Prairie Fen Series – Recognizing a Fen Neighbor

Welcome back to our prairie fen series! The first post took a broad look at what prairie fens are and why they exist. In this post, we will focus on key plants that act as indicator species for a prairie fen community. Using mostly pictures taken from our township’s own fens, we will also dive into the vegetation zones that characterize these unique habitats.

I have been fortunate enough to visit each prairie fen in our township parks. I am always amazed by the diversity of plants I find at each of these sites. I started this series because I had little knowledge of what a prairie fen was, and no idea that I lived among them. Unlike other wetlands, I found that prairie fens blend extremely well into the surrounding environment. Maybe this is why I and so many others were estranged from these fen communities that are my close neighbors here in southern Michigan! A fen could be right under your nose in your local natural area or even your backyard! I hope this post may guide you if you hope to get acquainted with the wondrous prairie fen.

Our prairie fens

We have three prairie fen habitats in three different parks. Each site is unique with its own plant community, land use history, and threats.

We have prairie fen habitat in three of our township parks: Draper Twin Lake Park, Paint Creek Heritage Area – Fen, and Fox Nature Preserve. The plants that have greeted me at these prairie fens ranged from recognizable prairie and wetland species to more specialized flora able to survive in difficult environments. With their unique conditions, prairie fens are biodiversity hotspots for plants, animals, and insects in Michigan.

As the book Exploring the Prairie Fen Wetlands of Michigan states, prairie fens typically support twice the plant species found in bogs. Although both fens and bogs exhibit difficult growing conditions, with pH ranges in the extremes, fens exhibit a wider diversity of vegetation types. My last post gave us an important clue to why this is: fens are fed by groundwater seeps. Not all parts of the fen get equal volumes of calcium-rich water, resulting in different growing conditions and different sets of plant species in each fen zone.

Even the topography of a fen depends on the flow and composition of groundwater. Wetlands are usually associated with depressions in the landscape. However, prairie fens can be found as domes within a wetland, on slopes, and in low-lying areas along lakes and streams. Basically, wherever calcium and magnesium-rich groundwater percolates to the surface in southern Michigan, there could be a prairie fen!

When identifying a prairie fen, do not exclude areas that form a mound or on a slope. Figure from Exploring the Prairie Fen Wetlands of Michigan

Other conditions such as peat accumulation and disturbances, both natural and human-caused, can play a role in fen vegetation types. According to Michigan Natural Features Inventory (MNFI), these zones in a fen may include wooded fen, sedge meadow, marl flat, and inundated flat. As reported by the Michigan DNR, the sedge meadow is typically the largest part of a fen, while the wooded fen is found in slightly elevated uplands around the edges. Historically, naturally-caused fires and those lit by Native Americans would burn into prairie fens and maintain a more open structure. Today, the wooded fen may occupy more of the fen and the sedge meadow less due to fire suppression throughout Michigan.

The four vegetation zones of prairie fens. Note that the prairie fens in our parks are not large enough to have all of the four vegetation zones present. All photos are from our township prairie fens except the marl flat, which was taken in Springfield Township.

Prairie fens can look different from one another depending on hydrology, topography, and fire history, so it may be tricky to determine if a wetland is a prairie fen. Luckily, we can use certain plant species as fen “indicators.” Prairie fens have high pH levels due to the calcium and magnesium carbonates in the groundwater, and some plants are only found in these calcareous conditions. Identifying these specialized “calciphile” plants would bring you to a prairie fen classification without having to identify each plant species in the community. However, the lower the habitat quality, the more difficult it is to determine if a habitat is a prairie fen remnant since cattails and other generalist wetland plants typically increase in abundance after disturbance.

The Michigan State University Extension resource on fen evaluation is helpful for all levels of habitat quality. They recommend surveying in late August and early September when many of the calciphilic species are in bloom. Some of the species listed below are calcium-loving, while others occur both in fens and a variety of other wetland types. Continue scrolling to see prairie fen indicator species found in each of the vegetation zones.

Wooded fen

Larix laricina – Tamarack

Eastern Larch, also known as tamarack, is a conifer that breaks all the rules. It is a deciduous conifer that also prefers to grow in the toughest conditions. Tamarack trees are often indicators of all types of peatlands, no matter the pH, but can grow in other wetland types too. Soon they will be turning bright yellow and will eventually lose their needles. The clusters of needles on short shoots that form firework-like sprays from the branches distinguish tamaracks from other conifers in Michigan.

