8 Urban ecology
Green InfrastructureGreen Infrastructure is the network of green spaces and water systems that delivers multiple environmental, social and economic values and services to urban communities. This network includes parks and reserves, backyards and gardens, waterways and wetlands, streets and transport corridors, pathways and greenways, farms and orchards, squares and plazas, roof gardens and living walls, sports fields and cemeteries. Green Infrastructure secures the health, liveability and sustainability of urban environments. It strengthens the resilience of towns and cities to respond to the major current and future challenges of growth, health, climate change and biodiversity loss, as well as water, energy and food security.
Biodiversity has been shown to be fundamental to healthy ecosystems and their ability to deliver ecosystem services. Biodiversity is therefore fundamental to human health and well-being, and issues of global biodiversity loss are a major area of concern. At the city level biodiversity is impacted on by habitat degradation and fragmentation. Research shows that retaining and enhancing ‘nature’ in urban areas has a wide range of human benefits. This is maximized in an ‘urban ecology’ approach in which nature is seen to be an integral part of the city, with people being part of a functioning urban ecosystem. Green Infrastructure can play a significant role in enhancing urban biodiversity including countering habitat fragmentation, and in linking the different ecological assets in green networks.
Figure 46 summarizes the biodiversity roles of Green Infrastructure.
Figure 49: Summary of biodiversity role of Green Infrastructure. By M. Ely
8.2 Urban Ecology
Today most of the world’s population lives in cities, and this is expected to reach 70% by 2050 (United Nations, 2008). Urbanization has shown to have dramatic impacts on ecosystems (Grimm et al., 2008). Recently the urban environment has gained the attention of an increasing number of ecologists (Fontana et al., 2011). Historically nature and cities have been seen as ‘mutually exclusive’ (Platt, 2004). Cities were often compact and highly urbanized, but had easy access to surrounding rural and natural landscapes (Hough, 2004). Just as cities and nature have been viewed as ‘mutually exclusive’, the natural and social sciences have similarly tended to operate independently of each other, despite an understanding of the interdependence of cities and nature (Alberti, 2008).An urban ecology approach sees humans, nature and the city as part of the same ‘urban ecosystem’ (Hough, 2004). This ‘urban ecosystem’ comprises the physical environment (both natural and man-made) and biotic communities (including humans as well as native and introduced flora, fauna and micro-organisms) (Tarran, 2006). The concept of ‘urban ecology’ sees the city as a habitat for people alongside vegetation, wildlife and built form (Moll and Petit, 1994).
The concept of ‘biophilic urbanism’ has been championed by Tim Beatley and Peter Newman for several decades, as a way to create more liveable cities (Beatley, 2009). The concept of biophilic urbanism is inspired by E. O. Wilson’s concept of ‘biophilia’ which suggests an innate affinity between humans and the rest of nature. Beatley proposes that incorporating nature in cities can produce many benefits for urban dwellers. Biophilic cities are seen to be in harmony with ecological systems, foster place-based relationships, and embody the attributes of nature in their design. In Beatley’s view, a city exemplifies ‘green urbanism’ if it (1) strives to live within its ecological limits, (2) is designed to function in ways analogous to nature, (3) strives to achieve a circular rather than a linear metabolism, (4) strives toward local and regional self-sufficiency, (5) facilitates more sustainable lifestyles, and (6) emphasizes a high quality of neighbourhood and community life (Beatley, 2000).
‘Urban ecology’ is a relatively new field involving the systematic study of urban ecosystems using an integrating multi-disciplinary approach, drawing on both the natural and social sciences (Grimm et al., 2008). Ecological models derived from natural settings have also been applied to urban areas (Lord et al., 2003). The city has also been conceptualized as an ecosystem created by humans specifically for human habitation (McIntyre et al., 2000). Urban ecology is a growing field which has been investigated in a number of journal articles (Pickett et al., 1997; Niemela, 1999; Platt, 2004). Recent books have also been published on urban ecology (Alberti, 2008; Marzluff et al., 2008) and on the broader topics of ‘green cities’ and ‘sustainable urbanism’ (Birch and Wachter, 2008; Farr, 2008; Beatley and Newman, 2009).
(Tarran, 2006) attributes the development of urban ecology in the late 1990s to a number of factors including:
- Increased urbanization and the need to make urban areas more habitable.
- Recognition by ecologists that disturbed ecosystems are more common than ‘pristine’ ecosystems and worthy of study in their own right.
- Increasing concern about human impacts on ecosystems, including biodiversity loss and the impacts of urbanization on aquatic ecosystems (Wallbridge, 1997).
- Recognition of an emerging sustainability crisis in cities.
- Recognition that the ‘ecosystem services’ provided by nature could be applied in urban areas (Daily, 1997).
Most recently there has been an increased focus on issues of sustainable urban development on the global scale, increased population growth and urbanization, and issues of climate change and water scarcity (Grimm et al., 2008).
8.3 Urban biodiversity
According to (Roetman and Daniels, 2008) ‘biodiversity is a term used to describe all living things and the variation within and between them. It includes plants, animals, fungi, and micro-organisms, and can be considered at various levels of complexity’. These include:
- Genetic Diversity- the variation within a particular species
- Species Diversity- the variation between different species
- Ecosystem Diversity- the variation within and between different ecosystems o fthe world, comprising habitats, the species that they contain and the processes and interactions occurring between the biological and physical components.
