Peatlands
One of my oldest memories of Ireland is standing in the narrow streets of Dingle Town in the twilight of a winter evening, the air heavy with the smoky-sweet smell of turf fires. A cold wind was blowing from the Atlantic and there even might have been some snowflakes in the air. Even today the unique aroma of smouldering peat encapsulates everything Ireland means to me, it’s the smell of a cosy seat by the fire, the smell of shelter, the smell of home.
Some years later I had moved to Ireland and was living in an old cottage in the middle of the bog. My kitchen window was looking out on a wide stretch of cutover-peatland that once had been an Atlantic blanket bog and over weeks and months I learned the sights and sounds of the bog. In spring when fresh green was sprouting out of the brown peat carpet the elusive hares threw all caution to the wind, chasing each other across the fields and along the old bog road. In summer the song of the skylark rang out over a sea of green, brown and white. Between the songs a blanket of silence lay over the landscape, the inaudible sound of long summer days in the bog. A closer look revealed pockets of blanket bog like it used to be. Small hummocks of colourful moss, the beautiful but deadly leaves of the sundew, intricate cushions of lichen and the delicate flowers of the bog asphodel. Later in the year when the bog had changed its colour again from green to brown the heart-breaking cry of the curlew described the dark days of winter and I was watching lapwings and barnacle geese while washing the dishes.
Back then I only started to learn about the secrets of the bog, the connection between men and peat and the journey the dark brown briquettes had undergone before ending up in a fireplace. I wasn’t aware of the thousands of years of growth and death, the layers of history and the stories that are wrapped up in the peat. I didn’t know about the days, weeks and months that are being spent in the bog every year, the wielding of the sleán to cut the sods, the turning of the sods and the backbreaking endeavour of footing them. Most of all I hadn’t seen yet what industrial turf cutting had done to the peatlands, hadn’t felt the sense of loss when looking over the brown, barren wasteland that had once been the Bog of Allen. Eventually I had become a bogman.
For the past 4000 years Ireland’s landscape has been dominated by peatlands. These inconspicuous habitats cover vast areas from the coastal fringes to the highest mountains and the open expanse of the Irish midlands. It is a landscape that reveals its understated beauty, a rich flora and interesting fauna only on closer examination. Over the course of a year the peatlands change their colour from a rich green which is sprinkled by vibrant dots of white, yellow, red, blue and countless variation thereof, to shades of warm brown and yellow that cover the wide and even landscape during the winter. On a global scale some 5 million square kilometres of peatland cover the land’s surface from the tundra and permafrost regions of northern Europe, Russia and Canada all the way to the southern hemisphere and Chile, Indonesia and Africa’s Congo Basin.
Peat, this uniquely brown and squelchy substance that the bogs consist of, is mainly made of dead plants that failed to decompose due to a lack of oxygen and the subsequent absence of microorganisms. However not all peat is the same. The two main variations of peatlands are the blanket bog, which can be further subdivided into Atlantic blanket bog and mountain bog, and the raised bog. The peat of those bogs differs significantly in both colour and consistency. Peat from raised bogs is mainly made of sphagnum moss and lighter in colour while peat from blanket bogs shows a very dark brown and consists mainly of grasses and sedges. A third type of peatland is the fen. Fens are the precursor to a raised bog and in terms of biodiversity one of the richest habitats in Ireland. Unfortunately fens are also one of the rarest habitats in Ireland today.
A fen starts its life as or near a water body. In total there are six different types of fen that differ mainly in their topography and hydrology. What differentiates a fen from a bog is a constant water supply other than precipitation that comes in form of an underground spring or nearby river. This water supply brings a range of minerals that support a wide variety of plant life. As a consequence a fen isn’t a uniform landscape but rather a kaleidoscope of open water, marsh and fen woodland which is also known as fen carr. A fen can support up to 200 different species of plants from grasses and sedges, which alone are represented by some 15 different species, to trees like willow, alder and birch. Numerous wildflowers also thrive here like marsh cinquefoil, devil’s bit scabious, meadowsweet, lady’s smock, wild valerian, marsh orchid, fly orchid and fragrant orchid and many others. This flora in turn supports a variety of other wildlife. Insects and other invertebrates like spiders can be found in large numbers. Snails are attracted to the fen because of its calcium rich water, wasps like the overwintering accommodation in the stems of bulrush and beetles welcome the diverse food supply for both themselves and their offspring. Not surprisingly these animals attract predators mainly in the form of birds. Resident species like wren, robin, dunnock, blackbird, song thrush, various finches and others are joined by summer visitors like the notorious cuckoo, whitethroat, willow warbler and spotted flycatcher. The lakes of the fen are occupied by moorhen, coot, teal, mallard and the little and the great crested grebe. In winter the population of waterbirds grows considerably when the residents are joined by seasonal visitors like wigeon, shoveller, tufted duck and whooper swan to name but a few. Under the surface of the water of the fen lakes the 3-spined and the 10-spined stickleback can be found and around the edges of the lake lives one of Ireland’s very few amphibians, the smooth or common newt. This rich wildlife attracts bigger predators that are not permanently resident in the fen like the kestrel and sparrowhawk that feed on the smaller birds and the otter and grey heron who don’t mind fish for breakfast or any other time of the day.
