Sheryn Pitman and Martin Ely
Barbara Hardy Institute & School of Natural and Built Environments, University of South Australia, Adelaide, Australia
Department of Environment, Water and Natural Resources, Adelaide,Australia
Waite Arboretum, University of Adelaide ,Adelaide, Australia
Green Infrastructure (GI) is a systems-based approach to the design and function of our towns and cities which aims to secure the health, live ability and sustainability of present and future urban environments. By investing in Green Infrastructure we strengthen the resilience of towns and cities to respond to the major challenges of growth, health, climate change, biodiversity loss and water, energy and food security.
While GI has been interpreted in various ways, it is effectively described as the network of planted green spaces and water systems that deliver multiple environmental, social and economic values and services to urban communities.The focus of most GI thinking is directed towards urban environments in towns and cities because these are the places where an increasing majority of people live and where lack of ‘green’can result in many problems. GI includes parks and reserves, backyards and gardens, waterways and wetlands, transport corridors and greenways, farm sand orchards, squares and plazas, roof gardens and living walls, sports fields and cemeteries.
Throughout the world and particularly in industrialised countries, Green Infrastructure is being embraced as an important component in the development and redevelopment of urban environments.Without Green Infrastructure cities and towns risk becoming urban deserts in the sense of being hostile and barren places where people are disconnected from nature and from each other.A rapidly growing body of evidence supports the key role of Green Infrastructure in providing critical life support for human habitats.
Three main perspectives of Green Infrastructure have been identified in literature and in practice.They include an Ecosystem services approach in which GI delivers services and benefits similar to those delivered by natural processes (Daily 1997)a Linked green spaces approach where by GI provides a healthy and sustainable alternative to the traditional‘grey’ or engineering services-based infrastructure (Benedict and McMahon 2002) and a Green engineering approach in which GI is seen as a specialised form of engineering infrastructure that replaces conventional elements with ‘green’ elements that perform ecosystem service functions such as storm water harvesting,waste management and energy efficiency (Margolis and Robinson2007). For example the City of Sydney labels energy trigeneration and a decentralised water networks as ‘green infrastructure’ responses to climate change (City of Sydney 2012).
The way of thinking most relevant to the work that needs to bed one to create healthy and sustainable places to live and work integrates all three with emphasis on the Linked green spaces approach. Networks of plants and water systems deliver services and functions that urban environments require and provide a ‘green’ framework for sustainable living and development.Evidence of the importance of Green Infrastructure in urban environments has been gathered from studies and reports around the world.In order to consider the values and benefits we have grouped them: human health and well-being; water,air, soil and climate; climate change; biodiversity; food; and economics.)
Human Health and Well–being
Research over the last 20 years has investigated connections between contact with nature and human health and well-being. Health and well-being are defined in the broadest sense to mean not only the absence of disease, but a state of physical, mental and social well-being. Abraham et al. (2010) reviewed the health promoting aspects of GI, which include physical well-being, mental well-being and social well-being. There isa clear link between the built environment (including landscapes) physical activity and health(Kent, Thompsonet al. 2011).Physical activity is promoted by access to nearby green spaces and well designed ‘walkable streets' (Giles-Corti, Broomhallet al. 2005).
A large body of research supports the psychological benefits of contact with nature.Early work undertaken in the United States by Rachel and Stephen Kaplan (Kaplan and Kaplan 1989) included research into the ‘restorative effects of nature’ and found that the natural environment can foster people’s well being and their ability to function effectively. Steven Kaplan ‘s Attention Restoration Theory proposes that contact with nature engages our ‘involuntary attention’giving our ‘directed attention’ (voluntary attention) the opportunity to rest, thus helping overcome the mental fatigue associated with continual directed attention (Kaplan 1995).
One of the best known studies of the restorative powers of nature was conducted by Roger Ulrich who showed that abdominal surgical patients had shorter post-operative hospital stays when accommodated in a room looking out on a stand of trees (Ulrich1984).Positive connections with nature have been found in a range of studies including reduction of ADHD symptoms (Faber Taylor and Kuo2009),reduced crime in inner city neighbourhoods (Kuoand Sullivan 2001) and strengthening of a sense of community (Kuo,Sulivanetal. 1998). At the University of Illinois Landscape and Human Health Laboratory, Kuo, Sullivan and others are researching inner-city residents’ responses to trees and other vegetation and the ways in which the physical and psychological health of individuals and communities can be improved with enhanced access to nearby nature.