8.3.2 Global biodiversity
Issues of biodiversity and ecosystem health have been shown to be fundamental to the delivery of ecosystem services from the global to the local scale. Biodiversity plays a fundamental role in the functioning of ecosystems and their ability to deliver long-term ecosystem services. Worldwide biodiversity loss is therefore an area of great concern (Groombridge and Jenkins, 2002). Links between biodiversity and human health and well-being have been well documented (Tzoulas et al., 2007) and loss of biodiversity impacts the quality of essential life support systems, the incidence and spread of infectious diseases and the potential for developing new treatments and medicines (Chivian and Bernstein, 2004).
8.3.3 Values of urban biodiversity
While loss of global biodiversity is a major concern, what are the specific benefits of retaining and enhancing biodiversity within cities and urban areas?
188.8.131.52 Ecosystem services
Biodiversity provides a wide range of ‘ecosystem services’ to human populations which underpin human health and well-being and economic prosperity (Millennium Ecosystem Assessment, 2005). Within cities biodiversity can help to:
- Regulate urban climate and microclimate
- Improve air quality
- Purify water
- Control stormwater runoff
- Improve soil fertility
- Recycle wastes
184.108.40.206 Ecosystem resilience
A recent focus has been on the role of biological diversity in engendering ‘resilience’ in natural systems, providing an ‘insurance policy’ allowing natural systems to recover from disturbances such as drought, fire and flood (Roetman and Daniels, 2008).
220.127.116.11 Quality of life
There is an increasing consensus that biodiversity is important for maintaining quality of life for people in general, and urban inhabitants in particular:
- On a sociological level, urban nature and biodiversity in cities contributes to human sense of place, identity and psychological well-being (Horwitz et al., 2001).
- (Sandström et al., 2006) have claimed that perceived quality of life might improve when the ‘fraction’ of nature in urban areas increases.
- Natural areas in cities provide the opportunity to directly experience nature (Miller, 2006). This is considered to be is a crucial aspect for restoration in a world with a highly urbanized population (Home et al., 2009a).
- The environmental attitudes of urban residents are largely formed by interactions with their local environment (Mayer and Frantz, 2004; Schultz and Tabanico, 2007).
- A recent study has shown the popularity of birds amongst the public (Home et al., 2009b). Therefore urban birds and their diversity represent a significant way in which people can experience urban nature. Such experiences are considered to be essential for the well-being of city inhabitants (Fuller et al., 2007).
- Animals, and urban wildlife are an important driver of our ‘sense of place’ in Australia, for instance the sound of magpies (Daniels, 2012).
- Biodiversity adds to a sense of place and builds place identity. People identify with their local flora and fauna (van Roon, 2005) and rare species are of particular concern (Mallawaarachchi et al., 2006).
- Personal experience of urban biodiversity by city residents can inﬂuence their opinions and can influence political decisions on environmental conservation matters (Turner et al., 2004; Dunn et al., 2006).
- Townsend suggests that the effects of the urban forest and other greenery are influenced by the quality, as well as the quantity, of the forest cover, which may be a reflection of greater biodiversity. (Townsend and Sick, 2011).
- An interview survey conducted by (Fuller et al., 2007)explored the benefits to psychological well-being from spending time in green spaces, with participants reporting greater well-being benefits in parks with a greater diversity of plant species and habitat types, ‘an effect that was not simply attributable to the area of the green space involved’ (Fuller et al., 2007).p.1.
18.104.22.168 Intrinsic values
Society also places a value on maintaining biodiversity for future generations for its scientific, educational and aesthetic values and also for its intrinsic value (Cork et al., 2006). Literature on the benefits of urban biodiversity tends to focus on the benefits to the human inhabitants of the city. This is an ‘anthropocentric’ or human centred approach. However, the values of preserving biodiversity can also be viewed from other perspectives. (Thompson, 2000) reviewed the different human attitudes to nature and environmental ethics and identified the following typologies or positions within environmental ethics shown in Table 23.
Table 23: Attitudes to nature and environmental ethics. Source: Adapted from (Thompson, 2000).
The greatest good for the greatest number.
We are responsible for stewardship of nature for human use and enjoyment.
Members of the biotic community have moral standing.
Ecosystems and/or the biosphere have moral standing.
We have a duty of care to the whole environment.
An eco-centric position sees intrinsic value in preserving nature and ecosystem biodiversity. Aldo Leopold’s, (1948) Land Ethic is an early statement of the eco-centric position, as is (McHarg, 1979) philosophy of Design with Nature, and James Lovelock’s (1979) Gaia hypothesis.
Professor Chris Daniels at the University of South Australia considers that the benefits of urban nature can be classified into three categories (Daniels, 2012):
- Benefits of people connecting with nature. Biophilia (Wilson, 1984) our intrinsic connection to nature, and the many benefits of interacting with nature, including creating our sense of place, human health and well-being and social cohesion benefits. The large body of evidence in this area is now seen as ‘incontrovertible’.
