Through direct impacts on host species, forest pest disturbances can alter forest productivity, shift successional dynamics and threaten ecosystem resilience. Despite the abundance of literature on the fate of host species, the associated impacts on residual non-host species remain elusive. The emerald ash borer (EAB, Agrilus planipennis Fairmaire) outbreak in North America, is causing vast ash (Fraxinusspp.) mortality affecting forest aboveground net primary productivity (ANPP), growth of con-specific tree species, bark-foraging bird behavior and soil microbial communities. Beginning in 2005, we deployed a network of permanent plots across Ohio to annually monitor tree growth, ash tree health, EAB population levels, canopy gaps, seedling establishment, and woody invasive species dynamics. Additionally, we sampled soils across 9 forests of central Ohio and analyzed them for differences in soil microbial communities.
Results/Conclusions
Despite the enhanced growth of residual trees, we detected significant reductions in ANPP associated with EAB induced mortality (~31%), and observed a non-linear response of ANPP to disturbance severity. Not surprisingly, residual tree growth responses exhibited a positive relationship with disturbance severity. In these forests, maples (Acer spp.) which were the second most prevalent genus after Fraxinus, exhibited the highest relative growth rates following disturbance. Dendrochronological analysis revealed that maple growth occurred concurrently with ash decline and was not related to canopy position. Additionally, differences in soil microbial community structures between non-ash plots and adjacent ash plots underlie the shifts to these systems and indicate that such disturbances may impact successional trajectories. Finally, EAB larvae provided a novel food resource for bark-foraging birds which after the outbreak preferred foraging on ash relative to non-ash trees. Furthermore, they exhibited density-dependent foraging behavior preferentially feeding on heavily infested trees with declining canopies suggesting the potential for population control. Our results may be applicable to large portions of temperate deciduous forests impacted by forest pests which result in diffuse mortality and suggest that forest pests could have long-term ramifications for the successional dynamics of impacted forests.