Arboriculture & Urban Forestry 46(5): September 2020 Arboriculture & Urban Forestry 2020. 46(5):371–384 URBAN FORESTRY ARBORICULTURE Scientific Journal of the International Society of Arboriculture & A Tree Selection Survey of Tree City USA Designated Cities in the Pacific Northwest By Joshua Petter, Paul Ries, Ashley D’Antonio, and Ryan Contreras Abstract. As urban areas expand, there are a greater number of urban trees; however, development often leads to a reduction in urban trees in many areas. A reduction in the canopy volume of trees results in a reduction in the number of benefits. Additionally, urban trees can have addi- tional stressors and must be more actively managed to maintain those services. Selecting tree species for the right site can lead to greater ben- efits and longer-lived trees. Increasing diversity of urban trees can help to mitigate some of the threats facing urban forests, such as invasive pests and climate change. We surveyed Tree City USA designated cities across Oregon and Washington to explore how they are selecting tree species for their municipalities. Responses were recorded for 79 out of 151 municipalities for a 52.3% response rate. Both open-ended ques- tions and descriptive statistics were used to triangulate how managers are selecting tree species. Emergent themes in open-ended responses indi- cate a variety of justifications for tree species selection and the challenges of balancing those criteria. There is evidence to suggest that these municipalities are actively diversifying the urban forest; however, there are still 10 municipalities that reported ash (Fraxinus spp.) in their top 5 most frequently planted species in 2016. Many municipalities are still planting large quantities of maple (Acer spp.). Overplanting certain gen- era and species can lead to an increase in susceptibility to pests and pathogens. We recommend an increase in consideration for the diversifica- tion of tree species in urban areas. Keywords. Emerald Ash Borer; Tree Species Diversity; Tree Species Selection; Urban Forest Managers. 371 INTRODUCTION The global population could reach 9 billion by the year 2050, and the fastest growth rates will be occur- ring in urban areas (Roberts 2011). Tree planting is an increasingly popular solution to address environmen- tal problems such as climate change in urban areas; the city governments of Los Angeles and New York have both proposed plans to plant 1 million trees, demonstrating their commitment to tree planting (Pincetl et al. 2013). In California, the total number of street trees has increased; however, the trees are more spread out, and there are many vacant planting sites (McPherson et al. 2016). Cumulatively, California’s street trees are estimated to have an approximately $1 billion impact from energy savings, carbon diox- ide sequestration, improved air quality, stormwater mitigation, and increased property value (McPherson et al. 2016). Urban Trees Different tree species and site locations can have dif- ferent impacts on social, ecological, and economic benefits; each tree should be appropriately sited to maximize benefits (e.g., cooling, stormwater mitiga- tion, wildlife habitat, and aesthetics)(McPherson et al. 1997). Trees, particularly evergreens, can help to remove air pollutants (Escobedo and Nowak 2009). Urban trees can help to sequester carbon, but the rate of carbon sequestration largely depends on the tree species (Nowak et al. 2002). Additionally, manage- ment practices (e.g., wood salvage vs. wood chip- ping) should be considered in terms of net environmental benefits provided by the tree (Nowak et al. 2002). Furthermore, urban residents have highly rated the benefits of cooling and stress relief provided by trees (Lohr et al. 2004). An arbitrary number of trees planted may not necessarily yield the desired ©2020 International Society of Arboriculture
September 2020
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