Building climate resilient urban forests: Impacts of irrigation and heat on tree establishment in a legacy city

Climate change is causing temperatures to rise across much of the earth, and this warming is amplified in urban areas due to the urban heat island effect. One of the most effective methods of reducing urban heat is expanding the urban forest. However, rising temperatures coupled with increasing drought intensity create challenges for the establishment of newly planted trees in cities. Obstacles to urban tree establishment are exacerbated in legacy cities, which have limited financial resources to plant and manage trees. In summer 2024, we conducted a large-scale field study in Dayton, Ohio, USA to address the challenges of expanding the urban forest in a legacy city. To determine low-cost solutions for urban forest expansion, we supplied 640 newly-planted native saplings with varying levels of irrigation investments across 20 parks in Dayton. We then monitored sapling survival, growth, and health in response to our irrigation investments and surrounding impervious surfaces within a 500-m radius of each planting site as a proxy for heat. We found that the effects of both irrigation treatment and surrounding heat varied among tree species. Overall, approximately 50% of planted saplings survived to the end of the growing season, and many saplings went missing due to anthropogenic disturbance. Therefore, we recommend a tailored approach to urban forest expansion which takes species, resources available for irrigation, and surrounding imperviousness into consideration to inform sustainable urban reforestation plans.