Raised Bog

At the end of the last glacial period approximately 11,700 years ago, the retreating ice left behind an undulating landscape, resulting in the development of shallow lakes across much of central Ireland. These lakes received nutrient-rich groundwater derived from glacial drift.

Reeds and sedges encroached around lake edges, their remains only partly decomposing under the water, which in time formed a thick layer of reed peat. The continuous process elevated the surface above the level of the surrounding groundwater and peat-moss species, solely fed by rain, took over and continued to grow upward. The result was a dome-shape peat mass called raised bogs averaging 7 m in depth.

Raised bogs were originally fens that became buried under ombrotrophic peat mosses (Sphagnum species). The vegetation, dominated by these mosses, keeps the peat surface waterlogged as the peat moss, growing above the water table has a very large water-holding capacity. Furthermore, peat mosses maintain an acidic environment that favours continued peat moss growth. Other plant species found on raised bogs are: heather (Calluna vulgaris [L.] Hull), bog cotton (Eriophorum angustifolium Honckeny and Eriophorum vaginatum L.E.), and numerous species of sundew and orchids.

Raised bogs are found mainly in the Midlands under moderate rainfall between 750 and 1,000 mm/year. Whilst they originally covered 311,300 ha, a quarter of all peatlands raised bogs were extensively damaged in the 20th century, being particularly suitable to industrial peat extraction. However, Ireland is still home to some of the best examples of raised bog in Western Europe and its bogs have been recognised as being of national and international conservation importance (EPA, 2011).

Due to the significant decrease in their range, habitat function, structure and area, raised bogs were given an 'Unfavourable Bad-Declining' status in a 2013 National Parks and Wildlife Service report on the status of bogs in Ireland (conducted every 7 years) (National Parks and Wildlife Service, 2014), with only 10% of the remaining bogs deemed suitable for conservation. For further information on the conservation status of Irelands raised bogs see the Irish Peatland Conservation Council website.

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