Oceanic valley bog

Oceanic valley bogs are essentially topogenous systems of permanently waterlogged, oligotrophic acid peats, maintained by a high ground water table seeping from impervious bedrocks or superficial deposits in low-relief landscapes of the oceanic parts of Europe, topographically completely isolated from other mire systems, though often embedded within landscapes of wet heath. The hydrological regime can be quite complex, with percolating waters sometimes channeled to a central soakway and outflow which has a more obviously soligenous character. The peat sustaining the valley bog habitat itself is usually thin, often less than 1.5m.

Although the valley mire flora may show some localised soligenous influence where water flow becomes more obvious, a poor-fen flora is typically sparse on the active surface and the usual dominants are peat-building Sphagnum species, which form a luxuriant carpet with a gentle hummock-hollow surface and bog pools in lower places. Compared with ombrogenous bogs, Eriophorum vaginatum and Scirpus cespitosus are very scarce and the usual monocotyledons are Eriophorum angustifolium and Molinia caerulea, both sometimes abundant, with Rhynchospora alba occurring around the pools. Erica tetralix and, on the gentle hummocks, Calluna vulgaris form a patchy canopy up to 3 dm tall and Myrica gale is locally abundant.

Among the associates, the most characteristic are Narthecium ossifragum, Drosera rotundifolia with, less commonly D. intermedia and D. anglica, Potentilla erecta and Vaccinium oxycoccos. Associated soakways may have vegetation resembling D2.3a Quaking mires with, for example, Menyanthes trifoliata, Potamogeton polygonifolius and Hypericum elodes or small sedges. Where valley mires occur within stretches of wet heath, grazing and burning often occur in the mire surrounds, but the high water table of healthy mires offers some protection against trespass of bigger herbivores .

Indicators of good quality:

• Water-table close to surface with wetter depressions and open pools.

• Absence of man-made ditches or gullies

• No patterns of erosion and drying

• (Relatively high) species richness (in flora and fauna)

• No indicators of ground-water eutrophication.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats