Habitats of North Carolina
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General Hardwood Forests
Ash Forests
General Description The overwhelming -- literally -- environmental factor defining this habitat is the threat posed by the Emerald Ash Borer (Agrilus planipennis). This introduced species was first detected in North Carolina in 2012 and is now bringing the same massive devastation to our native species of Oleaceae -- Ash species and Fringetree -- as it has already done in the Northeast (see Wagner and Todd, 2016). These plants, along with their specialized herbivores, are now threatened with extirpation, not only at the local level but across the entire state.

Ashes (Fraxinus sp.), along with oaks, hickories, and maples, are major components of the vast network of hardwood forests that cross the state. However, they now face catastrophic collapse: all of our native species of Ash are threatened by the Emerald Ash Borer (Agrilus planipennis), an exotic beetle that has killed millions of Ash trees since it was first detected in North America in 2002 (see Threats and Trends below). Along with the Ashes themselves, Wagner and Todd (2016) have identified close to 100 species of herbivorous Arthropods that specialize on (Fraxinus) species and whose fate, consequently, is intimately tied to that of their host plants. At least one fungus, Botinellus meruloides, has a close mutualistic relationship with one of the those insects, an aphid Prociphilus fraxinifolii) that feeds on the roots of Ash trees, is now listed by the IUCN as globally Vulnerable.

The Ashes themselves are found under a wide range of habitat conditions. White Ash (Fraxinus americana), Biltmore Ash (Fraxinus biltmoreana), and Small's Ash (Fraxinus smallii) are major constituents of dry-to-mesic upland stands of hardwoods, particularly on rich soils. Green Ash (Fraxinus pennsylvanica) is a common to dominant member of Piedmont alluvial forests and brownwater floodplains in the Coastal Plain. Carolina Ash (Fraxinus carolina), Pumpkin Ash (Fraxinus profunda), and Swamp White Ash Fraxinus pauciflora) are found in even more hydric habitats, including both brownwater and blackwater swamps. About the only hardwood habitats not occupied by one species of Ash or another are dry, acidic uplands, including felsic ridges, sandhills, and barrier islands, and forests growing on peatland soils.

For all of the insect members of this group, the presence of one or another of the Ash species is the critical habitat factor. Although specialists on (Fraxinus), most of these species feed on all members of this genus, with some also feeding on other members of our native Oleaceae, including Fringe Tree (Chionanthus virginicus); that species is also included as a member of this habitat group since it generally co-occurs with Ash species; has an overlapping set of specialist herbivores; and may also be threatened by the Emerald Ash Borer.

The Emerald Ash Borer itself, as a non-native species, is not included as a defining species although -- like the native Ash symbionts -- it is capable of feeding on all species of Ash, as well as other members of the Lauraceae. The overwhelming nature of the threat posed by this species is the main unifying environmental feature of this habitat, outweighing the differences in substrates, moisture, and other abiotic factors that separate the plant members of this habitat. Although the Ashes could be treated simply as environmental factors rather than as Determining Species, they have more conservation significance when considered as part of this habitat than they would as members of more the more general hardwood forest habitats associated with those various abiotic factors.

Abiotic Factors Geographic Regions: Lower Coastal Plain to High Mountains. USDA Hardiness Zones: 6-8. Landform: ridges, slopes, bottomlands, wet flats, and swamps. Slope Aspect: north, east, south, and west, also flat. Soil Moisture: Dry to hydric. Soil texture: loamy, silty,or mucky. Soil pH: acdic to circumneutral. Soil Nutrient Content: rich for most terrestrial sites to poor in blackwater swamps. Microclimate: cool to warm; dry to humid. Hydrological Features: streamheads on ridges and slopes, swamps in Outer Coastal Plain. Flood Frequency: essentially never flooded on ridges to permanently flooded in swamps. Flood Duration: nonexistent to permanent. Fire Frequency: uncommon on ridges, rare in swamps. Drought Frequency: uncommon in uplands, rare in swamp forests. Ice Storm Damage: high in the mountains, low in the Outer Coastal Plain. Wind Storm Damage: moderate. Insolation: canopies are well insolated, lower strata are deeply shaded.

Biotic Structure Key Species: the presence of Fraxinus species or Chionanthus is a requirement. Key Threat: Emerald Ash Borer. Vegetation Type: Closed canopy forests dominated by broadleaf, deciduous species in the uplands and bottomlands and by a mix of Cypress and hardwoods in coastal swamp forests. Other Biotic Features varies widely depending on the type of forest occupied by the different species of Fraxinus.

Co-evolved Species Groups Phagic and Competitory Symbioses:
Fraxinus species-Chionanthus virginicus // Agrilus subcinctus-Ceratomia undulosa-Capraita sexmaculata-Copivaleria grotei-Dynastes tityus-Manduca jasminearum-Marmara fraxinicola-Olceclostera angelica-Palpita magniferalis-Plagodis kuetzingi-Podosesia aureocincta-Prociphilus fraxinifolii-Sphinx chersis-Sphinx franckii-Sphinx kalmiae-Sympistis chionanthi-Xyloryctes jamaicensis

Mutualistic Symbioses:
Plant // Fungi Mycorrhizal Symbioses:

Fraxinus species // Durandiella fraxini-Mycosphaerella effigurata-Mycosphaerella fraxinicola-Piggotia fraxini
Insect // Fungi Trophic-Protection Symbioses
Prociphilus fraxinifolii // Boletinellus merulioides

Note that the Emerald Ash Borer is not included as a symbiont of our species of Ash, despite the fact that it feeds solely on members of the Ash family. In this case, however, there is no long history of co-adaptation between this invasive species and our native Ash species -- there is not any true symbiosis since that requires a long history of co-adaptation between the host species and their predators. Instead, we place the Emerald Ash Borer in the Exotic Invaded Habitat, which we reserve for species and habitats that are mutually alien to one another.

