New York State Fens

Nicole E. Muir-Hotaling

Definition
A fen is a minerotrophic, or mineral-nourished, wetland with water enriched in calcium and magnesium bicarbonates or sulfates. Fens generally occur on organic substrate (i.e. peat), but can be found on marl (calcium carbonate) deposits.  They also usually have an internal flow of groundwater at the root zone, and the water table remains at or near the soil surface for much, if not all, of the growing season.

Fens vary in the degree of minerotrophy from extremely poor, i.e. those with low levels of mineral input, to medium, to extremely rich, i.e. those with relatively large mineral inputs.  The minerotrophic gradient of poor to rich fen also coincides with the acidity gradient of low pH (acidic) to moderate pH (slightly basic).  Fens tend to have circumneutral waters (near neutral, pH=7.0), but range from an acidic poor fen with a pH=3.5 to an alkaline rich fen with a pH=8.5.  Fen vegetation can be herbaceous (usually graminoid-dominated), shrubs, or trees (with either a partial or a fully closed canopy); the composition of the fen community can be any combination of bryophyte, herbaceous, and woody species.  Fens occur only in areas with a specific range of pH and water table depth; once outside this range other habitats will form (Figure 1).

This definition contrasts with narrower definitions of fens which limit them to open vegetational (low herbaceous) communities, and usually require that they be a peatland, that is, having peat as the underlying substrate. 

Fens also differ from bogs.  Bogs are acidic peatlands whose only source of water and mineral nutrients is rainwater.  They are usually dominated by Sphagnum species (a type of moss) and ericaceous shrubs or conifers (usually spruces and pines) (Bridgham et al. 1996).

Fens occur in North America and Europe and have been reported from all provinces and most states in eastern North America.  Table 1 contains examples of the number of reported fens for several eastern states. 

Eastern North American fens can be divided into four geographic groups: boreal, midwestern, northeastern, and Appalachian (Figure 2).  Boreal fens in eastern North America tend to be large, patterned fens similar to fens in western Canada and northern Europe and Russia.  These fens cover vast areas of the land and consist of alternating linear ridges and hollows, generally perpendicular to the slope of the land, and hence to the direction of water flow.  These fens tend to have a lower pH and lower calcium concentrations than fens in other geographic regions, especially Atlantic Canada’s fens that have very low pH and calcium levels.  However, these fens still contain many of the same species that are found in rich fens further south and therefore are considered rich fens. 

Midwestern and northeastern fens are generally much smaller in size, often less than 10 hectares (24.71 acres), and contain many of the same plant species.   Fen flora in both these regions are usually dominated by taxa from three families: Asteraceae (asters), Cyperaceae (sedges), and Poaceae (grasses).  Midwestern fens also contain tallgrass prairie plant species that are not found in the northeastern sites.  Appalachian fens tend to be poor fens.

Fens can only be found in areas of calcareous bedrock or calcareous glacial deposits (Figure 3). Fens are found throughout New York State, although there are areas where few or no fens are known to occur, such as much of the Southern Tier, the Adirondacks, the Catskills, and Long Island (Figure 4). Fens also tend to occur as one part of a larger mosaic of wetland and upland habitats.

Classification
Fens, like other wetlands, have historically been classified based on their local hydrology, vegetation, and soil type.  Many different classification schemes have been developed for many different purposes.

The U.S. Fish and Wildlife Service classifies wetlands using a scheme developed by Cowardin and others and published in 1979 as “Classification of Wetland and Deepwater Habitats of the United States.”  In this classification, which is used in producing National Wetland Inventory maps, wetlands are defined by their vegetation (hydrophytes), soils (hydric), and flooding frequency (hydrology).  This system is hierarchical, recognizing five major systems (marine, estuarine, riverine, lacustrine, and palustrine), seven subsystems (based on hydrology), and numerous classes, subclasses, and dominants that variously describe the substrate, vegetative community, or dominant vegetation.  This classification scheme is not very useful for classifying fens because fens do not fall in a single class, and a single class may also include wetland types other than fens.  Fens, although always within the palustrine system, may belong to the moss-lichen, emergent, scrub-shrub, or forested wetland class. 

