Arboriculture & Urban Forestry 45(2): March 2019 grow a broader range of species (Lohr 2013) in time for planting projects (Pincetl et al. 2013; Campbell 2014) may be countered by local resident preferences for a limited mix of species within streets. At the finer scale of nearby streetscapes investigated in this study, we found significant preferences for the aesthetic features of streetscapes (i.e., maturity of trees and species mix), which can be classed as life fulfill- ing or as cultural ecosystem services. In contrast, street tree size and condition, which are critical to provi- sioning or life-supporting ecosystem services, and which are highly valued by urban forest professionals (Kirkpatrick et al. 2013a; Kirkpatrick et al. 2013b; Davison and Kirkpatrick 2014; Jones and Instone 2016) were not significant. Resident preferences for aesthetics above function and concerns about disser- vices is consistent with other studies at city-wide scales (Summit and McPherson 1998; Gorman 2004; Flannigan 2005; Schroeder et al. 2006; Heimlich et al. 2008; Escobedo et al. 2011; Birtles et al. 2014; Camacho - Cervantes et al. 2014). Yet, street tree species choices are more often decided at municipal, developer, or designer levels, whose professional streetscape pref- erences may not align with each other’s, let alone with residents’ and other stakeholders’ preferences (Gjerde 2011; Conway and Vander Vecht 2015). Divergent preferences can be linked to divergent functions of tree-lined streets, which have evolved from earliest European neoclassical symbols of luxury and power to please a small group of people to a mixture of aes- thetic, recreational, ecological, and economic contri- butions to the broader public (Lawrence 1993). Although mainstreaming of environmental benefits of street trees, such as air quality improvement, cool- ing urban heat islands, energy conservation, and stormwater management, has served to engage deci- sion makers (Silvera Seamans 2013), residents who live closest to this subset of the urban forest may con- tinue to require a balance between the aesthetic and functional features of street trees—supporting further exploration of an “ecological aesthetic” (Kazemi et al. 2011; Rosley et al. 2014). Within their nearest streetscapes, our study indi- cated that Brisbane residents prefer a limited mixture of tree species, which is not consistent with previous studies. Recreational users of informal parks (Qiu et al. 2013) and natural areas (Fuller et al. 2007; Botzat et al. 2016; Shanahan et al. 2017) and residents at regional scales (Ambrey and Fleming 2014) have been 47 found to prefer greater levels of diversity and complex vegetation. Our study suggests that home-owners and home-buyers do not prefer a rich mixture of species closer to home. Mixtures of species at this scale may challenge preferences for homogeneity, orderliness, and tidiness across built and non-built forms within streetscapes (Weber et al. 2008; Weber et al. 2014). In Australian cities it is common practice for residents to maintain the footpath zone, even though this zone is controlled by the municipality, which is also respon- sible for planting and maintaining the street trees (Plant and Sipe 2016). Residents in Australia consequently have a strong influence on the presence and species of trees in the footpath zone fronting their property (Kirkpatrick et al. 2012), which may spill over to their preference for the greater order found in lower species diversity at the streetscape scale. A threshold of tolerance of no more than six differ- ent street tree species in nearby streetscapes emerged from this study, beyond which preference declined. This provides quantifiable guidance for urban forest managers seeking to balance the need for increased diversity to maintain a sustainable and resilient urban forest and the needs of residents. The threshold can also be used to evaluate the estimated effect of Bris- bane’s streetscape policy. This Infrastructure Design Planning Scheme Policy – Streetscape Hierarchy – Neighbourhood Street, requires “a mix of species laid out in an informal manner with clusters of trees at 2- to 6-m centres” (Brisbane City Council 2014). For a collective of “neighbourhood streets” within a resi- dential zone, the policy would require the planting of no more than six street tree species within a 100-m length of street. Our findings suggest residents may therefore be supportive of the policy. Preferences for species diversity in streetscapes are likely to be highly location dependent. Within the limited scope of our study, we chose to further explore the influence of socio-economic status as a locational characteristic that has already been found to influence urban tree abundance in the form of canopy cover (Heynen et al. 2006; Shanahan et al. 2014). Limited species mixtures in nearby streets in our study area were more strongly preferred in locations with higher education and income levels. It is possible that more affluent and educated suburbs have lower levels of species richness within streets, and familiarity has reinforced this preference. Areas of socio-economic advantage are amongst older suburbs, in the case of ©2019 International Society of Arboriculture
March 2019
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