Ash population dynamics after two decades of Emerald Ash Borer infestations in Canada

The emerald ash borer (EAB) is one of North America's most destructive invasive insects, responsible for the death of millions of ash trees since its introduction. This study documents ash mortality, regeneration dynamics, and infestations in regenerating stems after two decades of EAB presence in Canada. We analyzed data from 46 long-term monitoring plots established in 2010 across four regions, two urban and two agricultural, encompassing riparian and woodland habitats. No ash trees larger than 10 cm DBH survived beyond seven years following the onset of EAB-induced mortality, though vigorous regeneration was observed in most sites. Reconstruction of infestation timelines indicated that EAB shifted to attacking smaller hosts only once large hosts were depleted, and among regenerating stems, 42% were infested at least once and 14% experienced five or more infestations. Larval densities were generally low, suggesting reduced carrying capacity in post-invasion forests, lower EAB fecundity and higher EAB mortality in regenerating stems. These findings highlight the complex interactions between EAB and its hosts, improving our ability to anticipate ecological outcomes and inform post-outbreak forest management strategies.