Upland Pools and Depressions
The 2015 North Carolina Wildlife Action Plan defines 41 priority habitats for the state. More information about this habitat can be found in Section 4.3.9.
Contents
Habitat Priorities
Surveys
- Investigate the status and distribution of species associated with Piedmont wetland habitats (e.g., Three-lined Salamander, Common Ribbonsnake). (Surveys Priority)
- Survey for all amphibian species associated with small wetland communities. (Surveys Priority)
Monitoring
- Monitor amphibian populations to detect incidence of fungal and viral infections (e.g., iridoviruses, chytridiomycosis).
- Determine population trends and persistence of small wetland breeding amphibian populations, particularly Mole Salamander, Eastern Tiger Salamander, Dwarf Salamander, and Four-toed Salamander.
Research
- Determine minimum upland buffers required to sustain at-risk amphibian populations.
- Study the efficacy and practicality of “toad tunnels” and other wildlife crossings that allow passage under roadways and help maintain connectivity between wetland metapopulations.
- Investigate minimum hydroperiods needed by priority amphibian species that utilize ephemeral pools and wetlands. Results can be used to determine when supplemental measures or intervention is needed to support breeding periods and metamorphosis during drought periods.
Management Practices
- Explore management strategies to eradicate undesirable species, such as bullfrogs, from wetlands.
- Employ hydrological restoration methods such as plugging ditches where ditches are affecting the hydrology of the pools.
- Promote the adoption of agricultural and forestry best management practices (BMPs) that reduce run-off, erosion, and pollution. The federal Farm Bill and other cost share programs provide incentives for land stewards to adopt these practices.
Conservation Programs and Partnerships
Description
Small, isolated wetlands, such as upland pools and depressions, are important areas of diversity for plants and animals, especially specialized amphibians that require these habitats for breeding. Upland pools and depression communities occur in all regions of North Carolina. Typically, they include shallow depressions which hold water in wetter parts of the year. Many are ephemeral, drying during some part of the year (often in summer), but are flooded long enough into the growing season to contain wetland vegetation that contrasts with the surrounding uplands. Water levels usually fluctuate over the course of a season, and also from year to year. Communities differ in overall hydroperiod, in soil, in slope, and in depth. Hydroperiod is the length of time that there is standing water at a particular location; it can also be defined as the number of days per year that an area of land is dry (Gaff et al. 2000). Some ephemeral (temporary) pools are wet enough to accumulate muck on the bottom, while others remain sandy.
Upland pools and depressions can be categorized into one of several types, including the following:
- Upland pools that occur in sites where the water is deep enough or long-standing enough to prevent development of a closed tree canopy. The vegetation varies widely, and it is likely that this type could be split into several community types. Trees of the upland depression swamp forest community type may occur around the edges.
- Upland depression swamp forests that occur in shallower depressions than upland pools, and are flooded for shorter periods. They usually occur on broad upland flats but occasionally on high ridgetops. They have a closed canopy of wetland trees. Understory, shrubs, and ground cover are usually sparse.
*Ephemeral (temporary) pools that are small, seasonally flooded depressions with gently sloping sides and are usually found in sandy uplands.
*Seeps that occur along slopes where groundwater trickles out of the surface and collects in small pools and will often trickle into streams.
- Clay-based upland depressions that typically occur as oval or round depressions with a clay base that allows them to hold water for at least a portion of the year. In the Sandhills and Coastal Plain, these depressions historically have had a Longleaf Pine upland where hot season fires burned regularly, creating an open-canopy, grassy wetland system with long hydroperiods. In the Coastal Plain and Sandhills ecoregions, pond basins may also be limesink depressions, Carolina bays, or swales between recent or older sand dunes.
- Limestone sinks occur over limestone formations. Scattered trees (Pond Cypress and Swamp Blackgum) may be present in both deep and shallow water zones and most ponds are surrounded by a dense shrub layer. These shrubby zones provide breeding habitat for shrub-scrub-nesting birds (Hunter et al. 2001a; Johns 2004) and these sites are used by wading birds for foraging/nesting and amphibians for breeding.
- Swale wetlands occur on barrier islands, such as in the Outer Banks, in areas where the freshwater aquifer saturates the soil and collects on the surface between sand dunes. These ponds will also have dense maritime shrublands in areas where water is shallow; in deeper water, they are characterized by emergent and submerged aquatic vegetation.