Moore and Bellamy (1974) present a peatland classification system based on hydrological flow-through.  This system has three main categories: rheophilous, transition, and ombrophilous.  Rheophilous peatlands are influenced by groundwater from outside the immediate watershed and are divided into four types depending on whether flow is intermittent or continuous and whether it occurs on the peat surface or underneath a floating mat of vegetation.  Transition peatlands are influenced by groundwater derived only from the immediate watershed, and are divided into two types based on continuous versus intermittent flow.  Ombrophilous peatlands are never subject to flowing groundwater.  This system may also be of limited use in classifying fens because they could be either rheophilous or transition, and fens are not necessarily peatlands in a strict sense.

In New York State, Reschke (1990) developed a classification system of ecological communities based on vegetation, recognizing 222 communities, 120 of which are wetland or deepwater habitats.  Of these, 46 are palustrine systems.  Within the palustrine category, Reschke recognizes 21 peatland types, 7 of which are referred to as fens.

Another approach to wetland classification, Brinson’s (1993) hydrogeomorphic classification, provides a framework for wetland evaluation rather than strict classification since there can be overlap in some of the proposed wetland types.  This hydrogeomorphic approach allows consideration of abiotic features that are directly linked to wetland function and are not considered in any of the wetland classification schemes mentioned above. 

Why Study Fens?
One reasons to study fens is that in New York State, and elsewhere, fens harbor a diverse assemblage of plants and animals that include a disproportionate number of government-protected species (Johnson and Leopold 1994).  For example, in northeastern Iowa, fens coveronly 0.01% of the land, but contain 18% of the state’s flora, and 20% of Iowa’s rare flora
(Nekola1994).
Fens are also interesting and challenging to study because of the number of variables involved in fen formation and perpetuation.  Fens and other peatlands generally develop in cold temperate climates of high humidity, mostly in the northern hemisphere (Mitsch and Gosselink 1993).  There must be an excess of water for a fen to develop.  In terms of a water budget this would be where precipitation plus surface and ground water inflow exceed evapotranspiration plus surface and ground water outflow (P + Si + Gi > ET + So + Go).  When peat is the substrate on which fens occur, peat development must exceed peat decomposition in order for peat to accumulate.

The bedrock and surficial geology of an area also affect whether a fen can develop.  Because fens are minerotrophic systems, the water entering a fen must receive its mineral input both directly from rainwater and from water flowing from the surrounding watershed.  The rock types that the water flows over and through in the watershed will affect the chemical composition of the fen water by contributing minerals through leaching (in solution) and movement of mineral-bearing particles (in suspension).  The most important constituent that rock-type contributes to a fen is calcium, which can come from three main rock types: evaporites (halite and gypsum), carbonates (calcite, siderite, and dolomite), or silicates (clays, quartz, and feldspar).  The combination of pH and calcium concentration in the water determines what type of fen will develop (Figure 6). 

In addition to climate and geology, hydrogeologic setting can affect fen development.  Because fens require the water table to be at or near the soil surface for much or all of the growing season, fens are limited in the number of settings in which they will form (Figure 7). The area towards the shoreline in figure 7 is characterized by large wetlands with gentle sloping watersheds.  Fens in this area are often fed by local, intermediate, and regional groundwater sources and are part of a highly fragmented matrix that includes agriculture, roads, and development.  The middle portion of the landscape figure has moderate to large wetlands that are typically on or near calcareous tills in New York State and are associated with agriculture.  The groundwater feeding these fens comes from local and intermediate range sources.  Fens furthest inland are in areas of higher elevation and steeper slope.  These fens are usually small and isolated, fed only by local groundwater sources, and little peat accumulates in them.

Vegetation may also vary within a fen due to minor changes in topography such as the formation of hummocks and hollows, or the variation caused by animal tracks and mounds (Crum 1988, Schwintzer 1981 as cited in Johnson and Leopold 1994, Carpenter and DeWitt 1993).In general, the distribution and abundance of fen species within a site are determined by spatial differences in pH, degree of minerotrophy, height above water table, water temperature (e.g. near springs water can be very cold compared to rest of fen), degree of shading, and colonization substrate (peat, marl, bryophyte mat).

