PEATLANDS
THE FORMATION OF PEAT
The process of forming peat takes place over centuries and consists in the slow accumulation of partially decomposed vegetation debris in wetlands called peatlands. In Canada, these wetlands have developed after deglaciation on poorly drained soils and shallow depressions, under cool, moist and oxygen-poor conditions. In this type of environment, bacterial action is much reduced resulting in a rate of plant production that exceeds the rate of decomposition. Over time, slowly decomposing vegetation debris accumulates leading to the development of a peat deposit that, in some places, can exceed 6 m in thickness. The rate at which peat forms in Canadian peatlands ranges from 0.5 to 1 mm per year.
Poorly drained site
on mineral soil
Accumulation of
organic matter
Infilling of the depression
and consolidation
Development of a
raised dome of peat
THE ROLE OF PEATLANDS
Peatlands provide unique ecosystems as rich as they are surprising because they rely on a distinctive operating mode in terms of their hydrology, their origin, their soil and the different species living inside them.
Peatlands reduce pollution levels in adjacent aquatic ecosystems by recycling elements, storing organic materials and trapping pollutants discharged into the water.
Although they exhibit a high water table and are often compared to sponges, peatlands play a limited role in attenuating flood peaks in their watershed during wet periods because they are already water-saturated. However, in dry periods, they can contribute to reduce summer flooding and to support low flows in rivers.
Since they accumulate organic matter over time, peatlands represent a significant carbon reservoir and assist in reducing the amount of greenhouse gases in the atmosphere. Restoring the natural functions of peatlands after peat harvesting allows the process of storing carbon to be restored.
Peatlands offer very particular conditions: they are home to a variety of mosses, carnivorous plants, shrubs and orchids. Some of these plants have medicinal properties and are used today in pharmacology. Peatlands also serve as a pantry, nesting areas and hunting grounds for several species of mammals, birds and insects. For example, the southern bog lemming (Synaptomys cooperi), the dragonfly (Somatochlora brevicincta) and the palm warbler (Dendroica palmarum) are closely linked to this unique habitat.
Peat is a popular element not only in horticulture but also for various other usages. The horticultural peat industry is an important economic vector in the regions where it operates because it provides high-quality jobs in often remote areas.
Peatlands provide many opportunities for recreational activities such as a bird-watching and nature photography. Another good example of recreational use is the Mer Bleue Bog located in Ottawa, the second largest bog in southern Ontario.
Peatlands are a perfect preserving agent! The analysis of the superimposed layers of peat helps in the collection of information on living species from the past. For example, the study of pollen preserved at various depths in a peatland allowed scientists to reconstruct climatic conditions and different vegetation types over the last 10,000 years.
TYPES OF PEATLANDS
There are two main types of peatlands: bog and fen. They differ from each other by their vegetation, hydrology and water chemistry.
Bogs are mainly characterized by a vegetation that is well suited to high-humidity conditions (high water table) and a general lack of nutrients. The surface of a bog is often raised in the form of a dome and its main source of nutrients comes from precipitation and wind.
Principal features
- Water and nutrients intakes are carried by precipitation (rain and snow) and wind
- Acidic water of pH < 4.5
- Dominant vegetation: sphagnum mosses accompanied with ericaceous shrubs and softwood trees (larch and black spruce).
Fens are mainly characterized by a high water table, but with a very slow internal drainage by seepage along very low slopes. The surface of a fen is either flat or very gently sloping; it receives water that has been in contact with upslope mineral substrate enriched with dissolved nutrients.
Principal features
- Water and nutrients intakes are carried by precipitation (rain and snow) and by groundwater runoff
- Acidic to slightly alkaline water of pH ranging from 4.5 to 7.5
- Dominant vegetation: brown mosses (from the Amlystegiaceae family) and herbaceous plants (sedges).
PEATLAND DISTRIBUTION
Peatland distribution in Canada’s provinces and territories (Source: Tarnocai et al 2011)
IN CANADA
Peatlands cover 113.6 million hectares in Canada, or approximately 13% of the country’s surface area, and are present in all provinces. The largest peatland concentration is located in the Hudson’s Bay lowlands of Ontario and Manitoba. Peatlands are also abundant in northern Alberta, central Saskatchewan, Quebec and in the Atlantic provinces.
In Quebec
Quebec has 11,6 million hectares of peatlands, which corresponds to about 8% of the province’s area, of which nearly 85% are located north of the 51st parallel.
In New Brunswick
New Brunswick’s peatlands cover approximately 2% of the province’s land surface with an estimated total area of 140,000 ha.
