Damaging invasive forest insects have profoundly affected North American forests and urban forests, particularly in the northeast and Lake States regions of the U.S. Our studies have shown emerald ash borer (EAB) impacts vary considerably among sites dominated by different ash species, reflecting the host preference of the beetles as well as the response of other vegetation. We assessed overstory vegetation and regeneration in sites dominated by Fraxinus pennsylvanica at three stages of the EAB invasion (the core, crest and cusp). We are currently documenting survival of F. americana in southeastern Michigan where EAB first became established. Vegetation, land-use classes, soils and other site-related variables surrounding the F. americana sites are being evaluated with spatial and point data in a GIS. Host preference of EAB documented in recent plantation studies with randomized blocks of multiple ash species reflects the patterns observed in forested settings.
Results/Conclusions
While F. pennsylvanica regeneration is abundant in the core, few overstory trees remain and newly germinated seedlings are absent. Lateral growth of non-ash trees has largely occupied canopy gaps, which will likely reduce the ability of young ash to reach the overstory. In crest and cusp sites, mortality of overstory F. pennsylvanica increased substantially from one year to the next, indicating patterns observed in core sites are likely to be common across much of the F. pennsylvanica range. In core sites with abundant F. americana, post-invasion survival ranges from roughly 10 to 90% of the trees. Adult EAB are captured on traps in these sites each year. The relationship between EAB captures and live ash phloem is weak, indicating EAB density is not limited by availability of ash phloem for larval development. Site-related factors that may contribute to very high or very low survival are currently being evaluated.