A fen is a peat-forming wetland system with a permanently high water level at or just below its surface. The principal source of nutrients is from surface or groundwater and the substrate is an alkaline to slightly acidic peat soil. The vegetation of fens is diverse and usually dominated by sedges (grass-like plants) and mosses. Fens occur throughout Ireland, most commonly in the west and midlands.
Difference between Fens and Bogs
Fens are less acidic and have relatively higher mineral levels than bogs. Therefore, fens are able to support a more diverse community of plants and animals.
Bogs are not connected to a waterbody such as a stream or lake and instead receive all their water from rain. Bogs are nutrient poor and sphagnum mosses are an essential component of them.
Conservation Status of Fens
Irish fens are primarily threatened by land reclamation, drainage and infilling. According to the Irish Peatland Conservation Council there has been a 77% loss of fen habitat in Ireland. Many fens in Ireland currently have an unfavourable conservation status.
Types of Fens
Three types of fen are listed on the EU Habitats Directive:
- Transition mires and quaking bogs (EU code 7140)
- Calcareous fens with Cladium mariscus (EU code 7210)
- Alkaline fens (EU code 7230)
Areas where dwarf shrubs, such as heathers and bilberry, exceed 25% of the cover are considered as heath. Heath is commonly formed over upland, peaty soils and often occurs in association with blanket bog and upland grassland. Heath can be described as being wet or dry depending on drainage and the depth of peat.
Difference between Heaths and Bogs
Heath can sometimes be confused with blanket bog. There are a couple of distinctions which can help to identify these two habitats from each other. Generally, if the peat is deeper than 0.5 m it is blanket bog. More usefully, sphagnum mosses which are an essential component of blanket bog are often not as common or absent in heath, and the surface of a heathland habitat is relatively drier.
Conservation Status of Heaths
Heaths, which often form parts of commonages, may be used as rough grazing land (typically for sheep), but overgrazing can impact negatively on heaths. Burning may be periodically used across large areas to suppress the dwarf shrubs and encourage grass growth, but uncontrolled and extensive burning is damaging to heathland. Another threat to heath is conversion to intensive agricultural grassland. Many heaths in Ireland currently have an unfavourable conservation status.
Types of Heaths
Three types of heath are listed under the EU Habitats Directive:
- North Atlantic wet heath (EU code 4010)
- European dry heaths – which includes both siliceous and calcareous dry heath (EU code 4030)
- Montane heath (EU code 4060)
For information on heaths within the uplands of Ireland explore ‘Guidelines for a National Survey of Upland Habitats in Ireland’
One of Ireland’s most characteristic habitats is the bog, with one-sixth of the island of Ireland covered by bog. Across the whole of Europe, including Ireland, bogs have been exploited as a source of fuel. With many of Europe’s bogs already destroyed, those that remain in Ireland now have an increased importance. Although most bogs appear similar, there are in fact two very distinct types:
- Blanket Bogs cover expansive areas and are generally formed in flat and gently sloping upland areas.
- Raised Bogs are generally smaller and form within basins in lowland areas.
Conservation Status of Bogs
The main factors that lead to the loss of bog habitat include epeat extraction, afforestation, overgrazing, drainage, burning, erosion and landslides. Many bogs in Ireland currently have an unfavourable conservation status.
Types of Blanket Bogs and Raised Bogs
Four types of bog are listed under the EU Habitats Directive:
- Blanket bog (EU code 7130)
- Depressions on peat substrates of the Rhynchosporion (EU code 7150)
- Active raised bogs (EU code 7110)
- Degraded raised bog (EU code 7120)
Due to the wet quaking nature of raised bog habitat it is generally unsafe for most stock and the habitat is not a priority for conservation grazing.
For information on bog habitats within the uplands of Ireland explore ‘Guidelines for a National Survey of Upland Habitats in Ireland’