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Biological History

Approximately two million years ago, severe cold conditions developed in northwestern Europe marking the onset of the Pleistocene or Ice Age. At the height of this period, ice sheets smothered Ireland and much of the European Continent, eliminating plants and animals that had evolved throughout the preceding era. When the ice relented it gave way to alternating cycles of warmth and cold spread over the last 750,000 years. The effects were profound. The development of flora and fauna was periodically encouraged only to be inhibited and largely eliminated later, with the result that the plants and animals found in Ireland today are the outcome of a most complex and not fully understood sequence of survival and migration, driven by the climatic oscillations of the Pleistocene.

It was only some 13,000 years ago, at the close of the Ice Age, that the cold began to lift, allowing a progressive development of vegetation and fauna which has continued through to the present day. The activities of the Neolithic farmers commencing some 6,000 years ago inaugurated the first anthropogenic modifications of Ireland’s biotic inheritance. Woodland clearance, initiated by those farmers, brought about many long-term ecological changes including the elimination of some species, redistribution of others and the introduction of alien flora and fauna. This chapter will explore the history and sequencing of Ireland’s vegetational history while detailing what is known about the origins of Ireland’s mammalian fauna and, in particular, highlighting the history of red and sika deer and the wolf. The pedigree of the frog and natterjack toad in Ireland, subject to much speculation, will be explored, along with the history of Ireland’s freshwater fish. Finally the many unresolved questions concerning the origin of some Lusitanian or Mediterranean–Atlantic flora will be considered, as well as the curious geographical distribution of certain plant species, especially in parts of western Ireland.

The Pleistocene or Ice Age

The latter part of the Ice Age, from about 750,000 years ago, has been characterised by a series of alternating warm phases – known as ‘interstadial’ if minor and without the development of closed woodland and ‘interglacial’ when full woodland cover developed – followed by colder phases. The interglacials and interstadials are thought to have been relatively short, in the order of 10,000–15,000 years, with temperatures close to today’s levels which allowed a rich flora to emerge before it was expunged by the next cold phase. The vegetation which developed during these warm periods was generally similar to that found in other parts of Europe, although the record from Ireland is far from complete.¹ The cold periods were longer in duration, lasting some 50,000–100,000 years, and ushered in arctic and tundra floras. During the most severe conditions the landscape was covered by ice in varying amounts making it difficult for living things to survive.

This chapter will follow the tentative chronological and stratigraphical sequence of the cold and warm stages of the Quaternary deposits over the past 500,000 years as proposed by Mitchell & Ryan.²

Years Ago	Proposed tentative stratigraphical sequence
13,000–10,000	Late glacial
35,000–13,000	Midlandian (Drumlin) cold
65,000–35,000	Aghnadarraghian mild
79,000–65,000	Midlandian (Main) cold
122,000–100,000	Fenitian mild
132,000–122,000	Eemian warm
302,000–132,000	Munsterian cold
428,000–302,000	Gortian warm
500,000–480,000	Ballylinian warm

Pollen remains from interglacial deposits

The Ballylinian warm (500,000–480,000 years ago) takes its name from an area south of Castlecomer, Co. Kilkenny, where fossil pollen remains in a 25 m thick deposit of lacustrine clay show that the warm climate allowed the development of open forest containing most of the trees present in Ireland today including fir, spruce, hornbeam, oak, alder, wing-nut (found today in Turkey and present in Ireland from an earlier period) and yew. In the open areas there were grasses and heaths, where rhododendron and many herbs grew.³

The most famous interglacial deposit in Ireland is of peat and mud lying underneath glacial deposits cut by the Boleyneendorrish River near Gort, Co. Galway. It was first discovered and described by Kinahan in 1865 and was reexamined in 1949 by Jessen, Anderson & Farrington. They investigated the pollen remains in the muds and peat and named this warm interglacial stage the Gortian.^4,5 The Gortian interglacial has been uncertainly dated as occurring some 428,000–302,000 years ago.² About 12 other similarly aged deposits have been so far investigated in Ireland, some of whose results have been reviewed by Coxon, Mitchell & Ryan and Watts.^1,2,6 The first plant species to appear at the onset of the Gortian interglacial phase, as summarised by Coxon, were the pioneering willow, juniper and buckthorn as well as many herbs and birch scrub. As the weather became milder the extent of pine and birch woodland grew while many other species – oak, elm, holly and hazel – are thought to have migrated into Ireland from other European ice-free areas. Unlike other interglacial sites examined in Britain, these Irish woodlands did not develop into a mature mixed oak forest but into heath, as increasing wet conditions fostered the growth of heather together with alder, yew, spruce and fir trees. The end result was a crowberry wet heath – to be replaced by tundra again when the Gortian period came to an abrupt end as temperatures plummeted. The next cold stage, the Munsterian, persisted from 302,000–132,000 years ago.

