The diversity of vascular plants in the barrens of Wisconsin’s Northwest Sands Ecological Landscape is poorly documented. Natural plant community succession and pine plantations have greatly reduced and fragmented what remains as barrens in this region. Recognizing the importance of this landscape, several management and property master plans were developed by the Wisconsin Department of Natural Resources (2015, 2016, 2017a, 2017b). In a collaborative effort, the Wisconsin Department of Natural Resources hired a Northwest Sand’s liaison in 2017 to work with national, state, county, industrial and private landowners to expand the early successional barrens. Documenting the flora of this landscape now is an important step toward creating a base line for future comparisons of vascular plant diversity and for measuring the successes of prescribed management.

The barrens of the Northwest Sands Ecological Landscape are a dynamic mosaic that shift between dry forests and woodlands to open, prairie-like communities depending on the frequency of disturbance. However, ecologically defining the barrens plant community is difficult. The historical records in the Midwest contain several instances of barrens that refer to plant communities that fall somewhere between forest and prairie (Hutchison 1994). Many terms (e.g., savanna, brush prairie, oak opening) have been used synonymously with places described as barrens (Heikens and Robertson 1994). Generally, barrens may be described as savanna-like communities dominated by grasses and low-growing shrubs and trees, with scattered larger oaks and pines (Curtis 1959, Wisconsin Department of Natural Resources 2015). Furthermore, these communities tend to be edaphic and to receive periodic disturbances, often in the form of fire (Anderson et al. 1999, Curtis 1959, Hutchison 1994).

While plant communities described as barrens have been documented throughout much of North America (Anderson et al. 1999), this study focuses on those of the Northwest Sands Ecological Landscape in northwestern Wisconsin, which covers approximately 5,066 square kilometers stretching from northwest Polk County to north-central Bayfield County (Figure 1) (Curtis 1959, Radeloff et al. 1998, Wisconsin Department of Natural Resources 2015). Most of the upland soils of this region are comprised of sand, loamy sand, and sand mixed with gravel. This combination results in quick infiltration of water into the ground and produces xeric conditions for the flora of the uplands (Wisconsin Department of Natural Resources 2015).

The barrens flora of the Northwest Sands has been influenced by several environmental and climatic conditions arising from the end of the Pleistocene approximately eleven thousand years ago. At the peak of the Wisconsin glaciation, the survey sites of this study would have been covered with glacial ice (Anderson 2006). As the climate changed and started to warm, species more adapted to the colder climate would have followed the retreating glaciers. Grasslands would have started to migrate northward as broadleaf forest species started moving into the region from the east and south. A dynamic interaction began to form as climate and fires interacted along this prairie and forest border (Anderson 2006). Interspersed between the boreal forest along the Great Lakes to the north, the broadleaf forests to the southeast, and the grasslands and savannas to the southwest were vast open areas of outwash sands, shallow glacial lakes, and tills. It is in this confluence that the Northwest Sands’ barrens developed, resulting in the diversity of species that we see today.

Prior to European settlement in the mid-1800s, the Wisconsin barrens, described as pine barrens in the Northwest Sands region by Curtis (1959), would have covered about 930,777 hectares (2.3 million acres). This plant community was concentrated in central, northeastern, and northwestern Wisconsin. Approximately 62%, or 3,141 square km, of the Northwest Sands Ecological Landscape was described as barrens communities (Wisconsin Department of Natural Resources 2015). The land also supported sedge marshes, lowland forests, and upland pine forests. These communities were often maintained by natural and intentional wildfires (Murphy 1931). Today, maybe as little as 20,000 hectares of barrens remain in a fragmented landscape on several county, state, and federally protected public lands (Radeloff et al. 1999).

