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 trait diversity of the urban canopy will likely confer the greatest ecosystem service benefits to the urban population and improve the resilience of the urban canopy to pests and climate pressures in the future.

越来越多的城市依靠城市森林来提供生态系统服务，例如温度调节，空气质量改善和雨水消减，这些城市成为城市的家园。气候变化可能会挑战城市森林提供这些服务的能力。热浪，干旱和暴风雨的加剧可能导致树木死亡。在魁北克市，工作表明，城市雨棚容易受到未来预计气候的影响，例如夏天更热更干燥。加剧这一威胁的是，在未来十年中，异国情调的翡翠灰虫有望杀死11％的市政树木。这些压力加在一起可能会导致在短期内大量丧失树冠和生态系统服务。

我们测试了损失的灰烬的重新种植策略是否可以使用基于功能特征的方法将森林社区转变为更耐气候的树冠，是否可以在短期内缓解或改善生态系统服务的提供。利用城市树木的市政数据库，我们针对三种不同的种植情景模拟了20年的树冠生长和替换：i）“照常营业”，ii）“分层”或iii）“以针叶树为中心”的种植策略，并比较他们提供的生态系统服务。

模拟的结果发现在补植方法之内和之间的生态系统服务供应之间存在明显的取舍。“以针叶树为中心”的方案可以最大程度地改善空气质量，减少雨水并降低冬季的能源需求，但是在城市中可以种植针叶树的地方受到限制。相比之下，“一切照旧”的情景实现了更大的树冠覆盖，碳固存和较高的夏季降温，但仍然容易受到气候变化的影响。跨树功能组进行分层补植将最大程度地增加冠层多样性，提供中等水平的生态系统服务并大大降低对未来害虫的脆弱性。