'Southern' Northern Hardwood

habitat photo
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Northern hardwoods reestablishing after grazing history (note open-grown sugar maple), Baraboo Hills, Sauk County. Photo by Mike Mossman.

Habitat Description

Habitat Crosswalk


This Habitat Page covers the northern hardwood forests of southern and central Wisconsin (roughly south of the Tension Zone; see Curtis 1959), where any combination of sugar maple, basswood, white ash, beech, or yellow birch comprises 50% or more of the basal area.  The Northern Hardwood cover type occurs throughout Wisconsin, but is most common north of the Tension Zone (WDNR 2010a).  Curtis (1959) and the Natural Heritage Inventory (WDNR 2005) consider this community (Southern Mesic Forest) to be distinct from northern hardwoods forests northward (Northern Mesic Forest).  In southern Wisconsin, northern hardwoods are most likely to occur on rich, well-drained soils, especially in historically less fire-prone areas such as protected valleys and on north- or east-facing slopes, although they are increasingly succeeding oak or central hardwood stands on mesic or dry-mesic sites, especially where seed sources exist nearby (Mossman and Hoffman 1989; Mossman 2011).  Sugar maple typically is the dominant species in northern hardwood stands.  Other associates include basswood, white ash, red and white oak, red maple, red elm, bitternut hickory, and black walnut.  Beech may occur in the eastern counties, near Lake Michigan, though much more so north of the Tension Zone.  Yellow birch also is more common in this type northward; in southern Wisconsin it is restricted to stream gorges and moist, rocky slopes, often within or near pine or hemlock relicts (Mossman 2011; WDNR 2011).

Northern hardwood stands typically have a dense canopy of mostly shade-tolerant species with a sparse shrub understory that may include scattered tree seedlings, saplings, and shrub species such as maple-leaved viburnum, alternate-leaved dogwood, choke cherry and witch-hazel.  Gooseberry often occurs in sites with a history of grazing, and invasive shrubs such as bush honeysuckles and common or glossy buckthorns are becoming increasingly abundant.  Common understory species include ‘spring ephemerals’ such as trout lilies, Dutchman’s breeches, spring beauty, false rue anemone, and toothwort.  Other common herbs are wild ginger, wild geranium, bishop’s cap, blue cohosh, Virginia waterleaf, woodland phlox, bloodroot, mayapple, trilliums, and violets (WDNR 2011, 2012).

Historical and Present-day Context and Distribution

As with other forest types, estimates for historic and current acreages of northern hardwood forests in southern Wisconsin vary.  Mossman and Hoffman (1989), using estimates derived from Lindberg and Hoving (1985), give a total presettlement figure of 4.8 million acres for southern Wisconsin upland forests of which the mesic type comprised 3.4 million acres.  This is similar to Curtis’s (1959) estimate of 3.4 million acres for southern mesic forest.  Finley (1976) estimated 2.4 million acres of sugar maple-basswood forests for southern Wisconsin, occurring mainly in a “fire shadow” north of the Wisconsin River and east of the Kickapoo Valley in the Western Coulee and Ridges Ecological Landscape (EL), and also in the Southeast Glacial Plains, Southern Lake Michigan Coastal, Western Prairie, Southwest Savanna, and Forest Transition ELs.  An additional 60,000 acres of beech-maple-basswood forests occurred in a long, narrow, north-south band along Lake Michigan on both sides of the Tension Zone, mostly in the Central Lake Michigan Coastal EL.

The extent of these forests has been much reduced since Euro-American settlement, largely due to clearing for agriculture as the soils are very fertile.  Currently, northern hardwood forests occupy some 520,000 acres in southern Wisconsin, or about 3% of the land area (WDNR 2011).  These forests are most prevalent in the Western Coulee and Ridges and Southeast Glacial Plains, and also occur in the Central Sand Plains, Southern and Central Lake Michigan Coastal, Southwest Savanna, and Western Prairie ELs.  Important sites also exist in the Central Sand Hills, Forest Transition, and Northern Lake Michigan Coastal ELs (WDNR 2012).

