Riparian forest conditions along three northern Michigan rivers following Emerald Ash Borer invasion

Abstract

Emerald Ash Borer (EAB; Agrilus planipennis Fairmaire (Coleoptera, Buprestidae)) has killed millions of ash (Fraxinus spp.) trees since its 2002 detection in southern Michigan and Ontario. Effects of EAB in riparian forests, where ash species are often abundant, could influence terrestrial and aquatic conditions but are largely unknown. We surveyed vegetation and coarse woody material within and between three gaps in riparian forests along stretches of three rivers in northwestern Michigan. Gaps were originally dominated by Fraxinus pennsylvanica Marsh. and Fraxinus nigra Marsh., which comprised 46%–71% of total basal area, while ash comprised <10% of basal area in forests between gaps. More than 95% of overstory ash were killed by EAB. Fraxinus pennsylvanica saplings were abundant in gaps but F. nigra regeneration was minimal. Few tree seedlings occurred in gaps, which were dominated by dense sedge mats. Aerial imagery showed the EAB invasion has resulted in 3.6–7.1 canopy gaps·km−1 and dead ash account for 13%–21% of total basal area within 100 m of the banks of all three rivers. Long-term monitoring will be useful to evaluate persistence of ash, particularly F. nigra, the stability of riparian buffers, and potential indirect effects of EAB invasion on the adjacent aquatic systems.