Habitat description
Calcareous wetlands are marshes, fens, and forested wetlands that are greatly influenced by calcium- and magnesium-rich alkaline groundwater. The key indicator of these communities is the prevalence of plants that depend on high calcium levels (“calciphytes”) such as shrubby cinquefoil, hoary willow, and rough-leaved goldenrod. Calcareous wetland vegetation is generally open to semi-open, but can be forested, and can occur in isolation, or as a part of a mosaic within a wetland system. Due to the combination of their unique water chemistry and relative rarity on the landscape, calcareous wetlands support some of the richest suites of specialized and imperiled species in Massachusetts.
Characteristic natural communities
Calcareous wetland habitat can be further subdivided into specific natural communities that vary based on slope and juxtaposition to aquatic features such as lakes, which in turn affects groundwater interactions and peat or muck deposition. These natural communities may intergrade along a continuum.
Learn more about the natural communities found in calcareous wetlands:
- Calcareous basin fen (S1)
- Calcareous seepage marsh (S2)
- Calcareous sloping fen (S2)
- Red maple-black ash-tamarack calcareous seepage swamp (S2)
- Calcareous pondshore/lakeshore community (S2)
Natural communities are given state rarity/imperilment ranks ranging from S1-S5 (S1: rarest/most imperiled).
Associated habitats
Depending on hydrology, parent soil material, topography, and land use, calcareous wetlands may be associated with a variety of other habitats including deep drainage or isolated lakes and ponds, gently sloping cold streams, acidic peatlands, marshes and wet meadows, and forest swamps and seeps.
Characteristic plants and animals
This specialized habitat supports a diversity of rare or uncommon plants including swamp birch, glaucus sedge, and several orchids including leafy white orchid and round-leaved orchid. Spotted turtles and northern leopard frogs often occur in calcareous wetlands, and American bitterns sometimes nest in more open calcareous communities. Other species that will make use of calcareous wetlands, including black bear, mink, wood turtle, and yellow warbler.
View a complete list of Species of Greatest Conservation Need associated with this habitat.
Ecological processes
The primary driver of these communities is a direct influence from calcium and magnesium rich alkaline groundwater. This groundwater (pH ranging from 6.0-8.1) creates an environment where only specialized vegetation can thrive. Occasional low severity fire can also be important to maintain the composition and structure of this habitat (especially the graminoid/forb-dominated communities) by further setting back seral and generalist succession. In the presence of calcium-rich alkaline groundwater and occasional fire, local site conditions will influence the expression of the specific community through such elements as topography, water-temperature, and substrate condition.
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 calcareous wetlands. Increased nutrient and chemical inputs associated with increased surface run-off and abnormal flooding related to storm events, storm water channeling into wetlands, agriculture, and wastewater effluent (pollution), may affect water chemistry and vegetation in these unique environments. Invasive species of plants such as common reed can also be a threat.
In some cases, beaver impoundments can negatively impact important calcareous wetlands, a natural process that can have negative conservation impacts given the extensive loss and degradation of calcareous wetlands from anthropogenic influences. In today's altered landscape where most remaining calcareous wetlands are under stress, a lack of adequate management can also pose a significant threat.
Climate change will impact calcareous wetlands. Specifically, changes in precipitation and the seasonality of precipitation events, as well as changes in groundwater levels, may dramatically influence the delicate hydrology of these sites. Changes in precipitation may also impact the concentration of calcium and other minerals, as well as the pH of ground and surface water. Additionally, increasing water temperatures may affect the decomposition process, which will have impacts on the peat-based community variants. Finally, an increase in atmospheric nitrogen deposition will further aid the establishment and spread of aggressive generalist and invasive species and further alter water chemistry.
Conservation actions
- Proactive habitat protection: Protect land adjacent to calcareous wetlands 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 calcareous wetlands 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 of calcareous wetlands and associated wetland complexes play in biodiversity conservation, flood mitigation, water filtering, and climate resiliency as part of broader communication strategies.
Restoration & management recommendations
Calcareous wetlands are designated as very high priority (tier 1) for restoration and management. Opportunities for conserving calcareous wetlands are incredibly limited due to their overall rarity. Therefore, protecting and/or restoring each remaining occurrence in the state is now very important. Most of the Commonwealth’s larger sites are receiving at least some management, though many of the smaller sites need attention. Historically, calcareous wetland communities persisted on the landscape due to their water chemistry, periodic low-severity fire, and in some cases, episodic natural grazing. However, these communities are also very sensitive to many anthropogenic disturbances, and as a result, nearly all post-settlement occurrences need some level of restoration to address modern stressors.
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, please see: habitat management priorities and planning.
The first step should be a thorough assessment of current site conditions and the identification of the specific stressors that need to be overcome. Calcareous wetlands are complex systems, and in many instances, there will be multiple stressors impacting a site. Therefore, it is important to focus not just on the symptoms of compounding stressors, but to instead understand the root causes and work to address them.
The following is an overview of restoration options; get details about specific management practices by clicking on the provided links.
