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Fraxinus nigra 

Scope: Global
Language: English
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Taxonomy [top]

Kingdom Phylum Class Order Family
Plantae Tracheophyta Magnoliopsida Scrophulariales Oleaceae

Scientific Name: Fraxinus nigra Marshall
Common Name(s):
English Black Ash

Assessment Information [top]

Red List Category & Criteria: Critically Endangered A3e+4ae ver 3.1
Year Published: 2017
Date Assessed: 2017-03-28
Assessor(s): Jerome, D., Westwood, M., Oldfield, S. & Romero-Severson, J.
Reviewer(s): Rivers, M.C.
Contributor(s): Miller, F.
Justification:
Fraxinus nigra (Black Ash) is suffering the devastating impact of a recently introduced invasive pest, the Emerald Ash Borer (EAB), that has rapidly spread across much of the native range of Black Ash and shows no sign of stopping. EAB infests and feeds on all North American ash species it has so far encountered. The nature of the infestation (larval feeding in the phloem) effectively girdles trees as small as 2.5 cm diameter at breast height (dbh) (many years before reproductive maturity), leading to death within five years of infestation. EAB therefore causes virtually 100% mortality of Black Ash populations. Black Ash is unable to persist for very long through vegetative reproduction and seeds only remain viable in the seed bank for at most 7-8 years, so regeneration after EAB infestation is minimal or nonexistent. Furthermore, EAB persists in forests in low population densities after major ash population crashes, so the orphaned cohort of Black Ash seedlings that remains is quickly infested as they reach a suitable size for EAB infestation. As such, a population decline of at least 80% over the next 100 years (and likely much faster than that) is assumed. Therefore, F. nigra is assessed as Critically Endangered  (CR) under criteria A3e+4ae.

Geographic Range [top]

Range Description:Fraxinus nigra (Black Ash) occurs from Southeastern Canada to Northeastern America (WCSP 2016). Black Ash ranges from western Newfoundland west to southeastern Manitoba and eastern North Dakota; south to Iowa; east to southern Indiana, Ohio, and West Virginia; and north from northern Virginia to Delaware and New Jersey.(Burns and Honkala 1990). In the northern part of its range, black ash is found from sea level to the highest elevations. In the southern part of its range, however, it grows only above 610 m in elevation.
Countries occurrence:
Native:
Canada (Ontario); United States (Connecticut, Delaware, Illinois, Indiana, Iowa, Maine, Maryland, Massachusetts, Michigan, Minnesota, Nevada, New Hampshire, New Jersey, New York, Ohio, Pennsylvania, Rhode Island, Vermont, West Virginia, Wisconsin)
Additional data:
Upper elevation limit (metres):900
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:Fraxinus nigra is a widespread species throughout the United States and into Canada, although it is found at lower densities than other canopy replacing tree speices (Klooster 2014). The US Department of Agriculture (USDA) estimates that as many as eight billion ash trees (from all Fraxinus species) live on US timberlands. However, populations of ash trees have been rapidly declining since the introduction of the invasive Emerald Ash Borer (EAB), Agrilus planipennis Fairmaire, 1888, from Asia to Detroit, Michigan in the 1990s (Haack et al. 2002).Studies have shown that EAB can spread rapidly, infest both healthy and stressed trees, and that ash mortality across an entire forest stand exceeds 99% within six years of EAB infestation (Knight et al. 2013, Klooster et al. 2014, McCullough et al. 2008). EAB can infest ash saplings as small as 2 cm dbh - well before trees reach reproductive maturity (McCullough et al. 2008, Aubin et al. 2015). Persistence of infested trees through epicormic or root sprouts is not a viable mechanism for survival, since these sprouts often show low vigour and only persist for a year or two before the entire tree eventually dies (Klooster et al. 2014, J. Romero-Severson pers. comm.). Black Ash seeds only remain viable in the forest seed bank for up to eight years (Burns and Honkala, 1990, Aubin et al. 2015). Recent studies of forests at the epicenter of the original EAB introduction (near Detroit, Michigan) revealed that even up to 12 years after initial outbreak, and at least seven years after >99% ash mortality in the region, a residual EAB population still had a stronghold on the forest, infesting nearly 20% of regenerating stems (Aubin et al. 2015).  EAB has decimated F. nigra populations and is rapidly spreading across the majority of Black Ash's range, without any treatment or remediation available. There is currently no evidence to suggest that the rate of spread of EAB, or its impact on Black Ash mortality, will decrease significantly. Therefore, under the precautionary principle, it is assumed that there will be at least an 80% population size reduction within the next 100 years (J. Romero-Severson and F. Miller pers. comm.).
Current Population Trend:Decreasing
Additional data:
Continuing decline of mature individuals:Yes

Habitat and Ecology [top]

Habitat and Ecology:Black Ash (Fraxinus nigra), a slow-growing tree found in northern swampy woodlands. Black Ash can form pure stands in swamps and hydric sites, and is even considered a climax species in sites with poorly drained peat or muck soil (MacFarlane and Meyer 2005).  Black ash is an important species of the forest cover type Black Ash-American Elm-Red Maple. It is a common associate of Northern White-Cedar and a minor associate of Balsam Fir, Black Spruce, Hemlock-Yellow Birch, and Tamarack. The seeds are an important food source for game birds, songbirds, and small animals, and the twigs and leaves provide browse for deer and moose (Burns and Honkala 1990).
Systems:Terrestrial; Freshwater
Generation Length (years):40-50

Use and Trade [top]

Use and Trade: Black Ash is used for paneling, furniture, and basketry (Ward et al. 2009). Due to mortality caused by the Emerald Ash Borer, municipalities are now spending billions of dollars removing dead ash from communities across the US and Canada (Kovacs et al. 2010).