Percentage of the peatlands surface area by country
Source : Xu, J., P. J. Morris, J. Liu and J. Holden (2017). « PEATMAP: refining estimates of global peatland distribution based on a meta-analysis. » Catena 160: 134-140. http://archive.researchdata.leeds.ac.uk/251/
IN THE WORLD
Peatlands cover some 423 million hectares of the Earth which represents 2.8% of the total land surface area (Xu et al., 2017). Peatlands are more widespread in Asia (38% of peatlands) and in North America (32%) followed by Europe (12%) and South America (11%).
Canada contains 27% of the world’s peatlands and is the second country with the most peatlands after Russia.
PEATLAND VEGETATION
In boreal and temperate regions, sphagnum mosses are one of the primary components of peatland vegetation. They play a very important role, as they give peat its valued horticultural properties and form a virtually unbroken cover where other plants may establish and grow.
Plants typical of bogs:
Since bogs are nutrient poor, wet and acidic, their biodiversity is low and composed of plant species that are specially adapted to these conditions. The bogs are usually made up of sphagnum mosses, ericaceous species (blueberry, leatherleaf, Labrador tea, rhododendron), carnivorous plants (pitcher plant, sundew), cotton grass, black crowberry, cranberry and black spruce.
Plants typical of fens:
Fens benefit from an input of mineralized water and display a greater biodiversity of plants. They are home to cattails, herbaceous and vascular plants, in addition to shrubs and the occasional tree. Some of the plants found in bogs also grow in fens. In fact, it is the presence of minerotrophic plants that determines whether a given peatland is identified as a fen or as a bog.
PEATLAND PLANTS
PHOTO GALLERY
Sphagnum mosses are water-filled plants that form green or reddish cushions. They consist of a main stem with tightly arranged clusters of branch fascicles usually including two or three spreading branches and two to four hanging branches. The top of the plant, or capitulum, has compact clusters of young branches. Along the branches and the stem are scattered leaves of various shapes; the shape varies according to the species. The leaves consist of two kinds of cells: small, green, living cells (chlorophyllous cells), and large, clear, structural, dead cells (hyaline cells). The latter have a larger water-holding capacity.
Sphagnum mosses grow quickly, from 2 to 12 cm per year. As the moss grows, its lower parts die and accumulate beneath the surface to gradually form peat. There are over 160 species of Sphagnum mosses growing worldwide.
It is a low shrub growing up to 50 cm tall with evergreen leaves. The leaves are wrinkled on top, densely hairy white to red-brown underneath, and have a leathery texture, curling at the edges. The tiny white flowers grow in hemispherical clusters and are very fragrant and sticky. Since it prefers drier conditions, Labrador tea is found mostly on hummocks (small mounds) and along the perimeter of peatlands. It is a popular ingredient in herbal teas and is widely used by Indigenous populations.
Sundews are perennial herbaceous plants forming rosettes. The name of this plant comes from the small drops of digestive juices that sit at the end of each leaf. This carnivorous plant traps and digests the insects that it needs to survive. Sundew grows in the moist, nutrient-poor, acidic soils amidst sphagnum mosses.
Cranberry is an evergreen, creeping, mat-forming plant with slender, intricately forking woody horizontal stems 30 to 150 cm long and upright flowering stems.
This plant has been used for food and for its medicinal properties by various Indigenous communities. The large cranberry is also a major commercial crop in North America.
This carnivorous plant is highly ornate compared to other peatland species. Inside their modified leaves, known as pitfall traps, a clever lining of downward-pointing hairs helps insects enter the cavity while blocking the exit. Once trapped, the insects struggle to exhaustion and drown in a pool of rainwater inside the leaf. A special enzyme generated by the plant dissolves the bodies of the trapped insects to supply valuable nutrients.
This herbaceous plant of the Cyperaceae family is a high (30 – 60 cm) tussocks-forming plant. It has elegant flower heads resembling tufts of cotton. It is common in natural peatlands but also as pioneer plants in disturbed areas.
This small rounded shrub of the ericaceous plant family is the most common vascular plant found in Canadian bogs. The underside of its leaves is speckled with rust-coloured spots. The plant is considered a herald of spring, as it blooms earlier than all other peatland species. This has given the plant its nickname «Cassandra» in reference to the Greek mythological figure who could predict the future but whose prophecies no one believed.
Carex is a vast genus of herbaceous plants of the Cyperaceae family, commonly known as sedges. The Latin name, Carex, comes from the Greek kairo, which means « I cut », in reference to the sharp edges of the leaves. The sedges resemble grasses, with their ribbon-shaped leaves and small, drab flowers. Unlike grasses however, sedges have full, triangular stems. Since sedges are very common, they are a food source for several species of mammals and waterfowl.
Scirpus are tall, blue-green herbaceous plants that grow in fens and marshes. They form large colonies that create natural nesting sites for birds. With their round hollow stems, cattails are used to make a wide variety of items, including carpets and mats. In addition, bulrush rhizomes and pollen were used as food by Indigenous populations.