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Ryan O'Connor
Natural Heritage Inventory Ecologist

Northern Hardwood Swamp

State Rank: S3     Global Rank: G4   what are these ranks?


Detailed Community Description from Ecological Landscapes of Wisconsin

General natural community overview

Counties shaded blue have documented occurrences for Northern Hardwood Swamp in the Wisconsin Natural Heritage Inventory database.

Northern hardwood swamps are deciduous forested wetlands that occur along lakes, streams, or in insular basins in poorly drained morainal landscapes. This community occurs across the state, but is most common in the northern ecological landscapes. The dominant tree species is black ash (Fraxinus nigra) but in some stands red maple (Acer rubrum), yellow birch (Betula alleghaniensis), and American elm (Ulmus americana) are also important. Some sites may also have a minor conifer component of northern white-cedar (Thuja occidentalis) or balsam fir (Abies balsamea). The tall shrub speckled alder (Alnus incana) may be locally common. The herbaceous flora is often diverse and may include many of the same species found in alder thickets. Typical species are marsh-marigold (Caltha palustris), swamp raspberry (Rubus pubescens), common skullcap (Scutellaria galericulata), orange jewelweed (Impatiens capensis), many sedges (Carex spp.), and groundwater-loving species like bristle-stalked sedge (Carex leptalea), American golden saxifrage (Chrysosplenium americanum), and swamp saxifrage (Micranthes pensylvanica). Soils may be mucks or mucky sands.

Defining Characteristics and Similar Communities

Northern hardwood swamps are characterized by relatively constant water levels, often with a groundwater component, and dominance by deciduous hardwood species, especially black ash. Relatively stable water levels lead to saturated soils that inhibit organic matter decomposition and the development of peat (muck) soils. They can be distinguished from southern hardwood swamps, which can also occur in northern Wisconsin, by their relatively stable water levels and higher prevalence of species that prefer saturated soils (see characteristic species above) while southern hardwood swamps are characterized by seasonally fluctuating water levels that usually drop by mid-later summer (similar to floodplains), higher proportion of mineral soils, and a higher prevalence of species that prefer these conditions 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). Northern hardwood swamps can be differentiated from floodplain forests by their occurrence around lakes, basins in till plains, or headwater streams rather than along major rivers, and their prevalence of species that prefer saturated rather than seasonally inundated soils.

Northern hardwood swamps have many similarities with northern wet-mesic forests (cedar swamps), especially as both black ash and northern white-cedar can be canopy associates in both communities. In general, sites that are dominated by hardwoods are best typed as hardwood swamps, while areas dominated by conifers are best typed as northern wet-mesic forest, though both types may occur and intergrade across large wetland complexes.

Rare animals

Species of Greatest Conservation Need

Wisconsin Wildlife Action Plan graphic

The following Species of Greatest Conservation Need are listed according to their level of association with the Northern 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.

Four-toed SalamanderHemidactylium scutatum2
Pickerel FrogLithobates palustris2
Mink FrogLithobates septentrionalis1

Ants, wasps, and beesScore
Confusing Bumble BeeBombus perplexus1
Indiscriminate Cuckoo Bumble BeeBombus insularis1

Aquatic and terrestrial snailsScore
Boreal TopZoogenetes harpa2
Eastern Flat-whorlPlanogyra asteriscus1

A Predaceous Diving BeetleHydroporus morio2
A Predaceous Diving BeetleHydrocolus persimilis2

American WoodcockScolopax minor2
Golden-winged WarblerVermivora chrysoptera2
Least FlycatcherEmpidonax minimus2
Red-shouldered HawkButeo lineatus1

Butterflies and mothsScore
Gray CopperLycaena dione1

Dragonflies and damselfliesScore
Swamp DarnerEpiaeschna heros1

Grasshoppers and alliesScore
Clear-winged GrasshopperCamnula pellucida1
Crackling Forest GrasshopperTrimerotropis verruculata1
Spotted-winged GrasshopperOrphulella pelidna1

Water ShrewSorex palustris3
Little Brown BatMyotis lucifugus2
Northern Flying SquirrelGlaucomys sabrinus2
Northern Long-eared BatMyotis septentrionalis2
Silver-haired BatLasionycteris noctivagans2
Woodland Jumping MouseNapaeozapus insignis2
American MartenMartes americana1

Wood TurtleGlyptemys insculpta2

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.

Scores: 3 = "significantly associated," 2 = "moderately associated," and 1 = "minimally associated."
Scientific Name Common Name Score
Geum macrophyllum var. macrophyllum Large-leaved Avens 2
Malaxis monophyllos var. brachypoda White Adder's-mouth 3
Myosotis laxa Small Forget-me-not 2
Poa paludigena Bog Bluegrass 3
Ranunculus gmelinii Small Yellow Water Crowfoot 1


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

Map of the Ecological Landscapes of Wisconsin.