The Pliestocene geology of Ireland showing the areas considered never glaciated and the extent of the older Munsterian glaciation (302,000–132,000 years ago) and more recent two cold phases of the Midlandian: Main: 79,000–65,000 years ago and Midlandian Drumlin: 35,000–13,000 years ago. From J.B. Whittow (1974). Geology and Scenery of Ireland. Penguin Books, London.

The Gortian floral assemblage contains several species whose history in Ireland is a matter of much conjecture. The occurrence of pollen from Mackay’s heath, Dorset heath and St Dabeoc’s heath opens up the possibility of their survival through the subsequent cold phases rather than a more recent postglacial arrival on land bridges from their southern headquarters in Portugal, Spain and France. Rhododendron, another Gortian species, possibly moved into Ireland to escape declining temperatures elsewhere in Europe at the time but is generally considered to have become extinct in Ireland at the end of the Gortian phase. Its reintroduction came during the eighteenth century and it has since spread into many habitats, especially deciduous woodland and peatlands. Two further species, considered north American in their current distribution – the slender naiad and pipewort – were also present in Gortian deposits. They, like the heaths and heathers above, could possibly have continued their tenure in the country through the subsequent Munsterian cold stage in areas not subjected to intense coldness, having arrived before the glacial period by migration through Greenland and Iceland when the water barriers were not so great. This would make the need for other explanations unnecessary – such as their arrival on the feet of migratory waders and geese from western Greenland and northern Canada and perhaps America from the end of the late glacial period onwards.

Palaeobotanists have found it difficult to correlate the Gortian interglacial deposits with other such deposits in Britain and Europe but Mitchell & Ryan believe that the closest fit is with the Hoxonian period in Britain and the Holsteinian period in Germany. Whatever the correlation, the Gortian interglacial is considered by some scientists to have been the last warm interglacial before the onset of the very cold Munsterian stage.⁷ The Gortian period provided the opportunity for the development of some 100 taxa of higher plants of which some 20 are not native of Ireland today.

Before the Munsterian ice was fully in place, the low ground turned into a polar desert. Only the toughest species of the Gortian vegetation could have survived these conditions while others migrated southwards to avoid the falling temperatures. Jessen was of the opinion that many of the species that migrated southwards before the advancing cold in Europe ended up in the Black Sea area. During the Munsterian glacial period large masses of ice flowed into Ireland from the Scottish Highlands and probably covered much of Ireland during its maximum extent. Limited areas of high land in the west and south probably remained ice-free. Low-lying areas, even along the Atlantic coastline, were characterised by a cold polar desert climate. Only the hardiest forms of flora and flora could have survived in Ireland when the Munsterian cold stage was at its maximum extent.

Mitchell & Ryan have put forward some evidence for the occurrence of two warm or mild phases (the Eemian and Fenitian) which followed the Munsterian cold stage and lasted from approximately 132,000–100,000 years ago, but more research is needed to establish the full nature of these interludes before the onset of the next cold phase, the Midlandian (Main) cold stage. Around 79,000 years ago it became severely cold with arctic and dry conditions until ice sheets formed and spread out from their two main centres located in an area from Donegal to Belfast and in the Midlands. A tongue of Scottish ice also passed down the Irish Sea. There were also ice caps in the Wicklow Mountains and the Cork and Kerry mountains. There were, however, substantial areas south of a line approximately between Askeaton, Co. Limerick, and the Wicklow Mountains that remained ice-free, and it was in this very cold region that many plants and animals would have had the opportunity to survive to then recolonise Ireland with the onset of warmer conditions commencing some 13,000 years ago.

During the Aghnadarraghian period, approximately 65,000–35,000 years ago, mild conditions set in. Remains of fossil beetles indicate summer and winter temperatures similar to those of today. The relatively warm conditions encouraged the development of temperate cool woodlands with hazel and yew. The earliest mammalian remains in Ireland, molar teeth, tusks and broken bones of woolly mammoth and musk ox bones (but see below), were found in gravel deposited on top of a band of lignite (brown coal) and date from over 50,000 years ago. The warm Aghnadarraghian mild phase was brought to an end with the onset of dry cold conditions which persisted for some 8,000 years before the development of more ice marking the Drumlin phase of the Midlandian cold stage, but conditions were sufficiently mild to allow the development of open grasslands with scattered birch and willow woodlands. It was in this environment that many mammals flourished, evidence of their occupation provided by bone remains in caves. The renewed ice possibly peaked around 25,000 years ago and then lasted until about 15,000 years ago when it started to melt, a process that took about 2,000 years.

Grass covered eskers, sinuous ridges composed of glacial outwash gravel.