Determining Species
Taxa Global RankState RankProbability of Extirpation (PE)
BEETLES
Agrilus subcinctus -
Capraita sexmaculata -
Dynastes tityus -
Xyloryctes jamaicensis -
FUNGI
Boletinellus merulioides
Durandiella fraxini
Mycosphaerella effigurata
Mycosphaerella fraxinicola
Piggotia fraxini
MOTHS
Ceratomia undulosa - Waved Sphinx G5S50.00
Copivaleria grotei - Grote's Sallow G5S40.0007
Manduca jasminearum - Ash Sphinx G4G5SU0.0020
Marmara fraxinicola GNRS2S30.0164
Olceclostera angelica - Angel Moth G5S3S40.0020
Palpita illibalis - Inkblot Palpita Moth GNRS2S30.0164
Palpita magniferalis - Splendid Palpita Moth GNRS4S50.0002
Papaipema furcata - Ash Tip Borer Moth GNRSU0.0020
Plagodis kuetzingi - Purple Plagodis Moth G5S3S40.0020
Podosesia aureocincta - Banded Ash Clearwing Moth GNRSU0.0020
Sphinx chersis - Great Ash Sphinx G4G5SH0.00
Sphinx franckii - Franck's Sphinx G4SU0.0020
Sphinx kalmiae - Laurel Sphinx G5S3S40.0020
Sympistis chionanthi - Fringe-Tree Sallow G5SU0.0020
SHRUBS
Chionanthus virginicus - Fringetree G5S50.00
HARDWOODS
Fraxinus americana - White Ash G5S50.00
Fraxinus biltmoreana - Biltmore Ash G5S40.0007
Fraxinus caroliniana - Carolina Ash G5S50.00
Fraxinus pauciflora - Swamp White Ash GNRSNR
Fraxinus pennsylvanica - Green Ash G5S50.00
Fraxinus profunda - Pumpkin Ash G4S40.0007
Fraxinus smallii - Small's Ash GNRS40.0007
APHIDS
Prociphilus fraxinifolii
Expected Number of Extirpations with a PE value (Sum of PE) = 0.0518
N = Number of Extant Species with a PE value = 15
Average PE = ENE/N = 0.0035
Number of S5 species = 5
Proportion of Secure Species = Number of S5 Species/N = 0.3333
Habitat Risk Index = ENE x (1 – PSS) = 0.0345

Estimated Risk to the Determining Species All of our Ash species are highly threatened with extirpation from the state over the next ten years and consequently should be state ranked as S1S2, whatever their current distribution and abundance. All of the herbivorous species are likely to suffer severe declines although some may be able to switch to Privet species as alternative hosts. For the insect species, we follow the estimates of endangerment given by Wagner and Todd (2016), assigning state ranks as follows: Very High Endangerment Risk = S1; High Endangerment Risk = S1S2; High to Moderate Endangerment Risk = S2S3; Moderate Endangerment Risk = S3.

Substituting Probabilities of Extinction for these state ranks, following the model used in this website, the average probability of extirpation for these species is 0.1621, which under our model is equivalent to a state rank of S1.

Estimated Security of the Habitat No species in this habitat are currently close to being secure. Although prior to the arrival of the EAB, Ash-containing forests were found across the entire state, with many large and/or well connected examples, none now appear likely to survive the onslaught of EAB, at least if current rates of destruction continue on pace.

Index of Habitat Imperilment The HRI value of 4.539 is fifth highest of all habitats presently included in our analysis. This reflects the high value of ENE for this group -- a high number of species are expected to become extirpated during this invasion event. No species are considered to be immune, meaning there is no counter-balance provided by the number of secure species.

Identified Risks The overwhelming threat to this habitat and its species is the depredations by the Emerald Ash Borer (Agrilus planipennis).

Observed Trends The Emerald Ash Borer was first detected in North Carolina in Granville County in 2013. With no effective way to control its spread (quarantining efforts have met with no success), this species has now spread across the entire Piedmont and Mountain regions of the state and is continuing to move eastward into the Coastal Plain (NC Forest Service, accessed 2022). Within the infected regions, massive kills of mature trees are taking place, both within natural areas and residential areas where this species was often planted as a shade tree.

Distribution Map
Distribution
Major Conservation Reserves
Priority Areas for Surveys and Conservation Protection
Stewardship and Management Recommendations
References North Carolina Forest Service. 2022. Emerald Ash Borer Frequently Asked Questions. Available online at: https://www.ncforestservice.gov/forest_health/fh_eabfaq.htm .

Pautasso, M., Aas, G., Queloz, V. and Holdenrieder, O., 2013. European Ash (Fraxinus excelsior) dieback – a conservation biology challenge. Biological Conservation 158:37-49.

Wagner, D.L. and Todd, K.J., 2016. New ecological assessment for the emerald ash borer: a cautionary tale about unvetted host-plant literature. American Entomologist, 62(1), pp.26-35. Available online at: https://academic.oup.com/ae/article/62/1/26/2194528

Updated on 2022-01-06 14:17:11