Habitat description
Acidic peatlands are open, semi-open, and forested wetland communities characterized by an accumulation of partially decomposed organic material commonly called peat and muck, 15 centimeters to well over 10 meters in depth. Peat is composed of spongy layers of sphagnum moss while muck is decomposed to the point that the original plant remains are altered beyond recognition. Peatlands are associated with acidic, low nutrient, and slow or stagnant water that is low in oxygen. Acidic peatlands may be found in a variety of landscape settings including along the fringes of lakes, ponds, rivers, and streams, as well as in kettlehole depressions or on slopes and flat terrain.
Characteristic natural communities and species
Acidic Peatlands can be subdivided into bogs, acidic fens, shrub thickets, and forested swamps based on hydrology, nutrient inputs, and characteristic vegetation. These subtypes may occur in isolation or in contiguous suites within the same wetland. Each subtype of acidic peatland includes several Massachusetts natural communities.
Bogs
Bogs are characterized by nutrient-poor, acidic water, peaty saturated soils, and shrubby low vegetation. Organic matter decays slowly, forming deep peat accumulations that separate vegetation from mineral soils and mineral rich groundwater. Bogs have a well-developed sphagnum moss mat containing shrubs such as leatherleaf, bog cranberry, dwarf huckleberry, high-bush blueberry, and sheep laurel. Unique and specialized plants such as pitcher plants and sundews are often present in this nutrient-poor environment because they are capable of trapping and digesting important nutrients from insects. Trees such as black spruce may grow as stunted individuals scattered across the bog mat or along the outer border of the bog.
Acidic fens
Acidic fens are peatlands where water moves slowly across the surface or through the upper layers of peat. This results in slightly higher oxygen concentrations, greater peat decomposition, and slightly more nutrients as compared to bogs. Acidic fens generally have peat made up of poorly decomposed sphagnum, other mosses, sedges, rushes, and woody material. Acidic fens may be shrubby or grassy and are characterized by shrubs such as water willow, leatherleaf, poison sumac, sweet gale, red-osier dogwood, meadow sweet, and sedges, grasses, and rushes.
- Acidic graminoid fen (S3)
- Acidic graminoid fen – spillway fen (not ranked)
- Acidic shrub fen (S3)
- Sea-level fen (S1)
Tall shrub thickets
Tall shrub thickets are dense shrub wetlands on peat soils with strong water level fluctuations. They are flooded by weakly mineral rich water and may be influenced to a lesser degree along their fringes by seepage water from the surrounding uplands. The herbaceous layer is weakly developed, and peat is exposed on much of the surface. Highbush blueberry, sweet pepperbush, mountain holly, maleberry, and swamp azalea are characteristic plants of the shrub thicket. Cinnamon fern and sedges are often found in the herbaceous layer with sphagnum under highbush blueberry in areas influenced by seepage water from the surrounding uplands.
Forested peatlands
Forested peatlands are acidic peatlands with greater significant canopy tree cover found in kettlehole depressions, along wetland drainage divides, pond margins, streams, and gently sloping seepage areas. Forested peatlands may also occur as a narrow band along the wet perimeter (or “moat”) of more open peatlands, where conditions are slightly more enriched due to surface runoff and groundwater seepage.
- Red spruce swamp (S3)
- Hemlock swamp (S4)
- Red maple–black gum swamp (S2)
Atlantic white cedar swamps
Atlantic white cedar swamps merit special consideration since they are rare throughout their range, which spans the Atlantic Coastal Plain from southern Maine to North Carolina and the Gulf Coast in western Florida, Alabama, and Mississippi. There are limited inland occurrences. Many Atlantic white cedar swamps contain high iron content in the soil and historically were logged for their valuable timber resources or mined for bog iron. Massachusetts and New Jersey contain more Atlantic White cedar wetlands than other states in the Northeast, and account for a large proportion of the remaining acreage of Atlantic White cedar range wide. Due to their limited distribution, Atlantic White cedar swamps call for continued preservation, active management, and restoration in Massachusetts.
- Northern Atlantic white cedar swamp (S1)
- Coastal Atlantic white cedar swamp (S2)
- Inland Atlantic white cedar swamp (S2)
Natural communities are given state rarity/imperilment ranks ranging from S1-S5 (S1: rarest/most imperiled).
View a complete list of Species of Greatest Conservation Need associated with this habitat.
