Liam Loftus G00179936 28th
February 2011
Blanket and raised bog formation with characteristic plant species associated with each habitat and
adaptations that enable them to tolerate this acidic and nutrient deficient habitat.
Peatlands are a type of ecosystem in which organic matter is produced faster than it is decomposed.
They occur in areas of impeded drainage and high rainfall. Waterlogged conditions reduce the
amount of oxygen in the soil resulting in the accumulation of
partially decomposed vegetation. The two main types of bog
in Ireland are raised bogs and blanket bogs.
Raised bogs are most abundant in the lowlands of
central and Midwest Ireland where annual rainfall is about
800-900mm. They are the result of peat accumulation in
shallow lake basins or topographic depressions. As peat
continues to accumulate the
surface of the bog is raised
above the surrounding landscape, forming a ‘dome’ shape. Raised
bogs are the oldest and deepest (up to 12m) bogs in Ireland. Their
formation dates back to about 10,000 years ago when shallow
lakes formed in poorly drained post-glacial basins. A process of
terrestrialisation occurred as vegetation gradually encroached onto
the open water from the lake margins. Lack of oxygen in the water
resulted in the partial decomposition and accumulation of plant litter. The arrival of Sphagnum
mosses marked the beginning of peat formation. The ability of
Sphagnum to retain water and to acidify the substrate brought
about great changes in the vegetation. Acting like a candle wick, it
drew water up to the surface and kept the bog permanently
waterlogged. As older Sphagnum died it accumulated as a layer of
peat which gradually raised vegetation above the water-table. Cut
off from mineral-rich water below the bog became increasingly
Fig. 1 – Peatland distribution in Ireland
Fig. 2 – Raised bog formation
Fig. 3 – Sphagnum Moss
reliant on rainwater as its sole source of nutrients. As a result plant species, capable of growing in
the mineral-poor environments, began to colonise the bog.
Today Sphagnum mosses still dominate the ground layer of raised bogs “forming living
carpets over the entire surface of hummocks, lawns and hollows.”1 Hummock-hollow complexes
allow for the formation of micro-habitats on the surface
since the slightest change in water level can have
dramatic changes in species composition. Hollows are
shallow water-filled structures supporting aquatic plants
such as Common cottongrass (Eriophorum
angustifolium), Bog asphodel (Narthecium ossifragum) and Bogbean (Menyanthes trifoliata).
Hummocks on the other hand lie are drier and tend to support heathers like Ling (Calluna vulgaris)
and Cross-leaved Heath (Erica tetralix).
Blanket bogs receive higher rainfall than raised bogs and generally occur on more
mountainous and coastal terrain. Due to higher levels of rainfall blanket bogs are more acidic,
having a higher pH of about 4.2. Blanket bogs are essentially man-
made features, aided somewhat by climate. During the Neolithic Age,
the first farmers cleared upland forests for agriculture. The exposed
soils became vulnerable to a process of paludification. Heavier rainfall
resulted in the leaching of minerals from the surface layers of the soil.
These minerals were deposited lower down in the soil profile and
formed an impermeable layer known as an ‘iron pan’. Rainwater was
thus prevented from draining away and the soil became permanently
waterlogged. Under these conditions peat began to accumulate,
covering the landscape like a blanket. Blanket bogs are extensive,
ranging from lowland landscapes in the case of Atlantic blanket bog to upland landscapes in the
1 1 C. O’Connell (1998) A Day on the Bog Field Studies Guide. Irish Peatland Conservation Council., p. 7.
Fig. 4 – Hummocks & hollows
Fig. 5 – Blanket bog formation
case of Mountain blanket bog. Atlantic blanket bogs are found in low-lying coastal plains and
valleys in mountainous areas of western counties. Mountain blanket bogs occur on relatively flat
terrain in the higher mountains above 200m and are more widely distributed than Atlantic blanket
bogs.
