Bog or Peatland
There are three major types of bog in Ireland: fens (which form where the bog is fed from ground waters rich in nutrients), raised bogs (which occupy the sites of former lake basins, and often form on top of fens, especially in the Irish midlands), and blanket bogs (which cover mountain tops or sloping ground, especially on the west coast).
Fens are bogs which form in lake basins. The community of grasses, sedges, and bryophytes is fed from ground waters rich in nutrients. They are very often an early stage in the formation of raised bogs which grow on top of the fen. Their depth can vary depending on their location but they are usually 2m to 3m in depth. Fens are amongst the most threatened habitats in Ireland, being small and easily damaged. Some of our rarest flowering plants and bryophytes are confined to fens.
Raised bog is almost pure sphagnum moss (susán) with scattered grasses and sedges, and these are the bogs from which moss peat is extracted. Sphagnum can grow on rainwater alone, and as long as grasses, sedges, and heathers cannot obtain sufficient nutrients from the bog, the sphagnum will continue to outstrip them in speed of growth, forming a huge dome of moss that gradually spreads outwards from the original lake basin from where it starts. Raised bogs probably began growing about 7,000 years ago. About a foot below the surface of a bog the water is deprived of all oxygen, and the dead remains of moss, other plants and even humans can be preserved indefinitely. Country dwellers used to store butter below the surface of bogs, and examples of ‘bog-butter’ are still occasionally found. Raised bogs are fragile because they are like a huge plastic bag full of water – as soon as you make a pin prick in them they drain away and collapse. These bogs are sometimes called red bogs, because the dry peat looks brownish-red in colour; in blanket bog the cut sods dry black.
Blanket bogs cover much of the hills and land along the west coast of Ireland. They are dominated by heathers, grasses, and sedges as well as sphagnum moss. Blanket bogs only develop in areas of the west, or mountaintops with particularly high rainfall (more than 1.3 metres per year). They began growing about 4,000 years ago when rainfall increased. On higher ground, bogs are often referred to as moorland, where they are somewhat transitional between heath (dominated by heathers) and bog (dominated by sphagnum moss). These bogs are a lot less sensitive to being cut, and continue to grow after harvesting. Below these bogs and raised bogs can be found the remains of forest trees that once dominated the Irish landscape. At Shanvallycahill, on the shores of Lough Mask, there is an amazing forest of pine stumps sitting on the original soil surface of 4,500 years ago. The blanket bog has been harvested for turf, which is used for heating. These trees died where they stood as the moss suffocated their roots.