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.


Wisconsin Wildlife Action Plan graphic

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


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

Central Lake Michigan Coastal

Fragmentation is a major issue in this Ecological Landscape since wetland forest is only 9% of the landscape and forested areas are embedded within a matrix of agricultural uses. Residential development is further fragmenting and simplifying this community type. Invasives such as Asian honeysuckles and buckthorns are a problem. Grazing can inhibit regeneration, destroy understory plants, and contribute to the spread of invasives. The best opportunities to protect the few remaining unprotected high quality sites are in the Door Peninsula Hardwood Swamp complex (northern Kewaunee County) and the Coppertown and Morrison swamps (Brown County). Grazing should be discouraged in this type.

Central Sand Plains

The type is extremely limited in this Ecological Landscape, and remaining patch sizes are small. Fragmentation is a major issue for these sites. Invasives such as Asian honeysuckles, garlic mustard and buckthorns are a problem. Dandy Creek Swamp in Meadow Valley Wildlife Area (Monroe County) is one example of protected northern hardwood swamp in this Ecological Landscape.

Forest Transition

Fragmentation is a major issue in this Ecological Landscape since northern hardwood swamps are typically found within a mix of forest and farmland. Residential development is further fragmenting and indirectly impacting this community type through increased runoff and altered hydrology. The central portion of this Ecological Landscape (Marathon, Waupaca, and Clark Counties) offers the best opportunity to maintain and enhance this community type. These areas are very susceptible to invasive, non-native species, so detection and control are critical.

North Central Forest

Altered hydrology is an issue in some parts of this Ecological Landscape, especially from road construction and development. This Ecological Landscape is the best place to maintain large forest blocks for this type, and to implement other conservation actions because of the abundance of the type and the large blocks of public ownership. Connectivity with other large forested areas should be maintained or enhanced, including the Chequamegon-Nicolet National Forests, and forested areas of Price, Iron, Oconto and Taylor Counties. Although forest management of this community is not practiced widely in this Ecological Landscape, careful use of alternative management techniques and best management practices in these areas is encouraged on public and private lands where they can be monitored long-term. Bur Oak Swamp, a site south of Crandon (Forest County), features a dominant bur oak/white oak hybrid. This unique variant may qualify as a separate community and warrants further research.

Northern Lake Michigan Coastal

Fragmentation is a serious issue in this Ecological Landscape. Invasives are a problem (e.g., garlic mustard). Grazing still occurs in this community in some areas of Door County. Very high recreational use in Door County is a factor in many kinds of impacts, including trail development that facilitates the spread of invasives, and fragmentation due to housing and roads. The best opportunity for protection is in the Door Peninsula hardwood swamp complex (southern Door County). There is some potential for impacts from invasive plant species such as reed canary grass, buckthorn and Asian honeysuckles, so detection and control are important.

Northwest Lowlands

There are some potential impacts here from invasive plant species such as buckthorn and Asian honeysuckle, thus detection and control are important. This Ecological Landscape has a relatively low human population density and lower road density, so there are fewer impacts from development and altered hydrology. Although not as many acres of this community type exist here as in some other Ecological Landscapes, the area presents a good opportunity for protection. Much of this community type is in public county forest and has not been managed (harvested) for many years. It is not likely to be harvested for many more years. The Norway Point Bottomlands State Natural Area in Governor Knowles State Forest (Burnett County) is a good, protected example of this community.

Southeast Glacial Plains

This type is limited in this Ecological Landscape, but includes patches along the Rock River. Where not protected through the implementation of conservation elements of local and regional land use plans, this type can be impacted by residential and commercial development. Huiras Lake (Ozaukee County) and Shaky Lake (Outagamie County), are good examples of this type and both are State Natural Areas.


Northern Hardwood Swamp Photos

Northern Hardwood Swamp Photo

Hardwood in the Baraboo Hills. Canopy composed of pole-sized yellow birch, black ash; the springy understory includes species tolerant of, or requiring, saturated soils.

Photo by Eric Epstein.

Northern Hardwood Swamp Photo

Black Ash swamp along the Uhler Trail in Iron County.

Photo by Christina Isenring.

Northern Hardwood Swamp Photo

Photo by Christina Isenring.

Northern Hardwood Swamp Photo

Photo by Christina Isenring.

Northern Hardwood Swamp Photo

Black ash swamp with Impatiens, skunk cabbage, garlic musard, Caltha palustris, and Equiseteum.

Photo by Christina Isenring.

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.

Last revised: Tuesday, August 30, 2022