How do Peatlands Form ?

It took thousands of years for peat to accumulate and create the conditions that we find in Maine's peatlands. The cool, wet climate of Maine and eastern Canada provides the perfect setting for peatlands to form. The development of peatlands is influenced by the lay of the land, or topography, the underlying soils, the way water flows through the soils (see section on hydrology), and the climate found in a particular region.

Most of Maine's peatlands are found in the central and eastern parts of the state, including the interior foothills, and the eastern lowlands and foothills. Glaciers retreated from Maine roughly twelve thousand years ago and left behind soils made up of clay, silt, sand, gravel and boulders. In some deep deposits of these materials, large blocks of ice were buried. After the ice melted, depressions were left in the landscape, many of which became ponds or lakes. In low areas of southern Maine, glacial soils were overlain by marine sand, silt, and clay deposited during the period of time when this region was flooded by ocean waters. The erosion of these glacial and marine materials on the landscape created conditions favorable for peat development.

There are two major ways that peatlands develop over time:

Terrestrialization is the process that forms "quaking" bogs. The peatland develops as a lake basin gradually fills in from the edges with sediment and peat-forming plants. These plants are only loosely attached to the lake bottom, or float above the water like a raft. As the peat layers grow, eventually the living plants may become raised above the water table and the nutrient conditions will change to that of a classic raised bog.

With paludification, a bog is essentially spilling over onto land that is dry. This can result from changes in climate, changes in the surrounding landscape that influence the way water flows around or in the system (beaver activity or logging of forests), or simply the spread of the peat mat as it continues to build up. This occurs naturally as lower layers of peat become compacted and impermeable, thus increasing the amount of water collecting or flowing from the edges of the bog. This is followed by a transition from upland communities to those characteristic of bogs.