- Alleviation of ‘Nature Deficit Disorder’. (Louv, 2005). There is now a large and growing gap between ‘people and nature’ in urban areas, with cities becoming larger, especially in Australia. In the current century the environment has become the ‘driver’ of social change, and there is a need to connect with nature to be able to engage the community in environmental debate. The issue also applies in engaging with other cultures which may not see nature as we do.
- Multi-functionality. The ‘multiple use’ benefits of open space and other forms of green infrastructure. In the past our open spaces have been dedicated to single use groups, such as sporting clubs or even environmental pressure groups, and tend to be fenced off from public use and used for only short periods of time. For example, people do not feel ‘ownership’ of the Adelaide Parklands as they are underutilized by the general community, and are subdivided up into a number of special use parcels. Instead the Parklands should be dedicated to delivering wider benefits including biodiversity preservation, water management and climate change adaptation. The concept of multiple use can be applied to other areas utilized by the community including roof tops, streets and public urban spaces.
8.4 The nature of urban biodiversity
8.4.1 Habitat fragmentation
According to the European Commission (European Commission, 2012):
‘Urbanisation, industrialisation, unsustainable agriculture and the continued expansion of grey infrastructure are increasingly eroding our natural fabric and natural capital’.
Landscapes have become more fragmented and polluted, which in turn has disrupted ecosystems and the patterns and level of biodiversity (Mazza et al., 2011). As shown in Figure 47 a fragmented landscape consists of small ‘patches’ of intact natural habitat. Large patches will continue to provide habitat for ‘interior’ wildlife species. Fragmentation into smaller patches, however, decreases the amount of interior habitat and increases the amount of edge. While some ‘generalist’ species may benefit from this fragmentation, the majority are negatively affected, particularly large animals with large territorial ranges (Weber, 2007). (Lucius et al., 2011) suggest that negative effects generally start to appear when about 70% of the original habitat has been lost. These impacts may include: changes in species, composition of different species, community structure, population dynamics, behaviour, breeding success, individual fitness and a range of ecological and ecosystem processes. As shown on Figure 48 the size and shape of remnant patches affect the amount of habitat available for interior wildlife species. Large areas are better than small areas, and circle-shaped areas are generally better than square-shaped or rectangle shaped ones(Barnes, 1999).
Figure 50: Large patches provide habitat for interior wildlife species. Fragmentation shown in B and C decreases the amount of interior habitat and increases the amount of edge. Source (Barnes, 1999) adapted from (Soule, 1991).
Figure 51: A patch’s size and shape affect the amount of habitat available for interior wildlife species. Large areas are better than small areas, and circle-shaped areas are better than square-shaped or rectangle shaped ones. Source (Barnes, 1999) adapted from (Forman and Godron, 1986).
The size and shape of patches is therefore an important consideration in the planning of urban areas to maximize habitat and biodiversity values, with large patches preferred, and connection of remnant patches with habitat corridors (Barnes, 1999a).
Figure 52: Patch size and shape considerations are important when planning for wildlife. Large circular patches are best for wildlife and are even better when connected by a corridor. Source (Barnes, 1999) adapted from (Soule, 1991).
8.4.2 Rural-urban gradients
Studies on urban birds have generally revealed a rural-urban gradient and negative impacts of urbanization (i.e. increasing sealed area) on bird species richness and diversity (McDonnell et al., 1993; Clergeau et al., 1998; Palomino and Carrascal, 2006).
8.4.3 Urban wildlife
Urban habitats and species are often considered to be less important than their wild or rural counterparts. Biodiversity, however, can be higher in cities than surrounding rural areas and may comprise a rich and diverse ranges of plants and animals, often occurring as unusual or unique communities (Angold et al., 2006). According to (Fontana et al., 2011):
‘Despite the strong and permanent human impact, urban biodiversity has generally proved to be surprisingly high’ p.278.
Many studies show a surprisingly high number of species and individuals present in cities (Marzluff, 2001; Palomino and Carrascal, 2006; Sattler et al., 2010a; Sattler et al., 2010b). It has even been found that ‘moderately urbanized’ areas often support higher ‘species richness’ than rural areas (Blair, 1996; Blair and Launer, 1997). Such species richness and diversity are generally considered to be good indicators of ecosystem health (Rapport, 1999). However, these indicators do not necessarily provide a full picture of species composition and community dynamics (Jost, 2006). Community analyses are used to explain changes in community composition (Moretti et al., 2006).
8.4.4 Impacts of urban densification
Impacts on tree cover
Policies of ‘urban consolidation’ which encourage smaller lot sizes and denser forms of urban development are supported by governments in most major metropolitan areas of Australia. In addition to creating smaller lots, the size and coverage of the average suburban houses has increased dramatically since the 1990s, whilst the average size of the private garden has substantially diminished (Hall, 2010). Large trees however require space to grow and an Honours research project at the University of Queensland investigated the impact of these trends in Brisbane through the use of existing tree cover and other spatial data (Daniel, 2012). The results showed that while urban trees on private property form a large component of Brisbane’s suburban environment, this has decreased with modern development, with 30% less canopy cover over parcels developed in the 1990s than over parcels developed before this period. For infill development, low-rise multiple unit dwellings exhibited negligible canopy cover (between 0 and 2.5% over most parcels sampled). While a decrease in tree cover was as expected, the magnitude of this change has significant implications for the quality of the suburban environment. Analysis of current planning policies showed that, even if residents would prefer not to plant large trees, development permitted under current parameters severely limits opportunities for future residents to do so, leading to a slow but permanent loss of tree cover on private property throughout the city’s suburbs. This research provides the first quantitative measures of the effects of planning and development policies on Brisbane’s tree cover and provide an evidence base for future planning and policy development.
