More than 85% of Australians live in cities, which are becoming hotter under climate change. The number of record hot days in Australia has doubled in the last 60 years, and heatwaves are becoming hotter, lasting longer and happening more frequently. For example, during a 2020 heatwave, Penrith in Greater Sydney’s far west, reached 48.9°C. This was the hottest day ever recorded in Greater Sydney, and the hottest place on earth that day.
Of Australian cities, Sydney and Melbourne experience most of Australia’s population growth. A lot of the urban residential growth in these cities takes place at the fringes, away from the cooling influence of the coast, and close to, if not within, these areas of extreme heat.
In accommodating growth in these large cities, greening has been a lower priority, despite the important role trees can play in cooling cities. Tree canopy cover is in decline throughout Australian cities (Hurley et al., 2020) in part because room for canopy on residential blocks has declined over time. This has implications for liveability, because suburbs struggle to provide the space required for greening for resident health and wellbeing. For example, many Australian local governments have ambitious targets for canopy cover increase but limited private space and contested public space to place additional canopy.
A key example of limited private space is the private residential development estates that have spread throughout the north-west of Western Sydney since the 1990s (Blacktown City Council, 2020). Houses within these estates can be developed with guidelines that prescribe limited space for private trees on a residential block (Figure 1). The space left available for trees on residential blocks is thus very limited, and public trees become a main source of canopy. Street trees on Australian urban roadsides have the third-highest contribution to canopy after residential land and parkland (Hurley et al., 2020).
Figure 1 A comparison of change in size and configuration of housing between post-war development (left) and contemporary residential blocks in greenfield development (right)
Greater Sydney and canopy
The NSW Government has set a target to increase tree canopy cover across Greater Sydney to 40%, from where it currently stands at approximately 22%. Crucial to achieving Greater Sydney’s canopy target, are 33 local government areas (LGAs) that individually implement tree planting and retention mechanisms, which ultimately affect Greater Sydney’ canopy growth as a whole.
18 of Greater Sydney’s councils saw an increase in canopy area between 2019 and 2022. Some, like Blacktown and Liverpool in Sydney’s west, have some of the lowest canopy of any council in Greater Sydney, but saw some of the highest tree canopy increases. Further to the east, we have seen declines in many of Greater Sydney’s leafier councils. In fact, every council but one that had a cover of 30% or higher in 2019 experienced canopy loss.
Figure 2 Canopy change across Greater Sydney local government areas, between 2019 and 2022 (DPE, 2022). It should be taken into account that canopy cover snapshots for 2022 are of a far higher resolution than for 2019, and this may affect the changes seen.
Urban tree governance and retention
Governance of urban forests shapes how, why and which trees are planted or removed (Konijnendijk, 2003). Part of Sophie’s PhD research focuses on Greater Sydney’s tree retention, as this process is crucial to keeping trees in the ground long term to achieve canopy targets. The aim of this research is to combine up-to-date canopy change analysis with an assessment of the regulatory and governance context of canopy management at the LGA level, to interrogate the dynamics of canopy gain and loss in Greater Sydney’s different LGAs. The use of a self-assessment tool, alongside in-depth expert interviews, and the results from the canopy change analysis, is currently in progress to pick apart the complexity of canopy loss and gain in Greater Sydney.
The mechanisms that may be used by local councils to plant or remove trees, found within these and other policy plans, might be classed into two categories: regulations and incentives (Ordóñez-Barona et al., 2021). Cities worldwide use regulations for both public and private trees (Ordóñez-Barona et al., 2021), and examples are outlined in Table 1.
Table 1 Regulatory and Incentive mechanisms used in private canopy retention adapted from (Ordóñez-Barona et al., 2021
Tree retention deep dive
Part of this research focuses on Greater Sydney’s tree retention, as this process is crucial to keeping trees in the ground long term to achieve canopy targets. The aim of this research is to combine up-to-date canopy change analysis with an assessment of the regulatory and governance context of canopy management at the LGA level, to interrogate the dynamics of canopy gain and loss in Greater Sydney’s different LGAs. The use of a self-assessment tool, alongside in-depth expert interviews, and the results from the canopy change analysis, is currently in progress to pick apart the complexity of canopy loss and gain in Greater Sydney.
How it relates to our work
Mosaic works with councils across Sydney, Melbourne and South-East Queensland to strategise for canopy growth and retention, through Urban Forest Strategy and other related greening and planning work. This work uses four essential elements of urban forestry (Figure 3) to holistically strategise for trees and greening at a council level.
The work of this thesis, and its focuses, is informed by applied work in urban forest strategy creation, using the rigor possible through impartial research, to compliment what mosaic already helps to apply on the ground for Australian councils.
Figure 3 Essential elements of an urban forest strategy from the Greener Neighbourhoods Guide (DPIE, 2021), a document created by TreeIQ and Mosaic Insights for the NSW State Government’s then Department of Planning, Industry and Environment
More information
This work is cofunded by Mosaic Insights and Western Sydney University, under the primary supervision of Prof Sebastian Pfautsch. If you’d like to know more please contact Sophie at Sophie.moore@mosaicinsights.com.au