Ash tree (Fraxinus spp.) seedling dynamics in emerald ash borer (Agrilus planipennis) infested forests

Background/Question/Methods

The introduction of emerald ash borer beetle (EAB) (Agrilus planipennis) to North America has caused ash (Fraxinus spp.) mortality and cascading changes in ash ecosystems.  The future of ash trees in natural habitats is dependent on the next generation.  The purpose of this study was to identify environmental variables that may have influenced ash seedling dynamics over time in Ohio.  Long-term monitoring plots have been surveyed yearly to understand the changes over time in ash tree habitats. We monitored the density of ash seedlings in 55 Ohio sites.  Each site had three monitoring plots that were 400m², with nested 4m² subplots placed in each cardinal direction.  In these subplots ash seedlings were counted and separated into categories of “new” or “established” based on the presence or absence of cotyledons.  We have also recorded percent cover class (<1, 1, 2-5, 6-10, 11-20, 21-30, etc.) for each seedling category, percent cover class of invasive plant species, habitat type, and canopy openness. 

Results/Conclusions

For northwest Ohio the majority of the mature ash trees were dead by 2008, a mast year in other parts of Ohio. The patterns of new and established ash seedling numbers were reflective of the masting seed cycle of mature ash trees in the region. For most sites, new seedling numbers declined over time after a temporary increase in 2009/2010. The number of established seedlings declined in 2009, increased in 2010, then decreased in the following years. Survival of new seedlings into the established size class was high. In northwest Ohio the number of new seedlings found was much lower than pre-invasion levels, with no differences found based on habitat type(hydric or mesic). Established seedling numbers were significantly different (p = 0.001) based on habitat type; wetter areas had a greater number of established seedlings. Knowing how environmental variables impact seedling dynamics improves our understanding of the ash population dynamics. Monitoring ash seedlings allows us to track the ecological recovery of ash, which provides insight into the role of ash in future forest dynamics.