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 |