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Wetland Plants and Plant Communities of Minnesota and Wisconsin

Introduction


PURPOSE

The primary purpose of this guide is to assist U.S. Army Corps of Engineers (Corps) personnel working with the regulatory program under Section 404 of the Clean Water Act and Section 10 of the Rivers and Harbors Act of 1899. It provides an easy-to-use, pictorial guide to wetlands primarily for individuals who are not botanists, although botanists may also find it useful. A secondary purpose is to provide a guide for individuals working with other agencies and programs dealing with wetlands. Finally, this guide serves to enhance public awareness of wetlands by illustrating their diversity and values.

APPLICABILITY

The guide specifically addresses wetland plants and plant communities of Minnesota and Wisconsin (Figures 1 and 2), but is applicable in general to wetlands of the entire Great Lakes Region. Note that the 144 plant species included in the guide do not represent, nor are they intended to represent, a listing of all plant species found in wetlands of Minnesota and Wisconsin. For a complete listing of these species, refer to the botanical references listed in the bibliography.

ORGANIZATION

This guide is organized by wetland plant community. In general, the wetland plant communities are organized according to water permanence and depth, and degree of soil saturation. Thus, the guide progresses from deepwater wetlands (I. Shallow, Open Water Communities) to temporary water-holding wetlands (VIII. Seasonally Flooded Basins). Photographs and descriptions are provided for each of the fifteen wetland plant communities, along with representative plant species of each. A particular plant species may occur not only in the wetland plant community under which it is listed, but in other wetland communities, and in some cases, upland communities. The other communities in which an individual plant species may frequently occur are provided under ECOLOGICAL NOTES. Note that upland plants occasionally occur in wetlands and, conversely, wetland plants occasionally occur in upland habitats. This is especially true in transitional areas between wetlands and uplands.

WETLAND DEFINITION

The definition of wetlands used by the Corps in its regulatory program is:
Wetlands are those areas inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs, and similar areas (33 CFR 328).
Refer to the Corps of Engineers Wetlands Delineation Manual (Environmental Laboratory 1987), or current federal manual, for a Methodology to apply this definition in the field.

CONCEPT OF A HYDROPHYTE

Wetland plants are hydrophytes (hydro = water, phyte = plant). These are plants growing in water or on a substrate that at least periodically is deficient in oxygen due to excessive water content. Hydrophytes have morphological, physiological and reproductive adaptations that allow them to thrive in inundated or saturated soils where non-hydrophytes (upland plants) cannot. Communities dominated by hydrophytes are referred to as hydrophytic plant communities.

CLASSIFICATION OF WETLANDS

A number of wetland classification schemes have been developed. Table 1 compares the fifteen plant communities of this guide to classification systems developed by Shaw and Fredine (1971), Cowardin et al. (1979), Curtis (1971), and the Wisconsin Wetland Inventory. As shown in Table 1, the fifteen plant communities of this guide correspond most closely to the wetland plant communities described by Curtis (1971) in The Vegetation of Wisconsin.

VEGETATION TENSION ZONE

Throughout the guide are references to a vegetation tension zone. The flora of Minnesota and Wisconsin is arranged in two major floristic provinces. A floristic province is a large area with a relatively uniform flora, delineated by a tension zone in which many species reach a common range boundary (Curtis 1971).

The vegetation tension zone then is a band between two floristic provinces marked by the intermingling of species from both (Curtis 1971). The two floristic provinces in Minnesota and Wisconsin are the "northern forest floristic province" and the "prairie- forest floristic province," which are illustrated by Figure 3. The vegetation tension zone through Wisconsin is shown according to Curtis (1971). A tentative vegetation tension zone through Minnesota is extrapolated from the original vegetation map of Minnesota compiled by Marschner (1930).

PRAIRIE POTHOLES

A portion of the "prairie-forest floristic province" in southern and western Minnesota deserves special mention. It is part of the Prairie Pothole Region (Figure 4). Prairie potholes are shallow, water-holding depressions of glacial origin found in the prairies of north-central United States and south-central Canada (Sloan 1972). These wetlands have great variability in size, depth, water permanence, and water chemistry (Sloan 1972, Stewart and Kantrud 1972). For example, prairie potholes can range in size from less than one quarter acre to several thousand acres. In terms of water permanence and depth, prairie potholes range from seasonally flooded basins that hold water for only a few weeks each year, to wet prairies, to shallow and deep marshes, to permanent open water. Water chemistry can be fresh, mixosaline, saline, or hypersaline. Multiple year wet and drought cycles are typical in the Prairie Pothole Region.

The two floristic provinces in MN and WI
Figure 3 (The Wisconsin portion of this figure is adapted from an illustration copyrighted by the University of Wisconsin Press. It is used here by permission.)


Generalized original limits of the PPR
Figure 4 - Generalized Original Limits of the Prairie Pothole Region of the U.S. and Prairie Provinces of Canada (adapted from Sanders 1982).

Prairie potholes are extremely important for North American waterfowl production. Although prairie potholes comprise only 10 percent of potential waterfowl breeding habitat in North America, it is estimated that 50 percent of waterfowl production occurs in these wetlands, with an even higher percentage occurring in wet years (Sloan 1972). Agricultural practices continue to degrade or destroy these important wetlands. However, there are federal, state and private programs and participants working to restore prairie potholes and the important functions and values they provide.

A deep marsh prairie pothole
The above photograph shows a deep marsh prairie pothole dominated by river bulrush (Scirpus fluviatilis) and hardstem bulrush (Scirpus acutus). It is part of the Victory Wildlife Management Area in Big Stone County, Minnesota.