Mountain blanket bogs can also be distinguished by it vegetation, particularly the absence of
Black Bog-rush (Schoenus nigricans). It is characterised by the presence of Deergrass
(Trichophorum caespitosum) and dwarf shrubs such as Ling (Calluna vulgaris) and Bilberry
(Vaccinium myrtillus). Atlantic blanket bogs are largely confined to wetter regions along the
western seaboard where the annual rainfall exceeds 1250mm. They have a typically ‘grassy’
appearance and are characterised by abundant Black Bog-rush (Schoenus nigricans), Purple Moor-
grass (Molinia caerulea) and bog cotton. Wetter areas display a variety of surface drainage features
which support aquatic plants such as bladderworts (Utricularia spp.) and Water Lobelia (Lobelia
dortmanna). Many of the same plants that live in raised bogs are also present in blanket bogs, but
overall, Sphagnum mosses do not dominate and as a result blanket bogs tend to have greater plant
diversity.
However, the challenging conditions of ombrotrophic bogs tend to limit the range of species
found in them. Some plants species are well suited to life in the bog, but others have had to adopt
various strategies in order to cope with the challenging conditions.
Carnivorous plants such as sundews, butterworts and bladderworts
are typical in nutrient poor ecosystems and supplement their diet by
absorbing nutrients (especially nitrogen) from insects. Other plants
obtain their nutrients through the capture of atmospheric nitrogen.
Bog myrtle (myrica gale) for example, houses the nitrogen-fixing
actinomycete in its roots which allows it to metabolise nitrogen gas from the air. Purple Moor-grass
has “recycling mechanisms in which nutrients are efficiently transferred from older to younger
leaves, and from leaves to overwintering below ground leaf-bases or buds.”2 In this way, 90% of its
2 M. Otte (2003) Wetlands of Ireland: Distribution, Ecology, Uses and Economic Value, p. 85.
Fig. 6 – Round-leaved Sundew
nitrogen and phosphorous is recycled. Waterlogging also presents a serious problem for many
peatland plants. Heathers which are usually found on drier bog hummocks have shallow rooting
systems to avoid inundation. They also have reduced scale-like leaves, waxy cuticles, and in-rolled
leaf margins in order to conserve water during the summer months. The internal system of Bog
cotton (Eriophorum augustifolium) allows it to transfer oxygen to its roots which are embedded in
deep waterlogged peat.
In order for peatlands to function effectively they must have a high water-table. If the water-
table is lowered, Sphagnum begins to disappear and the
decomposition of peat is accelerated. Surface drainage directly
affects the water-table and alters the species composition of the
bog surface. The living surface layer of the bog is the key to peat
accumulation. Once removed the
functioning of the bog is
destroyed. Peat extraction, through its systematic drainage and wide-
scale removal of surface vegetation, provides the biggest threat to
peatland destruction. Traditionally peat-cutting was largely confined
to bog edges, “progressed
relatively slowly and
usually allowed the bog
flora to regenerate.”3 However, the use of modern
machinery has accelerated the exploitation of peat for
domestic fuel. Large-scale peat extraction companies,
such as Bord na Móna produce about “5 million tonnes of peat annually (400,000 tonnes as
briquettes; 1.5 million tonnes as horticultural peat; 3.1 million tonnes of milled peat for electricity
generation.”4
3 J. Pilcher & V. Hall (2007) Flora Hibernica: The Wild Flowers, Plant and Trees of Ireland, p. 75. 4 M. Otte (2003) Wetlands of Ireland: Distribution, Ecology, Uses and Economic Value, p. 97.
Fig. 7 – Hand-cutting Turf
Fig. 8 – Turf drying
Fig. 9 – Drainage & Industrial peat extraction
Afforestation presents a major threat to blanket bogs, since surface drains are “installed at
5m intervals across the peatland surface [and] destroy the integrity of the surface vegetation.”5
Dense conifer plantations exclude typical
shade-intolerant bog species, while phosphate
treatment makes peatland susceptible to
colonization by invasive species. The use of
fertilizer in agriculture coupled with drainage
and land reclamation, serves to destroy
peatlands and reduce their biodiversity. The
intensification of sheep grazing on blanket bogs also has a dramatic effect on the vegetation, as
overgrazing can remove key upland species and lead to changes in composition. For example,
ground-hugging species like mosses and liverworts help to create micro-habitats for other species.
These plants are very sensitive to disturbance and once they are destroyed other plants soon
disappear. The cumulative effect of overgrazing, coupled with high winds and heavy rainfall, can
result in the gradual erosion of peatlands. Future changes in rainfall patterns, combined with
centuries of habitat loss, are likely to have a major impact on peatland ecosystems.
