Conference paper

Potential effects of climate change on Melbourne's street trees and some implications for human and non-human animals

Climate change Streets Trees Cities and towns Urban planning Streetscapes Melbourne
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Abstract: Melbourne has an extensive canopy of street trees that provides an important urban amenity and contributes both to human health and wellbeing and as food and habitat for non-human animals. There is some evidence that the composition of Melbourne’s street trees is likely to change as a result of climate change (Kendal et al. 2011). However, we know little about what these changes may be, and what this could mean for Melbourne’s human, avian and mammal inhabitants. Trees in urban landscapes have many important benefits to humans such as improved health outcomes (Mitchell & Popham 2008), psychological wellbeing (Kaplan 1995; Ulrich et al. 1991) and the provision of ecosystem services (Bolund & Hunhammar 1999). Street trees in particular have been linked to reduced incidence of asthma (Lovasi et al. 2008), increased house prices (Orland et al. 1992) and reduced air pollution (Yang et al. 2005). Street trees also provide benefits to non-human animals. The Rainbow Lorikeet (Trichoglossus haematodus) has expanded its range in urban Melbourne significantly which has been partly attributed to the planting of more native street tree species (Fitzsimons et al. 2003; Shukuroglou & McCarthy, 2006). Similarly, the Grey-headed Flying Fox (Pteropus poliocephalus) has become increasingly common in Melbourne, again at least partly due to the increased availability of food resources in streetscape plantings over native vegetation (Williams et al. 2006). There are probably more than a million street trees planted across greater Melbourne (Frank et al. 2006), and more than half of Melbourne’s residences have a street tree in the adjoining streetscape (Kirkpatrick et al. 2011). However, these street trees are not distributed evenly. The composition of street trees can differ greatly in different suburbs (Fairman et al. 2010). There are significant socioeconomic and climatic gradients occurring from Melbourne’s west to east (ABS 2006; BOM 2011). A study of the distribution of street trees in major Australian cities including Melbourne found that the likelihood of having a street tree is correlated with household income (Kirkpatrick et al. 2011). Global climate change is predicted to lead to a warmer and drier climate across much of south-eastern Australia, with a many models predicting at least several degrees of warming (Hennessy et al. 2007). In temperate areas, climate change is predicted to lead to the distribution of native trees moving towards the poles (Iverson & Prasad 1998), with particular locations losing some species better adapted to cooler locations and gaining species that are better adapted to warmer climates. Plant functional traits such as leaf width and canopy height change along climatic gradients (Fonseca et al. 2000). The trait profile of particular vegetation communities is predicted to change with climate change for traits such as the seasonal timing (phenology) of leaf and flower development (Hanninen & Tanino 2011) and leaf traits such as leaf mass per area and leaf lifespan (Wright et al. 2005). There have been few studies of the effect of climate change on cultivated urban vegetation, although it has been predicted to allow a wider range of plants from warmer climates to be grown and to affect the range and virulence of pests and diseases (Bisgrove & Hadley 2002). Most studies exploring street trees and climate change have focussed on the role street trees can play in mitigating the effects of climate change through carbon sequestration e.g. (McPherson et al. 1994; Gill et al. 2007). One study has explored the likely impact of climate-change induced drought on the suitability of particular street trees (Roloff et al. 2009), however recent research suggests that temperature rather than rainfall is a key driver of the distribution of urban vegetation (Kendal et al. 2011). Human behaviours such as irrigation (particularly during establishment) allow the barrier of inadequate rainfall to be overcome for many species, while temperature cannot easily be overcome. Cities with even relatively small temperature differences have relatively large differences in the taxonomic composition of their cultivated floras (Kendal et al. 2011). It is likely that some street tree taxa that have been well adapted to Melbourne’s historic climate are likely to be less well adapted to future climates, while other taxa may become better adapted to Melbourne’s future climate. This paper explores how the composition of Melbourne’s street tree may change under current climate change scenarios, and what the impact of this may be for both humans and non-human animals living in Melbourne.

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