Preserving new ash regeneration and stable age structure by protecting mature ash during the emerald ash borer invasion

Wide-scale mortality of ash trees caused by emerald ash borer (Agrilus planipennis, EAB) threatens Fraxinus spp. with regional extirpation, creating the need for strategies to conserve the ash gene pool.  In such an attempt, the Five River MetroParks (FRMP) in Dayton, OH initiated an ongoing program in 2011 to protect 600 mature (reproductive) ash trees with insecticide.  The goal of our study is to evaluate the efficacy of this management strategy on maintaining ash regeneration and a stable age structure throughout the course of the EAB invasion.  We set up 24-one hectare stands within six metroparks across a treatment density gradient (high, medium, low, and untreated control) to quantify the effect of insecticide treatment on ash demography (seed, seedling, sapling, and tree densities) and ash health (canopy decline rating).  Baseline densities (mean stems per hectare) of ash indicate a stable age structure with 20,950 ± 3021 seedlings, 130.2 ± 30.9 saplings, 41.1 ± 10.1 immature trees (< 10 cm dbh), and 91.7 ± 7.7 mature trees (≥ 10 cm dbh).  We found significant differences in seedling densities (p=0.001) and proportions of healthy (p=0.01) and dead ash trees (p=0.02) between study sites (metroparks), indicating variation of EAB impact across Dayton, OH.  However, no relationship was found between treated tree densities and abundance of new ash regeneration.  We anticipate that as ash mortality increases and treated trees become an increasingly larger proportion of the surviving ash population, the spatial relationship between treated trees and density of ash seedlings will strengthen.