Floodplains-Brownwater Systems
The 2015 North Carolina Wildlife Action Plan defines 41 priority habitats for the state. More information about this habitat can be found in Section 4.3.4.
Contents
Habitat Priorities
Surveys
- Document Bald Eagle nesting sites. (Surveys Priority)
- Design specific surveys to determine status and distribution of birds not adequately picked up by the Breeding Bird Survey in floodplain forests (e.g., the Cerulean Warbler, Swainson's Warbler, Kentucky Warbler, Worm-eating Warbler, Hooded Warbler, Prothonotary Warbler, etc.). (Surveys Priority)
- Conduct surveys to document the distribution, relative abundance, and status of wildlife species associated with brownwater floodplain forest habitats. Priorities include Swallow-tailed Kite, Cerulean Warbler, Wood Stork, bats, and species believed to be declining, at risk, or mainly dependent on floodplain forest communities. (Surveys Priority)
- Give secondary priority to surveys of species for which current distribution information is already available or for species that are considered common. (Surveys Priority)
- Determine the status and distribution of Wayne's Black-throated Green Warbler. (Surveys Priority)
- Determine the status and distribution of the Swallow-tailed Kite, Mississippi Kite, Yellow-crowned Night-heron, and Anhinga (as well as other colonial nesting waterbirds). (Surveys Priority)
- Determine the breeding and roosting status and distribution of the Chimney Swift in natural conditions along major floodplains with appropriate habitat conditions (e.g., older, hollow trees). (Surveys Priority)
- Determine the status and distribution of priority bat species, including Northern Long-eared Bat, Rafinesque's Big-eared Bat, Northern Yellow Bat, Seminole Bat, Southeastern Bat, Little Brown Bat, and Tricolored Bat. (Surveys Priority)
- Conduct small mammal surveys, especially for the Eastern Woodrat, with a focus on circumneutral soils (other small mammal survey needs include the Cotton Mouse and Southern Pygmy Shrew). (Surveys Priority)
- Determine the status and distribution of snakes using floodplain forest habitats (Taylor and Jones 2002). (Surveys Priority)
Monitoring
- Continue long-term monitoring of active Bald Eagle territories, successful breeding pairs, and fledged eagles.
- Expand and/or target monitoring systems to be able to assess current population status and trend information for all wildlife species associated with floodplain forest habitats.
- Develop monitoring for any North Carolina floodplain forest bird species that require specialized attention, since neither BBS nor standard point counts can adequately sample irregularly distributed or clumped species like Kentucky, Cerulean, and Swainson's warblers.
- Develop or enhance long-term monitoring for amphibians and reptiles (Taylor and Jones 2002).
- Develop or enhance long-term monitoring for most bat species (Ellis et al. 2002).
- Conduct long-term monitoring for floodplain forest birds (breeding, migration, and winter periods) in forest patches of varying size (Robbins et al. 1989; Doherty and Grubb 2000).
- Establish long-term monitoring for herpetofauna using floodplain forest habitat (especially breeding salamanders and snakes).
- Examine demographics and habitat use of bats in floodplain forests; there is also a need to identify, monitor, and maintain (or recruit) key bat habitats and microhabitats in floodplain forests (Ellis et al. 2002).
Research
- Research the genetic makeup of the coastal population of the Black-throated Green Warbler.
- Research the genetic relationships among floodplain salamanders.
- Ensure that research studies targeting birds are long-term, large-scale, replicated studies that have controlled experimental approaches and focus on population demographics and the response of species to habitat manipulations where appropriate (as outlined by the National Partners in Flight Research working group) (Donovan et al. 2002; NCWRC 2005). Similar research priorities are needed for other floodplain forest taxa including bats, small mammals, amphibians, and reptiles.
- Examine the impacts of long-term flooding regimes on ground-nesting birds (e.g., Swainson's Warbler) (Swift et al. 1984). Similar studies are also needed for salamanders.
- Determine the conservation and restoration efforts needed for canebrake rattlesnakes in floodplain forests (Brantley and Platt 2001).
- Conduct bird productivity research (especially neotropical migrants) with a focus on nest searching studies to determine the predator community and bird nesting success in patches of different sizes and with various landscape contexts (Rodewald and Yahner 2001).