The late glacial period and the development of woodlands

By the end of the late glacial phase some 13,000 years ago the ice sheets had melted and the final ordering of the rocky skeleton and cosmetic adjustments to the skin of the Irish landscape were complete. Mountains, hills and rocks had been scraped, scoured and polished by the flowing ice. Soil and boulders had been lifted up, moved over huge distances and dumped as rude morainic material and glacial till: sinuous ridges of outwash gravels or eskers, some extending over several kilometres and reaching 20 m in height, had established their presence in the Midlands. Miniature hilly landscapes made of drumlins or small hilly lumps of glacial drift, possibly formed underneath the melting ice sheets or dropped as dollops of material, had appeared. Lake basins were scooped out, valleys were formed.

As it emerged from the cold, Ireland entered what is known as the Woodgrange interstadial phase; a sort of mini-interglacial period without the full development of woodlands. The name comes from the shallow lake basin lying between drumlins at Woodgrange, Co. Down, where pollen was blown, settled, and remained preserved in the organic muds. Originally described by Singh,⁸ the Woodgrange pollen signatures were later recounted by Mitchell & Ryan. They chronicle the succession of plants that settled and spread in this area over a period of 3,000 years.

The first plants to emerge and fix themselves in the bare soil were sorrels, grasses and the dwarf willow. This initial growth is known as the grass/sorrel phase. Five hundred years later juniper and birch flourished while other pollen deposits showed crowberry growing close to the Atlantic coastline near Roundstone, Co. Galway. In those days the Irish landscape must have approximated that of arctic tundra with a smattering of birch woodland and juniper scattered over the ground. However, this initial growth was brought to an abrupt end as a renewed drop in temperature killed off the pioneering species.

Pollen diagram from Woodgrange, Co. Down. From Singh⁸.

A cold snap, triggered by a southerly movement of arctic waters down the Atlantic coast of Europe around 10,600 years ago, suppressed the birch and juniper development and opened up bare patches of soil only suitable for the more resistant grasses. This period, lasting some 600 years, is named the Nahanagan stadial by Mitchell & Ryan, after Lough Nahanagan in the Wicklow Mountains where glacier ice reformed as it did in other mountain corries under the renewed influence of freezing temperatures. Such extreme conditions only allowed the emergence of a sporadic plant cover, mainly of arctic-alpine species, growing at low altitudes and also at sea level along the western seaboard – as shown by pollen remains from Achill Island, Co. Mayo, and Waterville and Killarney, Co. Kerry. There was permafrost on the lowlands with a scattered plant cover, much of it made up of dwarf willow and other arctic species. The initial vegetation cover of the Irish lowland landscape was a succession of different plant communities consisting of grasses, mugwort and low scrub with juniper and crowberry. Open grasslands later developed, characterised by docks and sedges. The mugwort, Artemisia sp. was also common, as evidenced by the pollen remains, thus giving rise to the description of this period as the Artemisia phase. These grasslands endured for some 1,000 years as large herbivores – giant deer and reindeer – stalked and munched their way through the lush pastures. The Nahanagan cold snap snuffed out much of the start of postglacial life in Ireland and the process had to commence all over again – from a generally bare soil to grasses to shrubs to dwarf trees and eventually to mature woodlands.

During the next 4,900 years, from 10,000–5,100 years ago, the Irish landscape evolved from open tundra to a country almost totally swaddled by woodlands. Only the mountains, poking above the green canopy, and the rivers, lakes and bogs in the lowlands differed from their surroundings. Temperatures continued to rise, more than doubling the July mean temperature from about 7°C to 15°C, approximately the same as today. Because of these new climatic conditions, Ireland became available for colonisation by the flora and fauna that had survived on the ice-free and warmer European mainland and also possibly in parts of Ireland.

How Ireland acquired its flora and fauna is a continuing and unresolved saga. There are three principal scenarios. Firstly, many plants and animals may have entered the country before the Ice Age or during interglacial periods and survived in ice-free areas. The flora and fauna then colonised the landscape at the end of the Ice Age. Forbes first championed this preglacial survival hypothesis in 1846.⁹ It received support from Praeger in 1932 and Beirne in 1952.^10,11 Secondly, there may have been no Ice Age or interglacial survivors, and Ireland’s flora and fauna mostly arrived during the postglacial period, migrating from Britain and southern Europe when sea levels were some 130 m lower than present. This hypothesis was supported by Charlesworth in 1930, Godwin in 1975 and most recently by Mitchell & Ryan in 1997.^2,12,13 Finally, postglacial arrival may have been by aerial dispersion, chance methods, and introduction, deliberate or accidental, by early man. This hypothesis was postulated by Reid in 1899 and more recently by Corbet in 1961.^14,15

