Mire
The most extensive form of mire in County Durham is blanket bog, which is formed on acid soils where rainfall is high enough to keep the ground permanently saturated. These habitats contain few nutrients and only a small number of specialised plants are able to grow here.
The key plant species found in a bog are sphagnum mosses, which are able to hold more than 20 times their own weight in water. When these plants die the waterlogged ground prevents decay and in these acid conditions, the dead plant matter accumulates as layers of peat. Because their development requires rain, blanket bogs are found on plateaux and gently convex summits all over the wet west of the County, covering the hills from Stainmore to Wearhead, and Burnhope Seat to Middleton.
A variety of plants and animals are associated with blanket bog. Plants that flourish here are cotton grass, cranberry cross-leaved heath and bilberry, the food plant of the green hairstreak butterfly. As bogs are such specialised environments, bog pools contain insects not found elsewhere. These include water-skaters, spiders and beetles. Many species of dragonfly and damselfly lay their eggs in the pools.
In the summer adders enjoy the low-lying moist area of the bog, whilst in winter they hibernate in higher, drier places. Adders can move over large areas and their summer and winter homes may be several kilometres apart. They feed on common lizards and small mammals. Adders are very timid creatures, and although poisonous, rarely attack passers-by.
Flushes and Springs
Flushes and springs are types of mire whose water source either comes directly from the ground or has passed over another vegetation surface. As their water content does not come directly from rain they contain more nutrients than bogs, and different types of vegetation. They are usually quite small and are often linear, situated along watercourses.
Acid and neutral flushes are abundant in the western uplands of County Durham, where they usually occur in areas of blanket bog, dry heath or acidic pasture. They often contain some species of sphagnum moss mixed with rushes, sedges and grasses, with purple moor-grass, soft rush and common sedge. Basic flushes are rare in Britain, but the limestone that underlies the County has allowed patches of these colourful, species-rich habitats to develop. Glaucous sedge, lesser clubmoss, fairy flax and grass-of-parnassus are typical of these areas.
Fens
Bogs and fens are often confused, as their vegetation can be very similar. The distinction between these two habitats is based on their respective water sources. The water in a bog is still and obtained directly from rain, but the water in a fen flows, although this may happen very slowly. In this sense, fens are more like flushes than bogs, but are larger and more complex. A species rich fen may contain sedges, rushes, yellow iris, meadowsweet, water mint and marsh valerian. If a fen is in particularly good condition it may also contain orchids such as the early-marsh orchid.
Fens are a rare feature of the County Durham landscape, being rarer and more local than either flushes or true bogs.
This is partly due to habitat loss but mainly because County Durham lacks the combinations of geology, topography and climate which characterise the most fen-rich parts of the country.
Mire sites in County Durham include:
- Pow Hill and Derwent Reservoir - Durham County Council, Natural England and Northumbrian Water
- Ferryhill Carrs - Sedgefield Borough
- Moorhouse Upper Teesdale National Nature Reserve - English Nature