Not only do fens exhibit spatial diversity, but fens also vary over time.  Fens developed in New York State after the last ice age ended and the glaciers covering the landscape retreated.  Fens with a peat substrate record a history of their development in the layers of the peat similar to the history provided in rock layers.  The layers of peat can be extracted in a peat core, a vertical section of peat cut out and brought to the surface for study with the layering intact.  Different layers can be examined for identifiable plant and animal remains, for both large remains (macrofossils) that can be seen with the unaided eye and smaller remains (microfossils) that must be examined under a microscope.  These remains and the sediments associated with them can also be dated using radiocarbon techniques.  This allows researchers to piece together the historical plant communities that existed as the fen developed.

The pattern seen in vegetational changes over time suggest a successional pathway where fens are only one stage in habitat development.  Shown here is a proposed autogenic successional pathway where fens develop from lakes and may develop further into bogs or forested wetlands (Figure 8). Although upland forests are often considered the endpoint of succession or climax community, only a few data consistently support this hypothesis.  Therefore, it is not included in this successional diagram.

In addition to undergoing succession, communities may revert to an earlier stage by one of several allogenic processes (Figure 9). Often, the factors causing a reversion are considered disturbance factors such as beaver flooding or fire.  Fire may in fact be a necessary component for maintaining open fens and their diversity of plants.  For example, burned portions of a fen in northeastern Illinois had the richest flora with many rare species thriving (Moran 1981), fens in Wisconsin are maintained by fire (Curtis 1959), open areas with rare species in a Maine fen were caused by locomotive engine-ignited fires (Jacobson et al. 1991), and where fire was suppressed, tree and shrub species were invading Indiana fens (Starcs 1961).

Some disturbance factors may decrease rather than increase diversity.  For example, when the water quality of a northeastern Illinois fen was altered by the addition of sodium and chlorine from a nearby private septic system and an adjacent road, the diverse fen vegetation was replaced by a monoculture of Typha angustifolia (narrow-leaved cattail) (Panno et al. 1999).  The short-term effects of beaver flooding or grazing may also decrease plant diversity, but the long-term effects are poorly understood.  Furthermore, agriculture, gravel and sand mining, or peat mining can impact fen vegetation directly by clearing or indirectly by altering water quality or water levels.  Once disturbed, fens are often threatened by invasive species such as Phragmites communis (reed grass), Lythrum salicaria (purple loosestrife), or Rhamnus frangula (alder buckthorn).

Conservation and Management Research

Because fens harbor a diverse vegetation community, often with many rare species, there is much interest in preserving these unique habitats.  The successful conservation of fen diversity depends on the ability to sort out the relative importance of local and regional factors such as climate and physiography in controlling diversity at particular sites. 

Researchers from Cornell University and the State University of New York College of Environmental Science and Forestry are developing and testing a hydrogeologic classification (HGC) system for New York State fens, examining patterns in plant species diversity and water chemistry, and testing the effect of increased nutrient levels on fen vegetation.   Local factors affecting fens can often be linked to landscape-level processes, following the principles of the Hierarchical Theory of natural systems (Allen and Starr 1982).  Knowledge of where fens can occur throughout the state and what factors affect the development and perpetuation of diverse fen vegetative communities will aid managers in effectively preserving fens within New York State. For a description of this research Click Here.

Major Research Gaps
Although peatlands in general have been frequently studied, especially in Europe, we still lack a complete understanding of these wetlands.  Specifically in New York State and much of eastern North America there are major gaps in our understanding of fens.  Researchers at the SUNY College of Environmental Science and Forestry have identified the following four specific problems that can be addressed by further research.

1.      There are few published data on the number and size of fens within states and provinces.

2.      Few fen studies thoroughly examine vegetation and hydrogeochemistry at a number of sites within a region.

3.      Relationships between extant fen communities, successional stages, response to disturbances, and hydrogeological settings are unclear.