The most probable explanation is likely to be a combination of the three possibilities. Thus it would seem quite plausible for many species to have survived the Midlandian glaciation in the southern ice-free zones, and possibly earlier episodes of extreme coldness, while many other species may have arrived in Ireland during the postglacial period. The postglacial land bridge migration of flora and fauna has been strongly argued by Mitchell & Ryan. They postulated that land bridges between Ireland and Britain existed when the sea level fell to about 130 m below today’s levels exposing dry ridges of land, thus making it possible to cross dry-shod from the Lancashire-Cumbria area to Dublin, from north Wales to Co. Wicklow and from Cornwall to southeast Ireland. Ireland also had an Atlantic coastal ‘pathway’ linking it with southwest England, France and northern Spain. The sea fell to its lowest level some 15,000 years ago. By 10,000 years ago it was back to present day levels. Despite the appeal of the land bridge routes, the country could well have been repopulated from a reservoir of flora and fauna that had survived in the southern ice-free areas of Limerick, Cork and Waterford.

Late glacial Ireland. Column A gives the timescale for the last 13,000 radiocarbon years. Column B gives the names of the Irish type sites. Column C shows temperature trends, largely based on information from fossil animals and plants rather than instrumental measurements. Column D shows geomorphological and soil developments. Column E outlines vegetational developments. Column F lists mammalian records. From Mitchell & Ryan².

In support of their land bridge concept, Mitchell & Ryan explain the process whereby the retreat northwards of the large wedge of ice that filled the area now occupied by the Irish Sea created a land bridge which was ‘pulled’ northwards with the withdrawal of the glacier. It is argued that the great weight of the ice depressed the land underneath which was squeezed out laterally and at the front of the glacier. Pushing down a fist into a ball of dough would produce a similar effect with the dough squeezed out laterally and rising up around the edges. The squeezed-out land moved out sideways and in front of the ice as a sort of bow of land as the ice pushed southwards. On the retreat of the ice northwards up the Irish Sea area the forebulge of land also retreated. Mitchell & Ryan, drawing upon a detailed study by Wingfield of the British Geological Survey,¹⁶ postulated that the fore-bulge moved or was pushed into the south end of the Irish Sea area about 11,000 years ago, when it provided a land bridge link between Devon and Carnsore Point, Co. Wexford. As the glacier melted and retreated northwards up the Irish Sea so the fore-bulge followed, providing a sort of moving land bridge link, of a continually diminishing height, across which plants and animals were able to migrate into Ireland from west Wales. About 9,500 years ago the bridge was enveloped and submerged by the rising waters of the Irish Sea.

Outline curve to indicate possible course of sea level around Ireland during the last 40,000 years. From Mitchell & Ryan².

A land bridge also spanned what is now the English Channel, remaining open for business for approximately 2,500 years longer than the Irish-Welsh bridge. It was along this route that the plants and animals almost certainly moved from southern Europe to Ireland. They had about 1,500 years to travel across a ‘dry’ Irish Sea from Britain, having already trekked from the Continent into Britain over a ‘dry’ English Channel. It may seem a long time but in fact the colonisation process was a race against time as the immigration routes were being rapidly cut off by the rising waters, first in the Irish Sea and subsequently in the English Channel. Many species failing to cross the last bridge remained circumscribed to Britain, and the paucity of the Irish flora and fauna today is mainly – albeit not entirely – attributable to that late phenomenon. There remains, however, much conjecture and many difficult unanswered questions about the ways and means by which many animals and plants may have moved back into Ireland over the land bridges.^17,18

Many of the plants and animals involved in the migration process would have travelled a distance of at least 1,000 km by direct line, say, for example, from Luxembourg to Dublin. The time allocated for the trip (about 2,500 years including the 1,500 years when the Irish land bridge was open) would have allowed a rate of migration of 400 m per annum, a not unrealistic rate of progress. The pace of settlement was fast indeed as oaks were already growing in the south of Ireland 9,000 years ago while wild boars were being hunted near Coleraine, Co. Derry, by the first men on record. Wild deer too, had already established their presence in the Midlands some 8,400 years ago. However, opponents of the land bridge hypothesis would argue that these species were already present in the country and their populations expanded their range with rising temperatures.

Ten thousand years ago, pollen deposits were being laid down in a raised bog near Littleton, Co. Tipperary, starting an important historical archive and providing one of the most important chronologies of vegetational development in Ireland from 10,000 years ago to the present time.¹⁹ It tells the story of rich meadows of grasses, docks and meadowsweet which were quickly replaced by a juniper scrub mixed with willow trees. These low-growing species were subsequently overtaken by the taller downy birch forming the first real woodlands. Hazel then established itself with a patchy distribution of sometimes quite dense stands, while Scots pine also started expanding from about 9,000–8,500 years ago to produce a pine-hazel wooded landscape.