Threats [top]

Major Threat(s): Emerald Ash Borer (EAB), Agrilus planipennis, is by the far the most serious and urgent threat to Fraxinus nigra and, most likely, all other North American ash species. EAB is a flat-headed borer from the Coleoptera: Buprestidae insect group that is native to China, Japan, Korean Peninsula, Mongolia and eastern Russia. EAB was first discovered in Detroit, Michigan in 2002 (Haack et al. 2002), having likely arrived in the 1990s in infested shipping pallets or crates from Asia. EAB has spread rapidly (through natural dispersal and inadvertent human-mediated dispersal) since its first detection in Michigan. As of January, 2017, EAB has been detected in 30 states in the eastern and central US and two provinces in eastern Canada (USDA Animal and Plant Health Inspection Service), which represents the vast majority of the native range of F. nigra. EAB feeds on ash species and exhibits a preference for F. nigra and a few other North American species, although all North American species tested so far are highly susceptible to EAB infestation (Anulewicz et al. 2008; J. Romero-Severson and J. Koch pers. comm.). In addition to EAB's high preference for F. nigra, Black Ash also has a smaller range than other preferential trees such as Green and White Ash and is restricted to riparian habitats (J. Romero-Severson pers. comm). EAB larvae feed on and create extensive galleries within phloem tissue of ash trees, effectively girdling the trees and rapidly cutting off vasculature. EAB can spread rapidly and kill almost 100% of an entire ash stand within six years (Knight et al. 2013, Klooster et al. 2014, McCullough et al. 2008).  EAB can kill ash saplings before they reach reproductive maturity and residual EAB populations have been found in forests up to 12 years after the initial outbreak, outlasting Black Ash's seeds which can only survive in the soil up to eight years (McCullough et al. 2008, Aubin et al. 2015). One possible explanation of EAB persisting in forests after local ash populations are obliterated is host switching; in addition to being able to survive on all North American ash species so far tested, EAB was recently discovered living on White Fringe Tree (Chionanthus virginicus), another member of the Oleaceae family (Cipollini 2015). Moreover, in EAB's native range in Asia, other tree genera such as Juglans (walnuts) and Ulmus (elms) are suitable larval hosts. Black Ash’s entire range is included in the climate envelope projections for EAB (Sobek-Swant et al. 2012, Liang and Fei 2014). Although as of yet, ecological niche modeling studies and climate change predictions of future potential distributions of EAB in North America have struggled with uncertainty, ambiguity, and produced conflicting results (Sobek-Swant et al. 2012, Liang and Fei 2014, DeSantis et al. 2013), such that a recent ecological risk assessment declared that it is impossible to know how far north, south, and west EAB could spread, and so considered all populations of all North American Fraxinus species vulnerable to EAB infestation (Wagner and Todd 2016). Taking all of these observations into account, it is clear that EAB will rapidly kill all living F. nigra trees greater than 2 cm dbh that it encounters across the vast majority of the species' range. Furthermore, EAB can survive at low densities in infested forests of decimated ash populations, on alternative host plants, ready to infest any regenerating Black Ash sprouts until the trees finally die off and the seed bank is depleted. Therefore, until there is convincing evidence that EAB will be stopped before wiping out the entirety of the ash population in North America, it must be considered an imminent and all-encompassing threat (J. Romero-Severson and F. Miller, pers. comm.).

Conservation Actions [top]

Conservation Actions: Because of the great ecological and economic value of ash trees (and the cost of removing dead ash trees), much research and management effort is underway in multiple sectors, including government agencies, local municipalities, universities, horticulture, and botanical gardens. Through these efforts over the past 15 years, we have gained extensive knowledge of how the Emerald Ash Borer (EAB) infests and kills ash trees, EAB life cycles and dispersal rate, and factors influencing ash susceptibility in the wild. Many different EAB detection and management methods have been trialed and improved, including biological control and insecticides. Research into EAB and ash genomics has advanced. Extensive lab studies have also been conducted to test host susceptibility and to develop breeding programs for the handful of "lingering ash" that have been detected in the wild, which may harbor some EAB resistance genes (J. Koch and J. Romero-Severson pers. comm.). For a detailed review of of the history, biology, ecology, impacts and management of EAB see Herms and McCullough (2014). However, so far none of these efforts have uncovered a solution to halting the spread and destruction of EAB. As of yet, land managers and conservationists are simply managing forests and urban areas to slow the spread of EAB and minimize costs. The same stakeholders are also promoting a public awareness campaign to prevent human-mediated EAB spread through actions like moving infested firewood to as yet uninfested locations. Countywide quarantines have been in effect across dozens of states in the eastern US to prevent wood movement. Further research is needed to better understand the future spread of EAB and the impact of climate change on both ash and EAB distributions. Fraxinus nigra is found in 59 ex situ collections according to PlantSearch (BGCI 2017). However, unless the trees are treated with insecticide, they will be equally susceptible to EAB infestations. Botanic gardens and seed banks growing or holding F. nigra outside of the US and Canada represent important germplasm stores for this rapidly disappearing species.

Citation: Jerome, D., Westwood, M., Oldfield, S. & Romero-Severson, J. 2017. Fraxinus nigra. The IUCN Red List of Threatened Species 2017: e.T61918683A61918721. . Downloaded on 21 October 2017.
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