| dc.description.abstract | Emerald ash borer (EAB) (Agrilus plannipennis Fairmaire) (Coleoptera: Buprestidae) is the costliest invasive pest in North American history (Aukema et al., 2011; McCullough, 2019) due to its extensive killing of ash trees (Fraxinus spp.). Ash species account for 7.5% of all eastern hardwood forests, with an undiscounted compensatory stumpage value at $282.3 billion (Federal Register, 2003). The impacts of EAB invasion are expected to be more ecologically destructive than the loss of American chestnut from eastern hardwood forests in the early 1900s, increasing invasive species in forest understories (Hausman et al., 2010), contributing to forest mesophication (Dolan and Kilgore, 2018), and reducing the carbon sequestration abilities of forests (Fei et al., 2019). EAB-induced biomass losses are 1.813 Tg C per year above background levels, second only to Dutch elm disease (2.386 Tg C/year lost) (Fei et al., 2019). Because of this extreme threat, EAB has become an emerging model organism for understanding how invasive pests can alter ecosystems and reduce natural resources that are economically and socially valuable. It remains unclear whether white ash (F. americana) will persist or what form it will take following long-term EAB effects. White ash will likely lose its role as a timber species (Stewart and Krajicek, 1973) and will be diminished in its role as an ecologically valuable species. Previously documented host-insect dynamics provide some insight about potential paths forward for white ash. It is unlikely that white ash will persist similarly to American beech as mortality rates across North America have already exceeded beech mortality (Knight et al., 2013; Wieferich, 2013). Unfortunately, it is likely that white ash will follow a similar path as American chestnut in North American forests. American chestnut was functionally eliminated from the landscape (Anagnostakis, 1987) and exists only as root collar sprouts (Paillet, 2002; Jacobs et al., 2013). I examined whether two forms of vegetative regeneration, root collar and epicormic sprouts, were a viable persistence mechanism for white ash and what predicts their occurrence. I found that root collar sprouts, but not epicormic sprouts, have the potential to persist beyond primary trunk mortality. Presence of collar sprouts was not predicted by ploidy level or sex, but tree canopy status (TCS) and diameter at breast height (cm) (DBH) were significant predictors. Several populations also did not produce one or both forms. Count of both sprout forms was predicted by sex, and the overdispersion of zeroes was predicted by both tree canopy and diameter at breast height. My findings suggest that tree size and health during EAB-infestation will determine an individual’s chance of persistence via vegetative regeneration, but that tree sex will ultimately determine number of collar sprouts. | |
