Natural Resources
Conservation Service
Ecological site F091XY001WI
Poor Fen
Last updated: 9/27/2023
Accessed: 05/03/2024
General information
Provisional. A provisional ecological site description has undergone quality control and quality assurance review. It contains a working state and transition model and enough information to identify the ecological site.
MLRA notes
Major Land Resource Area (MLRA): 091X–Wisconsin and Minnesota Sandy Outwash
The Wisconsin and Minnesota Sandy Outwash MLRA is the most extensive glacial outwash system in the northern half of Wisconsin. The total land area of the Wisconsin portion is just under 1.4 million acres (2,170 sq miles). The northern half is a former spillway for Glacial Lake Duluth. The flowing meltwater from the draining lake has left behind thick deposits of drift and carved a terraced river valley now occupied by the St. Croix and Bois Brule Rivers.
The northeastern section – the Bayfield hills – is a collapsed outwash plain where drift deposits are thick. Lacustrine materials from Glacial Lake Duluth line the northeastern tip. Moving southwest, the landscape transitions into a large pitted outwash plain. This is an area of extensive kettle holes, and, where the underlying till is less permeable, kettle lakes with some interspersed morainic hills and ridges. The glacial drift deposits are thinner in the southwestern section, although there is still no documented surface bedrock within this MLRA.
The St. Croix and Bois Brule rivers share a channel that lines much of the northwestern border of this MLRA. In some places along the channel, the underlying reddish-brown sandy loam till of the Copper Falls Formation is exposed along cut banks, though most of it is covered by a mantle of outwash. Glacial lakes deposited pockets of fine-textured lacustrine materials, most of which were washed away or buried by glacial outwash and meltwater flowing through the channel. East of the channel, some of the silty and clayey lakebed deposits are found near the surface, where they impede drainage and contribute to the formation of extensive wetlands.
Historically, the area supported jack pine (Pinus banksiana), scrub, and oak forests and barrens. The northern portion also supported stands of red pine (Pinus resinosa) and eastern white pine (Pinus strobus) as well. Marsh and sedge meadow, wet prairies, and lowland shrubs dominated the extensive wetland complexes in the southern tip of this MLRA (Finley, R., 1976).
Classification relationships
Relationship to Established Framework and Classification Systems:
Biophysical Settings (Landfire, 2014): This ES is largely mapped as Boreal Acidic Peatland Forest, Boreal Acidic Peatland Shrubland, Laurentian-Acadian Herbaceous Wetlands, Boreal White Spruce-Fir Forest, Boreal White Spruce-Fir Forest, and Laurentian-Acadian Northern Hardwoods Forest
Wetland Forest Habitat Type Classification System for Northern Wisconsin (Kotar and Burger, 2017): The sites of this ES keyed out to two habitat types: Picea mariana-Larix/Ledum (PmLLe); Picea mariana-Larix/Nemopanthus (PmLNe)
WDNR Natural Communities (WDNR, 2015): This ES is most similar to the Black Spruce Swamp, Northern Wet Forest, and Northern Tamarack Swamp communities
Hierarchical Framework Relationships:
Major Land Resource Area (MLRA): Wisconsin and Minnesota Sandy Outwash (91X)
USFS Subregions: Bayfield Sand Plains (212Ka)
Small sections occur in the Mille Lacs Uplands (212Kb) subregion
Wisconsin DNR Ecological Landscapes: Northwest Sands
Ecological site concept
The Poor Fen ecological site is scattered throughout MLRA 91X in depressions on lake plains and outwash plains. These sites are characterized by very deep, very poorly drained soils that formed in thick, highly decomposed organic deposits of herbaceous origin. Sites are subject to occasional ponding in the spring and fall and remain saturated throughout the growing season. These soils meet hydric requirements. Precipitation and runoff from adjacent uplands are the primary sources of water, though these sites may also receive limited groundwater discharge and stream inflow. Soils are extremely acidic.
