Arboriculture & Urban Forestry 46(5): September 2020 to pests (Polakowski et al. 2011). It is unclear how other professionals in horticulture, arboriculture, and urban forestry utilize the term “diversity.” The 10-20- 30 rule can be viewed as a minimum standard for tree species diversity, but this rule could be further defined to increase diversity and minimize susceptibility to pests. Additionally, increased tree species diversity on a neighborhood scale may help to maximize bene- fits provided by those trees. Furthermore, managers should consider regional or national diversity as well. Many urban areas are increasing their tree species diversity locally, but the same tree species are being planted in many urban areas. With deliberate selec- tion of tree species that are uncommon in the area and continued management, local tree species diversity can contribute to broader regional diversity (Alvey 2006). Historically, many municipalities have planted large numbers of certain tree species—such as Callery pear (Pyrus calleryana)—which can become invasive (Cul- ley and Hardiman 2007) and have poor branch struc- ture. Among the challenges of increasing diversity are lack of awareness of new cultivars or species, as well as availability at nurseries (D’Amato et al. 2002). Tree selection is often influenced by what is grown in nurseries, which in turn is influenced by communica- tion between managers and nurseries (D’Amato et al. 2002). Tree planting goals should be tailored to the city’s climate, ability to plant trees, planting site char- acteristics, desired function from the trees, and ability to maintain those trees, not based on initiatives in other cities. Additionally, the city should create realis- tic tree planting goals that take into account the need for maintenance (e.g., structural pruning and tree removal) throughout the trees’ life spans. Many municipalities use canopy cover (i.e., the percentage of land covered by the trees’ canopy) as a quick way to provide a broad assessment of their urban forest. Exclusively using canopy cover as a measurement for the success of the urban forestry program can lead to an unsustainable system (Kenney et al. 2011). If man- agers solely rely on canopy cover to assess the urban forest, they may miss crucial details, such as tree age distribution, forest health, or tree species diversity (Kenney et al. 2011). As more municipalities estab- lish urban forest programs, survey research has explored how these programs operate (e.g., Kenney and Idziak 2000). 373 Study Context The number of papers published about urban forestry has increased since 2000; but as of 2011, only a small subset of those papers on urban trees have used sur- vey-based social science methods (Roy et al. 2012). Also lacking is qualitative research in urban forestry (McLean et al. 2007). The use of a qualitative frame- work can capture the context of social components, such as what residents prioritize in urban forest man- agement, whereas quantitative data are better suited for assessing the abiotic and biotic factors that influ- ence urban forest management (Ordóñez and Duinker 2014). Beatty and Heckman (1981) conducted one of the first major surveys of urban forest programs in the United States, which helped to illuminate some of the constraints faced by urban forest managers. Others have used data to provide advice on what tree species to plant (McPherson et al. 2002), but few studies have combined qualitative and quantitative data in a mixed-methods approach to see how managers are operationalizing these variables or practices. METHODS Study Area and Design We conducted research in the Pacific Northwest (PNW) states of Oregon and Washington. By only surveying Tree City USA designated cities (which invest $2 per capita in urban forestry, have an Arbor Day celebra- tion, have an established tree board, and have a tree ordinance)(Arbor Day Foundation 2020), we targeted municipalities that we thought had active urban tree management. There were 61 Tree Cities in the state of Oregon and 90 in the state of Washington in 2016; approximately half of the PNW population resided in Tree Cities (Arbor Day Foundation 2016a, 2016b). Our survey targeted those who plant primarily on public lands. Contacts for Tree Cities across the PNW were col- lected with assistance from the Oregon Department of Forestry and the Washington Department of Natu- ral Resources. A survey was designed in Qualtrics and was approved by the University Institutional Review Board. Prior to administration, the survey was reviewed and revised by the authors. Contacts from Tree Cities in Idaho were used to test the survey for internal and external validity (Vaske 2008). There was a 52.3% response rate, with 79 municipalities represented out of the potential 151 Tree Cities. Six ©2020 International Society of Arboriculture
September 2020
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