Importantly, more attractive urban green spaces can enhance opportunities for social interaction, fostering community ties and a sense of identity that has been found to be fundamental to human health and well-being (Maas, vanDillen etal. 2009a). According to Armstrong and Leyden, urban parks and other public places can enhance social integration if they facilitate social contacts, exchange, collective work,community building, empowerment, social networks and mutual trust (Armstrong 2000; Leyden 2003).Trees and greenery increase the attractiveness of places for people, in turn promoting community socialisation and passive surveillance, which can reduce crime and increase personal safety (Coley, Kuoet al. 1997;Kuo and Sullivan 2001; Kuo 2003).
A particular focus is on the role of Green Infrastructure in dealing with the emerging physical and mental health epidemic in Australian children (Malkin 2011).Writer Richard Louvin his book Last child in the Woods has coined the term Nature-Deﬁcit Disorder to describe the effects on children of enforced a lie nation from nature. These effects include a number of behavioural issues including diminished use of the senses, attention difficulties and higher rates of physical and emotional illnesses. Louvargues that sensationalist media coverage and paranoid parents have literally ‘scared children straight out of the woods and fields’ while promoting a litigious culture of fear that favours ‘safe’ regimented sports over imaginative play (Louv 2005). Two recent studies by Planet Ark have investigated the changing role of children’splay, and the health and well-being benefits to children of contact with nature.Rises in childhood obesity and mental health issues have been linked to dramatic lifestyle changes in the last 20 years. The 2011 study, Climbing Trees, found a dramatic shift in childhood play activity in the space of one generation (Planet Ark 2011).For example 64%of parents said that they climbed trees when young,compared with only19% of their children. A 2012 study,Planting Trees, investigated the intellectual,psychological,physical and mental health benefits of contact with nature for children (Planet Ark2012). This study reviewed local and international research in this field and revealed an emerging body of evidence that ‘contact with nature during childhood could have a significant role to play in both the prevention and management of certain physical and mental health problems, and informing environmentally responsible attitudes in future adulthood’.
Water, Air, Soil and Climate
Green Infrastructure provides a wide range of natural functions, often called ‘ecosystem services’, including cleaner water and air, healthier soils and more amenable urban climate and micro climates(Millennium Ecosystem Assessment 2003). Issues of global climate change and local extended drought have further highlighted the need to address a range of environmental issues, including making better use of Green Infrastructure in the public realm.
Vegetation cover plays an important role in the natural water cycle,modifying rainfall inflows, soil infiltration and ground water recharge, and patterns of surface runoff (Xiao, McPherson etal. 2006).Urbanisation, however, has seen the natural water cycle replaced by the‘urban water cycle’, with extensive impervious surface and highly efficient drainage systems dramatically increasing the quantity but reducing the quality of urban storm water runoff. This has negative impacts on the ‘receiving’aquatic ecosystems, while removing a valuable water resource from the city (Wong 2006). Water Sensitive Urban Design (WSUD) emerged during the 1990s as a new paradigm for the more sustainable management of the water cycle in the urban landscape (Argue2004).Green Infrastructure can play a vital role in helping to restore or better replicate the natural water cycle in urban areas. In particular, vegetated WSUD systems contribute in a number of ways: canopy interception (Xiao et al.2006); soil infiltration and storage (Bartens,Day et al. 2008); improved stormwater runoff quality through biofiltration processes (Denman, May etal. 2011);and flood damage control (Lull and Sopper 1969; Craul 1992).
More recently the concept of Water Sensitive Urban Design has been expanded to embrace the many ways in which water and more appropriate water management can enhance the ‘live ability’ and ‘resilience’ of our cities (Living Victoria Ministerial Advisory Council 2011).Along with the provision of safe, secure,affordable water supplies, WSUD supports greenland scapes that significantly enhance urban amenity, help to combat the impacts of the urban heat island effect, improve the health of urban waterways and provide opportunities for active and passive recreation. The emerging concept of the Water Sensitive City has three main ‘pillars’:Cities as Water Supply Catchments; Cities Providing Ecosystem Services; and Cities Comprising Water Sensitive Communities (Wong 2011).