Plant communities consist of typical Bog and Fen species. Sphagnum moss has almost continuous cover and other bog species, particularly those of Heath (Ericacea) family have high frequency of occurrence. Most common are leatherleaf (Chamaedaphne calyculata), Labrador tea (Ledum groenlandicum) and bog lauerel (Kalmia polifolia). The site can be treeless, sparsely wooded, or a forest. The only well-adapted and enduring tree species are tamarack (Larix laricina) and black spruce (Picea mariana). Other species that often occur, but show poor vigor due to nutrient deficiency and typically do not reach maturity, are paper birch (Betula papyriphera), white pine (P. strobus) and jack pine (P. banksiana).
Poor Fen sites are extremely acidic, much more so than their Mucky Swamp ecological site counterpart. The acidity is a result of limited interaction with groundwater that may be enriched with dissolved carbonates. In addition, the groundwater discharging into Poor Fen sites is likely passing through surrounding parent materials that are acidic (i.e. outwash sands). The extreme low pH limited vegetative growth.
Associated sites
| F091XY005WI |
Wet Sandy and Loamy Lowland These sites occur on depressions and drainageways on outwash plains and lake plains. They primarily form in sandy outwash are subject to some ponding and flooding. Soils are very deep and poorly or very poorly drained. They are saturated for much of the year. They may be adjacent to Poor Fen. They occur higher on the drainage sequence and are slightly drier. |
|---|---|
| F091XY007WI |
Moist Sandy and Loamy Lowland These soils formed in sandy outwash, sandy lacustrine deposits, sandy eolian deposits, or loess that is sometimes underlain by sandy or loamy till. Soils are very deep and somewhat poorly drained. They occur higher on the drainage sequence and are drier than Poor Fen. |
| F091XY011WI |
Sandy Upland These soils formed primarily in sandy outwash or sandy eolian deposits, but some sites formed in sandy lacustrine or loamy alluvium underlain by sandy outwash. Soils are very deep and are moderately well to somewhat excessively drained. They are neutral to extremely acid and lack a spodic horizon. They occur higher on the drainage sequence and are much drier than Poor Fen. |
| F091XY012WI |
Loamy Upland These soils formed in loamy lacustrine, loamy alluvium, loamy till, sandy outwash, sandy eolian, or loess deposits. Some sites have underlying lacustrine deposits, till, or basalt bedrock. They are moderately well or well drained. They occur higher on the drainage sequence and are much drier than Poor Fen. |
| F091XY015WI |
Dry Upland These sites formed in sandy outwash or eolian deposits. Soils are very deep, excessively drained, and lack a spodic horizon. They occur higher on the drainage sequence and are much drier than Poor Fen. |
Similar sites
| F091XY002WI |
Mucky Swamp Like Acidic Poor Fen, Organic Lowlands consist of deep herbaceous organic materials. These sites are also wetlands. They occur on drainageways, depressions, and floodplains and are very poorly drained. Some sites have mineral soil contact. They receive more groundwater than Acidic Organic Lowlands and are therefore more alkaline and have better growing conditions that Poor Fen. |
|---|---|
| F091XY003WI |
Floodplain These sites occur in depressions and flats on floodplains. They form in sandy to silty alluvium and are somewhat poorly to very poorly drained. They are subject to flooding. They are more alkaline and have better growing conditions that Poor Fen. Not all these sites are wetlands. |
Table 1. Dominant plant species
| Tree |
(1) Picea mariana |
|---|---|
| Shrub |
(1) Ledum groenlandicum |
| Herbaceous |
(1) Sphagnum |
Click on box and path labels to scroll to the respective text.
Ecosystem states
State 1 submodel, plant communities
| 1.1A | - | Mortality of canopy species from blow-downs, ice storms, or an increase in ponding frequency and duration from lack of transpiration. |
|---|---|---|
| 1.1B | - | Ponding frequency and duration increases dramatically. |
| 1.2B | - | Decrease in ponding frequency and duration. Sphagnum moss continues to grow and build up thicker layers, causing surface to be isolated from groundwater. |
| 1.2A | - | Ponding frequency and duration increases. |
| 1.3A | - | Decrease in ponding frequency and duration. Sphagnum moss continues to grow and build up thick layers, beginning to isolate surface from groundwater. |