Long-term survival and radial growth of four North American and two Asian ash species in a common garden exposed to emerald ash borer invasion.

Abstract

Four North American and one Asian ash species were planted in 2007 in 30 complete randomized blocks in a common garden in Ingham County, Michigan USA to evaluate host resistance and preference of emerald ash borer (EAB) (Agrilus planipennis Fairmaire), first detected in this area in 2003. Trees were protected from EAB colonization until 2012. We recorded current-year woodpecker holes and EAB adult exits on live trees annually from 2017 to 2022. Annual radial growth was quantified on increment cores from live trees and cross-sections from EAB-killed trees. Every Fraxinus nigra was killed by EAB by 2013. By August 2022, 63% of F. pennsylvanica, 12% of F. americana and 86% of F. chinensis trees had died. In contrast, F. quadrangulata trees were minimally colonized and remained healthy through 2022. Average (± SE) annual increment from 2007-2021 ranged from 2.65 ± 0.18 mm for F. quadrangulata to 4.61 ± 0.46 mm for F. chinensis. In an adjacent plantation planted in 2010, we assessed size, growth and EAB signs in 2022 on 12 live F. pennsylvanica and 12 Asian F. mandshurica. All F. mandshurica remained healthy with little evidence of EAB injury. Despite heavy EAB infestation, F. pennsylvanica radial growth in 2011 to 2022 remained relatively high. Results show F. nigra is highly preferred and vulnerable to EAB, followed by F. pennsylvanica, while F. americana is an intermediate host and F. quadrangulata is resistant. Of the 2 Asian species, F. mandshurica was resistant to EAB but F. chinensis trees were heavily colonized and most died.