Effects of Late Stages of Emerald Ash Borer (Coleoptera: Buprestidae)-Induced Ash Mortality on Forest Floor Invertebrate Communities

Emerald ash borer (EAB; Agrilus planipennis Fairmaire) is an invasive wood-borer causing rapid, widespread ash tree mortality, formation of canopy gaps, and accumulation of coarse woody debris (CWD) in forest ecosystems. The objective of this study was to quantify the effects of canopy gaps and ash CWD on forest floor invertebrate communities during late stages of EAB-induced ash mortality, when the effects of gaps are predicted to be smallest and effects of CWD are predicted to be greatest, according to the model proposed by Perry and Herms 2016a. A 2-year study was conducted in forest stands that had experienced nearly 100% ash mortality in southeastern Michigan, USA, near where EAB first established in North America. In contrast to patterns documented during early stages of the EAB invasion, effects of gaps were minimal during late stages of ash mortality, but invertebrate communities were affected by accumulation and decomposition of CWD. Invertebrate activity-abundance, evenness, and diversity were highest near minimally decayed logs (decay class 1), but diverse taxon-specific responses to CWD affected community composition. Soil moisture class emerged as an important factor structuring invertebrate communities, often mediating the strength and direction of their responses to CWD and stages of decomposition. The results of this study were consistent with the predictions that the effects of CWD on invertebrate communities would be greater than those of canopy gaps during late stages of EAB-induced ash mortality. This research contributes to understanding of the cascading and long-term ecological impacts of invasive species on native forest ecosystems.