Impacts on urban green space
Rapid urbanization has ignited concern about the potential effects on biodiversity conservation and quality of human life from scientists and policy makers alike (Dye, 2008). Foremost among these concerns is maintaining human well-being. Contact with the natural environment is a fundamental component of well-being (Wilson, 1984; Miller, 2005) yet opportunities for such contact are dramatically limited in urban areas. Predictions of the consequences of rapid ongoing urbanization for human well-being require information on how green space provision will change as cities grow. One way to achieve this is to study variation in green space provision within and among present-day cities. A research paper by (Fuller and Gaston, 2009), explores the relationships between urban green space coverage, city area and population size across 386 European cities. The researchers showed that green space coverage increased more rapidly than city area, yet declined only weakly as human population density increases. Thus, green space provision within a city is primarily related to city area rather than the number of inhabitants that it serves, or a simple space-filling effect. Thus compact cities (small size and high density) show very low per capita green space allocation. However, at high levels of urbanization, the existing green space network is robust to further city compaction. The authors conclude that, as cities grow, interactions between people and nature will depend increasingly on landscape quality outside formal green space networks, such as street plantings, or the size, composition and management of backyards and gardens.
Impacts on biodiversity
Urbanization causes severe environmental degradation and continues to increase in scale and intensity around the world, but little is known about how we should design cities to minimize their ecological impact. Two main types of urban development can be identified. With ‘urban sprawl’, low intensity impact is spread across a wide area, and with a ‘compact development’ intense impact is concentrated over a small area It remains unclear however which of these development styles has a lower overall ecological impact. A recent study compared the consequences of compact and sprawling urban growth patterns on bird distributions across the city of Brisbane (Sushinsky et al., 2013). The researchers predicted the impact on bird populations of adding 84,642 houses to the city in either a compact or sprawling design using statistical models of bird distributions.
The results showed that urban growth of any type reduces bird distributions overall, but compact development substantially slows these reductions at the city scale. Urban-sensitive species particularly benefited from compact development at the city scale because large green spaces were left intact, whereas the distributions of non-native species expanded as a result of sprawling development. As well as minimizing ecological disruption, compact urban development maintains human access to public green spaces, however, backyards are smaller, which impacts on opportunities to experience nature close to home. The results suggest that cities built to minimize per capita ecological impact are characterized by high residential density, with large public urban green spaces and small private backyards, and that there are important trade-offs between maintaining city-wide species diversity and people’s access to biodiversity in their own backyard.
Melbourne Urban Forest Strategy
Strategy: Improve biodiversity
Target: Melbourne’s green spaces will protect and enhance a level of biodiversity which contributes to the delivery of ecosystem services.
Over 40 per cent of nationally listed threatened ecological communities in Australia occur in urban areas. Loss of natural habitat, urbanisation, and air and water pollution have all impacted upon the survival of plant and animal species. A 2009 Victorian Environmental Assessment Council study showcased ten major threats to biodiversity in Melbourne including: fragmented landscapes, connectivity loss due to major roads, urban pollution, human impacts (e.g. rubbish and trampling), predation from cats and dogs, and competition from other introduced species. With the potential expansion of urban growth into brown and green field sites, the potential loss of biodiversity from these threats becomes even greater, highlighting the need to seriously regard biodiversity in our city.
In terms of biodiversity in the urban landscape, we recognise that cities and biodiversity have often
been mutually exclusive however research continues to demonstrate that urban areas can provide large opportunities for protecting and enhancing vulnerable species. Public parks and gardens, golf courses, remnant vegetation and private property gardens are capable of providing habitat for certain species.
This is not to underestimate the impact that urbanisation has had on biodiversity. Our imperative is to ensure protection and enhancement of vulnerable species. Whilst certain species (e.g. Eastern Quoll) face severe loss or even extinction due to loss of habitat, others (e.g. Brush Tail Possum) have adapted all too well to urbanisation, to the extent of becoming overpopulated in many inner areaparks.
Biodiversity in the City of Melbourne includes a wide range of wildlife species. The urban forest plays a crucial role in providing habitat, food and protection to wildlife as equally as it provides a diversity of plant species throughout the municipality.
In summary, healthy trees supported by adequate soil moisture and structural and biological diversity collectively contribute to healthy ecosystems. Taking all these factors into consideration is essential for setting and achieving our benchmarks and goals.Source: (City of Melbourne, 2011).
