UBC Theses and Dissertations

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UBC Theses and Dissertations

Finding urban trees for a changing world Samaha, Jehane Alexandre


The well informed selection of street tree species is crucial to improve the diversity and functionality of urban forests, with the potential to provide lasting environmental and socio-cultural benefits. This multi-method project aims to characterize the complexity of the tree species selection process: which selection criteria do street tree planting professionals value, and which tree species do professionals associate with valued characteristics? Furthermore, what barriers and knowledge gaps inhibit the improvement of tree species selection to accomplish urban forestry goals of increased diversity and function? Using an extensive online survey of the USA and Canada as well as a case study of interviews in Philadelphia, we found that: • A tree’s tolerance of urban stressors is more important than other major selection criteria. • Though ecosystem services are rated as important, professionals often lack the information necessary to apply these concepts to tangible tree selection decisions. • There are inherent trade-offs between many selection criteria, leading to planting choice compromises. • Professionals disagree on the qualities and planting suitability of many tree species. • The palette of tree species encouraged by professionals varies across climate regions. • Of the professional fields surveyed, urban foresters encourage planting the most diverse palette of trees, and landscape architects have the most diverse palette of trees that they discourage planting. Tree recommendations from the fields of urban forestry and arboriculture are the most similar. • A higher percentage of trees encouraged by public horticulture professionals are “rare” in the urban forest; collaborations with this professional field may have the potential to evaluate and expand the palette of street tree species. • There are high level barriers to implementing ideal selection criteria, including issues of budget, nursery supply, site conditions, lack of inventory data, public perception, and the lack of accessible and functional information on the characteristics of tree species. Expanding the palette of available street trees and increasing the availability and transfer of information on the characteristics of particular trees is a crucial step to increase biodiversity and the provisioning of ecosystem services in the face of urbanization and climate change.

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