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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.
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.