Natural Disturbances and Threats

Historically, windthrow was the major natural disturbance in northern hardwood forests throughout Wisconsin (WDNR 2010a).  This disturbance would have created small canopy gaps at relatively frequent intervals.  Extensive wind events were uncommon.  However, some larger openings created by wind or fire would have been necessary in order to regenerate the red, white, and black oaks that were common and often significant associates of the maple-basswood type, as well as other shade-intolerant and mid-tolerant species.  Grazing by native ungulates also may have contributed to forest succession, and lake-effect snows and ice storms likely played a role in forest development in the beech-maple-basswood forests along Lake Michigan (WDNR 2011).

With Euro-American settlement, large areas of northern hardwood forests in southern Wisconsin were cleared for agriculture, as the soils are very fertile.  In the Driftless Area, this was most prevalent in the more level valleys and flat ridgetops suitable for cultivation; slopes often were left wooded (though frequently grazed).  Clearing was more widespread in the east.  Many of these areas have since given way to urban and suburban development, particularly in eastern Wisconsin.  Few large forest tracts remain.  Parcelization and development pressure continually threaten existing forests.  Rural housing development has increased significantly over the past several decades, particularly in the Driftless Area (Radeloff et al. 2005).  This rural sprawl reduces the amount of interior forest, degrades and fragments restorable tracts, and can limit some management options.

As with forest types across southern Wisconsin, northern hardwoods have been affected by forest simplification, a phenomenon characterized by loss of species diversity and structure and increasing dominance of a few species in both canopy and understory layers (Rogers et al. 2008; WDNR 2010a).  Unsustainable logging practices such as high-grading and diameter-limit cutting have contributed to a loss of older age-classes and resulted in poor-quality stands.  Lack of management or strict application of single-tree selection has reduced species diversity by favoring sugar maple over other species.  Heavy livestock or white-tailed deer herbivory has reduced structural and species diversity, especially in the shrub and ground layers.  All of these factors, in combination with fire suppression, have led to the loss of the oak component in northern hardwood stands in the southern part of the state (see Steele 2012).

Exotic invasive plants are an ongoing threat to forest composition and structure, and especially threaten the display of early-spring-blooming wildflowers, or ‘spring ephemerals’, characteristic of this forest type.  When abundant, exotics can outcompete and exclude native herbs and shrubs, impede tree regeneration, and affect successional patterns and future forest conditions over large areas.  Among the most aggressive and problematic invaders in northern hardwood stands in southern Wisconsin are garlic mustard, common buckthorn, bush honeysuckles, Japanese barberry, autumn olive, and multiflora rose (WDNR 2011).

Two exotic insects pose threats to components of the northern hardwood type.  The emerald ash borer threatens the ash component, and gypsy moth threatens oaks and other species.

Hardwood forests in the northern U.S. have been extensively invaded by non-native earthworms, largely by human-aided dispersal.  These earthworms can alter soil structure and consume leaf litter, changes which alter seedbed conditions, reducing richness and cover of herbaceous plants, increasing dominance of grasses and sedges, and reducing tree regeneration and growth.  Such changes can have negative consequences for forest birds, particularly ground-nesters.  For example, on the Chequamegon-Nicolet National Forest in northern Wisconsin, northern hardwood stands heavily invaded by European earthworms in the genus Lumbricus showed decreased abundance of ovenbirds and hermit thrushes and reduced nesting success for ovenbirds, likely due to earthworm-caused reductions in leaf litter and increases in sedge cover that reduced nest concealment and increased predation rates.  Sugar maple-basswood forests may be more susceptible to earthworm effects than other forest types due to earthworm preference for calcium-rich leaf litter (Loss and Blair 2011; Loss et al. 2012; Fox et al. 2010).  While northern hardwoods are less abundant in southern Wisconsin than in the north, they are just as likely, if not more likely, to be invaded by earthworms due to the fact that they are more fragmented, closer to large population centers, and more heavily used by people (e.g., Kickapoo Valley Reserve; Kettle Moraine State Forest).