The Ojibwe are believed to have moved into the area of the Northwest Sands about 400 to 600 years ago (Milwaukee Public Museum 2023; Minnesota Historical Society 2023; Peacock 2022). They likely were using fire at varying intervals to support their communities (Loope and Anderton 1998), thus helping to maintain the openness of this barrens landscape. These intentional fires served many purposes that included regenerating and stimulating the growth of blue-berries and other fruits and nuts, clearing brush for campsites and maintaining trails and portages (Anderton 1999; Miller and Davidson-Hunt 2010; Williams 1994). During the mid-1800s, European settlers began draining wetlands and logging the pines. This led to large-scale landscape alteration, fire control, and the disappearance of wildlife, including waterfowl and cranes. Many sites were over-logged, farming was unsuccessfully attempted, and abandoned lands became tax delinquent. By the 1940s, the sandy soils were depleted of resources, and nearly two thirds of the land in the region was tax delinquent. The State of Wisconsin, with help from federal financing, began purchasing some of these tax delinquent lands to restore the original uplands and wetlands as public wildlife areas. It was also during this last period that an intensive tree planting and fire suppression program was implemented throughout the landscape. This resulted in closed canopies and forests for industrial uses. By the 1950s, managers were realizing that the early stages of barrens and prairie habitat were dependent on fire at frequent intervals (5–10 years) (Radeloff et al. 2000). As a result of this missing disturbance, the prairie and open barrens were disappearing from the landscape.

The barrens of the Northwest Sands Ecological Landscape include three natural communities described by the Wisconsin Department of Natural Resources (2015). The natural communities are comprised of pine barrens, oak barrens, and sand prairies. These communities form a mosaic on the landscape that grade into one another, making firm distinctions between the community types difficult. The communities are maintained today with frequent prescribed fires by site managers (Figure 2).

The pine barrens community of Wisconsin is savanna-like and usually comprises Pinus banksiana (jack pine) and less commonly P. resinosa (red pine) at the more northern sites. Shrubby Quercus ellipsoidalis (northern pin oak), Q. macrocarpa (bur oak), Corylus americana (American hazel), Salix humilis (prairie willow), Prunus pumila (sand cherry), and P. virginiana (chokecherry) are often common. The ground layer is dominated by prairie grasses and forbs (Wisconsin Department of Natural Resources 2022a). This type of pine barrens exists primarily in the upper Midwest, especially in Wisconsin, Michigan and Minnesota. These barrens are considered rare and globally imperiled by NatureServe (2020). Wisconsin has one of the most significant opportunities (and possibly the best opportunity) in North America to preserve, restore, and manage large-scale pine barrens communities (Wisconsin Department of Natural Resources 2017). Other similar barrens communities exist in the northeastern United States, but they are composed of a different assemblage of plant species. They often lack the prairie grasses and forbs that are present in Wisconsin’s barrens plant communities.

The oak barrens community of Wisconsin is similar to the pine barrens described above. One observable difference between the two communities is seen in the dominant trees. In the oak barrens community, Quercus macrocarpa and Q. ellipsoidalis are typically dominant. However, frequent disturbance through fire, poor nutrient levels, and low moisture levels usually leaves these trees stunted, multi-stemmed, and shrubby in appearance (thus they are occasionally referred to as grub oaks). These shrubby oaks often have an extensive root system that is much older than their above ground stems (Johnson et al. 2019). In southern and central Wisconsin, Q. velutina (black oak) often replaces Q. ellipsoidalis as a dominant oak. An additional difference from the pine barrens community is the presence of a more diverse prairie flora (Wisconsin Department of Natural Resources 2022b).

Sand prairie is the third natural community found in the surveyed sites. These areas typically lack the trees and woody shrubs seen in the pine and oak barrens communities. The sand prairie is dominated by prairie grasses such as Andropogon gerardii (big bluestem), Dichanthelium spp. (panic grasses), Hesperostipa spartea (porcupine grass), Koeleria macrantha (June grass), Schizachyrium scoparium (little bluestem) and prairie forbs (Wisconsin Department of Natural Resources 2022c). This community is found in the southern sites of our study.

One of our primary goals in this study was a thorough documentation of the flora with voucher specimens that would be accessible to future researchers. Additionally, this comprehensive study allows for site comparisons across the Northwest Sands Ecological Landscape using several different metrics. These data can be used to inform future plant community restoration efforts, invasive species monitoring, rare plant species monitoring and to serve as a point of comparison for future floristic work in the region.

