Habitats of North Carolina
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Floodplain Forests
Rich Wet Hardwood Forests
General Description This habitat consists of hardwood-dominated forests composed of species that are restricted to floodplains with rich alluvial soils. These are widespread along floodplains in the Piedmont and Mountains, especially along streams flowing through regions with mafic or calcarious substrates. In the Coastal Plain, they are found along brownwater rivers, originating in the Mountains or Piedmont, or on wet flats closely underlain by marl.

This habitat strongly overlaps with other floodplain forests but is confined to nutrient-rich soils, whereas the more generalized habitats can also occur in nutrient-poor floodplains, including blackwater river systems in the Coastal Plain. It also intersects with Rich Wet-Mesic Hardwood Forests and Rich Dry-Wet Hardwood Forests, but is more restricted to floodplains and its Determining Species do not range very far upslope from the bottomlands.

Also overlapping with Rich Wet Hardwood Forests are Cottonwood Forests and Ash Forests. Eastern Cottonwood is actually included within in the Rich Wet Hardwood Forests, but the species that are symbiotic with cottonwoods are not restricted to this habitat, also occurring in association with Swamp Cottonwood, Balsam Poplar, Bigtooth Aspen, and -- particularly northward -- Quaking Aspen. Similarly, Green Ash could properly be placed in this habitat but both it and its symbionts are treated in the Ash Forests habitat, based on the common threat to their existence posed by the Emerald Ash Borer.

Abiotic Factors Geographic Regions: Low Mountains to Lower Coastal Plain. USDA Hardiness Zones: 6-8. Landform: restricted to floodplains and wet flats. Soil Moisture: wet but not hydric. Soil Texture: alluvial/loamy to silty -- soils are friable and permit burrowing but are prone to inundation. Soil pH: circumneutral to basic. Soil Nutrients: high mafic mineral content. Microclimate: warm to cool, humid. Flood Frequency: annual to several times per year. Flood Duration: hours to days/ Presence of Pools: common to abundant year-round/ Fire Frequency: extremely rare. Drought Frequency: extremely rare. Ice Storm Damage: low to moderate. Wind Storm Damage: moderate (windthrows are common). Insolation: the canopy is well-insolated, lower strata are deeply shaded.

Biotic Structure Vegetation Type: Closed-canopy forests composed of broadleaf, deciduous trees. Strata Subcanopy, shrub, and herb-layers are usually well-developed. Woody debris and leaf litter plentiful except in flood channels or other areas frequently scoured by floods.
Co-evolved Species Groups Host // Phage-Competitor Symbioses:
Acer negundo // Adoxophyes negundana-Caloptilia negundella-Contarinia negundifolia-Leptocoris trivittatus-Periphyllus negundinis-Proteoteras willingana-Zale galbanata
Dichanthelium clandestinum // Cosmopterix clandestinella
Platanus occidentalis // Adoxophyes furcatana-Ancylis platanana-Corythucha ciliata-Ectoedemia clemensella-Ectoedemia platanella-Eratoneura hymettana-Eratoneura morgani-Gelechia albisparsella-Halysidota harrisi--Lithophane signosa-Misogada unicolor-Pococera militella
Populus deltoides // Septoria musiva
Ulmus americana // Scaphoideus crassus-Scaphoideus soleus-Theisoa constrictella

Host // Commensal Symbioses:
(host-specific lichens and bryophytes)
(host specific decomposers)

Mutualist // Mutualist Symbioses:
Carya laciniosa // Laccaria ochropurpurea (see Schlesinger, 1990). While Shellbark Hickory appears to form mycorrhizal assocations primarily with L. ochropurpurea, the fungus forms associations with a number of other hardwoods and with White Pine; consequently it is not a Determining Species of this particular habitat
(Pollinator Associations)
(Host/Disperser Associations)

Competitor Guilds:
Shellbark Hickory is highly shade tolerant and is a strong competitor relative to other tree species in its habitat (Schlesinger, 1990). Silver Maple,on the other hand, is relatively shade-intolerant and grows primarily along streamsides where it has little competition except for other levee species (Gabriel, 1990). Eastern Cottonwood is another highly shade-intolerant species that invades bottomlands following disturbance, matures rapidly, but is ultimately replaced by species more capable of reproducing under a closed canopy (Cooper, 1990). Several species appear to produce allelopathic chemicals to suppress the growth of rival species in their vicinity, including Shumard's Oak (Edwards, 1990a) and Swamp Chestnut Oak (Edwards, 1990b).

