Eisenman, T.S., Chang, S.E., Laurian, L. (2022). Stewarding Street Trees for a Global Urban Future. In: Brears, R.C. (eds) The Palgrave Encyclopedia of Urban and Regional Futures. Palgrave Macmillan, Cham. https://doi.org/10.1007/978-3-030-87745-3_226.
Street trees are one of the most prominent types of plants in the urban public realm. They define the street corridor, humanize the scale of cities, calm traffic, separate walkers from vehicles, and filter sunlight all while softening the urban fabric and introducing beauty in the form of flora. Importantly, trees can transform streets from utilitarian transportation corridors into places in which people want to be (Massengale and Dover 2014). This is especially important as human beings become an increasingly urban species; 2008 marked the first time that more people worldwide lived in urban than rural areas, and by the end of this century some three-quarters of humanity is projected to live in cities (Angel 2012), leading the contemporary era to be described as the “first urban century” (Hall and Pfeiffer 2000, p. 5).
In this dawning age of cities (Young and Lieberknecht 2019), people spend the vast majority of their time indoors (Brasche and Bischof 2005; Klepeis et al. 2001). Streets are by extension one of our most common experiences of outdoor settings, and these “travelscapes” represent an excellent opportunity to provide urban populations with the health and well-being benefits of nature contact, as evidenced by a robust body of literature (Frumkin et al. 2017; Hartig et al. 2014; Kuo 2015). This dovetails with increasing interest in urban greening, defined as a social practice of organized or semi-organized efforts to introduce, conserve, or maintain outdoor vegetation in urban areas (Eisenman 2016b; Roman et al. 2020). Greening includes a range of initiatives, policies, and incentives to vegetate the landscape of cities (Beatley 2016; Tan and Jim 2017), and it often includes ambitious tree planting initiatives (Eisenman et al. 2021; Nguyen et al. 2017; Young 2011). Of note, the systematic citywide planting of trees along streets was not common in most European and North American cities until the late nineteenth and early twentieth centuries (Campanella 2003; Dümpelmann 2019; Laurian 2019), but it has since become commonplace around the world (Lawrence 2006).
Yet, the actors and norms that guide street tree planting and management can vary in different cultural contexts. In North America, for example, urban forestry has traditionally focused on street trees, whereas European definitions of urban forestry relate more to forest ecosystems such as woodlands in or near cities (Konijnendijk et al. 2006). One study found substantial differences in why and how municipal leaders in North America and Scandinavia conduct inventories of urban trees. In both places, street trees figured prominently in urban forest inventories, and study participants mentioned operational planning and arboricultural maintenance as important rationales for this work. However, in North America citizen volunteers were important actors in conducting urban tree inventories, and this volunteer work may have spurred subsequent citizen engagement in local urban forestry activity. North American cities also emphasized a range of economic, environmental, and social benefits of urban trees as rationales for conducting inventories. In Scandinavian cities, by contrast, these benefits were not mentioned or recognized as important rationales for conducting urban tree inventories, nor did citizen volunteers participate in this work (Keller and Konjijnendijk 2012).
International dimensions are also important considerations when accounting for street tree planting and stewardship. While research suggests a basis for universal landscape preferences predicated on a shared evolutionary past (Appleton 1975; Ulrich et al. 1991), and studies consistently show reductions in stress when people have contact with vegetated landscapes (Frumkin et al. 2017; Hartig et al. 2014; Kaplan and Kaplan 1989)—including local trees (Suppakittpaisarn et al. 2019)—people have different perceptions of, and preferences for, urban trees (Konijnendijk 2008; Zhao et al. 2017). The same holds true for street-level vegetation. In Sapporo, Japan, for example, researchers found that people preferred sidewalk planting beds of flowers without trees over similar planting beds with trees (Todorova et al. 2004). By contrast, a study spanning four cities in the Netherlands found a strong preference for large trees along streets (Van Dongen and Timmermans 2019), while a study in Australia found that homes on streets with more than six different street tree species had reduced sale prices, suggesting a threshold beyond which people in this place will accept a diversity of street tree types (Plant and Kendal 2019). In Hong Kong, 94% of survey respondents supported street tree planting, but the most preferable streetscape attribute was high visual permeability (the openness of the street), suggesting that street trees should not be too large or too densely spaced.
International differences extend beyond landscape vegetation preference. For example, a comparative analysis of five capital cities in countries spanning three continents found substantial differences in street tree density and distribution; moreover, differences between cities in the same climate zone suggest that place-specific cultural dimensions such as urban form, aesthetic norms, and governance regimes are important factors in the density and distribution of urban street trees (Smart et al. 2020). People within a given city can also hold different perceptions of—and receptivity to—tree planting campaigns. In Detroit, Michigan, many neighborhoods targeted for street tree planting resisted such efforts, and this was explained by a lack of “procedural justice” and differing “heritage narratives” (perceptions of local history) between local residents and tree planting advocates (Carmichael and McDonough 2019).
The aforementioned distinctions illustrate the importance of comparative research on street tree planting and management, especially as greening (and associated constructs such as green infrastructure, ecosystem services, and nature-based solutions) becomes a common approach to planning for twenty-first-century cities worldwide. Unlike noncomparative research, comparative scholarship seeks to illuminate differences and similarities between the objects of analysis—in this case street trees—and their contextual conditions, such as culture and nationality. Comparative research can also illuminate the embedded customs and assumptions of a given place, which is especially important if they are taken to be universal (Esser and Vliegenthart 2017; Lewis-Beck et al. 2004). This is noteworthy in a globalizing world characterized by the widespread diffusion of information, values, and norms (Castells 1996). Vernacular distinctions are also important in an urban environmental discourse that is significantly influenced by Anglo-American and European tradition (Anguelovski and Martínez Alier 2014; Eisenman 2016a; Ernstson and Sörlin 2019).
This chapter seeks to enrich this conversation by offering brief case studies and comparative analysis of the typical actors and practices related to stewardship of urban street trees in three cities on different continents: Paris, France; Taipei, Taiwan; and Washington, DC in the USA. Each of these cities is the capital of their respective countries, so each subsection opens with a brief narrative addressing national and historic context. Each of these cases addresses both mature and newly planted street trees; and the respective cases draw upon a combination of academic literature, professional documentation, and select interviews with local experts.