The oak first put in an appearance around 9,000 years ago and quickly expanded its range together with the wych elm to form a high forest. As a result of this woodland expansion, the pine was pushed off the better Midland soils onto the poorer regions of the west. Alder also extended its cover but remained confined to the wetter areas, while the drier limestone soils attracted the ash. By then yew was already in Ireland.

Schematic pollen-diagram to illustrate the early development of the Littletonian woodlands in Ireland. From Mitchell & Ryan².

The deciduous woodland climax phase, dominated by a high forest of hazel-oak-elm-alder lasted for almost 2,000 years between 7,000 and 5,100 years ago. With the onset of wetter climatic conditions, alder had spread considerably and joined the dense forest of oaks and elms. Pine was very much restricted to the poorer soils of the west or other upland areas where birch was also competing for some ground.

These were the finest years of Ireland’s woodlands. Vast areas of the country were covered by a continuous mantle of trees. It was the time of the proverbial tree top walking squirrels, which travelled the length of Ireland from Malin Head, Co. Donegal, to Cape Clear, Co. Cork, without touching the ground.

Many trees such as the limes, hornbeam, beech, service, all the elms except wych elm, the field maple and the sycamore failed to reach Ireland and become established as native species. The black poplar, together with the grey poplar, was formerly considered by Praeger to be rare and an introduced species.²⁰ However, recent surveys, initiated by the Botanical Society of the British Isles, have discovered large numbers of black poplar on the River Shannon system as far north as Lough Allen, Co. Leitrim, and in the damp plains that form the headwaters of the Rivers Liffey, Co. Wicklow, and Barrow, Co. Laois, which are thought to be remnants of native woodlands. The population is reported to have a well-balanced age structure and is regenerating, especially on the shore of Loughs Allen and Ree. There is a young population on the east shore of Lough Allen which is thought to be unique.²¹ Slightly over half of all the trees examined had smooth trunks and lower branches, without bosses, or burrs – a feature distinguishing the Irish population from that growing in England where only 0.3% are without bosses.²²

All except the sycamore managed to set foot in Britain where, however, they remained restricted to the south and east. Limes, hornbeam, beech, service, all the elms except wych elm, the field maple and the sycamore were subsequently introduced to Ireland by man. Beech and sycamore perhaps arrived with the Normans during the twelfth century – although archaeologists have identified fragments of beech dating from a period between AD 600 and 1000, possibly imported – while lime species and hornbeam only came in the seventeenth or eighteenth centuries. Despite their non-native pedigree, both beech and sycamore have adapted and flourished in Ireland as if they were native. On the other hand, Ireland can claim one native tree that is missing from Britain, the strawberry-tree. This belongs to a small group of so-called Mediterranean-Atlantic species and is found in Portugal, northern Spain and western France but not in Britain, probably because it travelled up the western European coast and bypassed Britain.

When the woodland reached its zenith about 5,250 years ago, elm was the commonest tree on the good soils in the drier areas of the Midlands and eastern Ireland.²³ Hazel, formerly common all over the country, was now concentrated in the north-central areas while pine was most abundant along the western seaboard. This woodland tranquillity was, however, to be interrupted by a dramatic decline in the production of elm pollen some 5,100 years ago. Debate has raged as to the causes of this phenomenon: was it man-induced or the result of natural causes? Mitchell & Ryan put it down to a disease – a fungal pathogen Ceratocystis ulmi (Dutch elm fungus) – a situation re-enacted this century with devastating consequences. While no figures are available for Ireland, over 90% of the British elms died, involving an estimated 25 million trees, during the late 1960s and 1970s.

Early plantations of beech woodlands.

The decline of the elm followed soon after the arrival of the first Neolithic farmers about 6,000 years ago, together with their cereal crops and domestic animals. They landed on the shores of Ireland with polished stone axes that had sharp cutting edges and they opened up the first woodland clearances by chopping down the trees, as well as killing them by ring-barking, in order to grow crops. The natural collapse of elm must have come as a gift to them for they did not have to exert so much effort to get at the good soil. The forests were progressively reduced over the next 1,500 years and replaced by extensive grassland and heathland. This commitment to tree cutting and removal was intensified as new waves of Neolithic immigrants arrived, later followed by the Celtic invasions, the Vikings, the Normans and then the English planters. All of them took a bite at the woods, which were soon cleared for purposes other than agriculture, such as charcoal production for the smelting of iron ore, the construction of ships, barrels and houses and the curing and preservation of cattle hides with tannins derived from oak bark. All this went on with such vigour that by the end of the Tudor period, virtually all of Ireland’s native woodlands had been reduced to a miserable rag bag of scrappy and uneconomic patches in steep and rocky places that were not attractive for agriculture or any other purpose. The grass pollen that was now swirling in the air was deposited in lake water where it descended into soft mud sediments to remain unaltered. Ireland’s new grasslands – visible under the microscope today – had arrived. Today, grassland dominates, accounting for 93% of all the land used for agricultural purposes.

