Bogs - Northern Peatlands
Northern peatlands, commonly referred to as bogs, occur as thick peat deposits in old lake basins or as blankets of peat across the landscape. Their formation is due to the combination of cool temperatures and adequate rainfall in northern temperate regions around the earth. Michigan's northern peatlands are usually divided into two categories: bogs or fens. In scientific terms, the main difference between a bog and a fen is based on the connection of the peatland to a source of groundwater or mineral-rich surface water.
Bogs form in lake basins that are isolated from sources of ground water. Because normal rainwater (the only water source for true bogs) is slightly acidic, bog water tends to be slightly acidic. The acidic nature of bogs supports acid-loving (acidophilic) vegetation, especially Sphagnum mosses, and contributes to a deficiency in available plant nutrients. As a result, many plants, animals, and microbes have special adaptations.
An example of a unique adaptation can be found in vegetation such as the pitcher plant and sundew, which attain nutrients by catching and "digesting" insects.
Other vegetation adapted to the highly acidic and nutrient poor conditions include
- black spruce trees
- shrubs such as leatherleaf, blueberries, and cranberries
- sedges such as cotton grass.
Although bogs can form in a number of ways, the most common in Michigan is the development of a "quaking bog." Typically, this successional process involves a small isolated lake basin (most likely a depression created when a large block of ice melted after the glaciers retreated) that is gradually taken over by the accumulation of organic matter formed from the life and death of thousands of generations of plants growing on the edge of the basin. Since the production of plant material outstrips decomposition, the dead plants at the water's edge accumulate to form a floating mat of peat. Over many thousands of years, a mat of mosses, reeds, sedges, grasses and other herbaceous plants develops along the leading edge of the floating mat. The older peat is then colonized by shrubs and eventually trees such as tamarack and spruce which form concentric rings around the advancing floating mat. When one ventures out onto this floating mat, the ground underfoot "quakes" with every step.
If a true bog is at one end of the northern peatland spectrum, then a calcareous (alkaline) fen is on the other. A calcareous fen (sometimes called a true fen) receives water that has passed through mineral soils rich in limestone. The ground cover in these peatlands is usually dominated by grasses, sedges, or reeds instead of Sphagnum moss. A poor fen lies somewhere between a true bog and a true fen on the peatland spectrum. Due to the accumulation of peat over time, a gradual reduction in ground water flow through the fen occurs, and the water chemistry becomes more and more acidic. The resulting system is dominated by a combination of plants typically found in both bogs and fens, including sedges, Sphagnum moss, leather-leaf, tamarack, bog laurel, bog birch, and other plant species typically associated with bogs like sundew and pitcher plants.