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Black spruce swamp An acidic conifer swamp forest characterized by a relatively closed canopy of black spruce (Picea mariana) and an open understory in which Labrador-tea (Ledum groenlandicum) and sphagnum mosses (Sphagnum spp.) are often prominent, along with three-leaved false Solomon's-seal (Smilacina trifolia), creeping snowberry (Gaultheria procumbens), and three-seeded sedge (Carex trisperma). The herbaceous understory is otherwise relatively depauperate. This community is closely related to Open Bogs and Muskegs, and sometimes referred to as Forested Bogs outside of Wisconsin.
Mesic floodplain terrace These are deciduous forests developed on alluvial terraces along rich, infrequently flooding (or flooding only for a very short period) rivers draining into Lake Superior. The dominant trees are usually sugar maple (Acer saccharum), basswood (Tilia americana), and sometimes ashes (Fraxinus spp.). There is a diverse spring ephemeral flora (which in Wisconsin includes many southern species at their northern range limits), but by late spring, these may be overtopped by dense stands of ostrich fern (Matteuccia struthiopteris) and wood-nettle (Laportea canadensis).
Northern hardwood swamp (formerly called Northern Hardwood Swamp, this is a split from Curtis’ Northern Wet-Mesic Forest),
These are northern deciduous forested wetlands that occur along lakes or streams, or in insular basins in poorly drained morainal landscapes. The dominant tree species is black ash (Fraxinus nigra), but in some stands red maple (Acer rubrum), yellow birch (Betula allegheniensis), and (formerly) American elm (Ulmus americana) are also important. 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), skullcap (Scutellaria galericulata), orange jewelweed (Impatiens capensis), and many sedges (Carex spp.). Soils may be mucks or mucky sands.
Northern wet forest These weakly minerotrophic conifer swamps, located in the North, are dominated by black spruce (Picea mariana) and tamarack (Larix laricina). Jack pine (Pinus banksiana) may be a significant canopy component in certain parts of the range of this community complex. Understories are composed mostly of sphagnum (Sphagnum spp.) mosses and ericaceous shrubs such as leatherleaf (Chamaedaphne calyculata), Labrador-tea (Ledum groenlandicum), and small cranberry (Vaccinium oxycoccos) and sedges such as (Carex trisperma and C. paupercula). The Natural Heritage Inventory has split out two entities, identified (but not strictly defined) by the two dominant species (see Black Spruce Swamp and Tamarack Swamp).
Tamarack (poor) swamp These weakly to moderately minerotrophic conifer swamps are dominated by a broken to closed canopy of tamarack (Larix laricina) and a frequently dense understory of speckled alder (Alnus incana). The understory is more diverse than in Black Spruce Swamps and may include more nutrient-demanding species such as winterberry holly (Ilex verticillata) and black ash (Fraxinus nigra). The bryophytes include many genera other than Sphagnum. Stands with spring seepage sometimes have marsh-marigold (Caltha palustris) and skunk-cabbage (Symplocarpus foetidus) as common understory inhabitats. These seepage stands have been separated out as a distinct type or subtype in some nearby states and provinces.
Tamarack (rich) swamp This forested wetland community type is a variant of the Tamarack Swamp, but occurs south of the Tension Zone within a matrix of "southern" vegetation types. Poison-sumac (Toxicodendron vernix) is often a dominant understory shrub. Successional stages and processes are not well understood but fire, windthrow, water level fluctuations, and periodic infestations of larch sawfly are among the important dynamic forces influencing this community. Groundwater seepage influences the composition of most if not all stands. Where the substrate is especially springy, skunk cabbage (Symplocarpus foetidus), marsh marigold (Caltha palustris), sedges, and a variety of mosses may carpet the forest floor. Drier, more acid stands may support an ericad and sphagnum dominated groundlayer.