An ecosystem service provided by urban trees and other vegetation is that of improving air quality in cities. Plants have several natural functions:they remove atmospheric pollutants; oxygenate the air; and absorb carbon dioxide through photosynthesis (Brack 2002; Nowak, Crane etal. 2006).Studies show that gaseous pollutants are absorbed by leaves and either metabolized or transferred to the soil by decay of leaf litter, which may be particularly important in streets with high traffic volumes (Nowak 1994; Scott, McPherson etal.1998). The leaves of trees also collect and trap airborne particles on their surfaces. The most significant impacts on air quality, however, are through reductions in carbon dioxide and atmospheric pollutants (Nowak, Stevens etal. 2002).
A valuable benefit of Green Infrastructure to cities is that of climate modification, especially temperature reduction. The ‘urban heat island effect’ (UHI) refers to the phenomenon where the air and surface temperatures of cities are typically much higher than surrounding rural or vegetated areas, especially at night (Bornstein 1968; Rosenfeld, Akbari etal. 1998). Temperatures in cities on cloudless days have been found to be as much as 120C warmer than surrounding rural areas (Oke 1987). In Melbourne, researchers have reported a mean UHI of around 2 to 4°C and as high as 7°C depending on the location, time of the year and time of day (Morris and Simmonds 2000; Coutts, Beringer et al.2010).
The urban heat island effect results from the storage and re-radiation of heat by building materials and paved surfaces and from urban heat sources such as the burning of fuel for heating and transportation.Lack of vegetation in cities also contributes to the urban heat island effect. Reduced tree cover leads to both a reduction in shading of surfaces and a reduction in transpiration cooling by tree canopies in comparison with rural areas (Federer1976). Cities are also drier than surrounding areas,as the natural ground surfaces are frequently replaced with asphalt and concrete surfaces which create higher surface temperatures and reduce evaporation from the soil that may otherwise cool the surface (Miller 1980).
The urban heat island is now recognised as contributing to health risks in large cities such as Melbourne (Loughnan 2009). Urban heat island effects contribute to increased morbidity/mortality rates in ‘heatwave’ events, especially among the aged (Loughnan, Nicholls etal. 2008; Loughnan, Nichollset al. 2010; Tapper 2010). In Melbourne on days over 30 degrees C the risk of heat related morbidity and mortality of people over 64 years of age increases significantly. Evidence suggests that buildings with little or no surrounding vegetation are at a higher risk of heat related morbidity (Loughnan, Nicholls et al. 2008; Loughnan, Nicholls etal.2010; Tapper 2010).
One method of mitigating extreme summer temperatures in the urban areas is to adopt the‘cool cities’ strategy (Luber 2008). Trees and other vegetation modify urban micro climates and help reduce the urban heat island effect through two major natural mechanisms: temperature reduction through shading of urban surfaces from solar radiation, and evapotranspiration which has a cooling and humidifying effect on the air (McPherson, Herrington et al.1988; McPherson1994; Akbari, Pomerantzet al. 2001; Pokorny2001; Georgiand Zafiiridiadis 2006).
It is now widely accepted that human activities are contributing to global climate change due to increased levels of green house gases in the atmosphere (Thom, Caneet al. 2009).Green Infrastructure, especially urban trees, can play an important role in the two responses to climate change:climate change mitigation,and climate change adaptation.
While climate change mitigation strategies often include reduction of CO2 emissions through increased use of public transport and energy efficiency(Climate Works 2010), urban trees can contribute to net reductions in atmospheric CO2 through carbon sequestration and storage and also through avoided CO2 emissions due to building energy savings.Moore(2006)estimated that the 100,000 public trees in Melbourne would sequester about one million tonnes of carbon. In 2000, Brisbane’s residential tree cover was estimated to absorb the equivalent amount of CO2 emitted by 30,000 cars per year and to cool surface temperatures in the relatively mild month of October 1999 by upto 5 degrees Celsius (Plant 2006). Such performance can result in reduced demand for air-conditioning energy, leading to a reduction in carbon emissions from power stations (McPherson and Simpson 2001). It is important to balance these reductions against CO2 released by the decomposition of dead trees and vegetable matter, and emissions produced in the management of urban trees (McPherson, Simpsonet al. 2009).Similarly, the potential of urban trees for carbon storage should not be overstated,as street trees are often short lived and small in stature (Nowak and Crane 2002;McPherson 2008).