The early fauna of Ireland and cave explorations

Towards the end of the nineteenth century, a small and enthusiastic band of Irish naturalists led by the ornithologist Richard John Ussher was deeply preoccupied with the exploration of caves which they thought must contain the bones of animals, and possibly early man, that once roamed through and flew over the Irish landscape. The caves in the limestone areas of Ireland were probed and excavated with such dedication and energy that the movement could almost have been dubbed the ‘Victorian bone craze’. The hard core cave naturalists included Praeger, Scharff and Ussher. Their publications on the findings from Kesh, Co. Sligo, Castlepook, Co. Cork, and at several sites in Clare are a source of endless fascination.^24,25,26 They were quick to realise that the bones provided incontrovertible evidence of the prehistoric fauna. But the circumstances in which the deposition of bones had occurred clearly varied. Some animals adopted the caves as their homes while others occasionally sought refuge there. Many bones were the remnants of prey dragged into the caves by the larger carnivores such as spotted hyenas, bears and wolves.

The Midlandian cold stage as described above was not as severe as the Munsterian cold stage. It is named after the elongated ice dome that was located between Galway City and Castlerea, Co. Roscommon, which sent ice sheets southwards through the Midlands which petered out along a line from Kilrush in the Shannon estuary to Tipperary town and then northeastwards to the Wicklow hills. There were also local ice caps to the mountains together with valley glaciers in Donegal, Wicklow, Cork and Kerry. Temperatures in the ice-free zones were possibly similar to cold Continental conditions, approximating parts of Siberia today. The landscape, out of reach from the glaciers, was probably open grassland with scattered woods of dwarf birch and least willow with only small amounts of bare tundra.² It was in this environment that many of the prehistoric animals existed.

The earliest known remains of animal bones in Ireland come from the east shore of Lough Neagh at Aghnadarragh, near the village of Glenavy, where lignite deposits date from about 55,000 years ago. A number of teeth and bones of the woolly mammoth together with bones of the musk ox were found in the thin glacial covering sitting on top of the lignite and probably dating from over 50,000 years ago.²⁷ The bones of bison have also been reported at this site but may be the result of misidentification – bison are close relatives of the musk ox.² Plant and beetle fossils from the area suggest temperatures very similar to those of today, giving the period the characteristics of a warm interstadial. Two tree species – yew and hazel – grew in scattered woodlands. During this period it is likely but not proven by the discovery of bone remains that there were other large mammals in the Irish countryside such as Irish giant deer, reindeer, brown bear and spotted hyena. Some of these were to become extinct with the resurgence of ice during the Drumlin phase of the Midlandian cold stage (35,000–13,000 years ago).

The Drumlin phase opened as cool interstadial with massive ice developing later and peaking at 25,000 years ago.² As the temperatures nose-dived, many animals took refuge in nearby caves where their bones lay dormant until discovered by the cave explorers. Ussher’s, Praeger’s and Scharff’s findings included woolly mammoth, red deer, giant Irish deer, reindeer, brown bear, wild boar, mountain hare, Arctic fox, spotted hyena, Norway lemming and Arctic or Greenland lemming.

Interpretation of the historical sequence and associations of the species was beset by problems of shifting soil horizons due to water movements in the caves, much of which was caused by melting ice from the glaciers. Additional problems were created by badgers entering the caves much later, and disturbing the bones embedded in the soil when excavating their setts. There were also cases of collapsing ceilings bringing in intruders from the strata above the caves. Radiocarbon dating was not available to Praeger, Ussher and Scharff at the beginning of the century, hence the difficulty of disentangling the muddle of bones. It is only very recently, in last 25 years, that cave explorers have been able to place their finds accurately within a chronology.

In 1993 a selection of some 30 samples of known bones, recovered from caves by early investigators and entrusted to the quiet security of museums, had small extracts of collagen removed for radiocarbon dating at the Oxford University Accelerator Unit. The programme was devised by Woodman & Monaghan.²⁷ The project had three aims: to discover (i) which mammals were in Ireland before the final glaciers of the Midlandian cold stage; (ii) which animals were present afterwards in the late glacial period and (iii) which were present in the postglacial period from some 10,000 years ago.

