Fraxinus americana

This record is for the broad treatment of Fraxinus americana, including F. biltmoreana as indistinct, as recognized in Kartesz (1994, 1999). Nesom (2010) finds that Fraxinus biltmoreana and F. smallii are reproductively isolated from F. americana and accepts them as distinct species. Weakley et al. (2025) accept them as distinct, but calls them controversial with more work needed.

Fraxinus americana is throughout eastern and central North America from Nova Scotia to Florida and west to Minnesota and Texas but introduced for horticulture around the world. While the species is wide ranging and has many occurrences, it is suffering serious mortality due to the Emerald Ash Borer and has poor regeneration post infestation. Within six years of an invasion, the species can experience a nearly 100% decline with minimal regeneration. The Conservation Status of this species should be reviewed frequently to detect changes in the impact of the borer.

Fraxinus americana occurs throughout eastern and central North America from Nova Scotia to Florida and west to Minnesota and Texas. The species is introduced in Europe (England, Hungary), Africa, Pacific Islands (Hawaii), Australia (Nesom 2010). The species is also reported from Mexico: it is likely all reports from Mexico should be assigned to Fraxinus uhdei (syn. Fraxinus americana var. uhdei) (Nesom 2010). This conservation assessment is for Fraxinus americana in the broad sense, including F. biltmoreana and F. smallii.

The primary threat to this species is mortality and reduced regeneration associated with the Emerald Ash Borer, a phloem-feeding beetle native to Asia. The invasive Emerald Ash Borer (EAB), Agrilus planipennis Fairmaire, 1888, was introduced in Detroit, Michigan from Asia in the 1990s (Haack et al. 2002) and has since caused rangewide declines in ash populations. The beetles feed on the leaves and lay their eggs in crevices of the bark. Larvae feed in the vascular structures during the summer, creating serpentine shaped galleries. They typically prepupae overwinter in the trees with pupation lasting from April-May, when adults emerge. Emerald Ash borers cause significant damage to the foliage of the tree and the vascular tissues. The tree will typically die within two years of the infestation (Poland and McCullough 2006). Within six years of an infestation, up to 99% mortality was observed in ash species (Knight et al. 2013, Klooster et al. 2014, McCullough et al. 2008, Steiner et al. 2019). Green ash appears to suffer the greatest mortality and least regeneration post-invasion (Robinett and McCullough 2019). Tree saplings with 2 or more cm dbh can be infested (McCullough et al. 2008, Aubin et al. 2015). While an infested tree may push out root sprouts for one to two years, the tree usually dies (Klooster et al. 2014). The mass mortality of reproductively mature plants that would replenish the seed bank and the relatively short persistence in the seed bank (2-3(7) years) (Klooster et al. 2014), causes concern about the species ability to regenerate post-infestation. Emerald Ash Borer has been reported in most states and provinces where this species occurs (Emerald Ash Borer Information Network 2020).