Another benefit of Green Infrastructure is in assisting towns and cities to adapt to climate change (Shaw, Colley et al. 2007;Thom, Caneet al. 2009).While the impacts of climate change are difficult to predict and vary from region to region, likely effects in Australia include increased temperatures, reduced rainfall and extended periods of drought, increased bushfire risks and more extreme weather events such as storms and flooding (Suppiah, Preston etal. 2006). Climate change adaptation strategies include cooling of buildings and houses and cooling of the outdoor surrounds (Nice2012).Urban trees assist in reducing temperatures in cities through shading, evapotranspiration and wind speed modification (Akbari, Pomerantzet al. 2001).They can also play a role in relation to other climate change impacts such as providing shelter from predicted extreme weather events, reducing run off and flooding from extreme weather events and improving air quality in increasingly dense cities(McPherson,Simpson etal. 2006).
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, Korpela et al.2007)and loss of biodiversity impacts the quality of essential life support systems, the incidence and spread of infectious diseases andt he potential for developing new treatments and medicines (Chivian and Bernstein 2004). On a sociological level, urban nature and biodiversity in cities contributes to human sense of place, identity and psychological well-being (Horwitz, Lindsay et al.2001).
Urban habitats and species are often considered to be less important than their wild or agricultural counterparts.Biodiversity, however, can be higher in cities than surrounding rural areas and comprise a rich and diverse ranges of plants and animals, often occurring as unusual or unique communities(Angold,Sadler et al. 2006). 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 (EC2012). While urban street trees are often exotic species, it has been demonstrated that exotic trees do contribute to attracting wildlife (Tait,Daniels et al. 2005;Young and Johnson 2005).Street trees are utilised by a variety of bird species including native birds and especially those well adapted to the urban habitat (Tzilkowski, Wakeley etal. 1986;Fernandez-Juricic 2000). Kazemi et al.(2009)compared the biodiversity of six bio retention basins with other urban greenspaces in Melbourne.Greater species diversity was found in the bio retention basins compared with garden and lawn or grassed green spaces. They concluded that the in corporation of vegetated WSUD systems in urban streets and green spaces has the potential to enhance urban biodiversity. Importantly, Green Infrastructure can enhance‘connectivity’through the provision of biodiversity corridors and other linkages, a key aspect of the ecosystems approach to conservation(Vimal, Mathevetet al. 2011).
Food security is an issue of growing concern. Green Infrastructure and urban food are intimately related through the perceived needs to retain productive agricultural land on the urban fringe and to integrate food production into urban areas.Urban food production takes place in many ways and has been found to result in a wide range of human health and well-being outcomes.
The importance of preserving urban agriculture, including market gardens and farming, on the urban fringe is increasingly being recognised (Paster 2004;Mason and Knowd 2010).There is concern that suburban development is alienating viable agricultural lands in close proximity to urban centres (Sinclair 2009).Issues of climate change and sustainable development, especially the impacts of oil based transportation,highlight the benefits of retaining productive agricultural land in close proximity to cities (Knight and Riggs 2010; Pearson,Pearson et al. 2010). Urban or community based agriculture, and the consumption of local produce, have gained popularity in recent years as evidenced by the increase in farmers’markets and community gardens. Key health and well-being benefits include access to healthy food options and the opportunity to undertake physical activity implicated ingrowing and producing food(Mason and Knowd 2010).In a comprehensive study of the community garden movement in the United Kingdom,Holland (2004) p.1 concluded that while some gardens played a strategic role in food production,all gardens were‘based in a sense of community, with participation and involvement being particularly strong features’.Bartolomei et al. (2003) examined the social and health-promoting role ofa community garden scheme in a high-rise public housing estate in Sydney. The findings confirm the role of community gardens in strengthening social interaction.The scheme was associated with increased opportunities for local residents to socialise and develop vital cross-culturalties in a very diverse environment.