- Water quantity and quality restoration: Calcareous wetlands occur within a very narrow range of optimal groundwater-influenced hydrology. Even small changes to hydrology will have profound impacts on the vegetation composition and structure. Having too much surface water at a site is a very typical modern stressor of these communities, and will often be expressed in obvious ways, such as pooling water and the aggressive presence of generalist species like cattails. Beaver dams at the outflow of sites has become common at many sites, and informed remediation of beaver impacts can be an important management action. Increased runoff from development, and artificially constricted outflows (causeways, undersized culverts, etc.) are two other common stressors that regularly oversaturate calcareous wetlands. Conversely, reducing the natural amount of water on a site can also result in harm to the community by drying the substrate and reducing the harsh chemical and pH influences on the site. Both of these outcomes will lead to a reduction in the calciphytic wetland obligate plants that define the community and will often lead to a shift toward more generalist species dominance and changes to the overall community structure. Ditching (including historic ditching), up-flow restrictions and excessive groundwater extraction are all common ways that calcareous wetlands are stressed by reductions in the presence of groundwater. Partial or complete filling of ditches may be an appropriate mitigation strategy in some cases. It is important to work with an expert hydrologist or wetland scientist to assess hydrologic stressors and develop a remediation plan.
The chemical profile of any calcareous wetland is a delicate balance driven by natural groundwater influences that can be easily upset by unnatural inputs. There are myriad anthropogenic activities that can alter the chemistry and water quality, resulting in an increase of aggressive native generalist and invasive plants. Nutrient loading from agricultural and residential runoff, as well as the chemical inputs from nearby roads (especially road salt), can result in major compositional changes to a site. Reducing unnatural chemical inputs to a site by reducing these inputs in the greater watershed and addressing source points is a key remediation practice. In cases where addressing the chemical input directly is not possible (e.g., atmospheric deposition), addressing the symptoms is the key action (e.g., controlling invasive and aggressive generalist plants). - Invasive plant control: The need for vegetation control is typically the result of one or more stressors (especially altered hydrology and/or chemistry). Addressing the resulting increases in invasive and aggressive native generalist plants is critical in maintaining the long-term viability of these unique wetlands, but this approach should also be coupled with trying to understand and ultimately remediate the cause (see above).
- Invasive exotic plants: Phragmites, reed canary grass, glossy buckthorn and purple loosestrife are the primary invasive species that impact calcareous wetlands in Massachusetts. However, many of the invasive species known to occur in Massachusetts can be present and adversely affect these communities; even species that are generally considered to be indicators of terrestrial environments. The careful application of herbicide is the most effective way to treat nearly all invasive plants, though it will likely take several years to completely eradicate any established. The continued presence of invasive species in calcareous wetlands is likely 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.
- Cattail: The presence of cattails is strong indicator of hydrologic and/or chemical stressors (especially nutrient loading and elevated water levels). Unchecked, cattail can invade these systems and convert them to near monocultures (including native cattails and an aggressive non-native hybrid). Herbicide, specifically glyphosate in late summer, is an important tool for controlling invading cattails (it may take several years of treatment for established stands). Once cattail monocultures are reduced by herbicide application, their footprints will be quickly recolonized by the desirable seedbank of native obligates. Careful foliar applications are appropriate in monocultures, while more discrete applications (like glove wipe) are appropriate in lower density situations.
- Other aggressive generalist plants: The dominance of other clonal generalist native plants is signaling stress in a calcareous wetland (e.g., sensitive fern, lake sedge, some asters and goldenrods, some shrub species). These can quickly overwhelm a stressed fen reducing the viability of rare calciphytic plants. An increase in woody vegetation can also attract beavers to the site, who will quickly restrict the water flow and alter the site’s hydrology. Understanding and addressing the underlying stressors is important (altered hydrology, adverse chemical inputs), just as it’s important to directly treat the invading vegetation. Thoughtful use of herbicide is typically the best way to directly address these situations, and a best-case management scenario will also include remediating any underlying stressors. Cutting and treating the stumps of generalist woody vegetation, or carefully applying a foliar herbicide, are two effective ways of dealing with established generalist woody vegetation. However, it should be noted that all calcareous wetland communities support associated obligate shrubs (ex. hoary and autumn willow, poison sumac, etc.) that should not be eliminated. Woody plants can also be managed through the application of prescribed fire, and in some cases, very carefully planned grazing.
- Prescribed fire: Periodic low severity fire was an historically important element in maintaining the structure and specialized composition of calcareous wetland communities. Fire suppresses the establishment of generalist woody vegetation and reduces thatch buildup that can otherwise inhibit the germination of specialist plants, as well as result in the alteration of soil composition and chemistry. Whenever possible, prescribed fire should be considered an important part of any long-term management plan. However, burning in these communities poses a unique set of challenges, and attention to burn severity is especially important so that fire doesn’t ignite underlying peat.
- Grazing in calcareous sloping fens: The thoughtful application of grazing can be a useful tool to aid the initial restoration of calcareous sloping fens that have shifted toward a more generalist composition. The other calcareous wetland communities are typically too wet, have too sensitive a substrate, and/or have an incompatible structure/composition to reasonably support grazing. Grazing in certain sloping fens can be especially effective at suppressing/reducing woody vegetation and stressing clonal vegetation that is outcompeting obligate calciphytes. However, grazing alone will not be an effective long-term strategy for maintaining the integrity of these communities, as the continued pressure will eventually negatively impact calciphytic obligates while introducing a continually increasing nutrient load to the system. Grazing may also inadvertently introduce invasive species to a system, either through seeds transported within an animal’s fur, hooves or digestive tract, or through supplementary feed brought to a grazed site. Introducing grazing to a sloping fen for management purposes is a complex proposition, and finding a prescription that balances grazing pressure, nutrient inputs, physical disturbance to the substrate, and vegetative response is not only difficult, but also requires close monitoring and the ability to remain constantly adaptive in response to regularly observed results.