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Wetland Plants and Plant Communities of Minnesota and Wisconsin


A hardwood swamp
A hardwood swamp dominated by black ash (Fraxinus nigra). Also present are red maple (Acer rubrum), yellow birch (Betula alleghaniensis), sensitive fern (Onoclea sensibilis) and marsh marigold (Clatha palustris). Pine County, Minnesota.

Wetlands are very much in the news today, as their many functions and values are becoming recognized. The belated interest in this neglected natural resource has led to a flurry of efforts to protect, maintain, and restore wetlands in the face of insufficient basic knowledge and educational materials. While these deficiencies are being remedied, many questions are being raised by attempts to regulate uses and to minimize abuses and further losses of this resource. Much of the confusion over the values of wetlands and how to maintain these values arises from the great diversity of systems -- hydrological and biological -- that is included in the term "wetlands."

Questions that need quick, accurate answers include: How does one recognize a wetland and know what kind of wetland it is? Where does the wetland stop and the upland begin? What particular values does this wetland have -- for the owner and for the public? Which human impacts will affect these values? How might lost values be replaced? In creating or restoring a wetland, what type and/or functions should be stressed, among those that are practical? All these questions share an important principle, that of site specificity. Since each place on Earth is unique, we need "ground truth" to make wise decisions about natural resource husbandry. Thus, the decision- maker must be knowledgeable in the field.

For a start, we certainly need a detailed field guide to wetlands. Plenty of guidebooks exist for identifying species of plants or animals in the field. However, guides to ecosystems are rare and often too technical and specialized for general use. One reason is that a guide covering a continent or part of one would span too many geographic areas and climates to cover the same species throughout. The complexity of such a guide would thereby be unmanageable.

Here, however, we have a relatively small geographic area -- two states which share just two floristic provinces: the Great Lakes or northern conifer-hardwood forest region and the prairie-hardwood forest transition region. These provinces are separated by a comparatively narrow or steep gradient of climate and vegetation the "tension zone" of John Curtis. It is true that similar hydrologic systems and geologic origins may lead to different vegetation in the two zones. For example, a pothole (glacial kettle) may have marsh in the prairie and prairie-oak regions, and swamp forest in the more humid north and east regions where tree seeds can grow on downed logs and water levels fluctuate less drastically.

Nevertheless, the variation in wetlands within Wisconsin and Minnesota is small enough to be manageable, and this guide begins with a simple and workable outline-key for recognizing the main wetland types, which number only fifteen. Vegetation is the handle by which wetland types can be most easily recognized. Of course, vegetation is by no means the only element in wetlands. However, plant life is visible to the unaided eye at all seasons; it reflects the water regime and water quality faithfully; and it influences the wetland type and function. Vegetation also reflects historical factors such as climate, fires, and use/abuse intensity by animals and man. An example of human abuse is the introduction of alien pest species such as carp and purple loosestrife.

To this end, this guide provides relevant information on vegetation and does so in the best way -- by stressing groups of plant species which together characterize each wetland type. The three advantages of using floras -- that is, groups of plant species -- as indicators of wetlands, wetland types, and wetland values are:

  1. An individual species used alone might be misidentified and confused with a similar upland plant or one belonging in a different kind of wetland.
  2. Individual species have individual limits on their distribution that do not exactly coincide with those of any other, whereas a given wetland is sure to have several, if not all, of the characteristic species present.
  3. Since one type of wetland may grade into another, so that several types may occur in a single valley or basin, the locations of groups of species will help describe the actual situation, by mapping for the eye the gradients in environmental conditions that cause the wetland and its functions to vary from place to place. (For example, a peatland may grade from fen to bog, telling you that groundwater discharges at the former end while the latter is rainfed.)

The authors -- biologists respectively for the U.S. Army Corps of Engineers, St. Paul District and the Southeastern Wisconsin Regional Planning Commission, Waukesha -- represent wide experience in real life situations of wetland identification and natural resource planning. In other words, they know what information is pertinent and what questions to address. In this still experimental area (in both ecology and law), we can trust the direction they give us to understanding the wetland resource. This work will be invaluable in enabling citizens, organizations, and agency personnel to interpret and apply regulations for land use to specific sites, and to prioritize acquisition and other protection strategies. It is the perfect companion to such publications as Paulson's Wetlands and Water Quality: A Citizen's Handbook on How to Review Section 404 Permits. We hope this work will stimulate generation of similar guides to wetlands in other regions.

James Hall Zimmerman
November 12,1986

Dr. James H. Zimmerman passed away on September 28,1992. Whether in the classroom or the field, his expertise and insight had a profound influence on many ecologists and botanists, including the authors. We would like to dedicate this edition to his memory.


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