Projected changes in climate over the next 100 years are predicted to have significant effects on Wisconsin’s forests.  These changes may include increases in average temperatures; changes in precipitation and soil moisture; longer growing seasons; shorter winters; and more severe storm, flood, and drought events.  However, vulnerability varies considerably according to forest type, location (slope, aspect, etc.), and various other factors, and specific effects are difficult to predict.  Warmer temperatures may create less favorable conditions in southern Wisconsin for species like sugar maple while favoring certain oak and central hardwood species such as black oak, hickories, and black walnut, but how these species would respond to long-term changes in moisture patterns, and their ability to disperse across a fragmented landscape, creates additional uncertainties.  Habitat suitability likely will decrease for species such as yellow birch which are already in decline.  Invasive species, already seriously impacting forests across the south, also are expected to increase and become more aggressive as a result of warmer temperatures and increased concentrations of carbon dioxide in the atmosphere.  Insect pests and pathogens may also increase (WICCI 2010).

Related WBCI Habitats: Central Hardwood, Oak.

Overall Importance of Habitat for Birds

The bird communities of this forest type share characteristics with northern hardwood forests that are widespread north of the Tension Zone, and also with more typically southern oak and central hardwoods types.  In comparison with the north, southern stands tend to be smaller, and either isolated among more open and urbanized habitats, or embedded within a matrix of oak and central hardwoods.  Thus, their bird communities tend to be dictated largely by their surroundings and by the characteristics of the specific site (e.g., steep slopes or valley bottoms).  There are few species that are particularly characteristic of, or which most commonly occur in, this forest type.  Most notable among these is Acadian Flycatcher which prefers well-shaded, moist microsites such as stream gorges, draws, or bases of steep slopes, typically with a sugar maple canopy.  Others include Least Flycatcher, Veery, Wood Thrush, Black-throated Green Warbler, and Louisiana Waterthrush.  Species such as Broad-winged Hawk, Least Flycatcher, Veery, Black-throated Green Warbler, and Yellow-bellied Sapsucker are much more abundant and widespread in northern hardwoods north of the Tension Zone, whereas Acadian Flycatcher, Cerulean Warbler, and Louisiana Waterthrush occur almost entirely in the south.  The greatest value of the ‘southern’ northern hardwood type to birds is where it exists in structurally and compositionally diverse stands, intermixed with other forest types (especially oaks and conifer relicts), in extensive, unfragmented tracts.

As with other forest types, the bird community found in a particular tract of northern hardwoods varies according to numerous factors such as tree species composition, overstory and understory structure, soils, topography, and past management history, as well as landscape characteristics such as tract size, configuration, and surrounding habitats.  Common breeding species found in upland forests of southern Wisconsin across the moisture continuum from dry to mesic include Hairy Woodpecker, Downy Woodpecker, Red-bellied Woodpecker, Eastern Wood-Pewee, Blue Jay, Black-capped Chickadee, White-breasted Nuthatch, Red-eyed Vireo, Ovenbird, Scarlet Tanager, and Rose-breasted Grosbeak (Mossman and Hoffman 1988).

Species more characteristic of northern hardwood stands in the south include Yellow-billed Cuckoo, Yellow-bellied Sapsucker (mostly in the southwest, near river corridors), Acadian Flycatcher, Least Flycatcher, Yellow-throated Vireo, Veery, Wood Thrush, Black-throated Green Warbler, Cerulean Warbler (extensive, mature maple-basswood stands, especially in the Baraboo Hills), and Louisiana Waterthrush (along clean, rocky streams).  As in oak and central hardwood forests, interior openings of large tracts may have Blue-winged Warbler, Chestnut-sided Warbler, Kentucky Warbler, Mourning Warbler, and Hooded Warbler.  Ruffed Grouse may be present where early seral stages occur in the landscape, and Red-shouldered Hawk may nest near extensive tracts of floodplain forest.  Broad-winged Hawk may breed in some extensive tracts (Mossman 2011).