- Carolina bays with organic/peat substrates are relatively deep closed basins associated with pocosins, depression swamps, Pond Pine woodlands, bay forests, or Atlantic White Cedar forests. Occasionally they occur in shallow depressions associated with nonriverine communities such as swamp forests, wet hardwood forests, and wet marl forests with nonalluvial mineral soils (NCNHP 2010).
All of these natural community types often have abundant amphibian species. Those that dry annually or semi-annually benefit amphibians the most, due to the absence of fish, which would typically eat amphibian eggs and larvae. During heavy storm events, however, fish can be swept in by overbank flooding, reducing the suitability of these pools for amphibian breeding until they dry out again.
Location of Habitat
Upland depression communities occur throughout North Carolina but are often overlooked features on the landscape mainly because they are difficult to discern on aerial photographs unless they are quite large. In the Piedmont and in the Mountains, these small wetland communities can be found on broad upland flats and occasionally on high ridgetops. Ephemeral (temporary) pools are usually found in sandy uplands. Those that occur in the Piedmont are associated with mafic rocks or shale. Those in the Mountains occur on quartzite. Examples include Frogsboro Upland Depression Forest in Caswell Game Land; Badin Upland Depression Swamps in the Uwharrie National Forest; Meadow Flats in Duke Forest; and Bog Hole (Seventeen Frog Pond, Grassy Pond) in Sandhills Game Land in Scotland County (an unusually wet example, transitional to Small Depression Pond).
Carolina bays and limestone sinks are probably the best known examples of isolated wetlands in NC because they are easy to view on aerial or infrared photos of the region and they are generally obvious on the landscape. Carolina bays and clay-based upland depressions occur throughout the Coastal Plain, whereas limestone sinks tend to occur in clusters in areas along the lower Coastal Plain—numerous limestone sinks are visible around the Boiling Spring Lakes area in Brunswick County, NC.
Problems Affecting Habitats
Isolated, ephemeral wetlands are regarded as one of the most endangered, and simultaneously one of the most biologically productive habitats in North America. Wetlands of this type are characterized by unique assemblages of flora and fauna that are not associated with permanent-water wetlands. In the Southeast, they serve as critical breeding habitat for several endangered species of amphibians. Many declining species of plants and animals depend on or use isolated, temporary wetlands. Across the Southeast, most of these systems have been lost to draining for agriculture, commercial silviculture, and development. Others have been altered to retain the permanent water necessary to support fish populations. Further, many of the temporary wetlands that remain on the southeastern landscape have been greatly affected by lack of fire that would have naturally maintained them in an early successional condition. The resulting colonization by large overstory trees significantly alters these wetland systems such that they no longer support many of the rare species that depend on them.
The vegetation of upland ephemeral pools varies widely because of natural and human-induced differences among ponds. Factors related to human-induced changes such as ditching and lowering of water tables through agricultural and urban uses has caused some pools to completely dry or revert to forested wetlands. Some upland ephemeral pools are maintained as open-canopy emergent wetlands because of naturally long hydroperiods that prevent the colonization of trees and shrubs (e.g., limestone sinks with a groundwater connection).
However, many upland, isolated wetlands would have historically been maintained as open, “grassy” ponds through a combination of hydroperiod and fire regime processes (DeSteven and Toner 2004). In these situations, summer fires would occasionally burn through the dry basins, limiting the establishment and growth of fire-intolerant woody species and controlling the buildup of excessive amounts of peat (Florida Natural Areas Inventory 1990). Specifically, vegetation of clay-based depressions has been altered by fire suppression or exclusion in adjacent uplands, ditching of wetlands, or by intentional fire exclusion by maintaining fire lines around wetland habitats. Even where fire has been reintroduced into the Longleaf Pine ecosystem in the Southeast, most managers use winter or spring burning instead of hot, summer fires that would have naturally occurred in the past. Winter or spring fires usually do not burn through wetlands because water is often present in the pond basin at that time of year. Indeed, fire suppression or exclusion has been linked to the encroachment of trees into historically treeless ponds in the Southeast (Kushlan 1990; Kirkman et al. 1999; De Steven and Toner 2004).
