Why a bog is a better carbon store than a wood

Stand on a high moor on a drizzly August morning and it can feel like a bleak, empty place. It isn’t. Beneath your boots lies peat that has been accumulating since the last ice age, laid down by mosses, cotton grass and sedges at roughly a millimetre a year. A metre of peat represents a thousand years of patient work.

Peat soils cover around a tenth of the UK’s land surface and hold something in the order of three billion tonnes of carbon — many times more than all our woodlands combined. A living bog pulls carbon dioxide out of the air and locks it away in waterlogged, oxygen-poor conditions where decay all but stops. Drain it, and oxygen gets in. The same carbon starts leaking back out, and the bog flips from a store into a source.

What went wrong on our uplands

Most degraded moorland is degraded because of decisions taken for other reasons. From the 1950s onwards, thousands of kilometres of grips — open drainage channels — were cut across blanket bog to "improve" rough grazing. Some have cut a metre or more into the peat and drained the bog for tens of metres either side.

Add the other pressures and the picture is familiar to anyone who walks the Pennines, the Cheviots, the Flow Country or the hills of mid-Wales:

• Heavy grazing that strips the moss and heather layers and exposes bare peat.
• Rotational burning that can leave the peat surface dry, black and vulnerable.
• Atmospheric pollution that loads the bog with nitrogen and encourages rank grasses over sphagnum.
• Wildfire, which can smoulder in dry peat for days and release centuries of stored carbon in a week.

The result is bare peat hags, crumbling gullies, discoloured streams and a landscape that sheds water fast and holds carbon poorly.

The repair kit: sphagnum, dams and bare peat

Restoration is unglamorous, physical work, and it is remarkably effective. Three techniques do most of the heavy lifting.

• Gully blocking. Stone, timber, coir or plastic piling dams are placed across erosion channels to slow the water and raise the water table. Sphagnum and cotton grass then colonise the wet ground behind them, and the gully stops growing.
• Sphagnum reintroduction. Sphagnum mosses hold many times their own weight in water and are the engine of peat formation. Plugs and beads of locally sourced sphagnum are planted into wet hollows, often by hand, sometimes by helicopter on remote ground.
• Bare peat stabilisation. Exposed peat is dressed with lime, fertiliser and seed, then mulched with heather brash cut from nearby. The brash shelters seedlings, adds fibre and holds the surface against wind and rain until a plant cover takes hold.

Get the water table back within a few centimetres of the surface and the bog does the rest itself, given time and a reduction in grazing and burning pressure.

Reading the landscape as you walk

Restoration leaves signs you can learn to spot, and they make a moor walk far more interesting.

• Lines of small dams marching up a gully, often with peaty pools behind them.
• Brash-covered patches of dark peat, greening over within a season or two.
• Pale green sphagnum carpets in the wet hollows, springy underfoot and worth avoiding in dry spells.
• Cotton grass heads in June and July, the classic sign of a rewetting bog.
• Clearer, less peaty water in the streams below restored ground.

If you walk the same route each year, you will notice the change. Bare peat greys and greens, gullies fill with vegetation, and the bog starts to look like a bog again rather than a building site.

Walking lightly on fragile ground

Restored peat is easily damaged, and a few habits make a real difference.

• Stay on the path, even when it is muddy. Widening a trod across bare peat starts a new erosion line.
• Keep dogs on a lead from early spring through to late summer, when curlew, golden plover and dunlin are nesting on the open ground.
• Avoid cutting corners on zigzags and boardwalk sections; the edges are the weakest part.
• Take care with stoves and cigarettes. Dry peat can catch from a single spark and burn underground.
• Report problems — dumped waste, fly-tipping, damaged gates, new erosion — to the landowner or the relevant national park or upland partnership team.

Come equipped for changeable weather too: waterproof boots with ankle support, a paper map and compass in a case, and spare layers. Moorland navigation in cloud is a genuine skill, and the ground underfoot is often wetter than the map suggests.

A moor that works for wildlife and for us

A rewetted moor is not just a carbon store. Sphagnum holds water and releases it slowly, which takes the edge off downstream flooding and reduces the amount of discoloured organic carbon that water companies must strip out before it reaches your tap. Wet peat does not burn as readily, so wildfire risk falls.

Wildlife responds quickly. Dunlin, golden plover and curlew return to nest on wetter ground. Merlin and short-eared owl hunt the open moor. Adders and common lizards bask on the drier banks, while cloudberry, cranberry, bog rosemary and insect-eating sundews reappear in the wetter flushes.

None of this happens overnight. Peat takes a thousand years to build a metre, and a restored bog will not be pristine in your lifetime. But the direction of travel is set by the water table, and that is something we can put right with dams, plugs, brash and a bit of patience. Walk out, look for the sphagnum, and you are watching climate action that fits in a rucksack.