Changes in the bird community with succession in this forest type in southern Wisconsin are similar to those seen in other widespread forest types in the south (e.g., oak, central hardwood).  In a northern hardwood stand following a severe wind event or an even-aged regeneration timber harvest (overstory removal, clear-cut, coppice, seed tree, or 2nd-cut shelterwood) that leaves few or no trees left standing, the bird assemblage changes in a fairly predictable way as the stand passes through successional stages.  Recently cleared stands with open herbaceous cover and many shrubs and young saplings attract early-successional and shrub-nesting species such as House Wren, Gray Catbird, Common Yellowthroat, Song Sparrow, Eastern Towhee, Indigo Bunting, and Priority species Ruffed Grouse, Black-billed Cuckoo, American Woodcock, Northern Flicker, Blue-winged Warbler, and sometimes Red-headed Woodpecker if many snags remain.  Stands in open or semi-open surroundings may also have Priority species such as Field Sparrow or Brown Thrasher.  As the forest succeeds to dense saplings, the community simplifies: these species disappear (to the extent that shrubby openings do not persist) and are replaced by a few forest species, mostly generalists, such as Downy Woodpecker, Blue Jay, Black-capped Chickadee, American Robin, American Redstart, and the Priority species Rose-breasted Grosbeak and, sometimes (to the extent that canopy trees remain), Wood Thrush.  As the forest develops into pole timber, these same species (except American Redstart and Wood Thrush) may remain, with the addition of Least Flycatcher, Red-eyed Vireo, and Ovenbird.  After many decades, the maturation of the forest typically adds common forest species such as Eastern Wood-Pewee and Scarlet Tanager and the Priority species Yellow-billed Cuckoo, Yellow-throated Vireo, and, as the forest understory develops, Wood Thrush.  In forested tracts larger than about 500 acres, or in smaller tracts within an extensively forested landscape, mature forest may also provide breeding habitat for forest interior specialists such as Broad-winged Hawk, Acadian Flycatcher, and Cerulean Warbler (Mossman and Hoffman 1989, M.J. Mossman pers. comm. 2011).

Many of the same early successional species occur when partial disturbance from scattered windthrown trees, minor tree disease or insect outbreaks, or timber harvests (e.g., thinnings, 1st-cut shelterwoods, or group selection) produces low herbaceous and rank woody growth mixed with mature trees.  However, several other Priority birds may also be found including Veery, Mourning Warbler, higher numbers of Blue-winged Warbler and Rose-breasted Grosbeak, and many forest canopy species.  If these disturbed stands are embedded within an extensively forested landscape, then several additional Priority “interior edge” species such as Chestnut-sided Warbler, Kentucky Warbler, and Hooded Warbler often occur.  These partially disturbed stands maintain a more diverse blend of early and late successional species throughout their development, compared with cleared stands (M.J. Mossman pers. comm. 2011).

WBCI Priority Bird Species.  Species in boldface are currently proposed as Focal species for southern Wisconsin forests.