Placing a monetary value on Green Infrastructure, while potentially controversial, does help in the communication of benefits to stakeholders and the community, and can be fed directly into the policy decision making process (Vandermeulen, Verspechtet al. 2011).
Research has shown that Green Infrastructure can enhance the economic attractiveness of cities (Whitehead et al. (2005).A number of studies by Kathleen Wolf have investigated the effect of trees and landscaping on the commercial vitality of a range of US shopping centres, as measured by factors such as willingness to pay higher prices and travel further distances to shop in centres with trees and landscaping (Wolf 2004; Wolf 2004 a;Wolf 2005).Survey findings indicated that preference ratings increased with the presence of trees, indicating a clear valuing of the trees in terms of their amenity and visual quality. The presence of trees also appeared to influence consumer perceptions of businesses and the quality of their products. Respondents indicated a willingness to travel greater distances,visit more often and pay more for parking at locations with trees.These surveys also revealed a higher estimation of the value of business districts with trees (the amenity margin associated with trees ranging from 12% for large cities to 19% for small cities).
Researchers have also investigated the effects of street trees and nearby open space or water features on residential property values. For example a survey by the RealEstate Institute of Queensland in 2004 found that the value of homes in leafy streets were up to 30% higher than others in the same suburb (Plant 2006). While some of these studies include an ecdotal information, a number of recent studies have employed more sophisticated ‘hedonic pricing’techniques. Hedonic analysis uses the sale prices of comparable properties to isolate increases in market value due to specific variables, such as the presence of street trees.A recent study by Donovan and Butry (2010)used ahedonic price model to simultaneously estimate the effects of street trees on the sales price and the time-on-market(TOM) of houses in Portland, Oregon.On average,street trees added US$8870 to the sales price and reduced TOM by 1.7 days. In addition, the researchers found that the benefits of street trees spillover to neighbouring houses. Another recent study by Sander et al.(2010)used hedonic property price modelling to estimate the value of the urban tree cover in Minnesota.The results showed that a 10 percent increase in tree cover within 100 metres increases average home sale price by$1371 (0.48%)and within 250 metres by $836 (0.29%). There searchers concluded that the results suggest significant positive effects due to neighbourhood tree cover,for instance the shading and aesthetic quality of tree-lined streets, indicating that tree cover does provide positive neighbourhood externalities.
Another field of study is attempting to quantify the net economic values of the ecosystem services provided by Green Infrastructure. There has been considerable research effort in the US aimedat quantifying the economic benefits of urban trees,with the rationale of providing compelling evidence to encourage local and other authorities to strengthen tree planting programs. Benefits measured include air pollution reduction, stormwater runoff reduction, direct carbon capture, indirect emission reduction from the cooling effects of tree shade and higher sales prices of houses in leafy streets (Coder 1996; MacDonald 1996; Hewett 2002; Plant 2012). One example is a 1996 study of stormwater management costs, demonstrating that urban trees provided storm water management benefits valued at US$15.4 million in Milwaukee,Wisconsin, and US$122 million in Austin, Texas,by reducing the need for constructing additional retention, detention and treatment capacity (MacDonald 1996).A recent study at the Australian National University estimated that the trees in Canberra have an annual economic value of more than $23 million through energy reduction,pollution mitigation and storm water reductions (Killy, Bracketal. 2008).
A University of Adelaide study estimated the gross annual benefits from a typical medium sized street tree in Adelaide(Killicoat, Puzio etal. 2002).A four year old tree was estimated to generate a gross annual benefit of approximately$171 per tree, consisting of energy savings due to reduced airconditioning costs,air quality improvements, storm water management,aesthetics and other benefits.Stringer revisited this estimate in a 2007 paper and concluded that, with more adequate data and computer simulations, the gross benefits would actually be significantly higher(Stringer2007). In a follow up paper in 2009 the annual benefits fora typical Adelaide street tree were recalculated at approximately $424 per tree (Brindal and Stringer 2009).
