Two hundred years ago, high up on two large bluffs within what’s now Afton State Park, were strips of prairie that differed from Minnesota’s once vast tallgrass prairies, in that they occurred exclusively on steep, rocky, south-facing slopes along stream valleys.

These prairies and many others of its type in the region escaped being cultivated in the late 19th century, and since then have escaped development, left to be eaten up by the surrounding forests.

Local geography

Though mainly occurring in the Upper Mississippi River Valley, occurrences of bluff prairies extended north into the lower St. Croix River Valley of Washington County, particularly onto a landform known as the Cottage Grove plain. The plain was spared from glacial sediments during the late Wisconsin glaciation, instead left to be eroded by wind and water, leaving the terrain dissected and rolling.

The soil on the surface is thin and underlain by thick layers of bedrock that are exposed along stream valleys and glacial meltwater drainage channels. Bluff prairies also occurred on the adjacent river terraces.

Prior to European-American settlement in the early 1800s, bluff prairies were extensive across southern Washington County, and they had mostly escaped agriculture on a major scale until new designs in plows were introduced during the King Wheat era of the 1860s to the 1880s (City of Cottage Grove, 1986).

Today, bluff prairies are restricted to scattered slopes and bluffs too steep and rocky to plow and cultivate.

Bluff prairies are specialized ecosystems

Despite the unforgiving soil conditions and persistent sunlight throughout the year, healthy bluff prairies are lush with grasses and forbs and offer spectacular displays of blooming flowers throughout the growing season.

Pasque-flower, prairie violet, and puccoons are the first prairie plants to emerge in the spring, followed by tiny prairie blue-eyed grass and the bright orange blooms of butterfly-weed appearing in June. The late summer months are a profusion of vibrant colors, a grand finale of the season—asters, goldenrods, blazing stars, and prairie clovers, just to name a few.

Though the vegetation composition is similar to that of typical upland prairies, forbs such as downy paintbrush, ground-plum, and cylindric blazing star are characteristic of these bluff prairies and otherwise limited or absent from the region.

Bluff prairies of the region also offered ideal breeding habitat for eastern kingbirds, eastern meadowlarks, field sparrows, and American goldfinches. Larger rocks provided both shelter and basking spots for prairie skinks and garter snakes.

The Afton bluff prairies

Before Euro-American settlers suppressed the recurring fires that upland prairies of the region needed to avoid being overgrown by forests. The really dry soils and abundant prairie sod of the Afton bluff prairies would have acted as a giant tinderbox. With these much-needed fires eliminated from the equation entirely, a native species of juniper called eastern red cedar has proved to be a problem in many of Minnesota’s fire-starved prairies, the bluff prairies within Afton State Park especially.

Unlike the bluff prairies of Lost Valley Scientific Natural Area south of Afton that are well-known by botanists and maintained by DNR staff and volunteers, the largely hidden and difficult to reach bluff prairies on the St. Croix river terraces have been forgotten over time and most of them are now overgrown with red cedar. Some of these prairies lack prairie vegetation to some degree and would no longer be considered a prairie.

Plant specimens submitted to the Bell Museum herbarium records by Gerald Ownbey, late botanist and professor emeritus at the University of Minnesota, indicated that the Afton bluff prairies contained rich prairie vegetation as recently as the late 1980s. A map of Washington County’s biological communities in 1987 through 1989 indicates that the bluff prairies still contained prairie vegetation, but they had already become severely fragmented into small openings, separated by dense patches of red cedar.

I was optimistic that the prairies might still be there, and intrigued that there were prairies on such steep ground, hiding in a park that I’d been visiting since I was a kid with my grandparents. I then decided to go on an adventure late summer of 2019 to relocate the bluff prairies myself to see what has changed over time.

My experience

I’d seen bluff prairies in southeastern Minnesota in the past that contained prairie vegetation despite having abundant red cedar, so a part of me was optimistic that the prairie vegetation of the Afton bluff prairies were going to be relatively intact.

