White ash (Fraxinus americana) survival in the core of the emerald ash borer (Agrilus planipennis) invasion

摘要

Despite catastrophic ash (Fraxinus spp.) mortality observed by the mid-2000s in the epicenter of the emerald ash borer (EAB) (Agrilus planipennis Fairmaire) invasion in southeast Michigan, we noticed numerous live white ash (Fraxinus americana L.) in some forests in this region. In 2015, we inventoried overstory trees and regeneration in 28 white ash sites spanning 11 counties. White ash survival ranged from 0% to 100% of stems. Overall, 75% of 821 white ash trees, ranging from 10.0 to 44.0 cm diameter at breast height, and 66% of the white ash basal area, ranging from 0.3 to 3.5 m(2).ha(-1), were alive. Nearly all live white ash had signs of previous EAB colonization, but 83% had healthy canopies (= 10% canopy dieback). Green ash trees were recorded in 27 sites, but 92% were killed by EAB. Model selection indicated that variation in white ash survival was related to white ash abundance and distance of sites from the original EAB epicenter but not to green ash related variables or to the distance of sites from the Asian parasitoid release or recovery locations. Regeneration strata were dominated by white ash, suggesting that some white ash populations may persist in post-invasion areas.