Annex IV protected areas: water dependent habitats and species and high status sites

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3.8. Precipitation dependent habitats.

Habitat Code

Habitat Name

Structure and functions (Condition)

Overall Conservation Status


Northern Atlantic wet heaths with Erica tetralix (67)




*Active raised bogs (60)




Degraded raised bogs still capable of natural regeneration (66)




Blanket bog (*if active bog) (71)




Transition mires and quaking bogs (29)




Depressions on peat substrates of the Rhynchosporion (72)




*Bog woodland (21)



Note #: The number of SACs in which each habitat occurs as either a qualifying interest, or is present, is given in brackets. * Priority Annex 1 listed habitats are indicated with * and are bold-faced

Precipitation dependent habitats occur as a qualifying interest in 124 SACs nationally. These habitats all include groundwater dependent elements, or depend on groundwater support (discussed for each individual habitat below), but are retained as a separate habitat grouping because the principal land cover within them is generally precipitation dependent (ombotrophic). Damage to these habitats arises through land use pressures including drainage, burning (in an attempt to increase grass cover for livestock grazing), overgrazing, peat cutting, and afforestation. These land uses, either separately or in combination, tend to lead to erosion and loss of capacity to retain water, resulting in adverse impacts and pressures in watercourses in, and downstream of, wet heath and bog habitat areas. These include reduced low flows, increased peak flows and erosion potential in downstream watercourses, increased suspended solids loads, acidification and nutrient loadings arising from afforestation and forestry activities, and increased flood risk. Measures for wet heath and bog habitats, and for forestry, are therefore important for habitat protection and restoration, as well as for the management of downstream impacts. It should be noted that watercourses downstream of wet heath and blanket bog SACs may contain populations of Margaritifera margaritifera, which are identified as requiring measures under the Habitats Directive.

Northern Atlantic Wet Heath (4010) occurs in uplands throughout Ireland, and on lowland areas in the west of Ireland. It occurs on relatively shallow peats (30 – 80 cm), where there can be a slightly fluctuating water table rather than permanently waterlogged peat (more or less permanent water-logging is necessary for peat formation). It can occur in extensive areas, as a habitat mosaic with blanket bog, and can also develop as a secondary wet heath in previously cutover or disturbed areas of both blanket and raised bog.
Drainage, land reclamation, over-grazing by sheep, afforestation, and burning are the main pressures and threats to wet heath habitat. Ground water dependent poor fen habitats within wet heath are vulnerable to hydrological pressures including groundwater abstraction.

Raised bogs (7110, 7120) were abundant in the lowlands of central and mid-west Ireland, but most sites have been lost or severely damaged, in the first instance mainly by peat extraction. In Ireland raised bogs are confined to areas with an annual rainfall below 1250 mm. In areas of higher rainfall, raised bogs are replaced by blanket bog. Raised bog occur principally in land below 130m and are most extensive and abundant where the limestone plain is covered by a variable thickness of undulating glacial drift which originally provided suitable basins for the development of lakes and/or fens, which in turn acted as precursors to the bogs. The raised dome develops as peat formation extends the development of the bog above the level of ground water influence. Intact active raised bog is now extremely rare; and has declined by over 35% in extent in the last 10 years. Deterioration of the raised bog hydrology at current rates caused by peat cutting, drainage, forestry and burning seriously threatens the viability of the habitat. At some sites, restoration works and projects are showing positive results.
There is a direct groundwater contribution to the lagg portion of raised bog habitats, and the bog in general is supported by groundwater, making raised bogs vulnerable to arterial drainage, localised drainage, and groundwater abstraction. If present, these pressures lower the groundwater level under the bog, and reduce the groundwater contribution to the marginal lagg or the raised bog, allowing precipitation derived bog water to seep out of the bottom of the bog.

Blanket bog (7130) occurs along the Atlantic coast of Ireland on lowlands and uplands on slopes of up to c. 25 degrees, and on mountains in the rest of the country. Three types are recognised: lowland, highland, and mountain blanket bog, based on variation in the plant communities present. Areas flushed by mineral groundwater within blanket bog generally correspond to the Heritage Council habitat PF2 poor fen and flush, although Habitats Directive Annex 1 listed fen types can also occur. Many river catchments have their headwaters in blanket bog areas.
Extensive areas of blanket bog have been removed or highly modified, chiefly through reclamation, peat extraction, over-grazing, burning and afforestation, but also via erosion/landslides triggered by anthropogenic factors. Even though impacts have reduced substantially in recent years, agriculture, peat extraction, afforestation, wind farms and other infra-structural developments etc are still causing damage. Impacts from certain activities continue even after the damaging activity has ceased. Drought and extreme weather events predicted as a result of climate change are likely to increase erosion and blanket bog landslides, particularly on poorly vegetated areas, with consequent impacts on water quality in catchments within and downstream of bog areas. Local abstractions of, or discharges to, groundwater pose threats to groundwater associated flush and poor fen communities within blanket bogs.

Depressions on peat substrates of the Rhynchosporion (7150) habitat is associated with raised bog in the lowlands of central and midwest Ireland, and with lowland blanket bog and wet heath in western Ireland. The habitat becomes rare above 300m. The overall habitat conservation status assessment is favourable, despite the unfavourable assessment given to the associated habitats where it is found (e.g. raised bog, blanket bog and wet heath). This is mainly related to the pioneer and transitional nature of the habitat, and its capacity to develop in areas of damaged and degraded bog and wet heath .

Transition mire and quaking bog (7140) habitats support peat-forming vegetation that is transitional between acid bog and alkaline fens, in which the surface conditions range from markedly acidic to slightly base-rich. Individual sites will generally depend to some extent on groundwater, as well as precipitation, and possibly surface water. The vegetation normally has intimate mixtures of species considered to be acidophile and others thought of as calciphile or basophile. Transition mire and quaking bog can develop as a result of soligenous flow, but in most situations there is thought to be a direct groundwater contribution, providing hydrological support and minerals to the habitat and its vegetation.

In some cases the mire occupies a physically transitional location between bog and fen vegetation, as for example on the marginal lagg of raised bog or associated with certain valley and basin mires.

In other cases these intermediate properties may reflect the actual process of succession, as peat accumulates in groundwater-fed fen or open water to produce rainwater-fed bog isolated from groundwater influence. Many of these systems are very unstable underfoot and can therefore also be described as ‘quaking bogs’ or a floating scraw.

Drainage, land reclamation, peat cutting, afforestation, water pollution, dumping, and changes in hydrological conditions in particular groundwater abstractions, are the main pressures and threats causing damage to transition mire and quaking bog habitats.

Bog woodland (91D0) occurs on raised bog, with some sites on transition mire. It is typically dominated by birch trees, with a ground flora of Sphagnum mosses, and is actively peat forming. This habitat is sensitive to activities causing lowering of the water table such as drainage, peat cutting or afforestation.

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