Associated habitats
- Deep drainage lakes and ponds
- Shallow drainage lakes and ponds
- Coastal plain ponds
- Gently-sloping cool streams
- Forest swamps and seeps
Ecological processes
Acidic peatlands are strongly influenced by hydrology, nutrient inputs, water chemistry, vegetation, and macro and micro climatic conditions. Their topographic position on the landscape may influence fine-scale variation in snow accumulation, surface and groundwater flow, net radiation, and cold-air pooling within. Therefore, diverse landscapes supporting wetlands with peat accumulations are likely to be more resilient against climate changes and short-term climate extremes (e.g., drought), and may recover faster and persist better in response to disruptions than their low resilience upland counterparts. A few of the many ecological benefits acidic peatlands provide include stabilization of flood waters and stream flow, filtration of sediments and pollutants, sequestration of large stores of soil carbon and nutrients, sulfate reduction, and provision of specialized habitats for many declining flora and fauna. Acidic peatlands provide important microrefugia for wildlife and plants and help us understand the spatial distribution of species, their patterns of genetic diversity, and potential dispersal rates in response to climate shifts.
Depending on their landscape position and land use history, certain peatlands such as Atlantic white cedar swamps, acidic graminoid fens, and sea-level fens may be influenced by fire and benefit from periodic prescribed fire treatments in wetlands and adjacent uplands. The characteristic vegetation of these wetlands benefits from periodic prescribed fire treatments and improve habitat conditions for many plants and animals.
Threats
Land clearing in adjacent uplands associated with commercial and residential development, infrastructure placement of roads and utilities, and ditching or channelization related to storm water management (natural system modification) may disrupt natural hydrologic inputs and water levels in acidic peatlands. The direct conversion of peatlands for agriculture such as cranberry bog production and irrigation practices has occurred within southeastern Massachusetts. Peatland restoration within several former commercial cranberry bogs is currently underway. Peat substrates are highly sensitive to compaction from foot or vehicular traffic. The removal of peat stores, and severe wildfires associated with drought conditions release long-stored carbon reserves in these wetlands.
Increased nutrient and chemical inputs associated with increased surface run-off and abnormal flooding related to storm events, storm water channeling into wetlands, and wastewater effluent (pollution), may affect vegetation composition and accelerate decay of peat resources in these nutrient poor environments. In some cases, beaver impoundments can negatively impact important acidic peatlands, a natural process that can have negative conservation impacts given the extensive loss and degradation of peatlands across the landscape from anthropogenic influences.
Changes in vegetation and increases in invasive species such as the non-native invasive common reed or the shrub glossy buckthorn help serve as indicators of altered water chemistry, water flow, and water table fluctuations. Often the initial advance of these invasive plants helps to identify abnormal water inputs into a wetland, allowing managers to trace changes responsible for vegetation shifts within the peatland.
Increased shade and canopy closure within Atlantic white cedar swamps, and lack of periodic fire within these disturbance dependent wetlands and the surrounding landscape, prevent Atlantic white cedar regeneration. In the past, Atlantic White cedar could regenerate after a major disturbance, such as fire, windstorm, or hurricane. That is not likely to happen today because shade tolerant species such as red maple and white pine have increased in the surrounding uplands and the wetland ecotone and have a competitive edge in re-establishing over Atlantic white cedar, which is likely to survive in a closed canopy for only one to three years. White-tailed deer also contribute to lack of regeneration within Atlantic white cedar wetlands, as cedar twigs and foliage are preferred winter browse for deer.
Impacts from climate change threaten acidic peatlands as well. Sea-level fens, acidic graminid fens, and Atlantic white cedar swamps occurring in the coastal zone are vulnerable to sea level rise and elimination, especially if they are found adjacent to impervious surfaces, lack resilient buffers, and limited available space because of specialized hydrologic inputs which prevent their natural migration. Other potential effects of climate change on acidic peatlands are not well understood.
Conservation actions
- Proactive habitat protection: Protect land around acidic peatlands and other associated wetlands, including broad expanses of matrix forest to maintain healthy and resilient landscapes for people and biodiversity conservation. Prioritize sites supporting state-listed animals and plants and other SGCN, as well as other protection priorities identified in BioMap and other conservation planning tools (e.g., municipal open space plans).
- Habitat restoration and management: See recommendations below.
