The emerald ash borer (EAB) has been killing ash trees in the United States for more than two decades. What does that mean for ash populations and the forest ecosystems? Long-term monitoring plot data collected by Northern Research Station scientists and partners are helping us to understand the impacts of this invasive pest and to plan management and conservation strategies.

More than 150 monitoring plots across Ohio and 180 plots on the Allegheny National Forest in Pennsylvania were established in ash forests before the emerald ash borer (EAB) arrived and killed millions of trees and changed forest ecosystems. Continued monitoring in Ohio showed in detail how rapidly more than 99 percent of the large ash trees in these forests were killed. During the summer of 2019, with the Ohio plots in an aftermath phase and the Allegheny National Forest plots experiencing the initial impacts of infestation, these plots were revisited to identify the long-term impacts of EAB in these very different landscapes. Although the largest ash trees are now absent from the Ohio forests, abundant ash seedlings and saplings remain in many sites. Rare surviving large ash trees were also identified. Scientists found that in some forests, other tree species filled in gaps left by ash trees and maintained the structure and function of some forests, however other forests experienced drastic changes. As the long-term impacts of EAB continue to play out across different landscapes, monitoring plot data continues to inform tree breeding, conservation, forest management, and restoration strategies. Knowledge discovered through this research is helping forest managers plan for, mitigate, and respond to effects of EAB across the region.