What Did the Driftless Look Like?
I can't be the only person that has this impossible wish that I could go back to see what the world looked like before our human population boomed and moved into nearly every nook and cranny of the Earth? In graduate school in West Virginia, I borrowed a book by P. Pendelton Kennedy, "The Blackwater Chronicle", about his travels over Backbone Mountain and into "the land of Canaan". Kennedy's words and David Hunter Strother's (Porte Crayon) illustrations brought this presettlement landscape to life. It was amazing to read and see what this landscape that I knew pretty well looked like about 150 years before I had gotten to know it. I have always wanted something similar for Wisconsin and the Driftless but have not really found it (suggestions in the comments, please!).
So what did the Driftless look like before Europeans made there way here? Well, the Driftless is a pretty big place and it depends where you are talking about. And I think that point is generally lost in the conversation. I hear a lot of people say the Driftless used to prairie or savanna and that is true for for part of the Driftless but not all of it. As you will see, yes, much of the area was savanna but there are places within the Driftless that were dominated by closed mesic forests rather than the more open savannas we typically associate with the area. Even those savannas are human influenced - fire kept the oak trees dominant and sparse.
From Shea et al. 2014.
This figure starts to tell part of the story - there are significant elevation changes over small distances. We think of elevation altering the weather and precipitation only in the Western US where the mountains are significant but that is hardly true. The Ocooch Mountains are certainly "vertically challenged" compared to the Rockies and other Western mountains but they still affect the weather. I know I have been camping and watched storms either fail to deliver as they were diverted or get "stuck" in a valley and deliver significant rainfall. The Kickapoo River and some of the watersheds to the East / Southeast are quite different from the surrounding watersheds. In the figure below, remember where LdWI (Kickapoo-Wisconsin River Ravines) is as you will start to see that portion of the Driftless stand out as rather unique. And it seems that some of the watershed divides or larger rivers - particularly for the Kickapoo River watershed - served as a fire break, preserving a maple-basswood-elm forest in much of the Kickapoo watershed and some of the smaller watersheds to the South and East (see LdWI in the map below).
From Knoot et al. 2015.
Ecoregions are based on similarities in vegetation which are mostly due to similarities in climate, geology, and soils. These abiotic similarities lead to similarities in plant communities which is the way most environments are described scientifically. At the coarsest of scales, we are in a temperate forest biome or some similar descriptor that captures that the dominant vegetation are deciduous trees and that our climate is has four seasons. Biomes are largely the result of combination of temperature and precipitation along with their seasonality. Biomes are coarse descriptors, finer resolution tells us that local factors - slope, aspect, soil type and drainage, and other factors - may be responsible for local plant communities. For example, "goat prairies" along the Wisconsin and Mississippi Rivers occur on steep South-facing slopes with thin soils and wet / sedge prairies existed in a number of places where the groundwater is close to the land surface. The subsection ecoregions in the figure above are at a scale between biomes and the finer resolution plant communities described above.
Finley's pre-settlement vegetation map.
Finley's pre-settlement vegetation is based on original land survey data where early surveyors placed a stake every half mile in a grid and described the trees and other vegetation within view. These early surveyors experienced a much different Wisconsin and Driftless Area. But at the same time, it was not a landscape free of human influence as the native peoples had been in this area for about 10,000 years.
Fire has been important in determining almost all of the plant communities and their location. Before the coming of white man, the prairies and the open woodlands burned almost every year. Thus most of the southern part of the state was covered with prairie or oak savanna, an orchard-like community with a few large bur or white oaks growing in fields of grass. Only in the more protected places did forests survive. Some of these were oak but many were sugar maple-basswood-slippery elm forests. The lowlands were occupied by river bottom forest, and sedge meadow. With settlement, the fires were stopped, and the oak savannas grew up to the dense white oak-black oak forests found today. Most of the prairies have been cultivated, and at present, with the oak savannas, are among the rarest of our plant communities.
G. Cottam and O.L. Loucks, Department of Botany, The University of Wisconsin
As we start looking at a finer resolution, some new patterns begin to emerge. First, the Driftless Area had a diversity of plant communities but for most of it (nearly 70%), savanna was the dominant vegetative structure. Savannas have moderate to low density tree canopies with well developed understory dominated by prairie grasses. True prairies - those areas without trees - were much less common. Closed forest, which most of today's Driftless Area forest would be described as, were generally quite localized. Savannas were maintained by fire and in the absence of fire (damn, you Smokey the Bear!), these savannas evolved into the closed forests we see today.
From Shea et al. 2014.
Similar to Finley, Shea et al. 2014 used 19th Century Public Land Survey System (PLSS) data to reconstruct vegetation and a finer resolution. Most evident from the figure above is the heterogeneity across the Driftless Area. Prairies made up about 5.9% of the land area. White oak (22.6%), bur oak (16.3%), and the combination of the two oak species (14.3%) were dominant over half of the Driftless Area.
From Shea et al. 2014.