- Law and policy: Regulate and limit the impacts of development, pollutants, and water withdrawals. Innovative approaches to incentivizing compatible development, and farm and forest preservation should be considered where applicable.
- Conservation planning: Include key acidic peatlands and associated wetland complexes in conservation planning efforts at multiple spatial scales. (See BioMap as an example.)
- Monitoring and research: Monitor the health and trends of SGCN populations, plant communities, and other wildlife. Monitor the effectiveness of habitat management efforts and conduct targeted research to improve habitat and population management.
- Public outreach: Include information about the role acidic peatlands and associated wetland complexes play in biodiversity conservation, flood mitigation, water filtering, and climate resiliency as part of broader communication strategies.
Restoration & management recommendations
Due to their importance to Species of Greatest Conservation Need and vulnerability to stressors, acidic peatland habitats have been designated as high priority (tier 2) for restoration and management. The following is an overview of restoration options; get details about specific management practices by clicking on the provided links.
Before undertaking a project, it is important to establish clear goals that are compatible with site conditions. Factors to consider include identifying the resources required for restoration and long-term maintenance, and securing community, stakeholder, and institutional support. For more information, see habitat management priorities and planning.
Improve water quantity and quality within acidic peatlands and work with conservation partners, including land managers, transportation authorities at state and local levels, utilities, restoration ecologists, and regulatory permitting authorities to develop feasible plans for restoration. Implement priority actions aimed at removing impediments to natural hydrologic flow of ground and surface waters, reducing stormwater flooding and pollutants or chemical inputs such as salt and sediment. Acidic peatlands are dependent on natural cycles of wet and dry periods and relatively nutrient-poor water inputs which influence peatland type. Extended periods of standing water or drought are unfavorable for many acidic peatlands.
Wetland restoration within peatlands is complex and requires assessments and partnerships with hydrologists, restoration ecologists, fish and wildlife resource experts, and wetland regulatory permitters. Wetland restoration may involve removal of upper sand layers established during former farming practices, plugging of ditches, removal of water control structures and dams, establishing micro-topographic relief, re-establishing connections to other wetlands and streams. Understanding wetland attributes in the context of the surrounding landscape and below ground peat reserves will influence restoration outcomes and success. Restoration actions require sequential implementation to achieve the best results.
Assess and remove barriers to water movement (e.g., dam removal) and improve habitat connectivity for wetland and aquatic resources by repairing and constructing appropriate stream crossings, culverts, wildlife corridors, tunnels, and other crossings (channel restoration). Remove beaver impoundments that cause prolonged periods of high water and flooding in acidic fens, bogs, and forested swamps (wildlife control).
Apply prescribed fire in select acidic peatlands to restore wetlands and maintain gaps in the canopy of forest and shrub dominated peatlands, encourage regeneration of Atlantic white cedar, reduce fuel loads and the build-up of thatch from invasive species concentrations, improve habitat conditions that influence nutrient cycling and the retention of carbon stores, and improve habitat conditions for many wildlife and plant species of greatest conservation need (SGCN). While fire may restore and maintain plant composition and structural diversity in many acidic peatlands, its application may not be feasible in all cases and requires careful planning, permitting, and implementation. Planning requires a knowledge of a wetland’s hydrologic inputs, seasonal water table fluctuations, vegetation patterns, peat reserves, and smoke management considerations.
Create forest gaps through selective tree removal in targeted Atlantic white cedar swamps to encourage regeneration of cedar. In certain wetlands, a history of intensive logging of cedar and leaving of hardwoods has shifted the composition away from cedar to closed canopy hardwood swamp or mixed cedar and hardwood. In other wetlands, cedar may remain dominant in the forest canopy. Careful site selection and planning of selective tree removal operations to encourage cedar regeneration depend on many factors including cedar and maple seed sources, shrub layer thickness, water table level, deer browsing, and gap size. Peatland substrates are sensitive to disturbance by heavy equipment and forestry operations must be timed to avoid damage to sphagnum, hummock and mound microtopography, and shallow rooted cedar trees.
Document natural and unnatural disturbance events such as pathogen and insect outbreaks (i.e., hemlock looper or hemlock wooly adelgid), establishment and spread of invasive plants (such as common reed and glossy buckthorn), storm events, precipitation changes, temperature increases, extended drought periods, wildfire events, and shifts in native vegetative communities. Use this information to inform planning and management priorities such as water quantity and quality remediation, invasive species control, prescribed fire, and forest thinning practices.
