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Ryan O'Connor
Natural Heritage Inventory Ecologist

Alder Thicket

State Rank: S4     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 Alder Thicket in the Wisconsin Natural Heritage Inventory database.

Alder thicket is a minerotrophic wetland community dominated by tall shrubs, especially speckled alder (Alnus incana). Shrub associates may include red-osier dogwood (Cornus sericea), nannyberry (Viburnum lentago), cranberry viburnum (Viburnum opulus), wild currants (Ribes spp.), and willows. Among the characteristic herbaceous species are Canada bluejoint grass (Calamagrostis canadensis), orange jewelweed (Impatiens capensis), asters (Symphyotrichum lanceolatum, S. puniceum, and Doellingeria umbellata), boneset (Eupatorium perfoliatum), rough bedstraw (Galium asprellum), marsh fern (Thelypteris palustris), arrow-leaved tear-thumb (Persicaria sagittata), and sensitive fern (Onoclea sensibilis). This community type is sometimes a seral stage between northern sedge meadow and northern conifer swamp or northern hardwood swamp, but occurrences can be stable and persist at given locations for long periods of time. This type is common and widespread in northern and central Wisconsin, but also occurs at isolated locales in the southern part of the state. Alder thicket often occurs as a relatively stable community along streams and around lakes but can occupy large areas formerly covered by conifer swamps that were logged during the cutover era (1880s - 1920s) and/or where water tables rose. Stands of alder that originated following logging and/or wildfire will usually revert to forest, although on heavy, poorly drained soils, forest re-growth can be problematic owing to "swamping" effects.

Groundwater seepage is an important attribute of Alder Thickets. Seepage areas are often indicated by the presence of skunk-cabbage (Symplocarpus foetidus), marsh-marigold (Caltha palustris), swamp saxifrage (Micranthes pensylvanica), American golden saxifrage (Chrysosplenium americanum), and marsh pennywort (Hydrocotyle americana).

Defining Characteristics and Similar Communities

Alder thicket is defined as having few trees and at least 50% cover of shrubs (>5 feet in height), of which alder contributes at least half of the relative shrub cover. Similar communities include shrub-carr, which also has at least 50% cover of shrubs, but has a greater diversity of shrubs, often at least 4 or 5 species that are co-dominant. While alder is often present in a shrub-carr (especially in northern Wisconsin), it comprises less than half of the relative shrub cover. Alder thickets often intergrade with northern sedge meadows; either community can constitute the dominant matrix community across hundreds of acres, with pockets of the non-matrix community embedded within. Alder thickets also border and intergrade with hardwood swamps (or aspen stands on wet ground), but can be differentiated by having, on average, <25% cover of trees.

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 Alder Thicket 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 scutatum3
Mink FrogLithobates septentrionalis2
Pickerel FrogLithobates palustris2

A Predaceous Diving BeetleAgabus leptapsis2

American WoodcockScolopax minor3
Golden-winged WarblerVermivora chrysoptera3
Swainson's ThrushCatharus ustulatus3
American BitternBotaurus lentiginosus2
Rusty BlackbirdEuphagus carolinus2
Bell's VireoVireo bellii1
Black-crowned Night-HeronNycticorax nycticorax1
Long-eared OwlAsio otus1
Olive-sided FlycatcherContopus cooperi1
Spruce GrouseFalcipennis canadensis1

Butterflies and mothsScore
Midwestern Fen BuckmothHemileuca nevadensis ssp. 31

Dragonflies and damselfliesScore
Hine's EmeraldSomatochlora hineana1

Grasshoppers and alliesScore
Bruner's Spur-throat GrasshopperMelanoplus bruneri1
Spotted-winged GrasshopperOrphulella pelidna1

Northern Long-eared BatMyotis septentrionalis2
Silver-haired BatLasionycteris noctivagans2
Water ShrewSorex palustris2
Little Brown BatMyotis lucifugus1
Woodland Jumping MouseNapaeozapus insignis1

Eastern MassasaugaSistrurus catenatus3
Wood TurtleGlyptemys insculpta3
Blanding's TurtleEmydoidea blandingii2
Eastern RibbonsnakeThamnophis sauritus2
QueensnakeRegina septemvittata2
Plains GartersnakeThamnophis radix1

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
Caltha natans Floating Marsh Marigold 2
Canadanthus modestus Northwestern Sticky Aster 3
Carex backii Rocky Mountain Sedge 1
Carex swanii Swan Sedge 1
Eleocharis nitida Neat Spike-rush 2
Equisetum palustre Marsh Horsetail 3
Geum macrophyllum var. perincisum Large-leaved Avens 2
Listera auriculata Auricled Twayblade 3
Lonicera involucrata Fly Honeysuckle 3
Petasites sagittatus Sweet Colt's-foot 2
Pyrola minor Lesser Wintergreen 3
Sparganium glomeratum Clustered Bur-reed 2
Viburnum cassinoides Northern Wild-raisin 2


The following Ecological Landscapes have the best opportunities to manage for Alder Thicket, 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 Alder Thicket in Ecological Landscapes with opportunities for protection, restoration, and/or management. For more information, see the Wildlife Action Plan.