The radiocarbon results (given as median dates in years ago and rounded to the nearest 100), based on bones from Castlepook and Foley’s caves in Co. Cork and Shandon cave, Co. Waterford, showed that in the ice-free zones in Cork and Waterford giant Irish deer (32,100), reindeer (28,000), Norway lemming (27,900), woolly mammoth (27,200), brown bear (26,300), red deer (26,100) Arctic lemming (20,300) and Arctic fox (20,000) were present. During the late glacial period the following species were found in caves in Cork, Sligo, Clare and Limerick: reindeer (12,500 and 10,900), brown bear, (11,900 and 10,700), red deer (11,800), giant Irish deer (11,800), wolf (11,200) and Arctic lemming (10,000), showing that the first four species soldiered on into the late glacial period (13,000–10,000 years ago). The gradual warming up of the landscape was rudely interrupted by the Nahanagan stadial, during which the mean annual summer temperatures may have been less than 5°C. Many questions remain as to the impact of this sudden temperature reversal on flora and fauna. However, it should be remembered that Arctic foxes, Greenland lemmings, Arctic hares, ermines, wolves and musk ox as well as hundreds of insect and flowering plant species are able to survive Greenland winters when temperature drop as low as -20°C with summer temperatures higher than experienced during the Nahanagan stadial. The question applies to all the previous cold periods. If some animals and plants were able to survive the Drumlin phase of the Midlandian and subsequent Nahanagan stadial then the need to argue for their land bridge arrival in Ireland is considerably weakened. Many of the large herbivores disappeared, together with their carnivore predators, with the decline of their important grasslands.

Without further information from a large scale radiocarbon dating programme it will remain a moot point whether the known early mammals such as Arctic hares, red deer and wolf, and species such as stoats, otters, pine martens, etc., for which there is no evidence yet of their early occupancy, achieved a continuous presence in Ireland through to the postglacial period, when a warmer and a more environmentally friendly landscape re-emerged, or whether they re-entered Ireland as immigrants across the land bridge. All that can be said is that Woodman & Monaghan dated red deer bones from 4,200 years ago at Stonestown, Co. Westmeath and to 2,020 years ago at Sydenham, Co. Down and that brown bears were present in Ireland as recently as 8,900 years ago – as testified by remains at Derrykeel Bog, Co. Offaly. They were contemporary with the first human settlers at Mount Sandel on the lower reaches of the River Bann, just south of Coleraine, Co. Derry.

Animal bones recovered from County Clare caves. 1–5 Crane bones; 6 Hawfinch? 7 Arctic fox; 8 Domestic cat; 9 Irish wild cat. From Scharff et. al.²⁶

Lynch & Hayden have argued that the range contraction of the Arctic hare and stoat, both present in the Castlepook interstadial (35,000 years ago²⁸), before the Drumlin phase of the Midlandian period, into an ice-free southern Co. Cork, together with their genetic isolation from their assumed British and Continental mother stock, may have been sufficient time for both the stoat and hare to develop their subspecific characteristics.²⁹ They tested morphological differences by multivariate analysis of cranial measurements between Irish, English and Scottish carnivores – badger, mink, otter and stoat. Significant differences between English, Scottish and Irish badgers, otters, mink and stoat populations were demonstrated – the greatest were between the Irish stoat and its English counterpart, thus strengthening the argument for the stoat being a glacial relict species. Little evidence was found for musteline colonisation of Ireland via a land bridge between northeast Ireland and Scotland. The evolution of established subspecific differences which separate Irish hares and otters from their English relations would also have been facilitated by their genetic isolation provided by their presence in Ireland some 35,000 years ago.

Woodman & Monaghan also attempted to unravel the history of the horse in Ireland.²⁷ Was it introduced around 4,000 years ago or was it a survivor, in its wild form, from the late glacial to the postglacial period – as is the case in Britain? The subject is still open to debate as one horse bone, recovered from Shandon Cave, near Dungarvan, Co. Waterford, gave a radiocarbon date indicating that it was more than 40,000 years old.² This places the wild horse in Ireland long before a series of horse bones from five widely separated caves from Antrim to Clare, which gave a range of dates from 1,675–120 years ago. These latter datings would support the idea that the horse was introduced late to Ireland.

Red deer

Red deer were part of the rich mammalian fauna during the Midlandian stage prior to the Drumlin cold phase. Radiocarbon dating shows them present in Co. Waterford from at least 26,100 years ago with more recent records from 11,800 (Co. Sligo) and 4,200–2,000 years ago (Westmeath, Kerry, Clare and Down).²⁷ It would appear that they survived the Drumlin phase of the Midlandian cold stage, possibly along with other mammals whose bones have not yet been found, to earn ‘native’ status in the Killarney Valley, Co. Kerry. However, the degree to which the Killarney deer are unadulterated descendants of the original native stock is a complex and unresolved issue.

