Mosses are small, green, terrestrial plants that most people usually associate with the tropics or coastal rainforests. They are indeed a dominant plant type in those habitats, but also are able to grow in steppe desert or tundra habitats, in addition to many other habitats where most plants are unable to grow.

Although mosses share many features with vascular plants, they have many more unique adaptations or habits that make them different from these. There are three in particular that are of special interest: their small size, their restriction to microhabitats, and desiccation tolerance. It is the combination of all three that allows these small plants to grow in places that most plants can only dream about!

Compared to most vascular plants, mosses are quite small. The largest mosses in Canada are at most 20 cm tall and the smallest is less than 2 mm tall! The reason for their small size is their lack of wood. Wood provides most plants, like trees, the rigidity and strength that allows them to grow to enormous size. Being small may seem like a disadvantage because it prevents mosses from competing against larger plants for light and water. Far from being a disadvantage, small size allows mosses to grow in microhabitats where there is no competition with other plants. Microhabitats are ‘mini-habitats’ that differ from the surrounding environment in humidity or moisture levels, light, temperature, or substrate. Examples include rock crevices, tree trunks, and rotting logs.

The third feature that is unique to mosses is an adaptation termed ‘desiccation tolerance’. Desiccation tolerance allows mosses to dry out completely but upon re-wetting to become active and start growing again within minutes. This enables the mosses to grow on surfaces that dry out very quickly after they have been wetted, or to grow in extreme habitats.

During a 2013 survey of mosses in the Mackenzie Mountains, we found several species that showcased the ability of mosses to grow in difficult places. For instance, at one site near Carcajou Lake, a very small moss (Seligeria sp, “small limestone mosses”) that barely reaches two mm in height was found growing on the side of small rock crevices near the top of a barren rock knoll in the middle of wide expanse of tundra. Another species, Blytt’s granite moss (Andreaea blyttii), was found growing on boulders that had been recently exposed from under a cover of snow in a late melting snow patch at high elevation in the middle of August. And, a third species newly discovered in the NWT, water grimmia moss (Grimmia mollis), was found at high elevation growing on rock in a stream of meltwater from late snow. These are just a few examples of mosses that eke out a living in difficult habitats that are common in the mountains of NWT.

Although numerous interesting mosses were found on this 2013 survey, large areas of the NWT remain unexplored and poorly documented for their mosses. Effective conservation of these small plants will depend on further surveys to determine in some detail their diversity and occurrence on the landscape. Unfortunately, such surveys are few and far between.

The most recent, extensive, survey in 2018 focused on cataloguing the mosses associated with waterfalls along the Waterfalls Route, and searches were also conducted for the species at risk Porsild’s bryum. This species is listed as Threatened in Canada and is associated with shaded limestone cliffs that are bathed in seepage. While numerous new records of mosses were recorded, Porsild’s bryum was not found, a result that supports its rare status in Canada.

There are many questions asked about mosses, perhaps the most common is “How are they useful and can they benefit people?” From an ecological perspective, mosses are known to be important components of the environment. For instance, in peatlands, they control water flow over large areas by quickly absorbing large amounts of water (like a sponge) and releasing it slowly, thereby avoiding flooding. Peatlands are especially important in the NWT. Further, while mosses generally comprise a relatively small proportion of the biodiversity in many areas, they are nevertheless important in northern regions. About 35% of the total moss species known from Canada occur in the NWT!

Mosses have benefited northern peoples in many direct ways. For instance, peat moss and false willow moss are both used to mask smells from traps in winter. Also, peat moss and other mosses have been used in children’s diapers because of their absorptive properties and softness against the skin. Several mosses have been used as absorbents, fire starters, and for chinking; many generations have stayed warm during long winters with the help of mosses.

There are 495 species of mosses confirmed present in the NWT. At least one additional species is expected to be present.