- Examine the demographics, habitat-use patterns, and impacts of feral hogs on ground-nesting birds, salamanders, and small mammals (Warren and Ford 1997).
- Study the impacts of beaver and beaver ponds on species composition (both flora and fauna) to determine negative or positive impacts of beaver or beaver control measures.
Management Practices
- Wherever possible, maintain or restore floodplain forest connectivity, as floodplain forests are important distribution and dispersal corridors for many species (Bailey et al. 2004). This would benefit floodplain forest species such as the Northern Parula, Yellow-Throated Warbler, Prothonotary Warbler, Wood Thrush, Swainson's Warbler, and Acadian Flycatcher, as well as amphibians, Timber Rattlesnakes, and forest bats.
- Make efforts to retain old growth floodplain forest (for Chimney Swifts, bats, and herpetofauna).
- Ensure floodplain buffers of 300 to 600 feet in as many areas as possible. This would benefit floodplain forest species such as the Northern Parula, Swallow-tailed Kite, Mississippi Kite, Prothonotary Warbler, Wood Thrush, Swainson's and Cerulean warblers, and Acadian Flycatcher, as well as amphibians, Timber Rattlesnakes, and forest bats.
- Restore natural hydrology where dams have altered hydrology, such as on the Roanoke River.
- Work with partners to institute more natural water release regimes from dams.
- Floodplain buffers of 300 to 600 feet provide the most benefit for species such as Northern Parula, Yellow-throated Warbler, Prothonotary Warbler, Wood Thrush, Swainson's Warbler, Worm-eating Warbler, and Acadian Flycatcher, as well as amphibians, snakes, and forest bats.
Conservation Programs and Partnerships
Description
This ecosystem group includes the vegetated communities that occur on brownwater floodplains. In contrast to blackwater rivers, they carry heavy loads of mineral sediment, particularly clay and silt. The water is generally near neutral pH and high in nutrients. The deposition of sediment in the floodplain provides a periodic nutrient input that keeps the soils rich. Depositional topographic features such as natural levees, point bars, ridge-and-swale systems, and sloughs are well developed, with their size depending on the size of the river.
There are seven communities that occur in Coastal Plain brownwater floodplains: Levee Forests, Bottomland Hardwoods, Small Stream Swamps, Cypress–Gum Swamps, Semipermanent Impoundments, Oxbow Lakes, and Sand and Mud Bars (Schafale and Weakley 1990).
Location of Habitat
Brownwater rivers originate in the Mountains or Piedmont and flow eastward into the Coastal Plain ecoregion. Brownwater floodplain forests of various conditions and sizes can be found throughout the Coastal Plain ecoregion; however, the majority of them are associated with the Roanoke, Tar–Pamlico, Neuse, and Cape Fear rivers. The condition of Coastal Plain floodplain forests of all types have been greatly reduced in recent years throughout North Carolina and the entire southeast (Weller and Stegman 1977; Schafale and Weakley 1990) by a variety of anthropogenic factors.
Problems Affecting Habitats
Flooding
Factors that impact these systems include flooding regime patterns that have been changed by dams and other development, habitat fragmentation, changes in water chemistry and organic matter loads, increased nitrogen from agricultural and development-related runoff, exotic species and high-grading of stands and logging that reduces wide buffers. All of these factors individually or interactively produce abrupt or gradual changes in floodplain plant and wildlife communities. In particular, the sediment load in many brownwater rivers is now a major problem in the Coastal Plain, and even many blackwater systems now have high sediment loads (Schafale and Weakley 1990).
Increased frequency and/or severity of flooding will likely have a mix of positive and negative influences. Changes in rainfall regime may also induce water management that produces more floods of unnatural, destructive long duration. If floods become more extreme, channels may begin to migrate more. Increased scouring by more severe floods would create more early successional bar communities at the expense of mature communities on the banks. Increased magnitude of floods could affect higher terraces that now see little flooding. Leigh (2008) and Leigh et al. (2004) suggest that Coastal Plain rivers may be near a threshold for switching to a braided channel morphology. More large floods might mean increased area but reduced stability of sand and mud bars. Given the water availability in floodplains, drought is unlikely to stress floodplain ecosystems. The effect will be mostly in the form of allowing upland species to invade.