The barrens flora of the Northwest Sands Ecological Landscape was documented with 2,213 collections representing 71 families, 217 genera and 404 taxa. The largest family was the Asteraceae family with 81 different taxa. The Solidago (Figure 7) and Symphyotrichum genera were two of the most diverse genera documented in the family, each with ten taxa. Poaceae, Rosaceae, and Fabaceae were the next largest families, with 56, 30, and 22 taxa respectively. Crex Meadows had the highest species richness, with 264 taxa. The site with the lowest species richness was Motts Ravine with 140 species. Douglas County and Moquah Barrens also had a lower species richness with 159 and 157 species respectively. Table 1 compares the total and introduced species at each site. A complete list of species documented in this study is presented in Appendix 1.

We documented 78 new county records of 70 different taxa. Nineteen new records were collected from Polk County, 47 from Burnett County, six from Douglas County, and six from Bayfield County (Table 2).

Several species are nearly ubiquitous across all of the survey sites in the Northwest Sands. Many of these species are common or abundant throughout each site. They are often included in species lists and descriptions for the sites and barrens in the region. Table 3 lists taxa that were observed in at least seven of the eight survey sites. This list includes 12 graminoids, 56 forbs, and 22 shrubs and trees. One species on this list, Lilium philadelphicum (wood lily) (Figure 8), is rare and appears to be declining at these sites. Over the last decade, regional State Natural Area staff have seen substantial declines in many forbs, including L. philadelphicum. This is thought to be caused in part by increased deer herbivory and a greater reliance on herbicides for management (Magana, personal communication 2023).

The barren communities of the Northwest Sands Ecological Landscape represent a diverse assemblage of species. Several trends are noted in the distribution of species along the latitudinal gradient of sites from northwestern Polk County in the south to north-central Bayfield County in the north. There is a higher diversity of species in the southwestern sites in comparison to those in the northeast. The barrens of the southern sites are marked with a greater diversity of prairie species, while the barrens of the northern sites tend to have species more characteristic of northern dry forests and woodlands.

Management in the form of fire, robust scarification or tilling, and mechanical chopping, have been critical components in maintaining these sites as early successional barrens. Much of the recent expansion of barrens in the northwest sands is a direct result of two plans, the Wisconsin Sharp-tailed Grouse: A Comprehensive Management and Conservation Strategy (Fandel and Hull 2011) and the Northwest Sands Habitat Corridor Plan (Reetz et al. 2013). Fandel and Hull (2011) discuss the plight of the Tympanuchus phasianellus (Sharp-tailed Grouse) in Wisconsin. This is a species of greatest conservation need, and there was a desire to expand and protect high quality barrens habitat in the Northwest Sands. In an earlier study, Gregg (1987) found that fewer than 2000 birds existed in Wisconsin during a census survey of the early 1980s. Gregg (1987) recommended an aggressive landscape habitat management plan for barrens habitat throughout northwestern Wisconsin to prevent extirpation of the Sharp-tailed Grouse from the region. Since 1987, Sharp-tailed Grouse populations have fluctuated, and, in good years, some hunting has resumed. However, recent trends continue to challenge these birds. There was a 26% decrease in populations between 2020 and 2021 in the Northwest Sands, resulting in the cancellation of the hunting season of Sharp-tailed Grouse (Wisconsin Department of Natural Resources 2021b). Only Namekagon Barrens and the new Barnes Barrens have provided some stability and consistency for the Sharp-tailed Grouse.

The second plan, the Northwest Sands Habitat Corridor Plan (Reetz et al. 2013) recommends the creation of corridors to connect the eight sites of our study and other barren properties in the region. The potential habitat corridors, which contain fragmented forests of various growth stages, have been identified to reconnect currently managed barrens properties. These forests can be managed as rotating barrens, which would be made up of large blocks of forest that are harvested and regenerated in a systematic way. These corridors would provide critical habitat for wildlife to move between the larger managed barrens (Reetz et al. 2013). Expansion of this work continues at a rapid pace in Crex Meadows, Fish Lake, Namekagon Barrens, Barnes Barrens and a new area called Bass Lake Barrens that will link Barnes Barrens with Moquah Barrens (Bayfield County Forestry Department 2013; Wisconsin Department of Natural Resources 2015, 2016, 2017a, 2017b; USDA Forest Service 2009).

