Raised bogs are ombrogenous, i.e. are fed by rainwater, as they develop on deep peat which forms a barrier between the bog surface and groundwater sources. The habitat is relatively scarce in Wales and there are no ‘pristine’ examples, they have all been modified to a greater or lesser extent by peat cutting and drainage, with some examples also impacted by pipe-laying and burns. Two of the raised bogs in Wales are well known, however: Cors Caron for being the best example of a raised mire complex in the UK and Cors Fochno for being the largest single raised bog plateau in the UK. The reference state for raised bog vegetation and examples of modified states are given below.
The reference state for a raised bog should comprise what is referred to as a ‘hummock and hollow’ complex, where hummocks of ‘building’ bog mosses, such as Sphagnum papilllosum and Sphagnum subnitens, and ericoids form a mosaic with pool or ‘wet hollow species, such as Sphagnum cuspidatum, Sphagnum pulchrum and Rhynchospora alba. This hummock/hollow patterning…
One sign of peat cutting or drainage is the spread of purple moor grass (Molinia caerulea) on the bog surface, as seen here at Cors Caron, where it covers vast areas of secondary bog surface.
Another modified state of secondary raised bog, especially in wetter parts, can be extensive lawns of bog moss, particularly of Spagnum cuspidatum. In healthy raised bog habitat, Sphagnum cuspidatum would be just one component of the bog pool flora that forms a hummock and hollow complex on the raised bog plateau.