A High-Resolution Map of Emerald Ash Borer Invasion Risk for Southern Central Europe

Ash species (Fraxinus spp.) in Europe are threatened by the Emerald Ash Borer (Agrilus planipennis, EAB), an invasive wood boring beetle native to East Asia and currently spreading from European Russia westwards. Based on a high-resolution habitat distribution map (grid cell size: 25 × 25 m) and data on distribution and abundance of Common Ash (Fraxinus excelsior), the most widespread and highly susceptive host species of EAB in Europe, we assess the spatial distribution of EAB invasion risks for southern Central Europe (Austria, Switzerland, Liechtenstein, southern Germany, South Tyrol). We found highest F. excelsior abundance and thus invasion risks in extensive lowland floodplain forests, medium risks in zonal lowland forests and low risks in upper montane and subalpine forests. Based on average velocities of spread in Russia (13–31 km/year) and North America (2.5–80 km/year) from flight and human-assisted transport, EAB is likely to cover the distance (1500 km) between its current range edge in western Russia and the eastern border of the study region within few decades. However, secondary spread by infested wood products make earlier introductions likely. The high susceptibility and mortality of F. excelsior leave no doubt that this beetle will become a major forest pest once it reaches Central Europe. Therefore, developing and testing management approaches with the aim to halt or at least slow down the invasion of EAB in Europe have to be pursued with great urgency.