PATTERNED PEATLANDS

North of the vegetation tension zone is another group of wetlands deserving special mention. These are the patterned peatlands of northern Minnesota. A notable example is the Red Lake Peatland, which covers nearly 500 square miles, making it one of the largest continuous tracts of peatlands in the conterminous United States (Glaser et al. 1981). "Patterned" refers to the distinct and frequently striking landforms that compose these peatlands. Flarks, strings, ovoid islands, teardrop islands, raised bogs and fens are examples of names applied to these patterned landforms. Some of the plant associations of the patterned peatlands correspond to the communities described herein. However, other associations of patterned peatlands are not specifically described. Discussion of these specialized plant associations goes beyond the scope of this generalized guide. For a detailed description of the patterned peatland communities, publications such as Glaser et al. (1981) and Wright et al. (1992) should be consulted.

Below is a color infrared aerial photograph showing a portion of the Red Lake Peatlands in Beltrami County, Minnesota. Visible peat landforms and vegetation patterns include the following (numbers correspond to those on the photograph):

  1. Water tract where runoff is channeled across the peat surface; includes strings (peat ridges) and flarks (pools) arranged perpendicular to the direction of water flow. Dominant vegetation includes sedges (Carex).
  2. Streamlined tree islands (mostly tamarack with some black spruce) tapered in the direction of water movement.
  3. A smaller internal water tract.
  4. Sphagnum lawn.
  5. Ovoid island with a horseshoe-shaped black spruce forest and a non-forested interior.
  6. Straight lines are drainage ditches, the result of a failed attempt to drain the peatlands during 1905-1929.

Interpretation of aerial photography is from Wright et al. (1992).

The area shown by the photograph covers approximately 16 square miles.

Red Lake Peatlands
Red Lake Peatlands

FARMED WETLANDS

Millions of acres of wetlands in Minnesota and Wisconsin have been effectively drained and converted to non-wetland during the past 150 years, primarily for purposes of agricultural use. Millions of additional acres of existing wetlands are: (1) partially drained and cropped; or, (2) cropped under natural conditions (e.g., during dry periods). Partially drained refers to cases where wetland hydrology has been altered by such measures as ditching and/or tiling, but the area still retains sufficient hydrology to meet wetland criteria [e.g., see the Corps of Engineers Wetlands Delineation Manual (Environmental Laboratory 1987)]. An example is a deep marsh plant community that is ditched and converted to a fresh (wet) meadow community.

A shallow marsh prairie pothole, plowed and planted to corn

The example of a farmed wetland shown by the photograph is a shallow marsh prairie pothole basin that had been plowed and planted to corn, an upland species, at the start of the growing season. By midsummer, ponding and saturated soil conditions had resulted in drown out and crop stress (yellowed, stunted corn). The dark green vegetation in the basin is softstem bulrush (Scirpus validus), an obligate wetland plant, which is recolonizing the basin in spite of plowing earlier in the growing season.

NATIONAL WETLAND PLANT LIST

As part of the National Wetland Inventory undertaken by the U.S. Fish and Wildlife Service (Service), a wetland plant list has been developed by the Service in cooperation with a federal interagency review panel (Reed 1988, 1996). This list ranks individual plant species according to their probability of occurrence in wetlands as shown below.

Indicator Categories:

A positive (+) and negative (-) sign is used for the facultative categories. The (+) sign indicates a frequency towards the wetter end of the category (more frequently found in wetlands) and the (-) sign indicates a frequency towards the drier end of the category (less frequently found in wetlands).

A wetland indicator status that is in brackets [ ] reflects the opinion of the authors as to the probability of occurrence in wetlands of that particular species.

At the time this field guide went to press, the 1996 National List of Plant Species That Occur In Wetlands (Reed 1996) was in draft form for public review and comment. Since it was unknown what proposed changes would be adopted by the final version, the authors of this field guide primarily used the indicator status given by Reed (1988).

FACU DOMINATED WETLANDS

FACU species occur in wetlands 1 to 33 percent of the time and, in some cases, can be dominant species in wetlands. Examples include white pine (Pinus strobus) or jack pine (Pinus banksiana) swamps. The photograph shows a swamp dominated by white pine in Monroe County, Wisconsin. Soils are Dawson peat, a very poorly- drained organic soil. Hydrology is primarily groundwater seepages. No hydrologic modifications (e.g., ditching, tiling) have occurred at this site. Other plant species present are OBL or FACW species such as speckled alder (Alnus incana ssp. rugosa), skunk cabbage (Symplocarpus foetidus) and cinnamon fern (0smunda cinnamomea). Mature white pines have formed raised hummocks caused by shallow rooting, apparently a response to saturated soil conditions.

A swamp dominated by white pine

Another case where FACU species may dominate are seasonally flooded basins that are ponded early in the growing season, but are dry for much of the remainder of the growing season. See discussion of seasonally flooded basins. In addition, FACU species may dominate wetland basins during periods of drought, such as the multiple year drought cycles experienced in the Prairie Pothole Region.

NOMENCLATURE

Nomenclature follows Gleason and Cronquist (1991). However, a few exceptions were made in response to recent changes of nomenclature for certain species (e.g., Kartesz 1994). Common names were selected at the discretion of the authors.

MEASUREMENTS

Occasionally, the following format is used for listing measurements of a given character: (2)3-5(6) mm. This means the character is typically 3 to 5 mm. in size, but can range from a minimum of 2 mm. to a maximum of 6 mm.

ABBREVIATIONS

The following abbreviations are used in the text.

PHOTOGRAPHY CREDITS

Photographs are by Steve D. Eggers except for the following:

Donald M. Reed - Lake sedge closeup; swamp aster growth form.
Welby R. Smith - Western prairie fringed orchid.
Minnesota Department of Natural Resources - Aerial photography of the Red Lake Peatlands.


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