Economic modelling is now commonly being used in the United States to quantify the economic benefits generated by urban trees (USDA Forest Service 2005).The United States Department of Agriculture(USDA) Forest Service provides online tools such as i-Tree which allow communities to estimate the net economic benefits generated by their urban tree populations (McPherson, Simpson et al. 2005).The model can quantify benefits such as energy conservation, air quality improvement,CO2 reduction, storm water control and property value increases.Such economic modelling has been applied in a number of United States cities including Davis in California, Milwaukee,Minneapolis, Pittsburgh, Houston and NewYork (Maco and McPherson 2003). Importantly, these analyses are assisting cities like New York, Los Angeles, Portland, Sacramento and Baltimore to justify investments in major urban greening projects that address declining urban tree cover, increasing population and urban climate change.
Since i-Tree was first introduced in 2006, the tools have been adapted for application to regional Australian conditions.The i-Tree STRATUM was trialled by the University of Melbourne in a study of two Melbourne city councils: the central City of Melbourne, and the newer outer suburban City of Hume (NGIA 2011). Modelling shows that for the environmental benefits selected (carbon sequestration, water retention, energy saving, aesthetics and air pollution removal)the population of street trees in two suburbs of the City of Melbourne provides ecosystem services equivalent to approximately $1 million dollars, and approximately $1.5 million dollars in the City of Hume.On an individual scale,the trees in the City of Melbourne provide ecosystem services valued at$163 per tree, and in Hume at $89 per tree.
Rationale and guiding principles
Green Infrastructure is a systems based approach to the design and function of our towns and cities.Green Infrastructure underpins the health,live ability and sustainability of present and future urban environments. By investing in Green Infrastructure we strengthen the resilience of towns and cities to respond to major challenges of population and urban growth,health, climate change, biodiversity loss and water, energy and food security.
To achieve the potential benefits of Green Infrastructure it must be embraced as an integral element of the urban landscape. Government, industry and community sectors require a thorough understanding of the benefits as well as a robust capacity for design,development and maintenance.Planning and investment in Green Infrastructure needs to be guided by the following five principles:
- both newgrowth areas and redevelopments.
- Nature-based:Green Infrastructure utilises natural processes to provide essential services and functions that improve the quality of urban water, air,soil, climate and wildlife habitat.
- Collaboration: The design,development and maintenance of green infrastructure require open and ongoing collaboration between government, industry and communities.
- Evidence: Green Infrastructure policy, planning and design are grounded in science, the lessons of experience and emerging practices and technologies.
- Capacity: Green Infrastructure requires commitment to building motivation, knowledge, skills and access to resources.
Process in South Australia
The value and importance of Green Infrastructure are becoming understood and appreciated within government and industry organisations.A collaborative partnership managed by the Botanic Gardens of Adelaide, Department of Environment,Water and Natural Resources (DEWNR) involves Renewal SA (Urban Renewal Authority),State Department of Planning, Transport and Infrastructure (DPTI), and the Adelaide and Mt Lofty Ranges Natural Resources Management Board (AMLR NRM).
The Green Infrastructure project has undertaken a strategic planning process to identify the path ways and processes necessary to achieve effective,long-term change in the way Green Infrastructure is perceived, designed and managed. This process has involved consultation with government,industry and community stakeholders in the diverse fields of health,land and water management, sustainability and climate change, design,education, transport, recreation, land development, policy and planning.
Through research and development of a scientific evidence base,working closely with policy, planning and development agencies, identifying and assisting exemplar projects, developing resources and raising awareness through out the community, the project aims to facilitate the incorporation of GI within an integrated approach to urban design and development and to improve capacity for its development and maintenance in South Australia.
Connected networks of greenspaces and water systems under pin the functionality of towns and cities and impact directly on community health and well-being, liveability and sustainability. Plants and water form the basis for life and in an increasingly urbanised world,Green Infrastructure is essential in providing life support to towns and cities, the primary human habitats of the future.
The ultimate success of Green Infrastructure as anew ‘paradigm’requires: recognition of its values and benefits,by the whole community and at the highest strategic levels;capacity building in the institutions and organizations involved in implementing Green Infrastructure in its different forms;and incorporating Green Infrastructure as an essential, rather than optional,component in the urban development process.
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