Combining panel b with panel a above tells a more full story. Savannas, which Shea et al. (2014) defined as tree densities from 0.5 to 47 trees per hectare (less than 20 trees per acre), dominate the landscape. Within this savanna-dominated land, two large patches of closed forest are evident along with a smattering of smaller prairie patches. Open woodlands (47 to 99 trees per hectare) were present mostly along the edges of the closed forests and in the larger river drainages, the Mississippi River, in particular. The Kickapoo River is the largest river fully contained within the Driftless Area and the watershed sticks out as quite unique. Closed forest of sugar maple (Acer saccharum), American basswood (Tilia americana), American (Ulmus americana) and slippery (U. rubra) elm, and a few other species along with the oaks dominated the slopes of the Kickapoo and a few other Driftless watersheds.
From Shea et al. 2014.
At this scale, a number of relationships are evident. First, where you find bur oak (Quercus macrocarpa), you do not find sugar maple, elm, and basswood. Bur oak are one of the most drought and fire tolerant of trees in the Midwest and maples, elm, and basswood require significantly more soil moisture. Second, the Mississippi River valley is evident by the lack of oaks and the presence of sugar maple, elm, birch, black willow, and black and white ash species. This diversity of dominant species is likely because of tree species responses to small changes in elevation that occur over relatively short distances. A foot or even less of elevation change within floodplains can have pretty drastic effects on the suitability of that location for different riparian tree species. These riparian species are much less evident outside of the Mississippi River valley. While it is not to say that they did not commonly occur along smaller Driftless streams, I would have expected them to be common as witness trees. Witness trees were used as the first surveyors' benchmarks. These trees were often the largest trees or trees in sparsely forested areas where individual trees would be more visible over longer distances, a key character for a witness tree. A post about Driftless riparian areas will be forthcoming.
Changes to the Driftless Landscape
The Driftless is now dominated by agriculture instead of savannas - which were fairly easily converted to today's farm fields. Thankfully a few of the magnificent bur oaks - like That Tree - have been saved and provide us with a more interesting landscape. By far the most drastic change to the Driftless flora are the decline of white oak (Quercus alba) and the expansion of softwoods (boxelder, butternut, elms, and black cherry) that were once rare and "other" which is often represented by non-native species. We have more closed forests today, particularly on the hillslopes of the Driftless. Fewer steep slopes, compared to valley bottoms and plateaus, have generally been cleared of their open forests and savannas and converted to agricultural lands. Though many slopes were grazed which also contributed to the sediments that altered Driftless valleys.
From Knoot et al. 2015.
Quickly, a few trends here in addition to the decline of the white oak, the expansion of "other" and "other Eastern soft hardwoods" are an increase in cottonwoods (Populus deltoides), hickory, ash, and maple and basswood. The next two figures illustrate these changes and even show some pretty significant changes from the 1990's to the 2000's. There are likely a number of explanations around land use, historic forest clearing and regeneration, and other factors but the increase in precipitation, even over just the last few decades, is likely a significant contributor to the decline in oaks and the increases in other trees.
From Knoot et al. 2015.
Two regions - the Menominee Eroded Pre-Wisconsin Till (LaWI) and the Kickapoo-Wisconsin River Ravines (LdWI) that once stood out as unique are much less different than they once were. Menominee Eroded Pre-Wisconsin Till in the northern Driftless refers to the fact that it is "less drift-less" than much of the rest of the Driftless and was covered, in part, by glaciations that occurred prior to the Wisconsin Glaciation, our most recent glacial episode. Scientists have often written about the homogenization of fauna and flora as humans change our world and move species outside of their native ranges. We are certainly seeing this homogenization of vegetation in the Driftless Area, most likely due to a number of human impacts (forest clearing, timber harvesting, climate change, and introduced species).
It is getting to be time to wrap it up even though I feel there is so much more to write. The Driftless is more than just the vegetation but that is certainly the most logical place to begin the story of what the Driftless once looked like. How to sum up what the Driftless once looked like? Well, it does not look like it does now. Closed forests are more prevalent today and prairies and particularly savannas are much less common. Historically, it was largely a landscape dominated by savanna but mostly due the native people's use of fire and likely a drier climate. However, pockets and ribbons of mesic and floodplain forests existed as did a number of unique plant communities (i.e. aspen, pin oak, jack pine, tamarack), particularly along the margins of the Driftless. The oak and maple-basswood trees that were once most common have given way to other species. I began this by stating that the Driftless was not a homogeneous landscape but it is becoming more so today - much like the rest of our world.
Links to Other Sources of Information
Minnesota Natural Resource Atlas - Vegetation - Pre-Settlement
Belby, C.S., L.J. Spigel, and F.A. Fitzpatrick. 2019. Historic changes to floodplain systems in the Driftless Area, Pages 119-146 in Carson, E.C., J.E. Rawling III, J.M. Daniels, and J.W. Attig, editors, The Physical Geography and Geology of the Driftless Area: the career and contributions of James C. Knox. Geological Society of America Special Paper 543. The Geological Society of America. https://doi.org/10.1130/2019.2543(07).
Knoot, T.G., M.E. Shea, L.A. Schulte, J.C. Tyndall, M.D. Nelson, C.H. Perry, and B.J. Palik. 2015. Forest change in the Driftless Area of the Midwest: from a preferred to underdesirable future. Forest Ecology and Management 341: 110-120.
Shea, M.E., L.A. Schulte, and B.J. Palik. 2014. Reconstructing vegetation past: pre-Euro-American vegetation for the Midwest Driftless Area, USA. Ecological Restoration 32: 417-433.