Saving our ash: Insecticides and neighboring blue ash protect green and white ash in forests invaded by emerald ash borer

Emerald ash borer (EAB) has killed millions of ash trees throughout eastern North America, disrupting reproduction and regeneration, and creating the need for improved ash conservation strategies. We tested the relationship between density of ash treated with a systemic insecticide, and survival and reproductive potential of the surrounding ash population. Specifically, we compared the effects of 1) insecticide treatment on the health and flowering status of blue, green, and white ash, and 2) density of treated ash and presence of blue ash on survival, flowering status, and new regeneration. We established 24 one-hectare quadrats across a gradient of treated ash density (untreated 0, low 2-3, medium 4-6, or high 7-9 treated ash/ha) and quantified ash canopy health, flowering status, mortality, and seedling abundance. Overall, insecticide treatments protected green and white ash, but blue ash remained healthy regardless of treatment. Additionally, ash trees with lower canopy ratings were more likely to flower. Across treatment densities, ash survival, incidence of flowering, and new seedling abundance increased with treated ash density. In the presence of blue ash, incidence of flowering and new seedling abundance increased, but more green and white ash died from EAB. We conclude that treating at least 7 ash/ha can maintain ash reproduction and regeneration by protecting mature green and white ash through direct (insecticide treated ash) and associational (neighboring untreated ash) protection. Lastly, the presence of blue ash promotes reproduction and regeneration of all ash species, but may decrease survival of green and white ash.