Anthropogenic Habitats

Anthropogenic habitats or surrogate communities are habitats that may be similar to and at least partially mimic the structure and function of natural habitats. Today's anthropogenic habitats may be inhabited by an assemblage of species that historically used structurally similar natural communities. Some examples of anthropogenic habitats are non-native grasslands, mines and gravel pits, bridges and buildings, dredge spoil islands, and agricultural fields. What does and does not constitute an anthropogenic habitat can be an issue of considerable debate.

Many anthropogenic habitats have a distinct set of species that use them. For example, old mines are often used by bats, bridges are used by phoebes and cliff swallows, dredge spoil islands are used by terns and other colonial nesting birds, chimneys on houses are used by chimney swifts, and some tall buildings are used by peregrine falcons as nest sites. Other habitats such as agricultural fields and non-native grasslands are used by a wider variety of species as nesting and feeding areas. Some anthropogenic habitats are very important for wildlife and should be considered for protection (e.g., old mines). Others provide important habitats for many species and changes in management can have important effects on wildlife. For example, the conversion of hayfields and pastures to agricultural row crops is believed to be a contributing factor in the decline of grassland birds in the last 30 years. Some anthropogenic habitats are now important for sustaining Wisconsin's wildlife populations and should be considered when planning the management of the wildlife in the state.

The surrogate grassland community type has been fairly well defined and evaluated in Wisconsin through publications such as Managing Habitat for Grassland Birds: A Guide for Wisconsin (Sample and Mossman 1997). Some examples of surrogate grasslands are agricultural hayfields, small grains, pastures, fallow fields, and non-native grasslands. Surrogate grasslands currently represent the majority of grassland habitats in the state and are very important to the conservation of grassland Species of Greatest Conservation Need. Because of this, surrogate grasslands were specifically addressed as part of Wisconsin's Wildlife Action Plan.

Aspen-Birch

Aspen and birch-dominated forests make up a significant part of the forested landscape in northern Wisconsin. Although this type only occupied approximately 4% of northern Wisconsin circa 1800 (Schulte et al. 2002), it is now the second most common forest cover type in that region after maple. Aspen-birch is not a tracked natural community by the Natural Heritage Inventory (NHI), as it is a short-term early successional stage that under natural conditions would give way to other, more mature, forest types. However, Aspen-birch forests receive a high degree of management emphasis on both public and private lands due to their significance to the forest products industry and importance to several wildlife species and are described here to present a more complete picture of forest types in Wisconsin, as well as to illustrate how managers can increase habitat suitability for a greater variety of species within Aspen-birch forests if desired.

Aspen and birch-dominated forests can occur on a wide variety of landforms and soil conditions from outwash sand to lacustrine clay and from dry to wet moisture regimes. Stands with 50% or more of their basal area in trembling aspen (Populus tremuloides), big-toothed aspen (Populus grandidentata), or paper birch (Betula papyrifera) are included here; for stands with a smaller component of aspen and birch, see the relevant NHI community type. Aspen is a "pioneer" tree species generally growing in even-aged stands regenerated following a major disturbance such as catastrophic fire, blow down, clearcut, or coppice harvest. Aspen often outgrows other associated species and can form nearly pure stands. In undisturbed or unmanaged stands, more tolerant associates replace aspen over time through natural succession.

Other tree species associated with aspen and birch are variable and depend greatly on the soil type and moisture regime, but may include red maple (Acer rubrum), balsam fir (Abies balsamea), red oak (Quercus rubra), eastern white pine (Pinus strobus), and on mesic sites, sugar maple (Acer saccharum). Most other major tree species occurring in Wisconsin can also be found as occasional associates in aspen stand. Shrubs are also variable depending on the age of the stand and moisture regime but are typically absent to sparse when stands are young, dog-hair thickets, gradually increasing in density over time. Exceptions to this trend are clonal species that persist under moderate shade and resprout aggressively when cut, such as hazelnut. The ground layer is also extremely variable, depending greatly on soil type, moisture regime, and past disturbance.

Several bird SGCN (e.g. Golden-winged Warbler) utilize young stands of aspen at various life history stages. Another SGCN utilizes conifers embedded within aspen stands, such as Swainson's Thrush, which requires a dense understory of spruce and fir. Maintaining or increasing the conifer component is necessary for most SGCN to utilize these forests. In addition, landscape context is critical for most SGCN that utilize aspen and birch forests for part of their life cycle.

Conifer Plantation

Conifer plantations make up a significant part of the forested landscape and receive a high degree of management emphasis. They encompass a variety of conifer species, primarily red pine and white pine (Pinus resinosa and P. strobus), but also may include jack pine (Pinus banksiana), white spruce (Picea glauca), and tamarack/larch (Larix laricina). Conifer plantations are not a natural community tracked by the Natural Heritage Inventory (NHI) but are described here to present a more complete picture of forest types in Wisconsin, as well as to illustrate how managers can increase habitat suitability for a greater variety of species within this community type if desired.

Conifer plantations generally are associated with few Species of Greatest Conservation Need (SGCN), though they are used by some species, depending on tree size, density, and landscape context. Plantations differ significantly in the composition of secondary species (other non-target trees, shrubs, and herbaceous plants) depending on site history, site preparation, and management regime, and may range from very low to moderate diversity. In general, high floristic and structural diversity is associated with higher animal diversity.

On dry sites, very young jack pine or red pine plantations may resemble pine barrens structurally. However, practices such as the use of herbicide on competing vegetation reduce floristic diversity and limit usage by SGCN otherwise associated with pine barrens. Occasionally, conifer plantations on dry sites may fail (in part or completely), producing longer-term barren-like structures with the potential to provide habitat to barren-associated species (e.g., Kirtland's Warbler).

