IPRRG webinar: New Perspectives in Urban Forest Invader Management

​Presenter: Emma Hudgins, Carleton University (Ottawa, Canada)

​Abstract: Urban trees are important nature-based solutions for future wellbeing and livability, but are at high risk of mortality from invasive insects and pathogens. To plan effective mitigation, managers must know which tree species in which communities will be at the greatest risk, as well as the highest-risk species. This presentation will cover four different projects relating to urban forest health in the face of species invasions. First, I will summarize an economic impact assessment on United States (US) street tree mortality due to invasive insects. This approach combined models of street tree populations in ∼30,000 communities, species-specific spread predictions for 57 invasive insect species, and estimates of tree death due to insect exposure for 48 host tree genera. We estimated that 1.4 million street trees will be killed by invasive insects from 2020 through 2050, costing an annualized average of US$ 30M. Further, 90% of all mortality will be due to emerald ash borer (Agrilus planipennis, EAB), which is expected to kill virtually all ash trees (Fraxinus spp.) in >6000 communities. Secondly, I will discuss a recent project that has reformulated this impact model as an optimal control framework to determine the ideal management strategy for urban tree persistence. We found that the best management strategy always included a combination of site-focused (biological control) and spread-focused (quarantine) management measures, and that failing to use a mixed strategy could result in losses of upwards of one million street trees in the next 30 years. Thirdly, I will discuss the link between forest biodiversity and pest susceptibility, where a phylogenetic model indicates that diverse tree plantings reduce the probability that invaders will establish. Finally, I will discuss preliminary findings from a very recent ‘new perspectives in forest invader management’ workshop, featuring experts across the invasion response, including Indigenous knowledge holders.