Toxicodendron vernix – Poison Sumac

Similar to tamarack, poison sumac can be found in both acidic and calcareous wetland soils, mostly in southern lower Michigan. I often find that the leaflets of the compound leaves point upwards to the sky. Poison sumac has light gray bark and is less “twiggy,” or finely branched than many other trees and shrubs after it drops its leaves. The photo above (right) shows the awesome fall colors that they will change into. Poison sumac may also be found scattered throughout the sedge meadow zone. Note that species may overlap in several vegetation zones.

Sedge meadow

Parnassia glauca – Grass-of-Parnassus

Grass-of-Parnassus is not a grass, although the smooth stem does tend to blend in with the surrounding grasses. This flower also has nothing to do with Mount Parnassus in Greece. Grass-of-Parnassus is only found in calcareous conditions, making it an ideal fen indicator species.

Pycnanthemum virginianum – Virginia Mountain Mint

Not sure why the common name has mountain, however, the mint part of the name is very suitable. If you are not sure about the ID of a mint, look for the square stem and rub a few leaves between your fingers. Most mint species have that characteristic aromatic fragrance. Common mountain mint occurs in wet meadows like a prairie fen but is not specific to fens. If you look closely at the flowers they are speckled with purple.

Ohio Goldenrod and Riddell’s Goldenrod

Ohio goldenrod (Solidago ohioensis) is easy to identify by its lower, rosette leaves that get quite large, have one central vein, and are flat. The upper stem leaves do not get as big as the lower leaves. The leaves of Riddell’s goldenrod (Solidago riddellii) fold inward like a paper airplane and taper to a point at the end. They have three veins obvious near the base of the leaf blade. Both species have a flat-topped inflorescence and are calciphiles, meaning they are adapted to calcareous soils.

Marsh Bellflower and Kalm’s lobelia

Marsh Bellflower (Campanula aparinoides) on the left and Kalm’s lobelia (Lobelia kalmii) on the right are both calciphilic species that can easily be overlooked among the larger species in the sedge meadow. It is worth crouching down to see these delicate flowers.

Dasiphora fruticosa – Shrubby Cinquefoil

I see this shrub everywhere in residential landscaping. That being said, it is naturally found in alkaline soils and is an indicator of calcareous conditions. In Michigan, it is mostly found in high-quality wetlands.

Rhamnus alnifoliaAlder-leaved buckthorn

Alder-leaved buckthorn is our only native buckthorn and is generally a calciphile found in high-quality wetlands. Although they are a good indicator of prairie fens, they can be tricky as they look similar to their invasive relative; common buckthorn. I can tell the difference as the leaf tips are more pointed than common buckthorn, and the leaf veins more prominent.

Bog Birch and Sage Willow

These low-lying shrubs are great indicators as they tend to stand out and are easy to identify. Both bog birch (Betula pumila) on the left and sage willow (Salix candida) on the right prefer calcareous soils. Bog birch has small oval-shaped serrated leaves while sage willow has striking white-hoary leaves.

Inundated flat

This vegetation zone can be found on the edges of lakes or streams and is dominated by various sedges and rushes. Sedges and rushes are typical in inundated flats and are super cool, but since they are not easy to identify we won’t discuss them in detail here. The Fox Nature Preserve fen is the only prairie fen in our parks with an inundated flat.

Marl flat

Marl flats have strong groundwater seepage and are therefore highly alkaline. Due to the high pH, only species adapted to extreme conditions can survive and the flats are sparsely vegetated. Our township’s prairie fens do not contain marl flats.

Marl flat landscape was taken at Shiawassee Basin Preserve in Springfield Township.

Cypripedium candidum – White Lady’s Slipper

Marl flats contain the most radical plants from rare orchids to carnivorous species such as sundew and pitcher plants.

The most rewarding part of this season was finally being in on the secret of prairie fens. Now that you have been acquainted with some botanical residents of prairie fens, I hope these communities are no longer strangers. To protect imperiled ecosystems I believe we first need to be able to recognize them as fellow neighbors. Only by understanding its parts can we understand the needs of the community as a whole.

Stay tuned for the final post in the series! We will broaden our lens and discuss human-caused threats prairie fens are facing, and what our stewardship team is doing to help.