Fens are rarely a permanent landform and over time often develop into a raised bog. The process of fen and eventually bog formation started at the end of the last glaciation some 10.000 years ago when Ireland, especially the midlands area, was dotted with countless lakes, basins and floodplains. Around the edges of those waterbodies reeds and sedges developed and on the lakes floating plant communities thrived. Because of their origin these lakes supported only small numbers of microorganisms like bacteria and fungi which are vital for decomposition. As a result the dead members of the plant communities didn’t decompose completely but started to form layers of peat at the bottom and around the edges of the lakes. While Ireland experienced a more continental climate this was a very slow process but when the climate changed to the much wetter and milder Atlantic regime Ireland is known for today, events started to speed up. The fen peat eventually reached the surface of the lake which allowed at first reeds and sedges and later other plants to colonize the area. At this stage a fen was formed. Because dead plant material still didn’t decompose completely the layers of fen peat continued to grow. When the peat layers had eventually reached a thickness that didn’t allow the plants growing on the surface to reach the groundwater, their main source of minerals, a tipping point was reached. The only food source for the surface plants was now rainwater which is rather poor in minerals. In Ireland’s midlands this process was supported by the post-glacial rebound. The land, finally free from the weight of the glacial ice lifted itself and as a side effect the ground water level dropped. The loss of access to nutritious ground water triggered a radical change in the plant community. Bog mosses, mainly sphagnum species, which are known as the bog builders, moved in. These mosses changed the growing conditions further by lowering the soil and water PH and by doing so created a more acidic environment.
Sphagnum mosses exchange ions of hydrogen for the scarce mineral ions potassium, magnesium and calcium that are available in the rainwater. The resulting high concentration of hydrogen ions around the mosses and on the surface then creates the acidic conditions typical for all peatbogs. The dead sphagnum mosses continue this acidification by releasing organic acids into the peat layers. Sphagnum mosses also have the ability to store vast amounts of water, effectively water-logging the surface.
On top of the bog mosses specialized plants that were able to tolerate the new conditions started to thrive and so the foundation of a raised bog was laid. Over the following centuries the mosses and other plants built up layer upon layer of peat and grew the bog into a dome-shaped landscape of hummocks, lawns and pools. These domes then merged with neighbouring raised bogs and so the vast bog areas like the Bog of Allen that once covered some 6000 square kilometres, were born.
The combined layers of a raised bog can reach a height of up to 12 meters but only the top layer shows any signs of life. This top layer known as acrotelm is less than 50 centimetre deep and consists of a living growth of sphagnum moss, the plant communities that thrive on it and recently deceased plant material that just started the process of humification. The deeper layers of the raised bog are known as the catotelm. While the upper layer has a high permeability to water, the water movement decreases rapidly with every layer of peat it passes. The result is a living carpet of vegetation that floats on a watery concoction of dead plant particles. Around 98% of a raised bog are pure water and only the remaining 2% are made of solid material.
The majority of the plants that make up the living carpet are the sphagnum and some other mosses, brown and white beak sedge and ling and cross-leaved heath, all of which are perfectly adapted to the wet, acidic and open conditions of this landscape. These are joined by bog cotton, bog asphodel, bog rosemary, cranberry and numerous species of lichen. The most interesting bog plants are probably the carnivorous species that found a unique way to obtain the vital nitrogen and phosphorus. The round leaved and the oblong leaved sundew, the common butterwort, the bladderwort and the pitcherplant that was introduced from Canada into Co. Roscommon in 1906, have all found a way to catch insects to fulfil their nutritional needs. The sundews have modified their either oblong or round leaves to hold long stalks with a sticky drop on the end. Any insect that lands on those stalks gets stuck, the leaf rolls itself up and the trapped animal gets slowly digested. The butterwort catches its prey in a similar way, only here the leaves are spread out in a rosette on the ground and feature a carpet of tiny sticky hair that hold the victim in place for digestion. The bladderwort does things a bit differently. For one this plant doesn’t grow on the bog surface but thrives in the bog pools with only the small, yellow flower reaching above the water table. The underwater stems are then fitted with flask-shaped bladders. Once this bladder is being touched a little trap door opens and the unsuspecting meal is being sucked into the bladder where it is being digested. Other plans like heathers and the bog asphodel have formed a partnership with fungi to obtain the vital nutrients. The fungal partner, coiled around the roots of the host, provides nitrogen and phosphorus and in return receives carbohydrates it cannot produce itself.