4.      Single site studies are difficult to put in a context of scientific trends and conservation/management implications.

Fen Vegetation
Defining fens based on the occurrence of particular plant species can be problematic.  A plant may not occur on a given site for one or more of several reasons:  (1) a site may be outside of the geographic range of that species, (2) a site may not have the appropriate environmental conditions for that species, or (3) a site may be in a species’ range and have the right environmental conditions, but no seeds of that species have reached the site yet.

Nevertheless, certain vegetation is often considered indicative of different types of fens.

Printable Glossary

For more information contact:

Dr. Donald J. Leopold 
Department of Environmental and Forest Biology
State University of New York       
College of Environmental Science and Forestry           
1 Forestry Drive
Syracuse, NY 13210
dendro@mailbox.syr.edu

www.esf.edu/faculty/efb/facpage/leopold/default.htm

Dr. Barbara L. Bedford
Department of Natural Resources
Fenrow Hall
Cornell University
Ithaca, NY 14850

Interesting Links

U.S. Fish and Wildlife Service wetland classification (www.nwi.fws.gov/classifman/contents.html)

Federal endangered and threatened species (http://endangered.fws.gov)

NYS educational information (threatened and endangered species and geology) (www.dec.state.ny.us/website/education/edinfo.html)

Wetland regulation in NYS (www.dec.state.ny.us/website/dfwmr/habitat/wetdes.htm)

Sphagnum ecology  (http://members.xoom.com/temsch/)

Orchid biology (Cyndi Boesse’s page)

Acknowledgments
Thank you to Dr. Donald Leopold for providing much of the information and most of the pictures for this web page.  Thank you also to Kevin Godwin and James Shallenberger for providing additional information, including an overview of their research efforts and preliminary results investigating New York State’s fens, and to Kevin for his toad picture.  All photographs were taken by Donald Leopold except the spadefoot picture which was taken by Kevin Godwin.

Allen TFH, Starr TB.  1982.  Hierarchy.  Chicago (IL): University of Chicago Press.

Almendinger JE, Leete JH.  1998.  Regional and local hydrogeology of calcareous fens in the Minnesota River Basin, USA.  Wetlands 18:184–202.

Bridgham SD, Pastor J, Janssens JA, Chapin C, Malterer TJ.  1996.  Multiple limiting gradients in peatlands: a call for a new paradigm.  Wetlands 16:45–65.

Brinson MM.  1993.  A hydrogeomorphic classification for wetlands.  Vicksburg (MS): U.S. Army Corps of Engineers Waterways Experiment Station.  Technical Report WRP-DE-4.  79 p + appendices.

Carpenter QJ, DeWitt CB.  1993.  The effects of ant mounds and animal trails on vegetation pattern in calcareous fens.  Transactions of the Wisconsin Academy of Sciences, Arts, and Letters.  81:23–30.

Chasen DB, Siegel DI. 1986.  Hydraulic conductivity and related properties of peat.  Soil Science 142:91-99.

Cowardin LM, Carter V, Golet FC, LaRoe ET.  1979.  Classification of wetlands and deepwater habitats of the United States.  Washington DC: U.S. Fish and Wildlife Service.  Publication nr FWS/OBS-79/31.  103 p.

Crum H.  1988.  A focus on peatlands and peat mosses.  Ann Arbor (MI): University of Michigan Press.

Curtis JT.  1959.  The vegetation of Wisconsin: an ordination of plant communities.  Madison (WI): Univ. of Wisconsin Pr.  657 p.

Golet FC, Calhoun AJK, DeRagon WR, Lowry DJ, Gold AJ.  1993 (Jun).  Ecology of red maple swamps in the glaciated northeast: a community profile.  Washington DC: U.S. Dept. of the Interior, Fish and Wildlife Service.  Biol Rep 12.

Hunsucker R, Mueller RF.  1998.  Folly Mills calcareous wetland, Augusta County, Virginia.  Available at http://www.spies.com/~gus/forests/folly.htm.  Accessed on 7/18/2000.