When I first arrived at the park and turned my attention to the south bluff prairies, I hadn’t studied the park’s trail map very well and ended up neglecting to use the trail that conveniently went up and over the west side of the bluff, instead going up the east slope, which was unexpectedly overgrown with buckthorn and muddy. In hindsight, I could’ve hiked the other trail and easily avoided bushwhacking, not to mention picking up dozens of ticks!

I finally arrived at the top of the bluff after what seemed like hours, and it didn’t take long to locate the openings once I was there. It also didn’t take long, however, to notice the dense treeline of red cedar that lined the south side of the bluff—where the prairie was, according to the maps I’d had pulled on my phone.

I was relieved when I spotted a large enough opening in the canopy through a wide deer trail to be a prairie. Looking straight forward, you see that you’re above Afton Alps Ski Resort. Looking straight down, you see a steep drop with chunks of lichen-covered bedrock barely peeking out of the bluff, a thin carpet of prairie sod forming the matrix in between. Exploring was treacherous, to say the least, but this is just what I wanted to see.

Next course of action was to check out the vegetation.

Except for a small, yellow-flowered plant called hoary frostweed and a smattering of prairie grasses, signs of any other native forbs were absent, and many non-native species such as mullein, black medic, Queen Anne’s lace, thistles, sweet-clovers, and crown vetch had established into the thin soil. After a half hour search, it became clear I wasn’t going to find anything, so I continued north to the north bluff.

As a trail is located directly below the north bluff’s prairie openings, getting to them was much easier. Unfortunately, these prairies appeared to be in worse condition. Between each of the three or four scattered openings, red cedar had joined forces with buckthorn, forming nearly impenetrable forests with an understory largely devoid of growth besides new buckthorn. More bushwhacking ensued to reach these openings. These prairie openings were much more open and from a distance appeared to be undisturbed, until making the realization that the vegetation was similar to the south bluff prairie—native grasses and invasive plants predominant, native forbs absent.

What caused these disturbances in the prairies is currently unclear, to me at least, though a likely explanation is grazing. Perhaps cattle that were allowed to roam freely on pastures above the bluff prairies strayed down the slopes to graze on the prairie vegetation. The cattle would have trampled and disturbed the soil in the process, making it easier for red cedar and other invasive plants to establish and spread.

Restoration

Overall, I believe that the bluff prairies of Afton State Park have good restoration potential. Invasive plants and woody vegetation should be dealt with and native biodiversity should be reintroduced over time. This could include spreading prairie grass seeds already present on the prairies and re-introducing historical species such as ground plum, cylindric blazing star, purple prairie clover, sky-blue aster, and prairie dropseed. To help ensure future restoration, interpretive signs could be added to explain the sensitive restoration project, as well as its history.

I think that having the bluff prairies (yellow) restored would not only benefit the ecosystem and provide breeding habitat for a number of birds, mammals, and reptiles, but (with great caution and respect for the prairies) would also benefit students, photographers, or just nature lovers in general, because they would learn about restoration efforts and have just a few more native prairies to see and enjoy.

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Jaxon Lane is a college student, photographer, and lifelong nature enthusiast currently living in White Bear Lake, Minnesota. He is most interested in ecology, botany, and herpetology, and spends his free time in nature hiking and photographing wildlife and plant life. When not studying or out in nature, he also plays music and makes nature art.

References

Almendinger, J. C., Minnesota Biological Survey. (1990). Natural Communities and Rare Species of Washington County 1987-1989. Minnesota Biological Survey.

Minnesota Department of Natural Resources. (1979). A Management Plan for Afton State Park. Retrieved from the Minnesota Legislative Reference Library. https://www.leg.state.mn.us/docs/pre2003/other/811348.pdf.

Wovcha, D. S., Delaney, B. C., & Nordquist, G. E. (1995). Minnesota’s St. Croix River Valley and Anoka Sandplain: A Guide to Native Habitats. University of Minnesota Press.

Hobbs, H. C. & Goebel, J. E. (1982). S-01 Geologic map of Minnesota, Quaternary geology. Minnesota Geological Survey. Retrieved from the University of Minnesota Digital Conservancy, http://hdl.handle.net/11299/60085.