Determining Species
Taxa Global RankState RankProbability of Extirpation (PE)
Acer negundo - Box-elder G5S50.00
Acer saccharinum - Silver Maple G5S30.0058
Carya laciniosa - Shellbark Hickory G5S10.3584
Platanus occidentalis - American Sycamore G5S50.00
Populus deltoides - Eastern Cottonwood G5S40.0007
Quercus bicolor - Swamp White Oak G5S20.0460
Quercus michauxii - Swamp Chestnut Oak G5S50.00
Quercus shumardii - Shumard Oak G5S40.0007
Ulmus americana - American Elm G5S50.00
Adoxophyes furcatana GNRSU0.0020
Adoxophyes negundana - Shimmering Adoxophyes Moth GNRS3S40.0020
Ancylis platanana GNRS3S50.0007
Caloptilia negundella - Boxelder Leafroller Moth GNRS3S40.0020
Cosmopterix clandestinella GNRSU0.0020
Ectoedemia clemensella GNRS3S40.0020
Ectoedemia platanella GNRS3S40.0020
Gelechia albisparsella GNRS1S30.0460
Halysidota harrisii - Sycamore Tussock Moth G4SU0.0020
Lithophane signosa - Signate Pinion G5S3S40.0020
Misogada unicolor - Drab Prominent G5S4S50.0002
Pococera militella - Sycamore Webworm Moth GNRS3S40.0020
Proteoteras willingana - Eastern Boxelder Twig Borer Moth GNRS2S40.0058
Theisoa constrictella GNRSU0.0020
Zale galbanata - Maple Zale G5S40.0007
Carex squarrosa - Squarrose Sedge G4G5S30.0058
Carex tribuloides - Blunt Broom Sedge G5S40.0007
Carex typhina - Cattail Sedge G5S40.0007
Dichanthelium clandestinum - Deer-tongue Witchgrass G5S40.0007
Clematis virginiana - Virginia Virgin's-bower G5S50.00
Contarinia negundifolia
Corythucha ciliata
Leptocoris trivittatus
Eratoneura hymettana
Eratoneura morgani
Scaphoideus crassus
Scaphoideus soleus
Hypericum nudiflorum - Early St. John's-wort G5S40.0007
Ludwigia glandulosa - Cylindric-fruit Seedbox G5S40.0007
Rudbeckia laciniata - Cutleaf Coneflower G5S50.00
Steironema ciliatum - Fringed Loosestrife G5S50.00
Periphyllus negundinis
Septoria musiva
Expected Number of Extirpations with a PE value (Sum of PE) = 0.4943
N = Number of Extant Species with a PE value = 26
Average PE = ENE/N = 0.0190
Number of S5 species = 7
Proportion of Secure Species = Number of S5 Species/N = 0.2692
Habitat Risk Index = ENE x (1 – PSS) = 0.3612

Estimated Risk to the Determining Species Only two of the Determining Species of this habitat are at high risk, Shellbark Hickory and Swamp White Oak. Both of these species are primarily northern in their distribution and have their strongholds in the upper Midwest and Northeast (Roberts, 1990; Schlesenger, 1990). Both occur in North Carolina only in highly scattered, disjunct populations, with their biogeographic history and limiting factors in this region poorly understood. Chafin (2019) mentions that the slow maturation of Shellbark Hickories may make it vulnerable to timbering and that thick growth of Chinese Privet may inhibit the development of seedlings but whether these have historically played a role in limiting the distribution of that species in North Carolina is unknown.

The remaining species all have much wider distributions and although locally threatened in some isolated areas, are generally considered of low conservation concern within the state as a whole.

