A bioeconomic analysis of objective-based management options for late-stage emerald ash borer (Coleoptera: Buprestidae) infestations

Following its North American introduction, the emerald ash borer (Agrilus planipennis Fairmaire) (Coleoptera: Buprestidae) (EAB) has devastated ash populations (Fraxinus Linnaeus) (Oleaceae), largely extirpating the genus from infested regions. Previous cost-benefit analyses of EAB management options, including insecticidal injections, preemptive removals, and replanting, have examined early-stage infestations. This study tests options for late-stage EAB management based on ecological and economic objectives. We parameterized management decisions to evaluate tree counts, basal area, and urban forest value under 7 management options, varying if and when ash trees were injected, removed, and replanted with non-ash species. The simulation is applied to the remaining ash population in Mississauga, Ontario where tree coring and annual assessments determined that injected trees have reduced growth rates and are declining in condition. The results demonstrate that injections help preserve the ash population, maximize basal area, minimize spikes in annual costs, and reduce cumulative costs earlier in the 20-yr study period. However, long-term cost reduction is achieved through ceasing injections and removing ash as they die from EAB. Maintaining tree counts and maximizing net value is achieved through proactive replanting and winding down basal injections, coupled with a slow rate of removal, ultimately bringing the SLow Ash Mortality approach to a close.