The reduction of open-canopy, ephemeral ponds is a major reason for the loss of populations of some southeastern amphibian species (e.g., Gopher Frog) that depend on them exclusively for breeding (LaClaire 2001). Additionally, the encroachment of trees into temporary wetlands can have multiple adverse effects on the larvae of many amphibian species (Schiesari 2006; Thurgate and Pechmann 2007; Werner and Glennemeier 1999). The most obvious effect is increased evapotranspiration in the pond resulting in a shorter hydroperiod (Sun et al. 2001). Shorter hydroperiods may not allow larval amphibians enough time to reach metamorphosis (Skelly 2004).
Shading of ponds can also lower the pond’s water temperature, slowing the growth and development of larval amphibians (Blaustein et al. 1999; Skelly et al. 2002). Ponds with significant canopy cover may also suffer from lowered oxygen availability (Skelly et al. 2002) and reduced algal communities (Skelly and Golon 2003), both of which have detrimental effects on larval amphibian growth and survival. Further, increases in leaf litter associated with the establishment of overstory trees can substantially lower the pH in these degraded wetlands. Evidence exists that breeding habitats can indeed become too acidic for the successful hatching and rearing of some southeastern amphibian larvae (Braswell 1993 and references therein).
Climate Change Compared to Other Threats
Comparing climate change to other ecosystem threats can help define shortand long-term conservation actions and recommendations. In this comparison, the greatest threat to depression communities is likely to be habitat conversion. Habitat conversion occurs for various reasons, including suppression of natural fire regimes, development, and land use changes. Drier basins are destroyed by development or conversion to pine plantations, while wetter ones are degraded by these activities on the surrounding uplands. In protected examples, alteration of hydrology and effects of fire suppression are usually the most serious threats.
Climate change is likely to exacerbate existing effects, increasing the number and severity of droughts and increasing the amount of evaporation even in years of normal rainfall. If increased drought and severe weather reduces the ability to conduct prescribed burning, this may reduce fire even in the few examples that are getting burned. With respect to climate change, however, upland pools and their associated species are likely to respond differently from the surrounding forests. Table 4.23 summarizes the comparison of climate change with other existing threats.
Impacts to Wildlife
Members of this community all make use of upland pools for breeding, but make use of floodplain pools as well, at least where they are fairly well isolated from frequent overbank flooding. Windthrow pits may also be used and Four-toed Salamanders, in particular, make frequent use of seepage habitats. All Piedmont wetland habitats are especially important as breeding sites for amphibian species. Small wetlands can also be important breeding habitat for crayfishes. Wading birds, waterfowl, and songbirds may also use small wetland communities for nesting and feeding areas.
While often small in size, cumulatively these habitats provide critical breeding habitat for many amphibian species. Ephemeral and isolated wetlands are very valuable to amphibians because they typically do not support fish and other predators of amphibian eggs. The loss of ephemeral wetland communities in the Piedmont has strong ramifications for future amphibian populations. Amphibians in these communities depend on the surrounding uplands, and populations are lost or much reduced if the surrounding habitat is destroyed or altered. Pool-breeding amphibians that make use of these pools may potentially be as adversely affected by these changes as those associated with upland pools are by increased frequency of drought.
Increased road densities are correlated with declines in amphibian diversity and abundance (Vos and Chardon 1998; Findlay et al. 2001; Fahrig et al. 1995). Roads can cause heavy mortality for reptiles and amphibians and can effectively isolate breeding populations, or separate wetland habitats from upland habitats that are used during non-breeding portions of amphibian and reptile life cycles. The increase in impervious surfaces from the proliferation of roads causes excess stormwater runoff and pollution from point and nonpoint sources, which degrades water quality. Most amphibians are highly sensitive to changes in water quality.
All are likely to be strongly affected, particularly upland populations, by increases in prolonged droughts associated with climate change. Increased drawdown of groundwater levels, also the result of prolonged drought as well as increased human utilization, particularly in times of surface water scarcity, is another major threat for populations associated with floodplain pools or seeps. Floodplain pool populations are additionally likely to be adversely affected by increases in overbank floods that carry fish into their breeding sites. These impacts may be offset to some extent, however, by increases in the number of windthrow pits resulting from heavier storm damage.