©2023 International Society of Arboriculture 194 Tabassum et al: A Plant Selection Tool for Changing Urban Climates consensus approach. Finally, an extensive assessment of the species and trait matrix was performed by an industry expert (Gwilym Griffiths) to ensure accuracy. As well as traits collected from open sources, Which Plant Where contains additional information on heat and drought tolerance for a subset of 113 spe- cies and cultivars obtained from glasshouse experi- ments. This selection comprised a mixture of species both native and exotic to Australia, from a variety of different growth forms, and were species commonly available in the Australian horticultural market, as well as uncommon species less readily available commercially and infrequently planted in urban areas. These plants were subjected to experimental heatwaves and droughts in climate-controlled glass- houses to measure their physiological responses. Detailed explanations of how plants were droughted and subsequently ranked as drought tolerators and drought avoiders can be found in Marchin et al. (2020) and Tabassum et al. (2021b) respectively. An explanation of how plants were subjected to an exper- imental heatwave can be found in the Appendix. Co-Benefit Calculations Which Plant Where provides the opportunity for users to create multiple planting palettes to help design planting lists for urban greening projects. In addition to organising planting lists for specific projects, plant- ing palettes calculate key co-benefits that urban plant- ings can provide. Average co-benefits are automatically calculated when 10 or more plants are selected to form a palette. The co-benefits that are calculated by the tool are shade value, carbon value, biodiversity value, planting diversity, and total canopy cover (Fig- ure 1). Co-benefit calculations may be particularly useful for end users to assess whether their urban greening project meets standards such as tree canopy targets. An explanation of how these co-benefits are calculated within the tool can be found in the Appendix. Alternative Species When plants are selected for planting palettes, Which Plant Where provides alternatives to the selected spe- cies based on similarity in climate suitability, growth form, height, exotic/native status, and leaf loss (Fig- ure 2). This is to ensure that if substitutions need to be made for planting palettes, alternative species will still be climatically suitable. We also calculated the median value for both vari- ables across each postcode for the 3 future periods (2030, 2050, and 2070) from the set of 10 global cli- mate models. Each species was then classified as unsuitable, marginal, or suitable for each postcode and year based on the median values of the 2 climate variables for the postcode relative to the species’ cli- mate niche. Species were classified as unsuitable if the median value of either climate variable for the postcode was greater or less than the minimum or maximum values of the species’ climate niche. This indicated that the postcode would likely be too cool/ dry or hot/wet for the species. Species were classified as marginal if the median values of the postcode were within the 0% to 5% or 95% to 100% of the species climate niche for either variable. Species were classi- fied as suitable if the median values of the postcode lie within the 5% to 95% values of the species climate niche for both variables. Trait Collection We conducted an extensive literature review to col- lect trait information for the species in the tool from a variety of nursery (domestic Australian and interna- tional), government, university, botanical garden, landscaping, and horticultural websites. The col- lected trait data were refined iteratively following consultation with key stakeholders from the nursery and landscaping industries. These key stakeholders decided on a core set of traits which were essential to display for each entry in the plant selection tool: com- mon name(s), minimum and maximum height and width, origin, flower colour, flower period, leaf loss, shade tolerance, urban space type, and use. Other traits that were collected include information on envi- ronmental tolerances, soil conditions, and biodiver- sity benefits (see Table 1 for a full list of traits). Most of the traits that were collected had either continuous values (e.g., growth dimensions) or nom- inal values (e.g., flower colour) which were relatively easy to interpret. However, ordinal values, such as tolerance for drought, frost, and coastal conditions, were more ambiguous. For example, drought toler- ance in horticultural literature is described using a variety of terms such as “tolerates very high water deficit,” “occasional drought,” and “prefers regular access to moisture.” For these traits, we used the methodology described in Tabassum et al. (2021b), where terms were tallied and classified as high toler- ance, moderate tolerance, or no tolerance, using a
July 2023
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