Climate Variability
Inundation from sea level rise will create wholesale change to a tidal system in the downstream portions. Large expanses in these areas will shift to tidal swamps. Saltwater intrusion would likely affect long-term survivability of canopy species in the lower floodplain reaches. Saltwater intrusion could occur further upstream during floods or high storm surge.
Increased wind disturbance may cause some shifts in species composition, such as favoring sweetgum and loblolly pine over oaks in bottomland hardwoods. These will be relatively small compared to the past and ongoing similar effects of logging, but will exacerbate them. Increased wind damage would decrease average canopy age and increase the proportion of gaps. Increased tree growth rates may offset the structural effect to some degree. Bottomland hardwoods will likely be most affected by structural and compositional changes from increased wind storms.
No significant inland migration is possible for this community so there will be a net loss of acreage, mostly caused by inundation from rising sea level. Some Coastal Plain species may be able to expand into the Piedmont as the climate warms, but many of the differences between brownwater and inland floodplains are the result of geology rather than climate. There is an expectation that nonnative plants (e.g., Chinese Privet, Japanese Stiltgrass, Japanese Honeysuckle) will increase and there will likely be additional invasive species, such as the Chinese Tallow Tree.
Climate Change Compared to Other Threats
Comparing climate change to other ecosystem threats can help define short and long-term conservation actions and recommendations. While climate change is not the most severe threat, a combination of synergistic effects with other existing conditions could stress these systems to the point where several species are unable to persist. Other than rising sea level, the effects of climate change are particularly uncertain in these systems.
Changes in flood regimes and rising sea level are the most important climate effects. Climate change effects upstream of the tidal zone are likely to be limited and other existing threats are likely to be more significant.
Impacts to Wildlife
The few brownwater floodplains generally occur far apart on the landscape, are not hydrologically connected, and few have north–south courses, making it difficult for plants and animals confined to brownwater floodplains to move northward as suitable conditions are lost.
Large patches of floodplain habitat are absent in much of the Coastal Plain. Fragmentation of stands has contributed to the loss of intact large riparian corridors and the width of many riparian corridors has been greatly reduced. Breeding area–sensitive bottomland-hardwood birds have likely been impacted by the loss of large patches of intact woodland systems. Swallow-tailed Kite is an area-sensitive species and is now known to breed within the state along the Cape Fear River. High-grading of stands has changed plant species diversity and stand vegetative structure. Forestry activities (e.g., logging) have reduced colonial waterbird and eagle nesting areas, but wading birds make more use of timber-cleared wetlands for foraging.
Two cane-feeding moths are endemic to the region but also occur in blackwater floodplains and non-riverine swamp forests. Another cane-feeding moth appears to be significantly disjunct within the lower Cape Fear floodplain. Two hawthorn-feeding moths also appear to have disjunct populations in the lower Roanoke floodplain, as does the Cerulean Warbler. None of these species appear likely to be affected by climate change-related impacts.
Drainage of wetlands has exacerbated the problems in and adjacent to floodplain forest habitats. This habitat loss impacts all floodplain species, including furbearers, breeding amphibians, overwintering birds, and migrant species that use these areas as stopover sites. Water quality is also an issue in certain major river drainages that negatively affects many invertebrates, fish, amphibians, and reptiles (NCWRC 2005).
Long-duration flooding has had impacts on all ground-nesting bird species. Loss of old growth characteristics (canopy gaps, vine tangles, hollow trees, dead and downed woody material) and fragmentation of stands is a major concern. A lack of standing dead or older trees has impacted the availability of quality bat and Chimney Swift roosting and breeding sites and nesting productivity for species such as the Wood Duck and Hooded Merganser. Lack of downed woody debris has impacted a variety of amphibians and reptiles (NCWRC 2005).
Summary
In general, protection and restoration of natural composition and function, and protection of surrounding natural areas are the best way to improve the ability of these communities to adapt to climate change. Protection of a large and diverse pool of examples is the best way to ensure that many survive the future stresses.