Northern tamarack swamps are characterized by their moderately minerotrophic soil, canopy dominated by tamarack, and prevalence of tall shrubs, usually with at least 5% cover, often up to 25% cover or more. While tamarack may co-dominate (or even be locally dominant in) black spruce swamps, that community has more acidic soil, a sparse layer of tall shrubs (5% cover or less), and a more continuous carpet of Sphagnum moss. While Sphagnum moss occurs in northern tamarack swamps, it usually forms a discontinuous layer and is concentrated on hummocks elevated above the moderately minerotrophic groundwater or surface water. Northern tamarack swamps sometimes grade into alder thickets, which are generally classified as having fewer trees (<25% cover, usually much less) and higher coverage of tall shrubs (50% cover or more). Northern tamarack swamps also occur adjacent to central poor fens, which are also generally classified as having no more than 25% cover of trees.
Northern tamarack swamps are similar to southern tamarack swamps, but the latter tend to be more minerotrophic with a greater prevalence of calciphiles such as poison sumac (Toxicodendron vernix). Although the two communities generally occur in the northern and southern parts of the state, respectively, they do overlap somewhat in the central sands region. Although the region is within and south of Wisconsin's climatic tension zone, northern tamarack swamps are common in the ancient lakebed of Glacial Lake Wisconsin where flat, acid peatlands are underlain by nutrient-poor sands. Just to the east in the hills above the ancient lakeplain, southern tamarack swamps predominate due to the more minerotrophic groundwater seeping through the calcareous glacial deposits. Thus, nutrient status and the relative abundance of calciphitic species is more useful than latitude in differentiating the two communities.
