This is the third installment in a four-part series on the Empire Prairie. See Part 1 to learn more about my methodology for mapping the 1830s boundaries of the prairie, see Part 2 to learn about the mosaic of prairie and savanna that once extended across southern Wisconsin, and see Part 4 to learn about the Ho-Chunk presence on what this ancient grassland.

In the 1830s, southern Wisconsin was dominated by a vast savanna, and within that savanna was a near-treeless expanse of prairie (now called the Empire Prairie) that stretched across 129,000 acres. Today, only 168 acres of the Empire Prairie remain , one-tenth of one percent of what once blanketed the landscape. Those surviving remnants—along with about 37 acres of savanna within the 1830s boundaries of the prairie—support an extraordinary diversity of plant and animal life. Hauser Road Prairie alone is home to at least 148 plant species (including some that are state-endangered or threatened), along with animal residents that are generally rare in southern Wisconsin: meadowlarks (Sturnella magna), dickcissels (Spiza americana), badgers (Taxidea taxus), and a number of leafhoppers that can only be found in prairie remnants.

The phrase “prairie remnant” may mean something slightly different depending on who you ask, so I’ll do my best to briefly sketch its meaning. There are three factors that affect a patch of prairie’s remnant status:

1. Cultivation history (plowed vs. unplowed)

To be a remnant, a patch of prairie must, at the very least, have never been plowed. When farmers started plowing the prairie, they focused their efforts on flat, mesic soils where crops would grow easily. Steep hills with rocky, dry soil were not worth the effort to try to farm, and were therefore saved from the plow. For this reason, many of the Empire Prairie remnants are on steep hills with dry soil, and this can lead to the false impression that the Empire Prairie was, as a rule, very dry (dry or dry-mesic). It’s true that Hugh Jamieson’s report of crossing the Empire Prairie supports the notion that water was scarce, but certainly there existed sections of the prairie that were mesic (i.e., moist but well-drained). But since those mesic areas were plowed, the remnants we have of the Empire Prairie mostly lack species adapted to mesic soils: purple milkweed (Asclepias purpurascens), Sullivant’s milkweed (Asclepias sullivantii), wild onion (Allium sp.), Michigan lily (Lilium michiganense), prairie dock (Silphium terebinthinaceum), and wild quinine (Parthenium integrifolium), to name a few. It’s possible those species never lived on the Empire Prairie, but it also seems likely that they did live here and were locally extirpated when their habitat was converted to agriculture.

2. Prior fire regimes

In the absence of fire, prairies are colonized by shrubs and trees. Some grassland seeds can persist in the soil for many years, and then germinate when the trees are cleared by fire (or mechanically). But most seeds can’t stay viable for decades, so the longer a patch of land has been overtaken by woody plants, the less likely it is to rebound naturally to prairie. In southern Wisconsin, it was common practice to burn pastures to promote tender green growth for animals to graze on. It’s difficult to say exactly how common burning was, and when precisely pasture management moved away from burning, but Hugh Jamieson presents it as common on the Empire Prairie in the 1800s,¹ and we know that pastures were burned in Dane County well into the 1900s.²

Although I don’t know the burn history of the Empire Prairie remnants, it seems likely that a number of them were managed with fire until the mid-1900s. If this is true, then when conservation efforts began in the 1970s,³ some remnants may have only experienced a few decades of fire suppression, which could explain the diversity of species in these prairie remnants. Indeed, when looking at historical aerial imagery of these remnants and surrounding areas, it is striking how little woody encroachment there was in 1937 and 1955 (more on this below), which is consistent with the idea that fire was commonly used for the first half of the 20th century.

3. Past grazing intensity

Obviously prairies can withstand some grazing; herds of bison numbering in the tens of thousands previously grazed western grasslands, and smaller herds grazed in what is now Wisconsin, and probably in the Empire Prairie (see figure 2).⁴ But that grazing was sporadic, and only a small fraction of the landscape was grazed at any given time. Consider the example of bush clover (Lespedeza sp.), which bison are known to eat. Even if bison removed all the bush clover from an area, neighboring populations could recolonize the depleted patch. This contrasts with intensive pasturing practices that farmers often use, where grazing animals are confined to a relatively small area, and graze it over and over again. In this situation, once the bush clover has been removed, there is no surrounding population to recolonize, since the pasture is surrounded by agricultural fields.

While many prairie remnants have experienced some grazing, some were heavily grazed, and this manifests today in floristic communities with relatively low diversity. When ecologists try to determine past grazing intensity, they often turn to indicator species. Compass plant (Silphium laciniatum), for instance, tolerates light grazing, but will disappear under heavy grazing pressure. So its presence in a remnant suggests a history of relatively light grazing.

With all this in mind, remember that remnants exist on a spectrum. On one end are remnants that have been burned consistently and grazed minimally since White settlement, and on the other end are remnants that have been overtaken by woody plants or grazed heavily (or both). They’re all remnants, but the more degraded remnants may have lower biodiversity. It’s worth noting that many prairie remnants are actually restored to some degree. Beyond regular burning, to help remnants rebound, land stewards mow aggressive weeds, selectively remove woody species, and introduce seeds of missing species (usually from close by).

Mapping the Remnants of the Empire Prairie

I’ve been posting a lot about the Empire Prairie, and perhaps you feel inspired to visit a remnant of this historic prairie. To the best of my ability, I have mapped out the documented remnants of the Empire Prairie.