8.5 Biodiversity in Australian cities
In their book Adelaide, Nature of a City: The Ecology of a Dynamic City from 1836 to 2036, (Daniels and Tait, 2006) provide a comprehensive review of the impacts of urbanization on the biodiversity of metropolitan Adelaide and the current status of the different aspects of urban nature in the city. More recent research into the role of sustainability in Australian cities, including urban biodiversity, is being carried out by the Barbara Hardy Institute at the University of South Australia (Roetman and Daniels, 2011).
(Taylor et al., 2011) have investigated urban biodiversity from an Australian context. The authors note that ecologists generally ignored the biodiversity of cities until the later decades of the 20th century (Martin et al., 2010) but research into urban biodiversity is now ‘on the rise’ (Mayer, 2010). Urban biodiversity is complex, but with increasing urbanization the design of the built environment and associated green infrastructure becomes the main determinant of biodiversity (Muller et al., 2010).
8.5.2 Typology of urban species
According to (Taylor et al., 2011) from an ecological viewpoint Australian cities can be conceptualized as a ‘mosaic’ of fragmented habitat patches over the ‘grey’ urban landscape. This mosaic tends to be highly fragmented with many small patches of varying size, shape and biodiversity, separated by ‘abrupt’ edges (Johnson and Klemens, 2005). As shown on Table 24 this ‘mosaic’ provides an urban habitat for a wide range of ‘native’ and ‘adventive’ plant and animals, as well as cultivated plants and domesticated animals (Niemela, 1999a; Muller et al., 2010).
Table 24: Typology of Australian plants and animals: Source (Taylor, 1990) in (Taylor et al., 2011) p.180.
Species indigenous to the locality.
Individuals spontaneous in occurrence.
Species may be indigenous to the locality, but usually exotic or alien.
Individuals established and maintained by human agency.
Species alien or exotic to the locality.
Individuals spontaneous in occurrence.
Not an escaped cultivar or domesticate.
An escaped cultivar or domesticate.
According to (Taylor, 1990) Australia’s ‘urban vegetation’ comprises four main classes:
- Native vegetation, having both a canopy layer and an understorey (where present and distinct) dominated by plant species that are indigenous to the locality and spontaneous in occurrence.
- Relict vegetation, having a canopy layer dominated by native plant species that are indigenous relicts of the original native vegetation cover and an understorey (where present and distinct) dominated by cultivated or adventive plant species.
- Cultivated vegetation, having a canopy layer dominated by indigenous, exotic or alien plant species that have been deliberately introduced to the locality by human agency (cultivated) and an understorey (where present and distinct) dominated by cultivated or adventive plant species.
- Adventive vegetation, having a canopy layer dominated by plant species that are exotic or alien to the locality and spontaneous in occurrence (adventive), while the understorey is normally indistinct or dominated by adventive plant species.
The landscape of Australian cities tends to be dominated by ‘cultivated vegetation’ in landscaped public/private spaces, or adventitious on derelict sites. Extensive areas of ‘native vegetation’ are rare, and are usually ‘relict vegetation’, lacking the capacity to regenerate, and vulnerable to invasion by adventitious species (Johnson and Klemens, 2005). The ‘grey spaces’ of cities, and the fragmented patches of relict, cultivated and adventive vegetation are lacking in both native plant species and habitats for a range of native animal species.
Animal species vary in their tolerance to the stresses of an urban environment and can be classified as 'urban avoiders, 'urban adapters' or 'urban exploiters' (Blair, 2001; McKinney, 2002). Urban avoiders cannot survive in highly urbanized situations due to climatic stress, soil, water and air pollution, and high levels of habitat disturbance due to landscape maintenance, and high levels of human activity (Soule, 1991; Whitford et al., 2001; McKinney, 2002; Zerbe et al., 2003). Urban adapters tend to be small, mobile or arboreal animals, animals with amenity value for city dwellers (including charismatic bird species) and habitat generalists. Native animals with these characteristics may find better qualities of sustenance and shelter in the city rather than surrounding rural/natural areas. Urban exploiters are similar to urban adapters, but become so reliant on living in proximity to people that they may now occur mainly in cities.
Urban avoiders, adapters and exploiters
Urban avoiders cannot survive in the built environment as they cannot tolerate fragmented habitat, reduced food or shelter resources, environmental pollution, or introduced competition or predation. Large, mammalian predators are usually identified as urban avoiders, in some cases more because people avoid allowing them in, rather than the animal avoiding urban areas.
Urban adapters benefit from developed environments because there are increased food sources or shelter sites. Australian examples (both native and introduced) are brushtail possums, foxes, blackbirds, magpies and bluetongue lizards.
Urban exploiters, like adaptors benefit from food sources and shelter sites that are afforded by urban development, but these species are now so reliant on human activities that they are primarily, if not only, found in dense settlements like cities. Australian examples are black rats, redback spiders and spotted turtle-doves.Source: (Roetman and Daniels, 2008).