Jacobson GL, Jr., Almquist-Jacobson H, Winne JC.  1991.  Conservation of rare plant habitat: Insights from the recent history of vegetation and fire at Crystal Fen, northern Maine, USA.  Biological Conservation.  57:287–314.

Johnson AM, Leopold DJ.  1994.  Vascular plant species richness and rarity across a minerotrophic gradient in wetlands of St. Lawrence County, New York, USA.  Biodiversity Conservation  3:606–627.

Mitsch WJ, Gosselink JG.  1993.  Wetlands.  2^nd ed.  New York: Van Nostrand Reinhold.  722 p.

Moore PE, Bellamy DJ.  1974.  Peatlands.  New York: Springer-Verlag.  221 p.

Moran RC.  1981.  Prairie fens in northeastern Illinois: Floristic composition and disturbance.  In: Stuckey RL, Reese KJ, editors.  Proceedings of the Sixth North American Prairie Conference, Ohio State University, Columbus, OH.  Ohio Biological Survey, Biological Notes Nr 16. p 164–168.

Motzkin G.  1994.  Calcareous fens of western New England and adjacent New York State.  Rhodora 96:44–68.

Nekola JC.  1994.  The environment and vascular flora of northeastern Iowa fen communities.  Rhodora 96(886):121-169.

Ogle DW.  1989.  Barns Cahpel Swamp: an unusual arbor-vitae (Thuja occidentalis L.) site in Washington County, Virginia.  Castanea 54:200–202.

Orzell S, Kurz DR.  1987.  Floristic analysis of prairie fens in the southeastern Missouri Ozarks.  Pp 50–58 In: Clambey GK, Pemble RH (eds).  The prairie: past, present and future.  Proc. Ninth NA Prairie Conf., Tri-college Univ. Center for Environ. Stud., Fargo, ND.

Panno SV, Nuzzo VA, Cartwright K, Hensel BR, Krapac IG.  1999.  Impact of urban development on the chemical composition of ground water in a fen-wetland complex.  Wetlands 19(1):236-245.

Reschke C.  1990.  Ecological communities of New York State.  Latham (NY): New York Natural Heritage Program, N.Y.S. Dept. of Environmental Conservation.  96p.

Starcs H.  1961.  Notes on vascular plants of the Cabin Creek Raised Bog.  Proceedings of the Indiana Academy of Science.  71:302–304.

Sytsma KJ, Pippen RW.  1982.  The Hampton Creek Wetland complex in southwestern Michigan.  IV. Fen succession.  Michigan Botanist.  21:105–115.

Thompson CA, Bettis EA III. 1994.  Age and developmental history of Iowa fens.  J Iowa Acad Sci 101:73–77.

Weakley AS, Schafale MP.  1994.  Non-alluvial wetlands of the southern Blue Ridge- diversity in a threatened ecosystem.  Water Air Soil Poll 77:359–383.

Western Pennsylvania Conservancy.  1995 (31 Dec).  A study of calcareous fen communities in Pennsylvania.  Pittsburgh (PA): Western PA Conservancy, 316 4^th Ave.  Submitted to Dept. of Conservation and Natural Resources, Bureau of Forestry, Forestry Advisory Services.

Winter TC, Harvey JW, Franke OL, Alley WM.  1999.  Groundwater and surface water, a single resource.  Denver (CO): U.S. Geological Survey.  Circular 1139.  79 p.

Additional Useful Sources

General Guides:

Brown L.  1979.  Grasses: an identification guide.  Boston: Houghton Mifflin Co.  240 p.

Chadde SW.  1998.  A Great Lakes wetland flora: a complete, illustrated guide to the aquatic and wetland plants of the upper Midwest.  Calumet (MI): Pocketflora Press.  569 p.

Crum H.  1976.  Mosses of the Great Lakes forest.  Ann Arbor (MI): University Herbarium, University of Michigan.

Crum H.  1988.  A focus on peatlands and peat mosses.  Ann Arbor (MI): University of Michigan Press.