The animal life on raised as well as blanket bogs is a mix of only a few permanently resident species and more numerous visitors. The common frog is one of the more common species that calls the bog its home. The frogs come out of hibernation around March although in mild winters they can be out and about as early as January which makes them and their offspring vulnerable to possible cold spells. As soon as the animals are warmed up mating takes place and soon after the bog pools are filled with balls of frog spawn. A short time later the tadpoles emerge and over a period of 10 weeks grow into adult frogs. While frogs are commonly associated with water the adult animals only seek out pools and lakes during the mating season and for the rest of the year prefer a more terrestrial life. Therefor they can be found in a variety of habitats from peatlands and forests to the stark limestone pavements of the Burren.
The common or viviparous lizard, Ireland’s only native reptile, also rises from hibernation around March and mating also takes place soon after. Unlike the common frog however the female lizard carries the fertilized eggs inside her body where they grow into fully developed lizards that hatch after 3 months. Hibernation as well as their unusual breeding behaviour are an adaption to the cool climate in Ireland. Further south in the Mediterranean regions of the continent the common lizard can stay active throughout the winter and lays its eggs as it is commonly expected from reptiles. Like the common frog the common lizard is not bound to the bog and can be found in a variety of other habitats.
The same goes for most of the birds that can be seen on a raised or blanket bog. The majority are occasional or regular visitors and reside nearby. The red grouse however is very much at home in the bog. This reddish-brown coloured bird with the characteristically red combs over its eyes can mainly be found on the ling covered hummocks. Ling provides food, nesting material and shelter for this quintessential peatland bird. Due to the destruction of boglands as well as continuous hunting the breeding population of the red grouse is in decline and has halved over the past 50 years. The status of the other iconic bird of the bogs is even grimmer. Over the past few decades the resident curlew population has been reduced to only 3% of its original size. The raised bogs of the midlands, together with mountain bogs and the Shannon Callows, have once been a stronghold for these birds but only a few breeding pairs can be found today. The main reasons for this development are habitat loss and habitat fragmentation, the same reasons that drove out a gregarious wintering bird. The Greenland white fronted goose was once was common on all peatlands where it was feeding on the bulblike rhizomes of the white beak sedge. This bird spends the summers on the tundra of northern Europe to breed and travels to Ireland and Scotland for the winter months and because of its chosen wintering sites the bird was also known as the bog goose. Today the majority of the Greenland white fronted geese spend the winter at the Wexford Slobs and changed their diet to grass and certain seaweeds. Other resident peatland birds are the snipe, meadow pipit and the skylark that all share a similar plumage that in both colour and pattern resembles the wind-blown grasses and sedges of their habitat and provides perfect camouflage. While meadow pipit and snipe are perfectly happy with remaining hidden, the skylark makes its presence heard by rising straight up into the air and breaking into song that is carried across the lonely moorland.
Birds of prey like the peregrine falcon, merlin and hen harrier as well as members of the crow family like the raven and hooded crow can also be encountered on peatlands, especially the blanket bogs of the west coast but don’t reside there. The Irish hare is also no unusual sight on the blanket bogs as is Ireland’s most iconic mammal, the red deer that only survived in the boglands and forests of the mountains around Killarney but recently had been introduced back into Connemara.
While insects and other creepy crawlies are very well represented in a fen environment, they are rather scarce on raised and blanket bogs. The lack of overwintering opportunities, a limited food supply and fluctuating water levels make this an unattractive environment for most species. The bog pools provide the best environment for insects. Water boatmen and water skaters are a common sight on the surface while the great diving beetle spends most of its life, both as a larva and an adult, under water using its paddle shaped legs to glide through its kingdom and feed on tadpoles, up to 20 a day. Two very unique spiders are also at home in the pools and ditches. The water or diving bell spider spends most of its life under water by creating doomed webs and filing them with air bubbles, the diving bells that gave the spider its name. The other spider, the raft spider, is Ireland’s largest and also known as Jesus spider because of its ability to walk on water and can easily be identified by its broad white-yellow stripes that run along each side of its body. The raft spider lurks in the mosses at the edge of the pool and dashes across the surface once potential prey is being spotted.
The pools also provide the perfect breeding ground for midges and mosquitoes including the infamous and biting Culicoides impunctatus that can turn any summer visit to the bog into a nightmare. The latter are a main prey for dragonflies and damselflies. While the nymphs feed on the larvae in the bog pools the adult dragonflies and damselflies take the hunt to the air. Watching these elegant insects zigzagging across the bog on a warm summer day is one of the great events in nature aviation.
