How arthropods are directly and indirectly affected by ash dieback due to emerald ash borer

Background/Question/Methods

We assessed the impacts of the exotic emerald ash borer (EAB) on native arthropod species that are directly and indirectly associated with ash trees and forests in North America.   During the summer of 2006-2007, we studied the short-term cascading effects of ash dieback due to EAB on native carabid beetles in southeastern Michigan.  Carabid catches, diversity, and composition were compared among three ash cover types (black, green or white ash), and between two sizes of forest canopy gaps (small or large).  Using literature survey, we also determined which arthropod species that are associated with ash may become co-extinct with the demise of ash as a dominant tree species.

Results/Conclusions

Results from the field study indicate that trap catches and species richness of carabid beetles were higher in the small gap stands in 2006 that also had the most unique species.  There were negative relationships between carabid catches and percentage canopy gap formations and ash tree mortality in 2006.  Riparian carabid species were caught primarily in black ash, where they were further aggregated in the small gap stands.  Cluster analysis revealed that the black ash-small gap stands had the most distinct species composition that was significantly different from that of the large gap stands within the same cover type.  These trends indicate short-term shifts in successional pathways of beetle assemblages due to gap formations.  The literature survey revealed that 43 native arthropod species in six taxonomic groups are known to be associated only with ash trees for either feeding or breeding purposes, and thus face high risk of endangerment.  Another 30 arthropod species are associated with 1-2 host plants in addition to ash, and herbivory on these hosts may increase as these arthropods shift from declining ash trees.  Overall, the demise of North American ash species due to EAB is expected to lead to biotic loss with cascading ecological impacts and altered processes within forested ecosystems.