Increasing functional diversity of the urban canopy for climate resilience: Potential tradeoffs with ecosystem services?

•Climate change may challenge urban forests’ capacity to provide ecosystem services (ES).•Shifting canopy composition to climate-tolerant species could impact ES provisioning.•We model ES provisioning resulting from alternative canopy compositions.•More functionally diverse canopies provide greater ES provisioning.•Stratified replanting based on tree functional groups can mitigate multiple threats. Cities are home to an increasing number of people who depend on urban forests to provide ecosystem services such as temperature regulation, air quality improvement and storm water abatement. Climate change may challenge the capacity of urban forests to provide these services. Intensification of heat waves, droughts and strengthening storms could lead to tree die-offs. In Quebec City, work has suggested that the urban canopy is vulnerable to future projected climates, i.e. hotter and drier summers. Compounding this threat, the exotic emerald ash borer is expected to kill 11 % of municipal trees over the next decade. Together these pressures could lead to a significant loss of canopy cover and ecosystem service provisioning in the near-term. We test whether replanting strategies for lost ash, which shift the forest community towards a more climate-tolerant canopy using a functional trait-based approach, can help to mitigate or improve ecosystem service provisioning in the near-term. Using a municipal database of urban trees, we simulate canopy growth and replacement over 20-years for three different replanting scenarios: i) ‘business-as-usual’, ii) ‘stratified’ or iii) ‘conifer-focused’ replanting strategy, and compare their delivery of ecosystem services. Results from the simulations find clear trade-offs in ecosystem service provisioning within and between replanting approaches. The ‘conifer-focused’ scenario provides the highest level of air quality improvement, storm water abatement and reduced energy demands in winter, however there are limitations on where coniferous trees can be planted in cities. In contrast, the ‘business-as-usual’ scenario achieved greater canopy cover, carbon sequestration, and high summertime cooling, but remains vulnerable to climate change. Stratifying replanting across tree functional groups results in the greatest increase to canopy diversity, intermediate levels of ecosystem service provisioning and important reduction in vulnerability to future pests . We suggest that a replanting approach focused on increasing the functional tra