8.5.3 Concepts of nativeness
Such typologies of ‘nativeness’ are considered essential to understanding biodiversity in Australia and other southern hemisphere countries (Head, 2004; Meurk and Swaffield, 2007). In Europe and North America ‘nativeness’ is considered the norm for landscapes and plant species, while in Australia, New Zealand and South Africa urban landscapes are based on European models and invasiveness is the main characteristic of urban biodiversity (Head, 2004; Ignatieva, 2010). Since European settlement, over 27,000 exotic plant species have been introduced into Australia, and about 10 per cent of these have become established in native vegetation (Taylor et al., 2011). Similarly, exotic animal species have invaded Australian impacting on the biodiversity of the whole continent. According to (Muller et al., 2010) however urbanization, rather than invasion has now become one of the main threats to global biodiversity. For example Australia’s major cities are located in or adjacent to ‘biodiversity hotspots’ (Australian Government, 2009) and biodiversity impacts can extend more than 100 km from urban boundaries (Cincotta et al., 2000).
In Australia, therefore, the primary role of urban biodiversity conservation has been one of ‘nativeness’ (Ignatieva, 2010). There are also scientific arguments for conserving the unique ‘intrinsic’ values of Australian biodiversity in a global context (Muller and Werner, 2010). However, (Taylor et al., 2011) point out that;
‘…because cities are primarily human habitats, urban biodiversity cannot be valued solely in terms of its nativeness. In addition to the intrinsic (natural) value of the native biodiversity in urban areas, all urban biodiversity (native and introduced) has instrumental (or social) value because it provides a wide variety of productive, environmental moderation, ecosystem service and amenity benefits for the people who live in cities’ p.183.
8.5.4 Biodiversity of Adelaide
The recent book Adelaide, Nature of a City: The Ecology of a Dynamic City from 1836 to 2036 (Daniels and Tait, 2006) provides a comprehensive overview of the original biodiversity of metropolitan Adelaide, and the impacts of urbanization on the city’s wildlife and vegetation. (Tait and Daniels, 2004) also provide a detailed account of the changes in species assemblages within the Adelaide metropolitan area from 1836 to 2036.
Historically, Adelaide supported a diverse range of natural habitats. Before 1836, the Adelaide Plains supported approximately 1130 species of native and exotic plants, approximately 290 species of birds (including migratory and nomadic species) 40 mammal species, 56 reptile species and 7 species of amphibians.The authors created a database on native and introduced species present in Adelaide between 1836 and 2002 using 200 historical and recent sources of information. The data was then used to produce graphs showing the changes in species richness through time. Some of the overall patterns of change were:
- A 30% increase in the total number of all species, with around 132 native species lost and 648 introduced.
- Plants increased by 524 species (46% increase over the original).
- Native plant species have decreased by approximately 8% (89 species).
- Vertebrates experienced an overall decline of 12 species, or 3%.
- 50% (20 out of 40) of the original native mammal species were lost.
- Amphibians did not lose or gain any species.
The increase in total species numbers was found to be due to introductions (54% in plant species, 22.5% in mammals, 7% in birds, 3.5% in reptile species).With respect to birdlife, 286 species were present in 1836, and 283 species in 2002. 21 native species of birds were lost, while 20 introduced species arrived. The major decline in species richness began in 1959, with the greatest rate of extinction occurring over the past 30 years. The authors suggest several major reasons for the loss of native birds. Contributing factors include the loss of relatively un-fragmented habitat outside the city, changes in urban predators (such as foxes and cats) and changes in the nature of available habitats within the city (such as private and public gardens and street trees). The loss of native understorey plants, as well as increases in particular exotic plants in urban areas has also led to the change in species composition. An increase in resource competition between bird species and individuals, due to dwindling resources has possibly also contributed to population declines and subsequent extinction.
8.6 Responses to habitat fragmentation
It may not always be possible to preserve large areas of natural habitat within cities, however Green Infrastructure elements can act as reserves of species biodiversity within urban areas (Alvey, 2006).Green Infrastructure provides a means of enhancing biodiversity and reducing habitat fragmentation in urban areas (European Commission, 2012).
8.6.1 Ecosystems approach
One approach to addressing the changes caused by fragmentation has been to create ‘conservation areas’. In the past the focus has been on protecting particular species or habitats, but it is now recognised that there is a need to acknowledge ‘nature as a system rather than individual parts’ This has involved shifting the focus of conservation from the level of species or habitatlevel, to the ecosystem level (Vimal et al., 2011).
Science behind conservation at the ecosystem level
The shift to conservation at the ecosystem level is based on the large body of evidence that demonstrates habitat fragmentation is a threat to the survival of species (Boitani et al., 2007). Theoretically, it has its roots in island biogeography theory, which, although developed from work done on islands (MacArthur and Wilson, 1967), considers an island to be any area of suitable habitat that is surrounded by unsuitable habitat, for example, lakes surrounded by dry land or fragmented forests. Island biogeography theory states that the number of species found on an ‘island’ depends on immigration, ex-migration and extinction, where the two former processes depend on connectivity between different ‘islands’.
Further theoretical support comes from meta-population theory (Hanski, 1999) which suggests that no single population can guarantee long-term survival of a given species, but the combined effect of many connected populations could. As such, the long-term survival of populations depends on the cohesion of habitat networks as it determines whether or not local extinction and re-colonisation rates are in equilibrium. (Opdam et al., 2006). In turn, this maintains the structures, material and energy flows of ecosystems which can provide different ecosystem services.Source: (European Commission, 2012).
