Midwestern and Appalachian Acidic Peatland

These Sphagnum and shrub peatlands occur in basins south of the Laurentian-Acadian region down to near the glacial boundary in the northeastern and north-central U.S. Unlike the true raised bogs of boreal regions, the vegetation is not raised above the groundwater level. They are found in colder regions, mostly in areas where glacial stagnation left coarse deposits and glacial depressions (many are "kettleholes"). The basins are generally closed, i.e., without inlets or outlets of surface water, and typically small in area. The nutrient-poor substrate and the reduced throughflow of water create oligotrophic conditions fostering the development of Sphagnum peat and the growth of peatland vegetation. In deeper basins, the vascular vegetation grows on a Sphagnum mat over water, with no mineral soil development. Ericaceous shrubs and dwarf-shrubs (e.g., Chamaedaphne calyculata) dominate, with patches of graminoid dominance. Some peatlands may have a sparse tree layer. Although these are often called bogs, in most cases they are technically fens (albeit nutrient-poor ones), as the vegetation remains in contact with the surface water.

Trees include Acer rubrum, Picea mariana, and Pinus rigida. Shrubs may include Alnus incana, Chamaedaphne calyculata, Decodon verticillatus, Gaylussacia baccata, Gaylussacia dumosa, Ilex verticillata, Larix laricina, Myrica gale, Aronia melanocarpa (= Photinia melanocarpa), Spiraea tomentosa, Vaccinium corymbosum, Vaccinium macrocarpon, Vaccinium myrtilloides, Vaccinium oxycoccos, and Viburnum nudum. Forbs and graminoids may include Calla palustris, Carex lasiocarpa, Carex oligosperma, Carex pauciflora, Carex utriculata, Dulichium arundinaceum, Eriophorum vaginatum, Eriophorum virginicum, Lysimachia terrestris, Osmunda regalis, Triadenum virginicum, Utricularia sp., and Woodwardia virginica.

These peatlands occur in kettle depressions on pitted outwash and moraines and in flat areas and shallow depressions on glacial outwash and glacial lakeplain. Groundwater and surface water feed these temperate peatlands. It is not strongly calcareous and may be acidic in some places but not as much as boreal sites. These peatlands occurred in landscapes dominated by either forest or grassland/savanna. The fire regime is not well known but periodic surface fires likely helped limit the cover by trees. The basins in which these occur tend to be small and, where open water is still present, these peatlands form where wave energy is low (Swinehart 1997). These peatlands are characterized by organic soils composed of saturated peat that contains partially decomposed sphagnum mosses and frequently fragments of sedges and wood. The peat soils are acidic, cool, and characterized by low nutrient availability and oxygen levels. The water-retaining capacity of sphagnum peat is tremendous and as a result these are saturated, anoxic systems with water tables near the surface (Kost et al. 2007).

The cool, nutrient-poor water which feeds into this system favors peat development. This water can come from surface runoff or groundwater. Basins in which these peatlands occur are small, which limits the amount of nutrients that can be brought in by surface water. Groundwater sources flow through nutrient-poor, neutral to somewhat acidic substrates. Once peat begins to develop, it tends to create conditions favorable for continued peat development by contributing to the acidic, anoxic character of the water.

Alterations in wetland hydrology and agricultural development can threaten examples of this system. These can occur due to ditching, road construction, quarrying/mining, or development of crop fields or pastures that affect groundwater or surface waterflows into sites. Both reductions and increases in groundwater or surface water input can negatively affect this system. Partial drainage of a site can lead to increased fertility as peat decomposes; this allows species typical of richer swamps or uplands to colonize (Swinehart and Starks 1994). Increased surface waterflow can flood the peatland and transform it to an inundated wetland rather than a saturated peatland and can transport sediment and higher nutrient loads. Periodic fires infrequently help keep woody plants in check, and a reduction in this frequency will result in increased growth by these species. However, fires that occur when the peat has dried out (due to prolonged drought or a reduction in water input) can burn the peat and create mineral soil wetlands. Invasive species tend to increase after perturbations to other processes that maintain peatlands but can invade without changes, as well. Particularly aggressive invasive species that may threaten the diversity and vegetative structure of this peatland system include Frangula alnus (= Rhamnus frangula), Phalaris arundinacea, Phragmites australis, Typha angustifolia, and Typha x glauca. Disturbance near this system, whether crop fields, road building, urban development, or other activities, can serve as seed sources for invasive species.

This system is found from central New England to the Great Lakes and south-central Minnesota southward, generally associated with the glacial terminus or stagnation zones, and interior from the Coastal Plain.