Take some time to learn about Southern Michigan’s most underrated ecosystem, the prairie fen! In this three-part series, we will go over what a prairie fen is, how to identify this community by its plant species, and what threats they face. This first post offers a reflection on these globally rare, but locally abundant, biological treasures by comparing them to their more well-known cousin, the bog. We will start the series by looking at the geological events that formed these unique wetlands using photos and stories from Michigan’s largest prairie fen. Stay tuned for two more posts all about our Township’s own prairie fen plant species and its history of being overlooked.
Peatlands: Bogs and Fens
Wetlands have received a lot of hype recently due to their capacity for preserving biodiversity and mitigating climate change. According to the International Peatland Society, the majority of our world’s freshwater wetlands are composed of peatlands. Most peatlands are classified as either fens or bogs. The saturated, anaerobic (no oxygen) soils of these special wetlands do not allow rapid decomposition of plant matter, allowing net accumulation of peat over time. As a result, peatlands are the largest terrestrial storage for carbon, according to the International Union for Conservation of Nature (IUCN).
Although both peatlands are adept at producing incredible biodiversity and carbon storage, they do not receive equal attention. I’ve noticed that even among my science-driven peers, fens are not as well-known as bogs. In undergrad, I was taught more about bogs than fens. Perhaps because bogs are more widely distributed and occur more frequently in Michigan. Or possibly because the highly acidic conditions (low pH) of bogs make them a more singular group, while the fens have several different subtypes. In college, I remember briefly learning that fen wetlands were fed by alkaline (higher pH) calcium and magnesium-rich groundwater, and bogs by rainwater.
Expanding my knowledge of the wondrous prairie fen
In Michigan, the fen group is made up of five natural communities, including prairie fen (check out coastal fen, northern fen, poor fen, and patterned fen if you’d like to learn about the other fens). Prairie fen is appropriately named since it shares many plants found in nearby tallgrass prairies. Prairie fen is found only in the Midwest, thanks to our mighty glaciers.
In Michigan, prairie fens primarily occur in the two interlobate regions of the southern Lower Peninsula. We have one interlobate region on the west side of the Lower Peninsula, and other interlobate region called the Jackson Interlobate here in the southeast region. These regions have a complex array of hills and valleys caused by the consolidation and withdrawal of glacier lobes during the Wisconsin glaciation. As noted earlier, all fens are fed by spring water. In the hilly landforms of the Jackson Interlobate, gravity pulls water down through the glacial deposits rich in calcium and magnesium. The alkaline water eventually flows down to the bases of slopes, showing up as spring-fed fens.
The calcium-rich, alkaline groundwater can be a tough environment for plants. A special set of plants that we call fen “indicator species” tolerate these harsh conditions better than general wetland plants. When we find these plants we know to look closer to see if the surrounding wetland is indeed a prairie fen. Tune into the next blog post in this series to learn more!
My First Fen Visit
No amount of diagrams and reading can prepare someone for what a natural community is like until you are standing in one. I finally had the chance to experience a Michigan fen during the Eastern Massassauga Survey our crew helped with earlier this summer. The survey took place in Michigan’s largest remaining prairie fen in Springfield Township! On the drive there, my unconscious bias predicted the habitat to look similarly isolated and alien as an acidic bog.
I could not have been more naïve. In stark contrast, the landscape was alive and coherent. As I stood unstably on sedge mounds, I could hear what sounded like the thirsty noise of draining a bath. Only in the plants parted could I see where the peculiar sounds were coming from. Calcareous spring water, cold from being locked in the dark earth, ran in rivulets beneath us as we walked. There were also areas where streams flowed on top and through the vegetation. Water and earth weaved in and out of each other; I quickly realized that fens are interlaced with the rest of our sculpted landscape.
Unlike bogs, which similarly occur in depressions caused by melted glacier ice, prairie fens are not isolated pockets of water. These fens are often part of larger wetland complexes, often occurring on the edges of lakes or along streams. Prairie fen’s plant communities often also morph into surrounding environments like oak barrens and openings, even sharing the same historical need for fire disturbance.
Leaving Springfield’s fen, I rejoiced in the never-ending surprises that come with being a student of the natural world. I had no idea a peatland could feel so energetic. I had been under the impression that all peatlands were as dead as their layers of preserved organic matter.
The next post in this series will dive deeper into the dynamic life that these fens sustain using flora and fauna snapshots from our prairie fen along the paint creek trail. In the meantime, you can check out a previous blog about the Unique Wetland Communities Along the Paint Creek Trail to get some background on the work we do there.