Southern Hardwood Swamp

Definition

Detailed Community Description from Ecological Landscapes of Wisconsin

General natural community overview

Southern hardwood swamps are a forested wetland community type found in insular basins with seasonally high water tables. This type is best developed in glaciated southeastern Wisconsin, but was not of large extent even prior to EuroAmerican settlement. Finley (1976) classified less than 1% of southeastern Wisconsin as lowland hardwood forest, and this figure includes bottomland forests along rivers as well as southern hardwood swamps in closed basins. Dominant tree species are silver maple (Acer saccharinum), red maple (Acer rubrum), hybrids of red and silver maples (e.g., Acer X freemanii), and green ash (Fraxinus pennsylvanica). Associate tree species may include swamp white oak (Quercus bicolor), bur oak (Q. macrocarpa) and their hybrids, basswood (Tilia americana), and American elm (Ulmus americana); all of which may be a significant part of the canopy or subcanopy in sites impacted by emerald ash borer. Black ash may be present in southern hardwood swamps but is usually not dominant across the site. The groundlayer is often dominated by species typical of floodplain forests such as Virginia wild-rye (Elymus virginicus), white grass (Leersia virginica), common wood-reed (Cinna arundinacea), wood nettle (Laportea canadensis), false nettle (Boehmeria cylindrica), and Ontario aster (Symphyotrichum ontarionis). Southern hardwood swamps are also noted for a high component of lianas, including poison ivy (Toxicodendron radicans), Virginia creeper (Parthenocissus quinquefolia), and grapes (Vitis spp.). In the relatively undisturbed sites, there can be a rich spring flora. Microtopographic differences account for the existence of patches of spring ephemerals as well as many wetland species. The exotic reed canary grass (Phalaris arundinacea) has become dominant in the understory of many hardwood swamps.

This Natural Heritage Inventory community type partly includes the "southern wet-mesic forest" of the Curtis (1959) classification, although this Curtis type also includes the more common hardwood swamps usually maintained by groundwater seepage and dominated by black ash, red maple, American elm, and yellow birch. Curtis referred to this conglomerate type as "lacustrine forests" due to their frequent occurrence on lake plains, both around the margins of larger existing lakes and on extinct glacial lakes, although southern hardwood swamps also occur in lower-lying portions of till plains that may not have held ponded water for any significant length of time during or after glaciation. Southern hardwood swamps are not restricted to southern Wisconsin; the name rather refers to their similarly to swamps more commonly found in the southern Midwest, especially those of the poorly drained till plains along the Ohio River valley.

Defining Characteristics and Similar Communities

Southern hardwood swamps are characterized by their seasonally high water tables that usually dry out by late summer, location in basins not associated with major rivers, and flora that is intermediate between floodplain forests and more northern hardwood swamps. They are distinguished from northern hardwood swamps by their vertically fluctuating water levels rather than a relatively stable supply of groundwater, and thus lower proportion of peat (muck) soils due to soil drying out by mid-late summer allowing organic matter to decompose. They also tend to have a higher component of plant species that prefer these hydrologic conditions, such as those commonly found in floodplain forests (see description), whereas northern hardwood swamps have a higher prevalence of species preferring saturated soils such as marsh marigold (Caltha palustris), swamp raspberry (Rubus pubescens), orange jewelweed (Impatiens capensis), purple-stemmed aster (Symphyotrichum puniceum), lake sedge (Carex lacustris), blue-joint grass (Calamagrostis canadensis) as well as groundwater-loving species like bristle-stalked sedge (Carex leptalea), American golden saxifrage (Chrysosplenium americanum), and swamp saxifrage (Micranthes pensylvanica).

Southern hardwood swamps can be differentiated from floodplain forests by their occurrence in lakeplain basins or low-lying till plains rather than along major rivers (though they may occur near small streams), and thus their water is supplied by rain and snowmelt rather than by over-bank flooding. The lateral water movement in floodplain forests also leads to scouring, silt deposition and removal of organic detritus, processes that don't occur in southern hardwood swamps.

Rare animals

Species of Greatest Conservation Need

The following Species of Greatest Conservation Need are listed according to their level of association with the Southern Hardwood Swamp natural community type, based on the findings in Wisconsin's 2015 Wildlife Action Plan.

Scores: 3 = high association, 2 = moderate association, and 1 = low association. See the key to association scores for complete definitions.

Please see Section 2. Approach and Methods of the Wildlife Action Plan to learn how this information was developed.

Rare plants

The Natural Heritage Inventory has developed scores indicating the degree to which each of Wisconsin's rare plant species is associated with a particular natural community or ecological landscape. This information is similar to that found in the Wildlife Action Plan for animals. As this is a work in progress, we welcome your suggestions and feedback.

Landscapes

The following Ecological Landscapes have the best opportunities to manage for Southern Hardwood Swamp, based on the Ecological Landscapes of Wisconsin Handbook.

Major (3 on map)
A major opportunity for sustaining the natural community in the Ecological Landscape exists, either because many significant occurrences of the natural community have been recorded in the landscape or major restoration activities are likely to be successful maintaining the community's composition, structure, and ecological function over a longer period of time.

Important (2 on map)
Although the natural community does not occur extensively or commonly in the Ecological Landscape, one to several occurrences do occur and are important in sustaining the community in the state. In some cases, important opportunities may exist because the natural community may be restricted to just one or a few Ecological Landscapes within the state and there may be a lack of opportunities elsewhere.

Present (1 on map)
The natural community occurs in the Ecological Landscape, but better management opportunities appear to exist in other parts of the state.

Threats/Actions

What are conservation actions?

Conservation actions respond to issues or threats, which adversely affect species of greatest conservation need (SGCN) or their habitats. Besides actions such as restoring wetlands or planting resilient tree species in northern communities, research, surveys and monitoring are also among conservation actions described in the WWAP because lack of information can threaten our ability to successfully preserve and care for natural resources.

Threats/issues and conservations actions for natural communities

Considerations

The following are additional considerations for Southern Hardwood Swamp in Ecological Landscapes with opportunities for protection, restoration, and/or management. For more information, see the Wildlife Action Plan.

Southeast Glacial Plains

The North Unit of the Kettle Moraine State Forest includes some acreage of the southern hardwood swamp community type, though the area also includes species such as yellow birch and occasionally northern white cedar that are typically found in northern hardwood swamps. In this Ecological Landscape, the southern hardwood swamp type tends to be transitional to more northern types; this may be, in part, a tension zone effect. The Cedarburg Bog area contains occurrences of this type adjacent to conifer bogs, and they are also found in a hydrologically connected wetland to the north of the string bogs. Huiras Lake in Washington County is a site with swamp hardwoods occurring around an undeveloped lake and its associated conifer swamp. Intact or high-quality hardwood swamps are very rare. More survey work and better documentation are needed, and restoration techniques should be developed for degraded sites.

Southern Lake Michigan Coastal

Whitnall Park Woods, in the city of Franklin and village of Hales Corners, contains patches of southern hardwood swamp. Limited opportunities occur in some of the basins and perhaps in association with smaller streams which lack well-developed floodplains. Additional inventory work is needed.

Photos

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Southern Hardwood Swamp Photos

Note: photos are provided to illustrate various examples of natural community types. A single photograph cannot represent the range of variability inherent in a given community type. Some of these photos explicitly illustrate unusual and distinctive community variants. The community photo galleries are a work in progress that we will expand and improve in the future.