Which Tree Species Best Withstand Urban Stressors? Ask the Experts

Abstract

Abstract Background The importance of urban trees and their benefits to society are increasingly recognized. However, cities are a challenging environment for trees to grow and thrive. Current knowledge on tree vulnerabilities to existing urban stressors remains scarce and available only for a limited number of species and specific stressors. Methods Using the Delphi method with urban forestry experts familiar with the studied area and a closed-ended questionnaire, we sought to elucidate the tolerance of commonly planted urban tree species in northeastern North America to multiple urban stressors—air pollution, soil compaction, de-icing salts, insects and diseases, strong winds, ice storms, snow, drought, and extreme temperatures—as well as to assess which characteristics may capture a species’ ability to cope with these stressors. Results Ginkgo biloba, Gleditsia triacanthos, Quercusspp., andUlmusspp. were rated by urban forestry professionals as the most tolerant species in northeastern North America to the studied stressors. No species was listed as tolerant to all stressors. Furthermore, respondents disagreed on how a given species was likely to be affected by or respond to a given stressor. Conclusions Our study provides a powerful approach to gaining difficult-to-obtain information on trees’ vulnerabilities to environmental stressors and identifying the gaps that remain unaddressed. Our findings fill some of the gaps in our knowledge of city trees’ vulnerabilities, which makes the approach useful in practice to inform the choice of tree species that could be planted across our cities to build more resilient urban forests.