| Southeastern Wisconsin fens have been characterized by what is not known. They are defined by location in groundwater-fed areas, but discussion of the reasons for their occurrence in the region is based on circumstantial evidence and conjecture. To protect and properly manage these rare wetland systems, a comprehensive body of knowledge must be developed which addresses their floristic compositions and the reasons for their occurrence and distribution in southeastern Wisconsin. Potential site factors which have been hypothesized to influence fen vegetation patterns include moisture gradient, pH, conductivity, calcium values, organic matter, calcium carbonate concentrations, and calcite precipitation and fertility.; The goal of my research is to determine the nature of the floristic gradient between calcareous, prairie, and sedge fens, and to identify the potential environmental conditions that influence the floristic patterns. Vegetation sampling was done using Braun-Blanquet relevé methods at 14 selected fen sites. Floristic relationships among the sites were analyzed using a Detrended Correspondence Analysis ordination. Measurements of hydrology were made using maximum-minimum water level recording wells at each fen. The frequency of water levels within the root zone was determined and compared. Fen landscape position was analyzed with respect to slope face (aspect), slope angle, elevation, stand relief, and proximity to surface water bodies. Soil profiles were prepared for each fen site and samples were collected from the profiles for analysis. Analysis of the soil samples included organic matter, carbonate, available phosphorus, nitrate-nitrogen, and exchangeable calcium, magnesium, potassium, and sodium cation concentrations.; Floristically, calcareous and prairie fen sites had greater similarity in species composition compared to the sedge fen sites. However, environmental correlates examined were not found to be strong. Groundwater levels occurring in the fen root zones, particularly during the latter portion of the growing season and in drought years, appeared to be a physical factor correlated with differences in vegetation among fen types. Soil chemistry differences may also affect fen vegetation patterns as some nutrients appear to be highest in sedge fens and lowest in prairie fens. Landscape position did not appear to be a factor influencing the broad differences between these plant associations. |
