Although Australian cities, as they function currently, demonstrate environmental footprints that are not sustainable, they generally rank high on measures of livability. A range of elements contribute to the livability of a built environment: urban amenity; housing; transport; air and water quality; access to the natural environment; and heritage, social and aesthetic aspects.
Livability: Natural environment
Livability: Natural environment
Land conversion for urban development can destroy habitat, and introduce anthropogenic disturbances and threats (Forman 2014). These changes can affect myriad species and ecological processes (Grimm et al. 2008). Research has also shown that the effects of urbanisation on wildlife extend into adjacent habitats (Ilkin et al. 2015). (See Increased urban footprint and the Biodiversity report for further discussion of pressures relating to urban development.)
The natural environment continues to be affected less in smaller places and more in larger urban centres, which is directly related to population size. The natural environment is reduced by cities that go out rather than up because of density policies (Newman & Kenworthy 2015)—for example, residential development continues to encroach on Melbourne’s natural environment, because it has grown on its urban fringe as well as its dense inner city.
However, cities and towns can be important for biodiversity conservation, offering novel habitats and opportunities to integrate people in conservation (McDonnell & Hahs 2013, Newman 2014). Worldwide, 20 per cent and 5 per cent of bird and plant species, respectively, occur in cities (Aronson et al. 2014). In Australia, cities are disproportionately important for the conservation of species of national significance, with urban regions supporting more threatened species per unit area than non-urban regions (Ives et al. 2015). Recent years have seen increasing moves to offset the loss of natural environment at alternative locations, and strategic assessments to protect diversity.
In turn, the conservation of urban biodiversity has benefits for human wellbeing (Turner et al. 2004). Urban greening provides opportunities for recreation and active lifestyles (DITMCU 2013, Townsend et al. 2015), and interacting with urban biodiversity has been shown to benefit physical and psychological health, improve quality of life and raise real-estate prices (see Box BLT3).
Strategic enhancement of urban green space offers biodiversity gains. Strategies include increasing the total amount of green space cover, maintaining ecological structures as habitat islands and gardening with low-flowering native shrubs. More recent techniques that use the actual physical surroundings of buildings (green roofs and green walls known as biophilic urbanism; Beatley 2011) are also important. In addition, trees need to be managed for long-term sustainability. This includes retaining large, old trees in new developments, increasing the maximum standing life of urban trees, protecting regenerating areas, planting more seedlings, supplementing habitat features associated with large trees and ensuring that young trees have space to grow through time (Ilkin et al. 2015).
Adding natural green elements to the built environment promotes many other direct and indirect benefits. These include reducing air pollution, improving air quality and microclimate, and providing opportunities for carbon sequestration. Green elements also mitigate the ‘urban heat island’ effect, in which a city or metropolitan area can be significantly warmer than its surrounding rural areas because of human activities and the absorption of heat by building materials. A study undertaken for the City of Melbourne (Townsend et al. 2015) with heat maps of the Greater Melbourne area demonstrated that areas with few trees are warmer than treed areas. In Melbourne, researchers have reported a mean urban heat island effect of around +2 °C to 4 °C and as high as +7 °C depending on the location, season and time of day (Townsend et al. 2015). Appropriate urban vegetation can potentially maximise mitigation of the urban heat island effect and reduce vulnerability to heatwaves (see Increased extreme weather events).
Urban forests and greening support management of stormwater run-off and improve water quality by reducing the level of nutrients and toxicants that affect water quality and ecosystem health in our urban waterways and bays. For example, Melbourne’s metropolitan parks are estimated to release, on average, more than 31 tonnes of nitrogen per year. By contrast, under residential land use, the total amount of nitrogen loads expected would be about 213 tonnes per year. This is a decrease in nutrient loads of 182 tonnes per year. Without these parks, the additional nutrient loads would make their way into the waterways and bays of both Port Phillip and Western Port, where they can cause algal blooms and other negative environmental effects. Additional costs would then be required to maintain the quality of water at current standards (Parks Victoria 2015).
In i-Tree analysis, land surface cover was estimated for 139 local government areas in urban and semi-urban environments across Australia. The assessment covered 62,185 square kilometres of the most populous regions of Australia—approximately 68 per cent of the population of Australia live within these areas, and therefore they are the areas most heavily affected by the development of human settlements. Grass or bare ground was the most common land cover (47 per cent of the area), followed by tree canopy (39 per cent), hard surfaces (8 per cent) and shrubs (6 per cent) (Jacobs et al. 2014; Figure BLT37).
Local government areas with high ratios of hard surfaces to tree cover include Maribyrnong in Victoria, Fremantle in Western Australia, Holdfast Bay in South Australia and Rockdale in New South Wales. For these areas, converting hard surfaces to tree planting could be one approach to increase canopy cover. For central and inner-city areas, green roofs, green walls and more street trees could also be considered. In contrast, Wyndham in Victoria, Wannaroo in Western Australia, Gawler in South Australia and Camden in New South Wales had high ratios of grass or bare ground to tree cover, which suggests that the greatest potential to improve tree canopy cover in these areas would be to encourage new plantings on existing vacant land (Jacobs et al. 2014).