In the southern sites of our study, the importance of these communities for wildlife is only reinforced. In addition to providing habitat for numerous birds, reptiles, and mammals, the barrens are also habitat for many invertebrates. Perhaps one of the most significant is Lycaeides melissa samuelis (Karner blue butterfly). This federally endangered species is dependent on Lupinus perennis (wild lupine), which is commonly found in the southern sites (Figure 16). Maintaining the open savanna-like nature of the barrens is critical for maintaining a strong population of L. perennis and its obligate companion, the Karner blue butterfly.

In the northern sites, graminoids, oak scrub, and other woody shrubs continue to be the dominant features in the barrens. Anecdotally, these recent observations in tandem with over 20 years of visiting these sites, suggests a decline in some flowering forbs, such as Asclepias tuberosa, Rudbeckia hirta, Lilium philadelphicum, Liatris aspera, Monarda fistulosa and Monarda punctata. Future vegetative studies and observations could provide quantitative results of the changing landscape. If our suspicions are correct, these future studies would show that the barrens is experiencing a greater biotic homogenization while diminishing habitat values for insects, pollinators, birds and wildlife, as has been shown in other forest and non-forested ecosystems in Wisconsin. Future work could examine some further causes of habitat challenges in the barrens that may include deer herbivory, habitat fragmentation, management practices or lack thereof, a warming climate, anthropogenic disturbance, and mismatches in the synchronous relationship between flowering plants and pollinators.

Deer herbivory poses a serious threat to the proper functioning of these barrens ecosystems of the Northwest Sands Ecological Landscape. One of the first Wisconsin studies on the impact of deer was conducted by Alverson et. al. (1988). This study illustrated the negative impact of elevated Odocoileus virginianus (white-tailed deer) populations on the vegetation of northern Wisconsin. Over the ensuing 30 plus years the deer problem has intensified. Rooney (2009) describes the simplification and biotic homogenization of northern natural landscapes due to high deer densities browsing on forbs and woody vegetation in forested landscapes, which in turn favor graminoid species.

The increase in deer pressure on the vegetation coupled with decades-long changes in disturbance patterns (primarily fire suppression) may be related to an increase in the presence of Carex pensylvanica in the barrens. This species is normally considered a species of dry forests, but now is seen to be abundant in many areas of the barrens. In a floristic study conducted by Thomson (1945) in the barrens of the Brule River watershed, more than 127 species were documented, although Carex pensylvanica was not noted. Additionally, the work of Curtis (1959) lacks the inclusion of C. pensylvanica as a dominant, co-dominant, or associate species on his lists for pine barrens communities. In examining the northern sites of this study, we observed areas where monoculture stands of C. pensylvanica had formed. These dense pockets provide little opportunity for the establishment of other barrens species (Abrams et al. 1985). Long-term, this condition could further the degradation of sites, thereby reducing the diversity of plant species.

Our documentation of the flora of the region will provide data that adds to the vast body of knowledge of the region. The floristic quality assessments can serve as a baseline in strategic management plans (Magurran et al. 2010). They can be used to re-evaluate the flora at regular intervals in the future (e.g., once every 5 to 10 years). Lower values may indicate some changes in the environmental conditions on the sites that could influence future management decisions to maintain or increase floristic quality. Surveying after the implementation of management strategies would be highly beneficial to document the resurgence and expansion of barrens species that may be dormant or in the seed bank. Additionally, these surveys should target rare species listed by the state. It will be beneficial to document their responses to management and incorporate this information into conservation efforts in the future.

The expansion of the barrens on the landscape will allow plant populations to expand their narrow ranges of present day. It appears that there is a suite of plants (e.g., Allium stellatum, Asclepias ovalifolia, and others) that may lay dormant in the shaded forest of the region that will be expressed once trees are harvested. As continued restoration activities proceed throughout the Northwest Sands Ecological Landscape, future floristic studies will continue to expand our understandings of these ecosystems.