Estimated Security of the Habitat Seven of the Determining Species are considered secure in North Carolina, having state ranks of S5. This is a general reflection of both the large number of their populations -- most have representatives in all Piedmont and Montane river drainages and penetrate into the Coastal Plain along the four brownwater rivers in that region. Within those drainages, moreover, populations occupy long reaches of suitable habitat, although these are fragmented in several cases by large reservoirs.

Index of Habitat Imperilment
Identified Risks Conversion of habitats to agriculture and silviculture/ Filling in of floodplains for human habitation and other uses/ Creation of impoundments, which permanently destroy bottomland forests, cut off the flow of nutrient rich sediments, and alter the natural flood cycle/ Loss and fragmentation by clear-cutting and road construction/ Invasion by exotic species/ Increased risk of drought and fire due to climate warming/ Increased risk of severe flooding due to climate change/ Impacts to insect populations due to mosquito-spraying and use of insecticides on adjoining lands/ Impacts due to artificial lighting/ Loss of bottomland habitats in the Lower Roanoke and other brownwater rivers due to sea level rise and saltwater intrusion

Observed Trends Floodplains in the Mountains offer some of only flat lands in that area. Despite the threat of flood damage, these are the sites that have been most extensively developed for agriculture and human settlement in that region. The wide floodplains in the western Piedmont have also been extensively converted to agriculture, dating back to colonial times.

Large tracts of brownwater bottomlands have been destroyed on several of the state’s largest rivers due to reservoir construction: Randleman and Jordan Lakes in the Cape Fear drainage; Kerr, Gaston, and Roanoke Rapids on the Roanoke; Falls Lake on the Neuse; Lake Norman and Mountain Island Lake on the Catawba; and High Rock, Badin, Tillery, and Blewitt Falls on the Yadkin-Pee Dee River. Additionally, some losses are now occurring at the mouth of the Cape Fear River due to sea level rise and salt water intrusion, which is converting floodplain forests to open marshes.

In addition to conventional timber harvests, which continue to affect thousands of acres of natural forest lands, the development of the wood-chipping industry has created additional pressures.

Invasive species, particularly Privet and Stilt Grass, are significant problems in many bottomland habitats, overgrowing native herbaceous species and tree seedlings. These impacts may actually now be increasing due to the destruction of groves of Green Ash, which are creating large light gaps that favor the growth of the invasive plants (see Ash Forests for a discussion of the direct impacts of the Emerald Ash Borer).

In areas of bottomland hardwoods along the northern border of the state, where Gypsy Moths have become established, Bacillus thuringiensis (Bt) is frequently applied to suppress outbreaks. Widespread spraying of this agent, however, has impacts far beyond the Gypsy Moth and affects a large number of non-target species of moths and butterflies (see Hall et al., 1999). Within the group included in the Rich Wet Hardwood Forests, the five leaf-mining species are probably at low risk of exposure to Bt, but the rest are likely to be at risk since they feed on the external surfaces of the leaves where Bt is deposited.

Distribution Map
Distribution Tracts of this habitat occur across the state except for the high mountains and barrier islands, both of which lack floodplains in general. In the Coastal Plain, this habitat is also fairly scarce due to the nutrient-poor soils and acidic waters typical of this region. Most occurrences are restricted to the four brownwater rivers that flow through this area.

Major Conservation Reserves Within the Coastal Plain, the lower Roanoke Floodplain contains one of the largest and richest areas of Rich Bottomland Hardwoods, including large expanses contained within the Upper and Lower Roanoke Floodplain Game Lands, the Roanoke River National Wildlife Refuge, and several preserves owned by the Nature Conservancy. Smaller areas are protected as Game Lands along the lower Cape Fear, Neuse, and Tar Rivers and by Falls-of-the-Neuse and Singletary Lake State Parks. In addition to these state-owned lands, River Park North, owned by the City of Greenville, contains a small portion of this habitat located near the mouth of the river.

