Ash mortality caused by emerald ash borer alters ground beetle (Coleoptera: Carabidae) assemblages

Emerald ash borer (Agrilus planipennis, EAB), an invasive wood-boring beetle endemic to Asia has killed millions of ash trees since its introduction as North American species are highly susceptible.  Widespread simultaneous formation of canopy gaps from high ash mortality may alter microhabitat conditions (light, soil temperature, moisture) on the forest floor.  Increased light is predicted to decrease populations of sensitive invertebrates.  However, as dead ash trees fall, increased accumulation of coarse woody debris (CWD) may stabilize environmental conditions by increasing heterogeneity on the forest floor and buffering changes caused by increased light.  Ground beetles (Carabidae) are widely used as biological indicators of environmental change in forest ecosystems because they are habitat specific, a food resource for vertebrates, and regulators of decomposer populations.  The objective was to determine the effects of EAB-induced ash mortality on the ground beetle community.  A manipulative factorial experiment was designed in forests at NASA Plum Brook in Ohio with two treatments: presence/absence of light gaps and presence/absence of CWD.  Activity abundance and diversity was assessed with pitfall traps.  Soil temperature and moisture were measured adjacent to traps.  Canopy gap size was assessed with a densiometer, and categorized as large and small gaps.  Ground beetle species responded to the presence of light gaps, resulting in a shift in community composition.  Several species were found to be characteristic of closed canopy habitat.  The presence of light gaps altered environmental conditions on the forest floor by increasing soil temperature and moisture.  CWD had no effect on ground beetle assemblages.