The Convention on Biological Diversity (1993) has adopted the ecosystem approach where it defines an ecosystem as ‘a dynamic complex of plant, animal and micro-organism communities and their non-living environment interacting as a functional unit’ (Convention on Biological Diversity, 1993). The ecosystem approach aims to integrate the management of land, water and living resources in a way that promotes conservation and sustainable use. It also recognises that humans, with their cultural diversity, are an integral component of the ecosystem and gain benefits from ecosystems in the form of ecosystem services (European Commission, 2012).
Central to the ecosystem concept of conservation are the connections and interactions between species, habitats and resources. Ecosystems are not static, but are open, dynamic systems, and their interactions and connections evolve in space and through time (Fisher et al., 2009). Maintaining and enhancing connectivity is one way to help offset the losses caused by fragmentation. As shown on Figure 50 Green Infrastructure can enhance connectivity between natural areas, improving the ability of organisms to move through a landscape (landscape permeability) and minimizing further fragmentation (European Commission, 2012).
Figure 53: Landscapes consist of the matrix (the dominant feature), patches, and corridors that connect the patches. Source: (Barnes, 1999a).
8.7 Urban nature
8.7.1 Biodiversity indicators
It is important to identify thresholds of habitat variables linked to maintaining or enhancing biodiversity (Marzluff and Ewing, 2001). According to (Fontana et al., 2011):
‘Quantitative information on the effect of management actions on biodiversity is often lacking but is an indispensable basis for decisions by urban planners and managers’ p.278.
8.7.2 Birds as indicators
Birds are often chosen as indicators of habitat quality, as their ecology is well known, and they respond well to the availability of habitat structures (Clergeau et al., 1998; Evans et al., 2009). In cities, birds are widely considered as an optimal model group to study the ecological effect of urbanization (McDonnell and Hahs, 2008). There are strong inter-species differences in responses of birds to urbanization (Møller, 2009). Increased urban densification is therefore expected to lead to modifications of bird community composition and structure. Physical, abiotic conditions are similar between cities (Grimm et al., 2008), so bird communities are often comparable at different latitudes (Clergeau et al., 2006; Evans et al., 2009).
The following general patterns have been observed regarding the effects of urbanization on avian biodiversity (Fontana et al., 2011):
- Species richness and diversity decreases along urbanization gradients from moderately urbanized to densely built-up areas (Clergeau et al., 1998; Clergeau et al., 2006).
- Avian abundance, however, tends to increase along the same gradient (Clergeau et al., 1998; Palomino and Carrascal, 2006; Grimm et al., 2008), reflecting the dominance of few ‘generalist’ species leading to biotic homogenization) (Clergeau et al., 2006; La Sorte and McKinney, 2007).
- ‘Specialist’ species with more narrow ecological requirements tend to decrease with increasing urbanization (Clergeau et al., 1998; Fernández-Juricic, 2004; Devictor et al., 2007).
8.7.3 Enhancing urban bird populations
Several studies provide evidence that site factors such as the size of housing lots influence avian species occurrence in urban areas and that site scale decisions by property owners and developers can affect the nesting and feeding habitats for urban birds (McKinney, 2002; Grimm et al., 2008; Evans et al., 2009).
The following management actions have been devised by Fontana et al. (Fontana et al., 2011) with the aim of enhancing urban bird populations:
- Providing additional food resources (Gaston et al., 2007; Evans et al., 2009)
- Enhancing reproduction possibilities with nest boxes (Gaston et al., 2007)
- Increasing structural vegetation diversity (Böhning-Gaese, 1997; Chace and Walsh, 2004)
- Planting native in preference to exotic species (Chace and Walsh, 2004; Daniels and Kirkpatrick, 2006; Burghardt et al., 2009)
- Preserving vegetation patches in urban developments (Croci et al., 2008)
- Increasing connectivity between green elements within and around cities (Marzluff and Ewing, 2001; Fernández-Juricic, 2004)
A recent study by Fontana et al. (Fontana et al., 2011) in three Swiss cities, quantified key urban variables to predict changes in avian biodiversity when the urban habitat is modified. The researchers found that bird species richness and diversity were negatively affected by increasing the proportion of sealed area or buildings, while increasing vegetation, particularly trees had positive effects. Their models predicted a 54% increase in bird species, from 13 species in the absence of trees to 20 species with 46% tree cover.
Increasing the coverage and complexity of greenery was shown to enhancespecies richness and diversity at a relatively small urban scale, similar to findings obtained at larger scales (Lancaster and Rees, 1979; Clergeau et al., 2001). The results suggest that the amount of trees is the most important habitat variable for enhancing bird species richness and diversity in cities, as suggested by previous studies (Goldstein et al., 1986; Clergeau et al., 1998; Palomino and Carrascal, 2006; Sandström et al., 2006; Evans et al., 2009). According to (Fontana et al., 2011):
‘Increasing the fraction of tree cover in the urban matrix seems to be the most promising and efﬁcient measure to enhance bird species richness and diversity’ p. 283.
