Vegetation responses to simulated emerald ash borer infestation in Fraxinus nigra dominated wetlands of Upper Michigan, USA

The invasive emerald ash borer (EAB) (Agrilus planipennis Fairmaire (Coleoptera: Buprestidae)) is a significant threat to biodiversity and ecosystem processes in North American forests. Of particular concern is the fate of Fraxinus nigra (black ash), which is frequently a dominant canopy species across much of its range. To investigate the potential vegetation response to the loss of this foundation species, EAB-induced mortality was simulated in F. nigra dominated wetlands of Upper Michigan, USA. No growth response of residual overstory species occurred over the course of three growing seasons, which may in part be attributed to negative effects of post-treatment growing conditions, including prolonged inundation. A significant increase in non-Fraxinus sapling growth rate was observed, however. Mortality of F. nigra did not impact overall stem recruitment or regeneration, although species composition is shifting towards Acer rubrum (red maple) and Betula alleghaniensis (yellow birch) in the seedling layer. The herbaceous community exhibited the greatest response, nearly doubling in areal cover by the end of the study. Importantly, this expanded cover was not associated with decreased establishment of new woody seedlings, suggesting that increased competition between these functional groups has not yet impacted the potential for future recovery of woody vegetation in these forests.