Species name Status Habitat and/or Special Habitat Features
Ruffed Grouse bwf Now uncommon to rare, gone from many former areas; where patches of both early-successional and older forest occur.
Red-shouldered Hawk bmwf In extensive tracts adjacent to floodplain forest; nest in large trees.
Broad-winged Hawk bm In extensive tracts.
American Woodcock bmf In early-successional tracts, large openings; may feed in forest.
Black-billed Cuckoo bM Shrubby, open woods and edge.
Yellow-billed Cuckoo BM Fairly common; prefers large tracts, canopy.
Chimney Swift bmf Nests in chimneys, occasionally in large “chimney” snags within forest.
Yellow-bellied Sapsucker bmw Especially near floodplain forest, in Driftless Area coulees, and where white birch or aspen are present.
Northern Flicker BMw Scattered, where snags, open or semi-open canopy, open herbaceous understory; prefers drier sites.
Acadian Flycatcher bm Fairly common in interior of extensive forest, especially along streams, at bases of steep slopes or in well-shaded moist microsites.
Least Flycatcher BM Fairly common but irregular in both interior and edge, including pole-sized stands; often in colony-like breeding groups.
Yellow-throated Vireo BM Common and widespread in mature forest tracts >40 acres.
Veery BM Extensive dry-mesic forest where there are dense shrubs or rank, tall, diverse forest herb layer, especially damp or mesic microsites.
Wood Thrush BM In tracts >40 acres, where closed or semi-open canopy, especially with patches of tall semi-dense saplings.
Blue-winged Warbler BM Dry-mesic to mesic, shrubby forest openings, edges.
Golden-winged Warbler bm Rare; in same sites as Blue-winged Warbler.
Chestnut-sided Warbler bM Rare breeder in shrubby openings and edges of extensive forest; more common northward.
Black-throated Green Warbler bM Rare breeder, in large, mature, dry-mesic to mesic tracts that include sugar maple or sometimes conifers (white pine, hemlock).
Cerulean Warbler bm Mature forest with tall (>75 ft. high), diverse canopy species and structure; prefers oaks; extensive tracts.
Louisiana Waterthrush bm Along clear, rocky streams or springs within extensive forest.
Kentucky Warbler bm Uncommon in dry-mesic to mesic forest tracts >240 acres; often in dense or semi-dense damp, shrubby openings of natural or logging origin, and floodplain-upland boundary.
Mourning Warbler bm Similar to Kentucky Warbler, but more common, less restricted to very large tracts, extends into larger open-canopy patches.
Hooded Warbler BM Interior openings with dense shrubs and brambles; large tracts; prefers mesic or dry-mesic sites; uses pine plantations with shrubby understories in the Kettle Moraine.
Rose-breasted Grosbeak BM Common and widespread in forest interior or edge; prefers open or semi-open canopy with moderate to thick sapling/shrub growth.


The deciduous forest habitat objectives assigned to southern Wisconsin by the Upper Mississippi River and Great Lakes Joint Venture Implementation Plan (UMRGLJV 2007) are problematic.  They were generated using population estimates for “focal planning species” (Cerulean Warbler, Louisiana Waterthrush, and Kentucky Warbler) that are extremely low because they are based on data from the federal BBS, a survey that does not adequately sample these rare species or their habitats in Wisconsin.  The WBCI Southern Forests Committee recommends generating better population estimates for these species as well as for Acadian Flycatcher, a species more characteristic of extensive northern hardwood tracts, or mesic microsites within other forest types, in southern Wisconsin, from which more realistic habitat objectives may be determined.

Management Recommendations

The northern hardwood forest type historically was much more extensive in southern Wisconsin than at present.  Much of this former range has been permanently converted to other land uses.  In regions where northern hardwoods currently occur, they are increasingly expanding into areas formerly dominated by oak.  In some cases, they are succeeding the central hardwoods that initially replaced the oaks.  Because the oak forest type is critically important to many Priority southern forest birds, a balance must be struck between management to maintain and enhance northern hardwoods and management favoring oaks.