Central Sand Hills

Stream corridors and areas around spring seeps have potential for occurrences of alder thicket. Examples are found at Caves Creek Headwaters, Chaffee Creek State Fishery Area, Mecan River State Fishery Area, and Lawrence Creek State Natural Area (all in Marquette County). More extensive wetland inventories are needed in this landscape.

Central Sand Plains

This community type is common and widespread here and should be managed and protected as an integral part of the many wetland complexes. Good examples include Clear Creek at Fort McCoy Military Reservation (Monroe County), Robinson Creek, (Jackson County), Hulbert Creek (Sauk County), Necedah National Wildlife Refuge (Juneau County), and Little Roche a Cri Creek (Adams County).

Forest Transition

The best-documented opportunities in this Ecological Landscape occur in the eastern and northern parts of the Ecological Landscape, but the community is widespread here. Examples are at Pope Lake and Myklebust Lake (Waupaca County), along the Red River (Shawano County), Tenmile Creek Marsh (Rusk County), and Little Black River Sedge Meadow (Taylor County). More extensive inventories are needed. Grazing occurs in this Ecological Landscape and can degrade the habitat and lead to invasion by non-native plants. Past conversion of forests and wetlands to agricultural fields and pastures limits opportunities for management and protection.

North Central Forest

This Ecological Landscape is a good place to maintain the alder thicket community because of its abundance and large amount of land under public ownership. Examples occur on federal, state, and county forests in this Ecological Landscape, such as Dailey's Marsh, Hunting River Alders, and Wildcat Springs (Langlade County); Sidney Creek Swamp (Marinette County); and Ruby Swamp (Chippewa County). Altered hydrology is an issue in some parts of this Ecological Landscape, especially from road construction and residential development. Invasives are not a large problem at present, but should be monitored.

Northeast Sands

Examples occur on the Peshtigo River State Forest, and at Best Thicket, Chemical Creek Cedar Swamp, and New Athelstane Barrens (all in Marinette County).

Northern Highland

Many good examples of alder thicket occur on the Northern Highland-American Legion State Forest. Others are found at the Willow Flowage, Rice Lake-Thunder Lake Marsh, Holmboe Conifer Forest, Trout Creek, Tomahawk River Pines, and Bootjack Bog (all in Oneida County), Siphon Creek, Goodyear Springs and Salsich Springs (in Vilas County).

Northwest Lowlands

Although alder thicket is not widely distributed in this Ecological Landscape, there are good opportunities for protection (e.g., Ekdall Wetlands in Burnett County). Other examples may be found at Empire Swamp, Black Lake Bog, and along Ericson Creek (all in Douglas County). This Ecological Landscape has a lower population density and lower road density, thus fewer negative impacts from fragmentation and altered hydrology occur here. This community type is common on county forestland. It often occurs in the stream valleys between forested ridges and on the margins of large peatlands, which are common in this Ecological Landscape. Alder thickets should be managed as a complex with streams, lakes, sedge meadows, and a variety of peatland communities. Beaver impacts should be evaluated and beaver populations should be maintained at an appropriate level. There are some potential impacts from invasive plant species such as buckthorns and Asian honeysuckles, thus early detection and control are important.

Northwest Sands

Extensive corridors of alder thicket along streams and lakeshores should be maintained. An exceptional example occurs along the Upper Brule River. Other occurrences include many locations along the Upper St. Croix River, Osgood Spring Pond (Sawyer County), and Heffelfinger Spring Pond (Douglas County).

Superior Coastal Plain

Alder thicket should be maintained as a complex with streams, lakes, sedge meadows, and a variety of peatland communities. Significant occurrences include the Bibon Swamp (Ashland County), Superior Municipal Forest (Douglas County), Bark Bay Slough State Natural Area (Bayfield County), and the northern part of the Brule River State Forest (Douglas County). Reed canary grass is a problem in the western portion of the Ecological Landscape and around the City of Ashland.

Western Coulee and Ridges

Entire river corridors should be protected and sustained from lowlands well into uplands. Buffers within floodplains should be used to prevent compaction, trampling, and sedimentation. Grazing is a common practice in the wetlands of this Ecological Landscape, and can degrade the habitat and lead to invasion by non-native plants such as reed canary grass. Good examples occur at Silver Creek on Fort McCoy Military Reservation (Monroe County), Dell Creek State Wildlife Area (Sauk County), and along tributaries of the Kickapoo River (e.g., on the Kickapoo Reserve, Vernon County).


Alder Thicket Photos

Alder Thicket Photo

Speckled alder on the banks of Upper Brule River grade into tamarack-dominated swamp, then extensive stand of N white-cedar. Springs/seepages lace the wetlands bordering the river.

Photo by Eric Epstein.

Alder Thicket Photo

Alder thicket along the Brule River, dominated speckled alder with red-osier dogwood & winterberry.

Photo by Ryan O'Connor.

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