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Introduction to Peatlands
Bogs have historically been perceived as dangerous and mysterious places. The first time I explored a bog, I felt that sense of danger and wonder, and something else, a feeling of wildness that is usually hard to come by unless I am far from any signs of human development. I immediately understood why bogs are so often the setting of stories where magical creatures exist, not to mention the monsters. The sights, sounds, and smells seemed very new and very old at the same time.
Trees dwarfed by the harsh environment, thick-leaved shrubs with bright and pungent flowers, insect-eating plants, the quaking earth beneath me, all gave me the sense that here was a place where nature can be seen at its most timeless, and most enchanting. Every time I set foot into unfamiliar, boggy terrain, I feel as if something draws me forward, deeper into the wild. What are bogs, and what makes them places of such mystery?
The word "bog" is often misused - in common language it refers to a type of wetland called a 'peatland.' On these pages, we will use the more general term of peatland in reference to these wetlands, and clarify the difference between bogs and 'fens,' another type of peatland common in Maine and the Northeast.
What are Peatlands?
Peatlands are wetlands that form through the accumulation of partially decayed plant materials, or peat. Peat is commonly formed from sphagnum mosses (peat moss) and sedges. Plants that are adapted to saturated conditions grow on top of the peat and add more decomposing plant material. Because the accumulation of plant materials exceeds the rate of decomposition, the build up of peat grows deeper. The depth of peat in a particular wetland, the way water flows through it, and how it receives nutrients helps to define particular kinds of peatlands.
In Maine, we have many types of peatlands that fall under two major categories: bogs and fens.
In bogs, the peat has built up to such an extent that the living vegetation is raised above sources of surrounding surface water or underlying groundwater. These raised peatlands are called ombrotrophic (rain-fed), and receive water solely from the precipitation of rain, snow, or fog. Because the amount of mineral nutrients carried by precipitation is very low, bogs are the most nutrient poor of peatland communities. The lack of minerals contributes to highly acidic conditions in bogs. The plants, animals, and microbes that are characteristic of bogs have special adaptations to these nutrient poor and acidic conditions. Sphagnum or peat mosses are typically the dominant plant in raised peatlands, and are the most common plant to make up peat. Shrubby plants common to this wetland include labrador tea, small-leaved cranberry, and leatherleaf.
Plant decomposition is slow in raised bogs, so peat continues to build up over time. Eventually, water draining from the built up peat layers of the raised bog changes the way the water flows in the surrounding wetland communities, which may lead to changes in nutrient content, acidity of the water, and the types of plants that grow in these communities.
Fen is a less commonly known term for a specific type of peatland that receives some water from the ground or surface runoff in addition to precipitation. This water picks up minerals and nutrients as it comes in contact with soils and bedrock, leading to minerotrophic (mineral-nourished) conditions. Fens vary from being nutrient rich to nutrient poor, depending upon where the water comes from. A greater variety of plants grow in fens that have higher nutrient content. Fens also tend to be much less acidic, as the water from mineral soils surrounding or underlying the fens carries minerals that buffer or reduce the acidity. Many of the bogs you will see named on maps, such as Alton Bog, are actually fens.
Most peatlands in Maine are part of larger wetland complexes, which are made up of several different kinds of peatland and other wetland communities. For example, raised bogs often drain into fens, which then may transition into forested swamps before reaching the upland boundaries.
Why are Peatlands Important?
Peatlands play a significant role in the larger landscape. They provide habitat for a great diversity of native plants and wildlife, resting and feeding areas for migrating birds, a source of water that may supply downstream areas, protect water quality through purifying the water, and protect upland terrestrial areas from flooding. These wetlands also have value as areas for scientific research, nature study, and recreational use.