Butterflies and moths are also a regular sight in the peatlands, some 150 species can be encountered. Most of them however are not limited to peatlands and can also be found elsewhere. One of the bog specialists is the large heath. This butterfly comes in a range of peaty colours and has chosen bog cotton and other cotton grasses as its main diet and is therefore dependent on intact peatlands. The beautifully checkered marsh fritillary is one of the most endangered butterflies in Europe and feeds only on devil’s bit scabious. While this flower is not restricted to peatlands it prefers a wet environment and has become rare due to drainage and other modern farming practices.
The wet environment of peatlands should be ideal for molluscs but surprisingly these invertebrates are rather rare. The only common representative is the black slug which can mainly be found on blanket bogs. Raised bogs are virtually mollusc free which however doesn’t mean there aren’t any. In 1999 the rare Vertigo geyeri, one of 8 known whorl snail species known in Ireland, was discovered at Killaun Bog in County Offaly. These tiny snails grow only to a size of 2-3 millimetres and prefer the outer fringes of the raised bog where they can have access to mineral rich water. Because these outer fringes were often the first areas of the bog that fell victim to private or industrial turf cutting these molluscs lost most of their habitat.
It is estimated that once some 310.000 ha of the Irish midlands were covered in raised bog. In 1974 only 65.000 ha remained and by 1985 a meagre 20.000 ha had survived. Today only around 10% of the raised bogs are intact and these are scattered in small pieces over the central counties of Ireland, mainly Offaly, Westmeath, Longford, Roscommon and Kildare. Peat cutting, for private as well as industrial use, was the main reason for the disappearance of the peatlands. Other parts fell victim to drainage for agricultural use and commercial forestation.
A similar fate befell the blanket bogs of the west coast and mountain regions of Ireland. Of those only 28% remain intact, the rest was destroyed or damaged through turbary, mechanical turf cutting, commercial forestations and overgrazing.
Blanket bog is a relatively rare habitat and Ireland holds 8% of the world’s blanket bogs. The formation of the blanket bogs began in a similar way and at a similar time than the development of raised bogs. The blanket bogs originated in water filled hallows or shallow lakes and began to form in those damp places shortly after the last glaciation. For a few millennia the blanket bogs only thrived in those isolated and confined spots. With the beforementioned change in the climate these pockets of blanket bog began to spread. The increased precipitation washed out minerals from the soil which were deposited further down in the ground where over time an impenetrable layer known as iron pan was formed. As a result the ground became waterlogged which attracted the typical blanket bog flora dominated by grasses and sedges. Purple moor grass, black bog rush, deer sedge and bog cotton are the most common species. Wildflowers like milkwort, tormentil, lousewort and various heather species are also widespread as are the carnivourus butterworts and sundews. The mountain bogs in addition feature bog asphodel, bog rosemary, crowberry and billberry. Sphagnum and other mosses also occur but in much smaller numbers as they do in the raised bogs. As a consequence blanket bogs have a lower water storage capacity than raised bogs and are dependent on regular precipitation. To keep a blanket bog alive 1200mm of rain, drizzle or fog per year, spread out over at least 235 days are necessary. Another difference that sets raised bog and blanket bog apart is its growth. As the name suggests blanket bog spreads out over the landscape like a blanket unlike the raised bog that takes a vertical approach that results in its dome shape. Blanket bogs therefor only reach a depths of 2 – 6 meters. While the raised bogs of the midlands carry a gentle and embracing atmosphere the blanket bogs of the west coast emit a wild and desolate spirit. Especially the seemingly endless undulating carpets of the Roundstone Bog Complex in Connemara and the menacing landscape of Erris and Ballycroy in County Mayo with stark mountains ranges in the distance are the epitaphs of loneliness.
For a long time the bog was seen to be pretty useless apart from being a source for free fuel. After the forests had disappeared, burning peat was the only way to heat and cook in many parts of Ireland. Later peat also became a cheap way to produce electricity. Unfortunately by the time we had learned about all the real benefits of peatlands it was almost too late. Bogs are not only a unique and by now rare landscape with a rich biodiversity, they also allow us a glance into the past. Under the peat prehistoric landscapes like the Ceide Fields have been preserved and the layers of peat themselves hold a history of the local flora, climate and atmospheric composition that goes back for thousands of years. Bogs also act as a carbon sink and can store water in times of high precipitation which can be an important factor in flood prevention.
Currently the IPCC (Irish Peatland Conservation Council) and projects like The Living Bog - Raised Bog Restoration Project and the Active Blanket Bog Restoration Project have taken on the challenge to protect the last remaining intact bogs and restore damaged peatlands. Personally I will miss the smell of the turf fire but then again I rather rest on the squelchy stuff on a hot summer day than burn it in winter.
Carsten Krieger, February 2020
