Genetic, spatial, and temporal aspects of decline and mortality in a Fraxinus provenance test following invasion by the emerald ash borer.
We report a 6-year study of an irruptive invasion of emerald ash borer (EAB) into a 36-year-old comparison of 60 green ash (Fraxinus pennsylvanica Marsh.) and 5 white ash (F. americana L.) populations. As the infestation progressed, annual measures of EAB injury (density of adult emergence holes on the trunk, crown condition, and mortality) were significantly influenced by genetic effects (population and in some instances family within population), site quality (field blocks), and neighborhood (contagion effects over distances of 5-13 m). At the last measurement, 99% of green ash trees and 87% of white ash were dead, and most of the remaining few trees had badly deteriorating crowns. Although final destruction was nearly complete, the rapidity with which trees were injured and killed was moderated by genetic and site effects and influenced by proximity to infested trees. These facts suggest that some genotypes, especially on favorable sites, will disproportionately survive under future equilibrium conditions with lower densities of ash and EAB in the landscape.