East Dartmoor’s Mires

East Dartmoor National Nature Reserve contains a diverse mosaic of habitats across its 365 hectares. One habitat type that can sometimes be overlooked amongst the larger, more conspicuous woodlands and heaths are the mires.

Mires are wet and acidic habitats dominated by layers of partially decayed vegetation, known as peat, often 0.5 – 3.0 m deep. Hidden amongst combes or on the open moors, mires include rain-fed blanket bogs and valley-positioned fens which receive their water and mineral-supply from both the atmosphere and the surrounding ground.

The dark peaty layers can be seen at the edge of this small pool;  Open water is particularly good for dragonflies

Mires are extremely diverse, consisting of a patchwork of flora, grasses and open water. The National Vegetation Classification lists 38 different types of mire habitat in the UK. They are botanically amongst the richest communities in lowland heathland, containing fascinating and rare plant species such as the carnivorous Roundleaf Sundew (Drosera) and Common Butterwort (Pinguicula).

Plants of East Dartmoor’s mires – Bog Asphodel and the carnivorous Roundleaf Sundew

East Dartmoor’s mires also contain abundant Bog Asphodel, with its spikes of yellow Lily-like flowers. And amongst the patches of Rushes and Purple Moor Grass there are areas of Bog Pimpernel, Star Sedge and Marsh St. John’s Wort. Parts of the mire system are also covered in the heavily-scented Bog Myrtle which was once used in the UK to flavour beer before hops became the beer flavour of choice.

Mire habitats are also host to a range of invertebrates. The most prominent is the Golden Ringed Dragonfly, the longest Dragonfly species in Britain. Another common resident, the large Raft Spider, sits on floating vegetation sensing vibrations in the water caused by approaching prey and swims underwater when threatened.

Mires are host to a range of invertebrates, including the Golden Ringed Dragonfly (left)

Further to its biodiversity, Mires play a number of important atmospheric and hydrological roles. The colourful, spongey Sphagnum mosses that blanket the wetter parts of the mires help to control the rain run-off from the moors, soaking-up water and slowly releasing it during times of drought. This acts to reduce the likelihood of flooding and to mitigate the impact of potential floods. This process also filters the water leading to clearer rivers and reservoirs.

Colourful Sphagnum mosses soak up water helping to control the rain run-off from the moors
Sphagnum mosses soak up water helping control the rain run-off from the moors

Mires are also a significant store of Carbon which affects the composition of our atmosphere. 10 million tonnes of Carbon are stored in Dartmoor’s peatlands alone, equivalent to the UK’s industrial emissions of Carbon Dioxide in a single year.

By preserving important historical artefacts from the Neolithic and Medieval periods, the anaerobic peat conditions have also proved to be important for historians and archaeologists. For example, a 4,000 year old prehistoric burial site was discovered in peatland at Whitehorse Hill on Dartmoor containing exquisite examples of textiles, jewellery and basketry from around the world.

Despite their beauty and importance these habitats are vulnerable to a range of problems including nutrient increases, succession to wet woodland, reduction in species richness and loss of water.

Scrub clarance work on Mire site 600px
Volunteers clearing scrub and birch from the wetter areas on the NNR.  The succession to wet woodland is one of the threats to mire habitat

Mapping and survey work was conducted across the reserve this year to help land managers better understand the current condition and extent of the mire systems and to inform future mire management. A mire management plan is currently being drafted that will describe the work required to maintain and preserve the mires in the years to come.

Dartmoor ponies will be grazing the newly cleared mire habitat areas next year

Mire management largely involves controlling the surrounding scrub to prevent succession to woodland. Grazing cattle and ponies also play an important role, removing unwanted scrub and poaching the ground. Dartmoor ponies were successfully introduced to Vinnimore mire this year and have removed large amounts of scrub and bracken, opening up space for mire species to move into. Peat and Birch dams have also been used in parts of Trendlebere Coombe to raise the water table to encourage the spread of mire habitat there.

Boots in Mire Trendlebere Coombe_600 px wide

Written by Daniel Brown
Conservation Assistant 

 

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