Gleason HA, Cronquist A.  1991.  Manual of vascular plants of northeast United States and adjacent Canada.  2^nd ed.  New York: New York Botanical Garden.

Johnson CW.  1985.  Bogs of the Northeast.  Hanover and London: University Press of New England.

Newcomb L.  1977.  Newcomb’s wildflower guide.  Boston (MA): Little, Brown, and Co.  490 p.

Raven PH, Evert RF, Eichhorn SE.  1999.  Biology of plants.  6^th ed.  New York: W.H. Freeman and Co.  944 p.

Tiner RW.  1998.  In search of swampland: a wetland sourcebook and field guide.  New Brunswick (NJ): Rutgers University Press.  264 p.

Young SM (ed).  2000 (July).  Rare plant status list.  Latham (NY): New York Natural Heritage Program.

Selected fen literature – New York State:

Andrus RE.  1986.  Some aspects of Sphagnum ecology.  Canadian Journal of Botany 64:416–426.

Bernard JM, FK Seischab, Gauch HG.  1983.  Gradient analysis of the vegetation of the Byron-Bergen Swamp, a rich fen in western New York.  Vegetatio 53:85–91.

Falb DL, Leopold DJ.  1993.  Population dynamics of Cypripedium candidum Muhl. ex Willd., small white ladyslipper, in a western New York fen.  Natural Areas Journal 13:76–86.

Gehris CW.  1971.  Plant community development I Bergen swamp.  Proceedings of the Rochester Academy of Science 12:98–109.

McNamara JP, Siegel DI, Glaser PH, Beck RM.  1992.  Hydrogeological controls on peatland development in the Malloryville Wetland, New York (USA).

Paratley RD, Fahey TJ.  1986.  Vegetation-environment relations in a conifer swamp in central New York.  Bulletin of the Torrey Botanical Club 113:357–371.

Podniesinski GS, Leopold DJ.  1998.  Plant community development and peat stratigraphy in forested fens in response to ground-water flow systems.  Wetlands 18:409–430.

Seischab FK 1984.  Plant community development in the Byron-Bergen Swamp: marl-bed vegetation.  Canadian Journal of Botany 62:1006–1017.

Terlecky PM Jr.  1972.  The origin of a late Pleistocene and Holocene marl deposit.  Journal of Sediment. Petrol. 44:456–465.

Walker RS.  1974.  The vascular plants and ecological factors along a transect in the Bergen-Byron Swamp.  Proceedings of the Rochester Academy of Science 12:241–270.

Selected fen literature – Other areas in eastern U.S.:

Anderson DS, Davis RB.  1997.  The vegetation and its environments in Maine peatlands.  Canadian Journal of Botany.  75:1785–1805.

Bridgham SD, Pastor J, Janssens JA, Chapin C, Malterer TJ.  1996.  Multiple limiting gradients in peatlands: a call for a new paradigm.  Wetlands 16:45–65.

Glaser PH.  1987.  The ecology of patterned boreal peatlands of northern Minnesota: a community profile.  US Fish and Wildlife Service Report 85(7.14).  98 p.

Heinselman ML.  1970.  Landscape evolution, peatland types, and the environment in the Lake Agassiz Peatlands Natural Area, Minnesota.  Ecological Monographs 40:235–261.

Komor SC.  1994.  Geochemistry and hydrogeology of a calcareous fen within the Savage Fen wetlands complex, Minnesota, USA.  Geochimica et Cosmochimica Acta 58:3353–3367.

Schwintzer CR.  1981.  Vegetation and nutrient status of northern Michigan bogs and conifer swamps with a comparison to fens.  Canadian Journal of Botany 59:842–853.

Siegel D.  1988.  Evaluating cumulative effects of disturbance on the hydrologic function of bogs, fens, and mires.  Environmental Management 12:621–626.

Winter TC.  1977.  Classification of the hydrogeologic settings of lakes in the north central United States.  Water Resources Research 13:753–767.

Zoltai SC, Vitt DH.  1995.  Canadian wetlands: environmental gradients and classification.  Vegetatio 118:131–137.