«Proceedings of the th 14 National Street Tree Symposium 2013 ISBN: 978-0-9806814-1-3 TREENET Proceedings of the 14th National Street Tree Symposium ...»
Another benefit of Green Infrastructure is in assisting towns and cities to adapt to climate change (Shaw, Colley et al. 2007; Thom, Cane et 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 et al. 2006). Climate change adaptation strategies include cooling of buildings and houses and cooling of the outdoor surrounds (Nice 2012). Urban trees assist in reducing temperatures in cities through shading, evapotranspiration and wind speed modification (Akbari, Pomerantz et 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 runoff and flooding from extreme weather events and improving air quality in increasingly dense cities (McPherson, Simpson et al. 2006).
Biodiversity 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 and the 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 (EC 2012). 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 et al. 1986; Fernandez-Juricic 2000). Kazemi et al. (2009) compared the biodiversity of six bioretention basins with other urban green spaces in Melbourne. Greater species diversity was found in the bioretention basins compared with garden and lawn or grassed green spaces. They concluded that the incorporation 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, Mathevet et al. 2011).
The 14th National Street Tree Symposium 2013 Food 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 in growing 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 of a 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-cultural ties in a very diverse environment.
Economics 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, Verspecht et 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 2004a; 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 Real Estate 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 anecdotal 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 a hedonic 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 spill over 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%). The researchers 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 aimed at 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, storm The 14th National Street Tree Symposium 2013 water 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 storm water 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, Brack et al. 2008).
A University of Adelaide study estimated the gross annual benefits from a typical medium sized street tree in Adelaide (Killicoat, Puzio et al. 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 air conditioning 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 (Stringer 2007). In a follow up paper in 2009 the annual benefits for a 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 New York (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, liveability 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:
Integration: Green infrastructure is fundamental to urban planning and design frameworks for both new growth 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.
The 14th National Street Tree Symposium 2013 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).