilots gave insightful answers to the question: “how can we increase ecological connectivity in the city?”, it still left unanswered the question of where such an approach would offer the greatest impact? A partnership between the City of Melbourne and researchers from the Clean Air and Urban Landscapes Hub (CAUL) was formed to help provide this information. CAUL is a consortium of four Australian universities funded under the Australian Government’s National Environmental Science Program. In the Linking Nature in the City study, CAUL provides a method for spatially prioritising projects for different guilds of animals.

The ambition for the upcoming years is for this exploratory and research-driven work on streetscape ecology to inform a new generation of Urban Forest Precincts Plans. As mentioned above, the existing precincts plans are nearing their completion date, scheduled for 2022. Preparations of a new generation of plans will start soon with the belief, rooted in experience, that incorporating the findings from the urban ecology studies and pilots conducted to date will provide a reliable mechanism to turn such emerging practice into business as usual.