Develop long-term monitoring programs within wetland restoration sites such as Atlantic white cedar wetlands, bogs, acidic fens, and former cranberry bogs to determine vegetation changes related to hydrologic remediation, deer exclosure treatments, invasive species control, forestry operations, and prescribed fire. Certain management practices such as forest thinning and prescribed fire although beneficial can produce near-ground microclimate variation and should be monitored and appropriately timed to avoid impacts to wetland resources, peat reserves, and complement other on-going practices. Acidic peatlands are nutrient deficient, wet, and often colder microhabitats than the surrounding landscape, and therefore can serve as important microrefugia for wildlife and plants during climate change. It’s important to monitor and evaluate potential shifts in the ranges of target wildlife and plant populations to better understand the implications of climate change.
Design recreational access and outreach to avoid damage to peatlands and sensitive resources (access management). While visitation to acidic peatlands helps inform the public regarding their ecological importance and wetland function, access plans which focus on moving trails out of sensitive areas, using boardwalks and interpretive signage at limited peatland crossings and viewing areas, controlling access and capacity at parking areas and trailheads, establishing quantifiable thresholds to assess damage, and monitoring visitor use on a regular basis are recommended.
Additional resources
Burke, M. K. and P. Sheridan, eds. 2005. Atlantic white cedar: ecology, restoration, and management: Proceedings of the Arlington Echo symposium. Gen. Tech. Rep. SRS-91. Asheville, NC: U.S. Department of Agriculture Forest Service, Southern Research Station. 74 p.
Damman, A. and T. French. 1987. The ecology of peat bogs of the glaciated northeastern United States: a community profile. U.S. Fish and Wildlife Service Biological Report 85.
Laderman, A.D. 1989. The ecology of Atlantic white cedar wetlands; a community profile. United States Fish and Wildlife Service Biological Report 85 (7.21), Washington, D.C.
Mitsch, W.J. and J.G. Gosselink. 2015. Wetlands. 5th ed, John Wiley and Sons, publishers. New Jersey.
Mitsch, W.J., et al. 2013. Wetlands, Carbon, and Climate Change. Landscape Ecology, 28, 583-597.
Motzkin, G. 1991. Atlantic white cedar wetlands of Massachusetts. Massachusetts Agricultural Experiment Station Research Bulletin Number 731, Amherst.
Motzkin, G., W.A. Patterson III, and N. E.R. Drake. 1993. Fire history and vegetation dynamics of a Chamaecyparis thyoides wetland on Cape Cod, Massachusetts. J. of Ecology (18) 3: 391-402.
Mylecrain, K.A. and G.L. Zimmerman. 2000. Atlantic white cedar ecology and best management practices manual. Technical manual prepared under the editorial guidance of the New Jersey Atlantic white-cedar Initiative Committee for the New Jersey Department of Environmental Protection.
University of Massachusetts. 2017. Ecology and Vulnerability Freshwater Wetlands: Bogs and fens. Massachusetts Wildlife Climate Action Tool.
Examples
| Natural community | Site name, location | Ownership | Boardwalk/trail |
|---|---|---|---|
| Level bog and tamarack–spruce bog | Hawley Bog Preserve, Hawley | TNC/Five-Colleges | Yes |
| Level bog/Atlantic white cedar bog | Ponkapoag Bog, Canton | DCR | Yes |
| Acidic graminoid fen/Atlantic white cedar swamp | Hockomock Swamp WMA * | MassWildlife | Road crossings |
| Coastal Atlantic white cedar swamp | Marconi Cedar Swamp, Wellfleet | National Park Service | Yes |
| Inland Atlantic white cedar swamp | Douglas State Forest, Douglas | DCR | Yes |
| Red maple–black gum swamp | Oakham WMA, Oakham | MassWildlife | No |
| Red spruce swamp/tamarack–black spruce bog, level bog | Harvard Pond, Petersham | Harvard Forest | Perimeter trail & road crossing |
| Hemlock swamp | Wolf Swamp WMA, Brookfield | MassWildlife | No |
| Windswept bog wetland restoration | Windswept Bog, Nantucket | Nantucket Conservation Foundation | Perimeter trail & road crossing |
*Largest freshwater wetland in state (16,000 acres) encompassing several towns: Bridgewater, West Bridgewater, Easton, Norton, Raynham, and Taunton