Northern Wisconsin Wetlands

A wetland is an area saturated by surface or ground water long enough to support vegetation adapted to life in saturated soil conditions. No two wetlands are exactly alike. We can, however, classify wetlands into some broad categories. In the field, it is often difficult to classify wetlands without a detailed look at the hydrology, vegetation, and types of soils.

Marshes

A marsh is a wetland developed on mineral soil and characterized by emergent aquatic plants such as cattails, reeds and rushes that grow in shallow water. Marsh soils have a high mineral content and plant biomass productivity is high. Marshes are among the most productive of all wetlands for waterfowl and muskrats. There are few true marshes in northern Wisconsin.

Northern Sedge Meadows

Northern sedge meadows are wet, "grassy" meadows. They have a moderate amount of mineral nutrients and are dominated by a low growth of various sedges and grasses.

Shrub Swamps

Shrub swamps are rich in minerals and have understories of various grasses, sedges and ferns. There are two types of shrub swamps in Wisconsin. Alder thickets are dominated by speckled alder and occur primarily along streams. Shrub-carrs are dominated by species of willow and red-osier dogwood. They occur in areas with a supply of mineral ground or runoff water. Shrub-carrs are uncommon in northern Wisconsin.

Conifer and Hardwood Swamps

Forested swamps are rich in minerals and highly productive. Examples of swamps include northern white cedar swamps and black ash swamps.

Peatlands

Peatlands develop in cool, humid regions where water drainage is blocked. In northern Wisconsin, glaciers formed the landscape into shallow lakes and depressions conducive to the formation of peat. Peat is a soil made up of partially decomposed plant remains. It develops under water-soaked conditions, and has a low content of nutrient minerals. There are two distinct types of peatlands.

If the water flowing across the peatland surface originates on an adjacent upland, the vegetation can be quite distinctive. Such a peatland is called a fen. Fens are dominated by sedges and grasses, often with scattered shrubs such as bog birch and tamarack. Fens are fairly rich in minerals and moderately high in productivity. Rich fens have high mineral nutrient content while poor fens have only moderate mineral nutrient availability. Most of the fens of northern Wisconsin are poor fens.

If the peatland surface is raised slightly above the level plain, the mineral-rich water will be diverted, and the peatland becomes a bog. Bogs accumulate water-soaked organic matter and are characterized by plants that can grow under water conditions of relatively high acidity and low nutrients.

Muskeg

Over time, bogs can develop into muskeg. Muskeg is an acid peatland supporting black spruce, an understory of shrubs, and a ground cover of sphagnum mosses. Without disturbance, muskeg can dominate peatlands for thousands of years.