Habitat description
Forested swamps and seeps are wetlands dominated by trees with soils that remain saturated for much of the growing season, often with standing water in the spring. Forested swamps usually occur as patches within surrounding upland forest, either in isolation or as a part of larger wetland complexes. Forested swamps are often dominated by red maple, and species composition is influenced by local climate, hydrology, and soil/bedrock chemistry. Forested seeps are a subset of forested swamps that are often relatively small, with groundwater reaching the surface due to topography, underlying bedrock, or presence of other impermeable layers.
Characteristic natural communities
Forested swamps and seeps can be divided into distinct natural communities. Red maple swamps are the most common forested wetlands in Massachusetts. Red maples often occur with other hardwood tree species in particular settings as reflected in the natural communities listed below. Some variants include conifers such as hemlock. In MassWildlife’s habitat classification, certain wetlands that are forested and have characteristics such as peat accumulation or high pH from calcareous bedrock are included in acidic peatlands or calcareous wetlands.
Learn more about the natural communities found in forested swamps and sweeps:
- Black gum–pin oak–swamp white oak "perched" swamp (S1)
- Red maple–black ash–bur oak swamp (S2)
- Red maple–black ash swamp (S2)
- Red maple–black gum swamp (S2)
- Red spruce swamp (S3)
- Rich conifer swamp (S3)
- Hemlock swamp (S4)
- Forest seep community (S4)
- Red maple swamp (S5)
Natural communities are given state rarity/imperilment ranks ranging from S1-S5 (S1: rarest/most imperiled).
Characteristic plants and animals
Forested swamps provide breeding and/or foraging habitat for a variety of amphibians including state-listed blue-spotted salamanders and marbled salamanders, and many other common species (e.g., spotted salamander, spring peeper, gray treefrog). Species of Greatest Conservation Need (SGCN) birds such as the Canada warbler and northern parula sometimes breed in forested swamps, and many other birds and mammals use forested swamps for portions of their life cycle. Several state-listed and/or SGCN plants also depend on this habitat.
View a complete list of Species of Greatest Conservation Need associated with this habitat.
Associated habitats
Forested swamps and seeps may be embedded within upland or may occur in association with other wetlands including marshes and wet meadows, riparian and floodplain habitat, vernal pools, acidic peatlands, calcareous wetlands, and shrub swamps. Forested seeps and sections of forested swamps may function as vernal pool habitat if standing water is present with the appropriate depth and hydrologic period.
Ecological processes
Forested swamps develop on poorly drained areas throughout the state. Depending on the physical setting, forested swamps receive water through surface runoff, groundwater inputs, or stream and lake overflow, and setting is the primary determinant of plant community structure and composition. Although some swamps are on mineral soils, most have some amount of muck, which are shallow to thick organic layers, overlying mineral sands, silts, or even bedrock. Peat accumulation is minimal at most sites for most types of forested swamps, but some accumulation does occur. Many occurrences of forested swamps have some groundwater seepage at their edges, which increases species and habitat diversity.
Beaver dams can significantly alter hydrology, eventually flooding understory vegetation, and killing overstory trees. After beavers abandon an impoundment and dams are breached, the habitat may eventually revert to forested swamp. The cycle of beaver occupation, abandonment, draining, forest regrowth, and wetland recolonization can be lengthy, playing out over many decades.
Threats
- Development: Development in the wetland watershed, and other land use changes can lead to decreased water quality (pollution; e.g. road salt runoff) and altered wetland hydrology (natural system modifications; e.g. from groundwater withdrawals).
- Invasive species: Changes in water levels and quality can lead to invasion by nonnative invasive species such as common reed, reed canary grass, purple loosestrife, bush honeysuckle (Lonicera spp.), glossy buckthorn and common buckthorn.
- Climate change: Climate change analyses project varying scenarios for the northeastern United States. Although total precipitation is expected to increase, other common predictions include warmer temperatures, longer and more severe summer droughts, shorter but more intense winter and spring floods, and reduced extent and duration of winter snow cover. Taken together, such changes could alter the hydrology (e.g. water levels) of many forested swamps in the region. Expected outcomes include seasonal drying of wetland soils when water tables drop during extended droughts, which could facilitate changes in dominant vegetation. Conceivably, smaller forested swamps could be lost entirely, while larger ones could contract in area or become fragmented. These scenarios would also likely lead to a change in the species composition of impacted wetlands.
Conservation actions
- Proactive habitat protection: Protect land around forested swamps, prioritizing sites supporting state-listed animals and other SGCN, as well as other wetland 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.
- Conservation planning: Include key forested wetlands and wetland complexes in conservation planning efforts at multiple spatial scales. (See BioMap as an example.)
- Public outreach: Include information about the role forested swamps and associated wetland complexes play in biodiversity conservation, flood mitigation, water filtering, and climate resiliency as part of broader communication strategies.
Restoration & management recommendations
The following is an overview of restoration options; get details about specific management practices by clicking on the provided links.
Control of invasive and competing understory plants: The careful application of herbicide is the most effective way to treat nearly all invasive species occurrences in forested swamps and seeps, though control may take several years of treatment to control established invasive species due to persistent seedbanks and the clonal nature of certain species. It should also be noted that the continued presence of invasive species in forested swamps and seeps may be an indicator of an underlying stressor such as altered hydrology or unnatural chemical inputs, and therefore addressing both the invasive species and the underlying stressors is critical to restoring the long-term viability of a site.
Water quantity: Increased runoff from development, and artificially constricted outflows (causeways, undersized culverts, etc.) are stressors that can alter the hydrology of forested swamps. Conversely, reducing the natural amount of water on a site can also result in harm to the community by drying out the underlying soils. Ditching (including historic ditching), up-flow restrictions and excessive groundwater extraction are ways that forested swamps may be stressed by reductions in the presence of surface or ground water. Partial or complete filling of ditches may be an appropriate mitigation strategy in some cases. It should be noted that once hydrologic stressors are identified, any hydrologic remediation should only be undertaken after a thorough assessment of the site’s hydrology—including the expected outcome of the remediation—has been completed.
Water quality: There are many anthropogenic activities that can alter the chemistry of forested swamps and seeps, often resulting in an increase of invasive plants. Nutrient loading from agricultural and residential runoff, as well as the chemical inputs from nearby roads (especially road salt), can result in compositional changes to the plant community. Reducing unnatural chemical inputs from point and non-point sources is a key remediation practice. Addressing altered hydrology, such as culverts and drainage swales that contribute to chemical runoff, and managing symptoms like invasive and aggressive plant growth are essential actions for restoration.