Within the Piedmont, the largest expanse is included within the Pee Dee National Wildlife Refuge. A number of tracts of NCWRC Game Lands protect bottomland forests along several tributaries of the Tar, Neuse, and Cape Fear Rivers, including some large areas located in the non-impounded portions of Falls and Jordan Lake project lands owned by the US Army Corps of Engineers. State Parks within this region that protect areas of bottomland forests include Eno River, Haw River, Raven Rock, Mayo River, Hanging Rock, and Pilot Mountain. Small but highly significant tracts of rich bottomlands are also protected along the Triassic Basin portion of New Hope Creek by Durham County. Several city-county parks in the Charlotte area similarly protect bottomlands along tributaries of the Catawba River.

In the Mountains, the New River State Park protects some of the best remaining tracts of bottomland forest in that region.

Priority Areas for Surveys and Conservation Protection The tree species have been well-surveyed in most high quality examples of this habitat. Several areas have also been surveyed for macro-moths but only a few have had comparable surveys for leaf-miners and other micro-moths.

The lower Roanoke and New River floodplains have been well-studied for macro-moths but need more work on micro-moths. The Pee Dee NWR needs a general moth survey.

The highest conservation priority for this habitat is probably the Rocky Point Marl Forest, which is the sole target for conservation of the Nutmeg Hickory Forest habitat.

Stewardship and Management Recommendations Promote floodplain forests as important carbon sequestration reserves, flood control areas, and water-quality enhancing systems. Limit clear-cutting and prohibit filling in of floodplains for development. Create buffers along adjoining slopes to limit impacts due to human encroachment. Combat spread of exotic invasives, particularly Privet. Use Gypsy Moth-specific control agents to combat outbreaks of this exotic species in bottomland forest habitats generally and specifically in high-quality examples of Rich Wet Hardwood Forests.

References Chafin, Linda G. 2020. Species profile for Carya laciniosa. Georgia Biodiversity Portal, Wildlife Resources Division, Wildlife Conservation Section, Social Circle. Available online at: https://georgiabiodiversity.org/natels/profile?es_id=20584

Cooper, D.T. 1990. P. deltoides Bartr. ex Marsh. var. deltoides. Eastern Cottonwood (typical). In: R. Burns and B. Honkala (Technical coordinators). Silvics of North America, 2. Available online at: https://www.srs.fs.usda.gov/pubs/misc/ag_654/volume_2/carya/laciniosa.htm

Gabriel, W.J. Acer saccharinum L. Silver Maple. In: R. Burns and B. Honkala (Technical coordinators). Silvics of North America, 2. Available online at: https://www.srs.fs.usda.gov/pubs/misc/ag_654/volume_2/carya/laciniosa.htm

Hall, S.P. 1999. Inventory of the moths and butterflies of the lower Roanoke River floodplain.
Report to the North Carolina Natural Heritage Program, Division of Parks and
Recreation; Raleigh, NC.

LeGrand and Hall, 2014. A Natural Heritage Inventory of the Roanoke River Floodplain, North Carolina.

Matthews et al., 2007. Natural vegetation of the Carolinas: Classification and description of Piedmont alluvial plant communities of the Cape Fear River Basin. Available online at: http://cvs.bio.unc.edu/pulse/Report_74.pdf

Rogers, R., 1990. Quercus bicolor Willd. Swamp White Oak. In: R. Burns and B. Honkala (Technical coordinators). Silvics of North America, 2. Available online at: https://www.srs.fs.usda.gov/pubs/misc/ag_654/volume_2/carya/laciniosa.htm

Schlesinger, R.C., 1990. Carya laciniosa (Michx. f. Lould.), Shellbark Hickory. In: R. Burns and B. Honkala (Technical coordinators). Silvics of North America, 2. Available online at: https://www.srs.fs.usda.gov/pubs/misc/ag_654/volume_2/carya/laciniosa.htm

Well, O.O. and Schmidtling, R.C. 1990. Platanus occidentalis L. Sycamore. In: R. Burns and B. Honkala (Technical coordinators). Silvics of North America, 2. Available online at: https://www.srs.fs.usda.gov/pubs/misc/ag_654/volume_2/carya/laciniosa.htm

Updated on 2021-12-17 12:34:56