Sphagnum mosses are plants which you might easily overlook as you squelch through our bogs. They are star players in the creation and persistence of these wetlands though, thanks to their ability to retain water. They provide habitats and soil conditions for a wide variety of wildlife, and are part of the vital carbon storage system that Irish bogs provide.
Sphagnum is the name given to a genus (the grouping of life above species) of mosses that occur in Irish bogs. There are 24 species of Sphagnum in Ireland, and show several different growth habits – some form spread-out “carpets” on the surface of the bog, while other form lumpy hummocks or “pincushions”. Mosses differ from other plants in that they are “non-vascular” – this means they do not possess a dedicated internal system to transport food and water, and also lack roots. They absorb water through their bodies, and are anchored in their substrate by structures called rhizoids. This means they are somewhat restricted to living in wet places where their bodies can physically hold onto water. They do this exceptionally well however, absorbing up to 20 times their weight in water by collecting it in the hummocks and carpets they form, as well as inside their bodies.
It is this ability to retain water that makes Sphagnum such an important member of the bog ecosystem. Bogs are created in areas where water drains from the soil very poorly, and where an accumulation of dead plant material can occur. In lakes with poor drainage, plants such as Sphagnum which die can settle at the lakebed, where they decay very slowly due to the poor oxygenation of the water. At the lake’s banks, more Sphagnum and other plants can grow on top of this material, assisting in the conversion of the lake to bog. As plant material builds up, it begins to compress under its own weight to form peat, and eventually the lake becomes filled with dead plant material – what was once a lake is now a bog! The continued growth of Sphagnum is very important to the persistence of bogs – it plays a vital role in retaining water in the bog system, and preventing the decay of plant material.
Different species of Sphagnum grow tolerate different levels of moisture, nutrients and acidity in our bogs, and so you will different types in different areas of the bog. Sphagnum cuspidatum (feathery bog-moss) grows in bog pools for example, lurking just beneath the surface of the water. Other species such as Sphagnum magellanicum and Sphagnum papillosum grow on the above-water surfaces of the bog in mats or low hummocks.
Sphagnum plants provide a lot of benefits for other wildlife in our bogs. Their dead parts act as a substrate for larger plants like heathers to grow in. Microscopic life thrives amongst Sphagnum as well – the water they hold onto forms the habitat for creatures such algae, amoebae and worms. These creatures in turn provide a food source for animals such as frogs, dragonflies and damselflies, and beetles. Sphagnum species help to acidify the soil of the bog too during their process of extracting nutrients from the soil. This acidic soil doesn’t sound too pleasant to us or many of our ornamental houseplants, but plants with special adaptations to acidic, waterlogged soils thrive here. Heathers and bog cotton provide not only beautiful flowers, but also food for insects and birds. Carnivorous plants also make their homes in our bogs, needing to trap and digest animals to make up for the poor nutrient content of bog soil. These include the sticky-stemmed sundew which traps and curls around flying insects, and bladderwort, which sucks aquatic insects into specialised digestion chambers.
- Around 1,085 megatonnes (1,085 million tonnes) of carbon is stored in Irish bogs, which accounts for more than half of all the carbon stored in our soils in just 16% of our land area!
- Sphagnum moss was once harvested widely during World War 1 for use as wound dressings – it absorbs blood and pus just as well as water!
- Spahgnum mosses are used in gardens to modify the soil and as a potting medium – to help preserve our bogs, why not try starting your own compost heap using kitchen and garden waste instead?
Written by Tom Murphy