Article Figures & Data
Figures
- Figure 1.
Ranking scores for the 5 species identified as the most tolerant to each studied stressor by the experts in the Delphi survey. The ranking score indicates agreement (or disagreement) with statements among experts (n = 7). The higher the ranking score, the higher the agreement regarding species tolerance. For instance, Ginkgo biloba was ranked first for air pollution with an average score of 1.83 on a scale of 1 (highest score) to 5 (lowest score), meaning that G. biloba was consensually regarded as tolerant to air pollution.
- Figure 2.
Ranking scores for the 5 species identified as the most intolerant to each studied stressor by the experts in the Delphi survey. The ranking score indicates agreement (or disagreement) with statements among experts (n = 7). The higher the ranking score, the higher the agreement regarding species intolerance. For instance, Pinus strobus was ranked first for air pollution with an average score of 1.5 on a scale of 1 (highest score) to 5 (lowest score), meaning that P. strobus was consensually regarded as intolerant to air pollution.
- Figure 3.
Most frequently mentioned urban tree species as tolerant or very tolerant to the studied stressors in the closed-ended questionnaire.
- Figure 4.
Number of times (N) the experts in the Delphi survey (n = 7) chose the “do-not-know” option and did not rate a given species as tolerant (blue) or intolerant (brown) for each stressor.
Tables
- Table 1.
Tree species used in the closed-ended questionnaire (n = 20). For each city, the 5 most abundant tree species in the public tree inventory are listed. Within each city, species are listed alphabetically.
Halifax Montréal Ottawa Québec City Toronto Boston New York Syracuse Acer platanoides Acer platanoides Acer platanoides Acer platanoides Acer platanoides Acer rubrum Acer platanoides Acer negundo Amelanchier sp. Acer saccharinum Acer rubrum Acer saccharinum Acer saccharinum Acer saccharum Gleditsia triacanthos Acer platanoides Pyrus calleryana Fraxinus pennsylvanica Acer saccharum Fraxinus pennsylvanica Gleditsia triacanthos Prunus serotina Platanus × acerifolia Acer saccharum Tilia cordata Gleditsia triacanthos Gleditsia triacanthos Quercus rubra Malus sp. Quercus rubra Pyrus calleryana Rhamnus cathartica Ulmus americana Tilia cordata Tilia cordata Tilia cordata Picea pungens Tsuga canadensis Quercus palustris Thuja occidentalis - Table S1.
Categories that emerged from the responses from the first round to the question about urban tree species characteristics related to their tolerances to urban stressors.
Categories (examples) Retained/omitted in subsequent round Climate (e.g., summer heat) Omitted Tree management (e.g., pruning) Omitted Site conditions (e.g., soil) Omitted Origin (native or non-native) Retained Growth strategies (fast vs. slow growth) Retained Leaves (e.g., leaf form, shape, surface characteristics) Retained Roots (e.g., deep vs. shallow root systems) Retained Other (e.g., health status) Retained - Table S2.
Characteristics of the most stressors-tolerant and stressors-intolerant trees as indicated by the participants in the Delphi survey.
Tolerant Intolerant Air pollution Good health, thick leaves Thin leaves De-icing salts Waxy leaves, tolerance to soil compaction and drought Conifers, shallow roots, thin bark, require moist and well-drained soils, planted without protection or protocol Drought Soil-compaction tolerance, deep roots, waxy cuticles, good health, native species from drought-stressed places, salt tolerance, good water-storage capacity Shallow roots Extreme temperatures Deep roots, waxy surfaces, leaf pubescence, regulation of water loss, old age Shade tolerance Ice storms Dense wood, good structure, strong attachments, decay free, flexible branches Poor structure, narrow branch unions, evergreen, bark inclusions (or “ingrown” bark), weak wood, fast growth, wide crown Insects and diseases Good health, adaptation to different environmental conditions No agreement Snow Deciduous, dense wood, good health, decay free, early defoliation, flexibility in the limbs, good structure Deciduous, poor structure, weak attachments, weak wood, late defoliation, wide branches, fast growth Soil compaction Seasonal-flooding tolerance, drought tolerance, hard wood, native species from wetland sites Drought intolerance, slow growth Strong winds Good structure, deep roots, stable rooting, slow growth, dense wood, good health Poor structure, shallow roots, dense crown, weak roots, fast growth Level of study (degree) Number of participants Doctorate 4 Master’s 14 Bachelor’s 13 Professional or Associate’s 5 Job title Number of participants Researcher 8 Arborist 9 Technician in arboriculture and horticulture 3 Professional educator 2 Director, deputy director in Forestry & Parks Department 4 Agent at NRCS, NRCan 3 Landscape architect 1 Did not answer 6 - Table S5.
Years of working experience of the participants in the closed-ended questionnaire in arboriculture and urban forestry.
Number of years Number of participants 1-5 8 6-10 4 11-15 1 16-20 3 20-25 3 > 25 14 Did not answer 3
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