8.7.4 Native versus exotic species
With regard to the effect of native vs. exotic plants on urban birds, studies in North America (Donnelly and Marzluff, 2004) and Australia (Daniels and Kirkpatrick, 2006) have found a higher correlation of native bird species with native plants than with exotic plants. Also in Australia, White et al. (White et al., 2005) found lower bird species richness and modiﬁed community composition in areas dominated by exotic vegetation, compared with areas dominated by native vegetation. In their study (Fontana et al., 2011) noted that more than 60 bird species can breed in Swiss cities, which is (approximately one third of all regularly breeding species in Switzerland. However endangered and priority bird species are ‘specialists’ and are under-represented among urban birds Therefore providing optimal habitats in urban areas cannot substitute for bird protection measures outside the city (Miller, 2006).
8.7.5 Biodiversity and urban trees
Street trees can also have ecological benefits in terms of enhancing biodiversity and creating urban wildlife habitats and corridors. However, street tree plantings often comprise monocultures, lacking species diversity, limiting biodiversity and exposing street tree populations to the threat of species specific diseases (Richards, 1993; Alvey, 2006; Frank et al., 2006). Street tree plantings also do not usually include the creation of an understorey habitat. Street tree plantings may also exhibit a preference for exotic cultivated species, rather than native or indigenous species (Moore, 2003; Hough, 2004). However, it has been demonstrated that even exotic trees play some role in attracting wildlife (Tait et al., 2005; Young and Johnson, 2006). Street trees are utilized by a variety of bird species, including native birds, especially those well adapted to the urban habitat (Tzilkowski et al., 1986; Fernandez-Juricic, 2000). Layering of vegetation, with trees, shrubs and understorey plantings, enhances biodiversity and also contributes to the total biomass and ecological services provided.
8.7.6 Biodiversity and Water Sensitive Urban Design
(Kazemi et al., 2009) investigated the biodiversity of six bioretention basins in Melbourne, compared with other urban green-spaces. Greater species diversity was found in the bioretention basins compared with garden and lawn type green-spaces. It was concluded that the incorporation of vegetated WSUD systems in urban streets and green-spaces has the promise of enhancing urban biodiversity.
8.8 Biodiversity guidelines
‘Rapid industrialisation, urbanisation, population growth and resource consumption in Australia have modified the environment and these factors will continue to drive change. Importantly, changes that reduce the ability of ecosystems to function will increase the difficulty and cost of obtaining resources and removing wastes, and reduce the aesthetic and recreational benefits we derive from nature. We now have the knowledge and capability to influence future environmental change in a positive way. In order to reduce the negative impacts of climate change, water shortages and the loss of biodiversity, cities must be developed to incorporate, and therefore take advantage of, natural processes’ (Roetman and Daniels, 2008).
(Roetman and Daniels, 2008)provide guidelines for including biodiversity as a component in new urban developments in Australia:
- Suitable building sites should be planned that mould the streets and infrastructure to the landscape (Tyne, 2000).
- Wherever possible, water courses should be left intact (Tyne, 2000) and vegetation left along waterways, or replanted (van Roon, 2005).
- Avoid fragmenting existing vegetation and habitat.
- Design biodiversity corridors within developments that link with surrounding environments.
- Where roads bisect the habitat of wildlife, traffic calming designs may be useful.
- To mitigate the impact of development on aquatic biodiversity, limit impervious surfaces (van Roon, 2005).
- Maintenance costs, resources, and effort can be reduced by using indigenous species (Tyne, 2000).
- Vegetation should be water sensitive, non-invasive, a sensible mixture of natives and exotics; consider all biodiversity (not just trees and grass).
- Urban consolidation reduces the impact of cities on the surrounding landscape, but can reduce biodiversity and the natural environments within cities. For this reason, consideration must be given to increasing urban biodiversity in innovative ways, including rooftop gardens (Tyne, 2000; Daniels and Tait, 2006).
As shown in Figure 54 (Roetman and Daniels, 2008) also illustrate the principles of habitat size, shape, and structure to improve biodiversity in urban areas.
Figure 54: Principles of habitat size, shape, and structure for urban biodiversity planning. Source: (Roetman and Daniels, 2008) based on Diamond, 1975 and Soulé, 1991.
- Urban development has impacted, and will continue to impact significantly on global biodiversity, which underlies healthy ecosystems and their ability to deliver ecosystem services which are essential to human health and well-being.
- Within urban areas natural habitats are replaced with urban ones, resulting in habitat fragmentation and biodiversity loss.
- Research shows that biodiversity, under certain measures, can be quite high in urban areas, however this may be a form of ‘urban nature’ comprising species better adapted to life in cities.
- Nature and the city were once considered mutually exclusive, however researchers in the natural sciences are now investigating ‘urban nature’, and the concept of nature has been expanded to include the ‘urban ecosystem’ of which humans are part.
- Urban densification has been found to have a major impact on biodiversity, tree canopy cover and open space provision.
- Urban nature and high levels of biodiversity in cities have been shown to have a number of human health and well-being benefits.
- Green Infrastructure initiatives which promote biodiversity and ecosystem health include the retention of remnant vegetation, the provision of large habitat ‘patches’ and the linking of those patches with habitat corridors.
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