©2023 International Society of Arboriculture 316 Barron et al: Scenario Modelling for Resilient and Diverse Urban Forests in Densifying Cities Despite this densification, the city has managed to maintain its relatively high level of urban greenness (Czekajlo et al. 2020; Lantz et al. 2021), in part due to the Greenest City 2020 Action Plan, which set numer- ous goals for increasing access to nature compared to the 2010 baseline (City of Vancouver 2015). Specific aims included ensuring all residents live within a 5-minute walk of a park, greenway, or other green- space; planting a total of 150,000 new trees over the course of the decade; and increasing tree canopy cover to a total of 22% by 2050 (City of Vancouver 2015). This final goal was successfully reached a full 3 decades early, with the city calculating a citywide canopy cover of 22% in 2020 (Vancouver Board of Parks and Recreation 2020). Having met this goal, at the end of 2020, the Vancouver Board of Parks and Recreation then set a citywide target of reaching 30% tree canopy cover by the year 2050—while also seeking to advance equity by focusing on canopy-deficient neighbourhoods; increase connectivity between trees and other forms of greenspace, such as parks; and support the city’s broader climate-change mitigation efforts (Vancouver Board of Parks and Recreation 2020). Scenario Setting To develop a granular understanding at a small scale, modelling scenarios were built in a proxy area (or “sandbox”) of 1,600 m by 1,600 m in size. The sand- box was created by piecing together 16 smaller, man- ageable urban blocks (400 m by 400 m in size), generated and arranged in previous research (Lu et al. 2021; Lu et al. 2023). The relevant characteristics incorporated into the model were based on a neigh- bourhood in southeastern Vancouver that had less than 10% canopy cover at the study’s 2020 baseline. In addition to being in need of a significant planting effort to meet the city’s 2050 canopy cover goal, the area is expected to rapidly densify, with its population growing by roughly a third between 2020 and 2050 based on mid-point provincial projections with input from local planners (more details in Lu et al. 2021; Lu et al. 2023; Czekajlo et al. in press). Data on the neighbourhood’s built environment were derived from a range of sources, including Metro Vancouver, a regional governing body that is respon- sible for planning for urban growth and maintaining and developing parklands across the region (Metro Vancouver 2022); BC Assessment, which assesses and documents property information from across the province (BC Assessment 2022); and the Pacific Institute for Climate Solutions’ Energy Efficiency in the Built Environment project, which modelled the effects of a range of policy solutions to climate change (Salter et al. 2020; Lu et al. 2023). Integrating these data, the sandbox was populated with a total of 15,164 residents in 2020, predominately living in single-family homes (75% of the parcel area). Other residence types and land uses were relatively uncommon at baseline, with 4% of parcels in the area consisting of multi-unit dwellings, 6% commercial properties, 1% mixed-use, 1% civic, and 8% parks or greenspace. Additional details regarding the sandbox inputs are provided in Czekajlo et al. (in press). Scenario Aims Each of the 4 modelling scenarios focused on expand- ing the urban forest to contribute to the City of Van- couver’s 2050 goal of 30% canopy cover (Vancouver Board of Parks and Recreation 2020), but they incor- porated slightly different criteria to reach this outcome. The scenario that formed the focus of the current study—referred to as “scenario 4” in Czekajlo et al. (in press)—prioritized planting new trees to create “blue-green streets” as a specific form of green infra- structure. Based upon the City of Vancouver’s defini- tion, such blue-green streets integrate green features (including trees and other “park-like elements”) in a manner that also supports hydrological (or blue) functions, thereby helping to achieve the city’s goal of increasing access to nature while also providing essential regulating ecosystem services, such as flood management and improved water quality (City of Vancouver [date unknown]). These blue-green streets comprised 2 thoroughfares within the sandbox for which the planting programs were specified to be resilient to the increased heatwave-associated drought and flooding expected in the region. In addition to meeting these resiliency criteria, larger trees were preselected as the preferential option, in part due to their increased ability to shade the higher volume of pedestrian and cycling traffic planned for these routes. Finally, the scenario embedded Santamour’s 30-20- 10 guidelines for diversity: planting no more than 30% of any family of trees, no more than 20% of any genus, and no more than 10% of any single species (Santamour 1990). All in all, scenario 4 (S4) aimed to achieve the urban tree trifecta: identifying resilient
November 2023
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