Over a fifth of Scotland is covered by peaty soils. Soils built up over thousands of years – mainly by sphagnum mosses as they grow and die down. Layer upon layer, turning from lush carpets of green, gold and red to sometimes metres-thick blankets of dense, black peat. Without healthy sphagnum mosses there are no healthy peatlands.
To mark National Plant Health Week, we thought it would be a good time to talk about sphagnum mosses. Partly to explain why it’s so important they are healthy – but also because they are fascinating plants in their own right!
There are over 30 different species of sphagnum mosses found in the UK – and at least 380 worldwide. It’s this variety that gives those peatland carpets their beautiful patterns of colour and texture. Different species come in shades from deep red to vibrant orange, dark forest-green to palest eau de Nil. They each have their favourite positions across the bog – some preferring wetter, some drier conditions, some liking shade while some are sun-lovers.
The diversity of these mosses is what also makes sphagnum so good for other wildlife. The mounds and hollows, ridges and pools produced by these miniature plants create ideal homes for a wide variety of other plants and animals. You’ll find tiny insects and spiders, sundews and bog cotton, for example, and the bigger creatures that then feed on them – like dragonflies and moths, birds and lizards.
And it’s also what makes peatlands so good at slowing the flow of water off the hills. The rough surface of the bog that sphagnum creates is perfect for trapping rainfall, releasing it slowly instead of letting it rush off the surface to flood land lower down the catchment.
But sphagnum mosses do this for their own benefit – not ours! By each having their own niche across the surface of the bog they can avoid competing with each other for space, meaning they can all get enough moisture, light and nutrients for their needs. However, all sphagnum mosses need a lot of water. They don’t have any roots, so rely on growing in a very wet environment where they can absorb the water though their tissues. As they grow and rot down, they actually alter their environment to make it more hospitable for themselves – and less so for other plants.
In their sphagnum species showcase, the IUCN UK Peatland Programme describes how sphagnum takes up calcium and magnesium ions in the water, and puts out hydrogen ions, which makes the environment more acidic. These mosses like acidic conditions, as many other plants can’t grow and compete with them so easily. They also have compounds in their cells which inhibit decomposition. This slows the rotting process when they die, keeping the nutrient level low, which again stops other plants competing so successfully. It’s an added benefit for us that this builds up layers of carbon-rich peat that are vital to helping us tackle our CO2 emissions.
This is why water table needs to be near the surface on peatlands; to keep the sphagnum – the building blocks of the bog – healthy and growing. If the peat is drained, grasses, trees and heather start to encroach on the drying ground, beginning a vicious circle where the more vigorous plants start sucking the water out of the peat, making it drier still.
While some of Scotland’s peatlands are in good condition, over three quarters of them have been damaged, making it difficult for sphagnum mosses to thrive. Peatland ACTION is working hard to reverse this damage. Peatland restoration aims to raise the water table again, allowing sphagnum mosses to re-establish and create those healthy, multi-coloured carpets that are so important for the wildlife, and people of Scotland.
You can find out more about Peatland ACTION’s work on our Peatland ACTION web pages.
Scotland's Nature 
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