<div>Emerald ash borer (EAB) ( <i>Agrilus planipennis</i> Fairmaire), an
invasive, phloem-feeding beetle native to Asia, has killed millions of
ash ( <i>Fraxinus</i> spp.) trees in North America since it was detected
in southeast Michigan in 2002. Consistently high mortality of black ash
( <i>Fraxinus nigra</i>) and green ash ( <i>F. pennsylvanica</i>) which
often occur in riparian forests is a concern given their role in
regulating soil moisture and shallow groundwater levels. We monitored
hydrologic processes in a riparian forest in southwest Michigan to
assess impacts of EAB invasion and subsequent ash mortality. From
2018-2022, we recorded soil moisture, depth to groundwater and
meteorological variables at 15-min intervals throughout the growing
season in a canopy gap following EAB-caused ash mortality and in
adjacent, unaffected forest in the Augusta Creek riparian zone.
Groundwater contributions to evapotranspiration (ET <sub>G</sub>)
were estimated using a groundwater level fluctuation (WLF) method.
Significant differences in volumetric soil moisture content (16-26%
higher in the gap than forest), average depth to water (10 cm in the gap
vs 70 cm below land surface in the forest) and mean daily ET
<sub>G</sub> (0.6 in the gap vs 3.0 mm per day in the forest)
persisted across four growing seasons. Within the gap, prolonged
saturation of the near surface may be contributing to a shift from a
forested riparian ecosystem to herb and sedge-dominated wetland. These
differences have implications for an array of riparian zone ecosystem
services, a concern given the extent of ash mortality already sustained
in much eastern North America.</div>