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