What is sphagnum moss and why is it important?

Wednesday 7 December 2022

Jenny Bennion

Jenny is our Peatlands Communications Officer, working hard to let people know all about just how precious our peatlands really are. Jenny is never happier than when scrambling around in bogs and mosslands.

Sphagum moss by Ross Hoddinott/2020VISION

Sphagnum moss is a very special type of moss which is only found in wet acidic areas such as peatlands, in fact it creates the peat itself. Find out how it does this and why it matters…

We find mosses everywhere; on damp shady walls, in our lawns, and growing along the edge of paths. And whilst all moss is special, sphagnum moss is very special indeed. Sphagnum moss is found on peatlands and other wet habitats, and is in fact the keystone species of our precious peatlands.

Like all mosses, sphagnum is a non-vascular plant which means that it grows without roots and absorbs all of the water and nutrients it needs directly through the surface of its leaf-like scales. Sphagnum in particular thrives in wet and acidic conditions. In fact, sphagnum moss is able to actually change the pH of its habitat, making it more acidic to suit its preferred growing conditions.

Video: Bog chemistry - what makes bogs acidic?

Red and green sphagnum mosses growing in a healthy peatland habitat — Sphagnum mosses by Mark Hamblin/2020VISION

How does sphagnum moss form peat?

Apart from a few open water bog pools, a healthy peatland will be covered in a carpet of sphagnum mosses. This will feature numerous different varieties of sphagnum mixed in with other specialist peatland plants such as cotton grasses, heathers, bog rosemary, sundews, bog cranberry, white beak sedge, bog asphodel, along with other mosses such as common haircap.

The combination of this dense carpet of vegetation and the acidic water-logged conditions means that as the top layer of plants grow, the lower layers become effectively ‘pickled’ (in fact bog water is as acidic as the vinegar in a jar of pickled onions!). This means that the vegetation only partially decomposes. Over time this then becomes compressed and forms peat.

Video: How acidic are peatlands?

What has sphagnum moss got to do with the climate emergency?

As peat forms from only partially decomposed plant matter it means that the carbon that has been absorbed by the plants through photosynthesis whilst they were living becomes trapped in the peat. The waterlogged and anaerobic (without oxygen) conditions results in the carbon being locked away in the peat for millennia.

Peatland habitat with green sphagnum moss and white cotton-grass seed heads — Little Woolden Moss in Greater Manchester is an example of a lowland raised peat bog.

In fact, peatlands are our largest terrestrial carbon store. Whilst they only cover between three-four per cent of the world’s surface, they store a third of all soil carbon – that’s twice as much as rainforests!

In the UK, peatlands only cover about 12 per cent of our land surface, but store as much carbon as the forests of the UK, France and Germany combined. And the amazing thing about peatlands is that as they continually form peat they are able to sequester (absorb) even more carbon from the atmosphere, making them a vital natural resource in our fight against the climate emergency.

However, as soon as a peatland is damaged or degraded in any way all of that stored carbon is released into the atmosphere as carbon dioxide. Scarily at least four per cent of all UK greenhouse gas emissions come from degraded peatlands, a massive number when you think that aviation accounts for approximately seven per cent of emissions.

How can sphagnum moss help alleviate flooding?

Sphagnum moss is able to absorb up to 20 times its own weight in water, holding it in special empty cells within its structure. This means that sphagnum and the peat it forms acts like a giant sponge, absorbing rainfall and releasing it slowly. Peatlands can therefore act as amazing natural flood mitigators.

However, if a peatland is dry and degraded then the water will run straight off the surface straight into water courses and can actually make flooding worse.

Green sphagnum moss held in a hand — Sphagnum moss at Winmarleigh Moss SSSI by Simon Hutchinson

Can sphagnum even support biodiversity?

Yes! Without sphagnum there are no peatlands. These amazing habitats support a wide range of rare and specialised plants and animals. Everything from our native carnivorous sundew to endangered curlews rely on peatlands to survive.

And sphagnum moss itself is really diverse. There are approximately 30 species of sphagnum in the UK, with over 300 species known globally. Our UK varieties come in numerous shades of green, yellow, brown, orange and red. Some species such as sphagnum cuspidatum favour fully aquatic conditions, whilst others concentrate on forming giant hummocks above water level, such as the wine-red sphagnum rubellum.

We should all love sphagnum!

So yes, sphagnum is moss. But it is so much more than ‘just moss’. It is a climate change challenging, flood fighting, biodiversity boosting superhero! If you ever get chance to visit one of our amazing peatlands, plunge your hand into sphagnum’s soft, squishy mass, give it a pat and say a huge ‘thank you’!

Find out more about our peatlands work