In recent years there has been a change in attitude to bogs. More and more people are
recognising the greater value of peatlands beyond merely a resource to be exploited. Irish peatlands
provide us with another kind of resource because they represent a unique habitat type. There is no
other habitat type in the world where the rate of decomposition of organic matter lags behind the
annual production. Peatlands are also a valuable ecosystem type and as such they are an essential
part of the biosphere. They play a fundamental role in sequestering atmospheric carbon dioxide
through peat deposition and bog restoration is one of the most cost-effective ways of avoiding
greenhouse gas emissions.
Peatlands are also an invaluable educational facility. They contain records of past
environments within their layers of peat. As a result the “pollen and archaeological remains
5 Ibid, p. 98.
Fig. 10 – Conifer plantation
preserved in peat represent a most important archive for the history of man and the landscape since
the Ice Age.”6 The waterlogged, acidic and nutrient-deficient nature of Irish peatlands also provide
us with a good example of an extreme habitat, with communities and assemblages of species
specifically adapted to these conditions and rarely found outside of them. Ireland’s extreme Atlantic
environment means that Irish peatlands support combinations of plants and animals not found on
peatlands anywhere else in Europe. The disappearance of the Irish bogs would have serious
consequences for plant and animal species, as their last refuge would be destroyed. Ireland
represents a very significant location in European and Worldwide study of this habitat type, and in
conserving this resource, possessing almost 200,000ha of actively growing raised and blanket bogs
which are of increasing European conservation importance.
6 C. O’Connell (1998) A Day on the Bog Field Studies Guide. Irish Peatland Conservation Council., p. 13.
Bibliography
Brooks, A., & Agate, E., (2004). Waterways and Wetlands: A Practical Handbook. British Trust for
Conservation Volunteers.
Cronk, J.K. (2001). Wetland Plants: Biology and Ecology. Lewis Publishers, U.S.A.
Fossitt, J., (2000). A Guide to Habitats in Ireland. The Heritage Council, Dublin.
Haslam, S.M., (2003). Understanding Wetlands: Fen, Bog and Marsh. Taylor & Francis Group,
London.
Keddy, P.A., (2000). Wetland Ecology: Principles and Conservation. Cambridge University Press,
Cambridge.
O’Connell, C., (1998). A Day on the Bog Field Studies Guide. Irish Peatland Conservation Council,
Dublin.
Otte, M. (2003). Wetlands of Ireland: Distribution, Ecology, Uses and Economic Value. University
College Dublin Press, Dublin.
Pilcher, J., & Hall, V., (2007). Flora Hibernica: The Wild Flowers, Plant and Trees of Ireland. The
Collins Press, Cork.
Websites
IPCC – The Irish Peatland Conservation Council, online, retrieved February 2011, from
http://www.ipcc.ie/
Coillte’s LIFE Project, online, retrieved February 2011, from
http://www.coillte.ie/aboutcoillte/news/archive_pre_2010/news_2008/coilltes_life_project_restorin
g_raised_bog_in_ireland/
Coillte, online, retrieved February 2011, from http://www.raisedbogrestoration.ie/
National Parks & Wildlife Service, online, retrieved February 2011, from
http://www.npws.ie/en/PublicationsLiterature/BogResearchReports/
Bord Na Mona Website, online, retrieved February 2011, from
http://www.bnm.ie/corporate/index.jsp?&1nID=93&pID=102&nID=391
Images
Retrieved online February 2011
Fig. 1 - http://www.askaboutireland.ie/
Fig. 2 - http://www.wesleyjohnston.com/users/ireland/images/raised_bog_formation.gif&imgrefurl
Fig. 3 - http://www.pitcherplant.com/images_2/red_sphag.jpg&imgrefurl
Fig. 4 - http://www.gret-perg.ulaval.ca/uploads/pics/Tourbiere_3x.gif
Fig. 5 - http://www.wesleyjohnston.com/users/ireland/images/blanket_bog_formation.gif
Fig. 6 - http://www.mikebaker.com/plants/1280/DSC_0284.jpg
Fig. 7 - http://www.ipcc.ie/cutturfcuttingbank.jpeg
Fig. 8 - http://static.panoramio.com/photos/original/10480900.jpg
Fig. 9 - http://bordnamona.wikispaces.com/file/view/P1010533SM.jpg/33347039/P1010533SM.jpg
Fig. 10 - http://www.birdguides.com/i/articles/002315/forsinard2.jpg
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