Growing a diverse urban forest: Species selection decisions by practitioners planting and supplying trees

• Surveyed landscape architects, NPOs, retail garden centers and municipal staff.
• Different actors used varied criteria to make tree species selections.
• Tree supply was a central factor in tree planting and sales.
• Information needed about how to select species to build resilient urban forest.

With the adoption of ambitious goals to grow and diversify the urban forest, municipal and non-municipal planting efforts have increased in many North American cities. A better understanding of the decisions made by those engaged in planting and supplying trees is needed to understand if and how municipal goals are being addressed, provide insight into ways the urban forest may be changing, and more broadly shed light on urban socio-ecological dynamics. This study explores tree species selection criteria used by practitioners involved in urban tree planting and supply to better understand current planting activities. Surveys and interviews with landscape architects, non-profit organizations, retail nurseries and garden centers, and municipal forestry staff in Toronto (Ontario, Canada) were conducted to identify the factors each group considers when selecting tree species, with emphasis on the influence of pests and tree availability. Differences in species selection criteria exist between the four groups, with variations primarily related to consideration of neighboring species and native status, key factors when managing for a resilient urban forest. However, divergent decision criteria between landscape architects and municipal staff actually translated into very similar common planting lists, while two non-profit organizations shared a similar emphasis on native species but planted very different species. Pest knowledge and influence on species selection varied among the actors, but all groups indicated that availability affected what was planted or sold. Results highlight the need for conversations about ways different actors can select species to contribute to a diverse and healthy urban forest.