Mosses are primitive plants that, while small and easily overlooked, control water in many of our district’s ecosystems and are vital in keeping atmospheric carbon in balance. They are unlike trees, shrubs, herbs and ferns in having no specialized transport tissue (plumbing for moving water from roots to leaves). Their leaves are just one cell thick. They have no flowers or seeds. Instead they reproduce by spores, but also by cloning themselves from fragments. In spite of their association with damp locations, mosses are remarkably capable of surviving drought. They can reabsorb water as soon as it is available, have incredible powers of cellular repair and can start to photosynthesize once re-hydrated even after being stored inside in a collection envelope for months.
Their big impact on the environment is partly due to their small size. Being low to the ground and without transport tissues they have large specialized leaf cells in direct contact with their environment. This means they are capable of rapid water absorption and thus absorb extreme rainfall events. Their ability to clone themselves from fragments means they can rapidly colonize almost anywhere and both create and stabilize soils. They can gain scarce nutrients from poor soils and even bare surfaces because they are very good at cation exchange. They dump positively charged hydrogen ions into the environment to bump loose and trade for a positively charged nutrient ion. They are much more effective than many other plants at this trick, which in some situations allows them to take over, by increasing the acidity so much that other plants can no longer access nutrients. This, and their ability to create and tolerate waterlogged conditions is how a peat bog is built.
Last week the World Wildlife Fund released a map https://wwf.ca/carbonmap/ of Canada’s peatland carbon stores, created by fascinating research out of McMaster University’s Remote Sensing Lab. It shows dense carbon stocks in a huge swath of Northwestern Ontario and northern Manitoba, as well as significant deposits around Lake Winnipeg. Of interest locally is that the machine learning algorithm they used to create this map picked up one of our bogs, the Agassiz Peatlands Provincial Park near Gameland, as one of the denser deposits.
Soils store much more carbon than plants, and among soils peatlands are the richest in carbon. Peatlands get their name from partially decomposed plant matter which we call ‘peat’, much of it mosses such as sphagnum moss. Peat can accumulate to great depths when mosses grow over themselves over the centuries but don’t fully decompose in the cold, acidic and waterlogged environments where they thrive. The WWF map background estimates that in northern Canada, one square metre of peatland contains about five times as much carbon as the same area of Amazon rainforest. While the carbon stored in typical tropical or boreal forest soil is between 100 to 500 years old, boreal peatland carbon can be up to 10,000 years old. This means that although our bogs are carbon sinks, it is important to recognize them as old sinks more likely to leak their vast carbon stores than to be of help in drawing down carbon dioxide if we’re not careful with them.
Bogs do not grow quickly, and the carbon in them represents carbon locked in over a long period of time. In Alberton Township the Rainy River Valley Field Naturalists established an interpretive boardwalk trail in a bog which was mined for moss during the second world war. While walking the trail you will feel as though you are surrounded by a soft cushion of deep sphagnum, but if you explore the area on google maps you’ll notice that although it was last mined more than 50 years ago, you can easily see traces of the harvest. As Canada is home to one quarter of the world’s remaining peatland carbon stores, disturbance for development, drainage, thawing and increased decomposition of our peatlands is likely to put us on the wrong side of the carbon balance sheet.
Ilka Milne is President of the Rainy River Valley Field Naturalists. The Rainy River Valley Field Naturalists promote appreciation, education, conservation and wise use of our natural environment in the Rainy River watershed. Visit us at www.rrvfn.org