Landscape-level Recommendations

  1. Plan forest management on a landscape scale to determine the most appropriate areas for management focused on maintaining and enhancing northern hardwoods (with little or no oak component) and management favoring oaks (refer to the Oak Habitat Page (Steele 2012) for detailed oak management recommendations).  Large blocks of the northern hardwood type exist in the Northern Unit of the Kettle Moraine State Forest, Baraboo Hills, Lower Wisconsin State Riverway, Kickapoo Valley, and areas of dolomite bedrock south of the Wisconsin River in Grant County (WDNR 2012).
  2. Protect and connect existing forest tracts.  Modeling has shown that the percentage of forest cover is an important landscape-level habitat suitability feature for many priority forest birds (Thogmartin and Knutson 2007; Thogmartin et al. 2004).
  3. Older forest is currently lacking, and provides important habitat for various priority birds (WDNR 2005).  Retain some patches across the landscape where managed old-growth is the goal or where harvest is excluded and the forest is allowed to mature naturally (Bakermans and Rodewald 2009).
  4. Encourage cross-boundary cooperation among landowners in order to increase the efficiency and effectiveness of forest management (Knoot et al. 2010).

Site-level Recommendations

  1. Articulate clear site-level management objectives that have been developed within a landscape context.
  2. Manage for the northern hardwood type where it currently occurs in sites it would have occupied historically (e.g., north- and east-facing slopes; draws; moist microsites within oak forest, etc.).
  3. Wherever feasible, convert northern hardwoods to oak or maintain/increase the oak component in northern hardwood stands.  Refer to the Oak Habitat Page (Steele 2012) for detailed oak management recommendations.
  4. In stands containing mature oaks where management to regenerate oak is not feasible, retain oaks as long as possible (WDNR 2010a).  Consider deferring management or applying extended rotation or old-growth management (WDNR 2010b), particularly if maintaining bird habitat is the goal.
  5. Where oak management is not feasible, manage northern hardwoods for compositional and structural diversity by:
    • Applying extended rotation or managed old-growth management to some stands.
    • Using group selection techniques that create canopy gaps >40 m2 in size (Bakermans and Rodewald 2009).
    • Retaining some large-diameter trees as well as living and dead cavity trees, snags, and coarse woody debris.
    • Maintaining or increasing tree species diversity, including yellow birch, white pine, or central hardwood species (e.g., hickories) as appropriate, and beech in the Lake Michigan counties.
    • Creating and maintaining a diversity of size- and age-classes (WDNR 2010, b).
    • Mimicking natural disturbance through stocking and gap-size diversity.
  6. Reduce deer densities whenever feasible, especially where implementing management to maintain or favor oaks.  Deer herbivory can give sugar maple a competitive advantage and contribute to homogenization of species composition and declines in native understory plants (WDNR 2010a).
  7. Control invasive species, especially garlic mustard, buckthorn, and honeysuckle, and eliminate where possible; employ management practices that limit the spread of invasives.  Refer to WDNR Forestry Best Management Practices (BMPs) for invasive species (WDNR 2009).
  8. Limit or exclude livestock grazing within forests.  Heavy grazing can alter understory plant composition, damage trees, hinder regeneration, and cause soil compaction.  Cattle also lead to increased nest parasitism by attracting Brown-headed Cowbirds (Knutson et al. 2001).

Ecological Opportunities

Ecological Landscape Opportunity Management Recommendations
Western Coulee and Ridges Major All
Central Lake Michigan Coastal Important All
Central Sand Plains Important All
Southeast Glacial Plains Important All
Southern Lake Michigan Coastal Important All
Southwest Savanna Important All
Western Prairie Important All
Central Sand Hills Present All
Forest Transition Present All
Northern Lake Michigan Coastal Present All

Research Needs


Key Sites

Key Partners

Funding Sources

Information Sources


Contact Information

Steele, Y.  2013.  'Southern' Northern Hardwood Habitat Page.  In Paulios, A. and K. Kreitinger (eds.).  2007-2013.  The Wisconsin All-Bird Conservation Plan, Version 2.0.  Wisconsin Bird Conservation Initiative.  Wisconsin Department of Natural Resources, Madison, WI.

Kreitinger, K., Y. Steele and A. Paulios, editors. 2013.
The Wisconsin All-bird Conservation Plan, Version 2.0. Wisconsin Bird Conservation Initiative.
Wisconsin Department of Natural Resources. Madison, WI.

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