Landscape context is important for many SGCN that use conifer plantations for at least part of their life cycle, with some preferring stands near other forest or savanna habitats (e.g., northern dry forest, pine barrens, or oak barrens). As conifer plantations mature past normal rotation age, they may develop habitat attributes similar to late-seral northern dry-mesic forests or northern dry forests and support SGCN more typically found in those forest types. Examples include nest trees for Northern Goshawk or winter habitat for Spruce Grouse. Management of conifer plantations is a potential source of impact on SGCN and their habitat, but the nature and intensity of management in turn determines the nature and extent of the effect. Herbicide use when establishing plantations can be detrimental to plant and animal species. In addition, furrow and trench planting at least temporarily disturb ground layer grasses, forbs, and associated SGCN. Use of established best management practices and integrated approaches increases the role of conifer plantations as potentially suitable habitats for SGCN, and additional research and monitoring will continue to improve habitat over the long term.

Riverine Impoundment - Reservoirs

Impoundments (also known as reservoirs) are artificially created standing waterbodies, produced by dams on streams or rivers. Because of the diverse nature of streams, rivers, and dams, these waterbodies can vary greatly in size, configuration, flow patterns, water chemistry, and biota. Impoundments are near as numerous and diverse in characteristics as natural lakes, with larger and more southerly waters having the richest fish faunas. Most often the waterbodies are dominated by warm water fishes, particularly the Centrarchidae family (sunfishes).

Surrogate Grasslands

Of Wisconsin's 2.1 million acres that were native prairie when Europeans arrived 150 years ago, less than 10,000 acres (<0.5% of the original acreage) of varying quality native prairie remains today. The midcontinental grassland biome has been greatly reduced and degraded throughout its range, generally from farming and grazing and conversion to woody vegetation with the cessation of fires, but also from urban and suburban development. Tallgrass prairies and related oak savannas are now the most diminished and threatened plant communities in the Midwest and among the most altered in the world. As a result, an estimated 15-20% of the state's original grassland flora is now considered rare. Grassland mammals and birds have fared somewhat better, using surrogate grasslands such as hayfields and pastures for their survival needs. However, with the conversion from pastures and hayfields to more row crop agriculture, some grassland birds and mammals have also been dramatically impacted over the last 30 years. For example, grassland birds as a group are the fastest declining bird group in the state.

Surrogate grasslands now represent the vast majority of grassland habitat in the state and are similar in structure to the former prairies that occurred in Wisconsin. Surrogate grasslands include agricultural habitats such as hayfields, small grains (oats, wheat, and barley), row crops (corn, soybeans, and potatoes), fallow fields, old fields, pastures, and set-aside fields (e.g., CRP) planted to non-native cool-season grasses (such as smooth brome (Bromus inermis), Timothy (Phleum pratense), redtop (Agrostis gigantea), orchard-grass (Dactylis glomerata), bluegrass (Poa pratensis and P. compressa), and quack-grass (Elymus repens)) or native warm-season grasses (such as big bluestem (Andropogon gerardii), little bluestem (Schizachyrium scoparium), Indian grass (Sorghastrum nutans), switch grass (Panicum virgatum), and side-oats grama (Bouteloua curtipendula)). Examples of other surrogate prairie grasslands include young conifer plantations, orchards, parks, golf courses, airports, roadsides, cut-over or burned-over forests, and mossed bogs (bogs from which Sphagnum moss has been removed for commercial purposes). Surrogate grasslands also include other idle grasslands, such as those on public or private lands managed for wildlife. Usually, idle grasslands are composed of non-native grasses and forbs, but they also can be plantings of one or several native prairie species but typically fall far short of the rich species diversity of the original prairie.

Surrogate grasslands occur in every ecological landscape in Wisconsin; however, the highest concentrations of surrogate grasslands are in the Western Prairie, Western Coulee and Ridges, Southwest Savanna, Central Sand Plains, Northwest Sands, and Southeast Glacial Plains Ecological Landscapes. It is estimated that roughly 3 million acres of agricultural land currently provide surrogate grassland habitat.

Transportation-Utility Corridor

Transportation and utility corridors are linear tracts of land that extend continuously across all types of terrestrial and aquatic land cover, natural or constructed, rural, suburban, or urban. While transportation and utility corridors are not independently sustainable biological communities, we feel it is necessary to distinguish them because of their ubiquity throughout Wisconsin and the important influence they have on the flora and fauna of our state, their habitats, and the ecological processes they depend upon. Corridors can vary greatly in width, length and depth of disturbance, as well as the portion occupied by structures like transmission poles, the area of impermeable features like road surfaces, and the intensity of vegetation management. Although there is considerable variation in how they are constructed, managed, and maintained, transportation and utility corridors are all subject to practices that control vegetation through mechanical or chemical means, altered soil conditions, altered surface and subsurface hydrology, and controlled and repeated access and disturbance. Depending upon their location and applied management practices, these corridors offer opportunities for the dispersal of native or invasive species and for sustaining open habitat types like grasslands and savannahs, but also contribute to the loss and fragmentation of forested, shrub, and wetland communities. They may create an open corridor or edge habitat that improves resource diversity in otherwise continuous habitats no longer subject to natural processes that control succession and gap formation. Or, break up continuous habitat into smaller patches and diminish habitat quality through increased predation and exposure.

Associated Rare Species and Ecological Landscapes

Understanding relationships among Species of Greatest Conservation Need (SGCN), habitats/natural communities and ecological landscapes help us make decisions about issues affecting SGCN. Download the Wildlife Action Plan association score spreadsheet to explore rare species and ecological landscapes associated with these anthropogenic habitats.