To determine the boundaries of documented Empire Prairie remnants, I inspected 20th-century aerial imagery⁵ to determine what areas had been plowed in the previous century. Of course, it’s possible an area was plowed in the 19th century, then allowed to return to grassland in the 20th, so the methodology isn’t perfect. In some cases, like the example below from the Hauser Road Prairie, the current boundaries of the prairie include areas that were at one point plowed, but have reverted back to prairie without human intervention beyond prescribed burning. For the purposes of this cartographic exercise, I consider those areas to be prairie restorations, not remnants.

Below are some more detailed maps of the Empire Prairie’s remnants (as well as remnant savanna). Note that, for the purposes of these maps, I consider prairie with woody encroachment to be savanna, so these maps lack some nuance. I’ve also mapped out prairie restorations that I know of. Not all these areas are publicly accessible, so make sure to do your research before visiting one.

Southwestern Remnants

The oak savanna at Frederick’s Hill lies right at the edge of the 1830 prairie boundary, so if you stand on that hill and look north toward the new prairie restorations at Pheasant Branch, you can try to imagine what the savanna–prairie boundary once felt like. The area just south of the Pheasant Branch prairie restoration is currently wetland, which might be surprising, given that surveyors described that area as prairie. But keep in mind that the water level of Lake Mendota has been artificially raised nearly five feet, and that little pocket of prairie is only a half-mile upstream from the lake’s edge. My suspicion is that area was historically dry prairie, but now drains poorly with Lake Mendota’s higher water level.

Westport–Waunakee Remnants

The Westport Prairie is probably the best place to visit if you’re new to prairie remnants connoisseurship and want to dip your toes in. Unlike many of the Empire remnants, it has an extensive trail system, and the north drumlin has very dramatic topography with expansive views. Plus it is home to many rare plants. The Westport Prairie previously consisted of four disparate remnants, but over the last decade, Groundswell Conservancy has been using seeds collected from within the remnants to expand the prairie into the adjacent croplands. Today, the remnants are mostly linked together, and in the coming years they’ll expand the prairie even further.

North of Waunakee Remnants

In my opinion, the Hauser Road Prairie—owned and managed by The Prairie Enthusiasts—is the crown jewel of the Empire remnants. I’ve flattered it enough at the beginning of this post, so I won’t wax poetic any further. Waunakee is expanding northward, so there is a real risk that the farmland adjacent to the Hauser Road Prairie will eventually be converted to housing subdivisions, preventing any possibility of expanding the prairie through restoration.

Goose Pond Area

There’s only one remnant here: The University of Wisconsin’s Arlington Farm Prairie. North of that is probably the most ambitious restoration project in the former Empire Prairie, concentrated around Goose Pond (recall that Hugh Jamieson described this as the only source of water in the prairie).

Mud Lake Remnants

The Hagen Unit prairie is the largest remnant of the Empire Prairie, but I cannot vouch for its quality, since I have not yet made the trek out to see it. Note that the original plat maps were not wildly accurate, so even though the Mud Lake Unit prairie appears to be mostly outside the 1830s boundary, that could just be because of error in the map drawing process.

Finding remnants with satellite data

Using the information I have on documented prairie remnants and restorations, I trained a machine learning algorithm to identify other possible remnants of the Empire Prairie using freely-available satellite imagery and topographic data. Based on that work, I’ve identified a few additional remnants, but I won’t map them here since they’re all on private property. But if you’re a conservationist looking for landowners to reach out to, let me know! ■

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Notes

1. Describing his experience on the Empire Prairie in the mid-1800s, Jamieson writes: “Sometimes fires were set purposely, that the young fresh grass might spring up earlier than it would if the old dry grass was left to cover the ground and prevent it from thawing out as the old grass would do if not burned off. When these fires were set purposely, it was generally done by some of the few people who at that time lived along the margin of the prairie or in the timber near it, so that what few cattle they did have might find green feed as early in the spring as possible.” Quoted in James Edwin Jones, ed., A History of Columbia County, Wisconsin: A Narrative Account of Its Historical Progress, Its People, and Its Principal Interests. Vol. 1. Lewis Publishing Company, 1914, page 313. ↩︎
2. The Pleasant Valley Conservancy in Dane County reports oral histories of burning pasturelands until the mid-1900s. In their 1941 article on Dane County peatland pastures, Frolik reports regular burning of pastureland (albeit on peatland). A. L. Frolik, “Vegetation on the Peat Lands of Dane County, Wisconsin.” Ecological Monographs, no. 1, 1941. While neither report directly shows burning of the upland Empire Prairie in the 1900s, they establish that burning was a common pastureland management strategy at the time. ↩︎
3. As far as I know, the Westport Drumlin Prairie was the first Empire Prairie remnant to be conserved, with the land established as a State Scientific Area in 1979. Wisconsin Department of Natural Resources, “Supplemental List of Newly Established State Scientific Areas.” Supplemental insert (no date). In Clifford E. Germain, William E. Tans, and Robert H. Read. Wisconsin Scientific Areas 1977: Preserving Native Diversity. Technical Bulletin no. 102. Madison, WI: Wisconsin Department of Natural Resources, 1977. ↩︎
4. A. W. Schorger, “The Range of the Bison in Wisconsin,” Transactions of the Wisconsin Academy of Sciences, Arts and Letters 30 (1937): 117–30. ↩︎
5. Thanks to statewide aerial imagery programs, the entire extent of the former Empire Prairie was photographed in 1937, 1955, 1962, 1980, and 2000. ↩︎