This past Saturday morning, I had the opportunity to visit three of northeastern Indiana's best fen preserves with Nate Simons of Blue Heron Ministries and Indiana Department of Natural Resources - Division of Nature Preserves. In this and my next two posts on this blog, I will focus on the plant communities and some of the plants and butterflies we saw during our five or so hours of botanizing these highly diverse and interesting sites.
A fen is a unique wetland type that receives much of its water via groundwater flow. Fens are often mineral-rich systems, but mineral-poor fens also exist. Another unique wetland community that occurs in northeastern Indiana is bog; bogs differ from fens in that they are located in historic glacial lakes and therefore are not connected to groundwater flow, receiving nearly all of their mineral-poor water from precipitation. In northeastern Indiana, fens are often located at the base of glacial moraines. Groundwater coming from the sandy or gravelly moraine picks up calcium and other minerals and often surfaces as a seep or spring, then begins to flow downslope through the soil towards a river or lake (as in the photograph above, taken at the point where Nasby Fen is adjacent to the Pigeon River). A hardpan layer (often marl) beneath the ground surface keeps the water close to the surface as it continues to follow the gradient. This results in a surface soil layer (often muck) that is nearly always saturated with calcium-rich water. This groundwater often surfaces at other points in the fen, known as marl flats, where the marl layer is at the surface.
Above is another photograph of Nasby Fen, the larget fen in the Pigeon River system (and maybe in the state). In this photograph, you can see the diverse structure and composition of a typical northern Indiana fen. These fens consist of a mix of species common in other plant communities that are not expected to be seen growing together. Plant species typical of tallgrass prairies, such as Big Bluestem (Andropogon gerardii), Little Bluestem (Schizachyrium scoparium), and Indian Grass (Sorghastrum nutans) are often found associating with plant species typical of sedge meadows and marshes, such as Tussock Sedge (Carex stricta), Shining Aster (Aster firmus), and Spotted Joe-Pye Weed (Eupatoriadelphus maculatus). In addition to these plants, fen indicator species that thrive in calcareous conditions make this seemingly hybrid plant community a distinct entity. Some of these species include Shrubby Cinquefoil (Dasiphora fruticosa ssp. floribunda), Grass of Parnassus (Parnassia glauca), and Sticky Tofieldia (Tofieldia glutinosa).
In the photographs above and below of Sawmill Fen, you can see more of the species richness and diversity that helps to define these nutrient rich systems. Fens and sedge meadows often can be found at the same site, and it is sometimes difficult to determine where the fen ends and where the sedge meadow begins, as many of the plant species found in fens are also found in sedge meadows. Fens in northeastern Indiana are usually graminoid-dominated systems, but in the absence of disturbance (such as fire) and with a lack of soil moisture, shrubs including dogwoods (Cornus spp.) and willows (Salix spp.) increase in abundance, leading to a decrease in grasses, sedges, rushes, and forbs.
Extensive restoration in the form of shrub removal and prescribed fire has taken place to maintain the high level of biodiversity present in these graminoid fens. This biodiversity includes more than just the plants. For example, the rare Eastern Massasauga rattlesnake (Sistrurus catenatus) is at home in fens, making use of the adjacent glacial moraine uplands later in the season.
As you can tell, the photograph above is not a fen; instead, this is one of the gravelly glacial moraines adjacent to the third preserve we visited, Lime Lake Fen. The plant community on this moraine consists of an oak-hickory woodland, with approximately 100 trees per acre. Nate told me that before restoration began in this woodland, you couldn't see five feet in front of you as a result of the dense undergrowth of the non-native shrub Autumn Olive (Elaeagnus umbellata). These shrubs and some native species including Wild Black Cherry (Prunus serotina) and Sassafras (Sassafras albidum) were removed, and native species characteristic of woodlands were seeded to restore this important but often overlooked and underappreciated habitat. Burning has also been utilized to maintain the open understory characteristic of an oak woodland. Several species from the oak woodlands present historically at this location are now reoccurring at the site, coming back either from the seed bank or from propagules that had been suppressed by the dense woody understory for many years.
The photographs above and below show Lime Lake Fen, which, as the name implies, is adjacent to one of the several lakes known as Lime Lake in northern Indiana. You can see a distinct difference in the plant communties in the two photogaphs. The photograph above was taken near the base of the glacial moraine, where groundwater is flowing through mucky soil towards Lime Lake. The photograph below, on the other hand, was taken in a marl flat on the perimeter of Lime Lake. If you click on the photograph above to expand it, you can see 18-wheelers in the distance; amazingly, this beautiful site is adjacent to the Indiana Toll Road! Unfortunately, the nutrient input from the toll road has led to an abundance of the invasive Narrow-leaved Cattail (Typha angustifolia) and Hybrid Cattail (Typha x glauca) closest to the highway.
From my commentary and these photographs, I hope that you can see why fens are amongst my favorite plant communities. My next post will take you from these landscape views into the dense vegetation, highlighting some of the colorful flowering species that we saw while botanizing these preserves.