Scharff wrote of ‘red deer which still survives in a semi-domesticated and not entirely pure strain in the forests of Killarney.’³⁰ Moffat stated in 1938 that ‘These Deer cannot be claimed as a perfectly pure breed, for inter-breeding has occurred with imported animals, and the extent to which this has prevailed is not easily estimated. The Red Deer at Muckross have, however, at least a fair claim to represent in the main the old native stock that is known to have been abundant throughout Ireland in early historic and pre-historic times.’³¹ Finally, Whitehead declared in 1964: ‘Of the three established herds, only the Kerry deer can claim descent from the original wild stock, but even these cannot be considered as being perfectly pure bred.’³² Whitehead has produced the only evidence questioning the status of the deer. He reported that during the nineteenth century both Lord Kenmare and Mr Herbert of Muckross, Co. Kerry, brought in fresh blood which included five stags from Co. Roscommon – presumably from the herd at Croghan House Park, Boyle, where a small herd existed until 1939. Around 1900 Lord Kenmare brought in a stag from Windsor Great Park, England, which was liberated in Derrycunihy wood. Also at this time some stags from Muckross were rounded up and sent to Scotland in exchange for Scottish stags. Since the latter arrived, occasional bald-faced deer have been seen in Derrycunihy. They may be the descendants of deer from the Glenlyon area of Perthshire possibly included in the exchange.³² The red deer in Kerry today are confined to the Mangerton and Torc mountain ranges and number about 600.

A recently born red deer calf (F. Guinness).

At the National Park at Glenveagh, Co. Donegal, the red deer herd was established in 1891, when two stags and four hinds were brought in from Glenartney deer forest in Perthshire, followed in 1892 by a stag and nine hinds from Langwell deer forest in Caithness. Subsequently, whenever fresh blood was required it was introduced from either England or from other parks in Ireland such as Colebrooke, Co. Fermanagh (1910), and Slane, Co. Meath (1947–9).³²

Sika deer

In 1860, Lord Powerscourt introduced four sika deer from Japan to his demesne in Co. Wicklow. Ireland was the first country in Europe in which these deer were bred successfully.³³ Within 24 years, numbers had increased to 100 – not taking into account individuals shot or sent to other parks – and reached 500–600 strong by the early 1930s. Many slipped out into the Wicklow hills and its woodlands where they flourished. Lord Powerscourt mated red with sika deer and produced fertile offspring which was indicative of their close biological relationship. Once started, the hybridisation process spread outside the demesne into the Wicklow Mountains, uplands and forests, where it is unlikely that there is any true red deer left today. In other words, this particular tampering with nature brought about the extinction of a species, albeit only the Wicklow population of red deer. The lessons learnt will hopefully discourage other potential Noahs from introducing non-native species and dabbling in cross-breeding experiments.

Rump patterns of the red (left), fallow (centre) and sika deer (right). From G.B. Corbet & N.H. Southern (1977) The Handbook of British Mammals. Blackwells, Oxford.

Lord Powerscourt, however, was not the first. The Normans had done it before him, bringing both the rabbit and fallow deer into Ireland during the twelfth century. Rabbits became pests, successfully competing with other herbivores for grass, but at least they did not interbreed with other species. Fallow deer provided sport, food and ornament and could be considered as an ecologically benign species although they may cause damage to forestry, agriculture and horticulture.

Lord Powerscourt was a prominent member and one of the vice-presidents of The Society for the Acclimatisation of Animals, Birds, Fishes, Insects and Vegetables within the United Kingdom, founded in 1860 and disbanded in 1865. Its purpose was to ‘acclimatise and cultivate those animals, birds etc., which will be useful and suitable to the park, the moorland, the plain, the woodland, the farm, the poultry yard, as well as those which will increase the resources of our seashores, rivers, ponds and gardens’.³⁴ Apart from the sika he brought in other foreign creatures to Ireland: axis deer, Sardinian mouflon (wild sheep), sambar deer and several colour varieties of the red deer including the wapiti or Canadian deer. Fortunately none of these ‘took’ or became acclimatised to Ireland. He also introduced roe deer but nothing is known of the results apart from the fact that they never survived at Powerscourt or elsewhere in Wicklow. Henry Gore-Booth was more successful in the early 1870s and established a small feral population of roe deer on his estate at Lissadell, Co. Sligo. They survived, apparently restricted to the estate, for about 50 years before being shot out.

In 1865, some of the Powerscourt sika deer were sent to the deer park at Killarney. Some 20 years later, they successfully spread throughout the surrounding woodlands, opening up the possibilities of hybridisation with the reds. In the face of this threat, a small number of Killarney red deer was transported during the 1970s to Inishvickillane, a remote and privately owned island off the Kerry coast. They settled down well and are self-sustaining today in a herd of over 50 individuals. Another small group of red deer from Killarney has been established within the Connemara National Park, Co. Galway, where there is no prospect of them interbreeding with sika deer.

Lissadell House and estate, Co. Sligo, the site of roe deer introduction in the early 1870s.

Wolves

Like the red deer, the wolf is an ancient Irish mammal, and one of the several species that became extinct in Ireland in historic times. It was predominant in Irish woods until the end of the seventeenth century, but man, under instruction from the English authorities, soon got the better of it. What organised hunting could not do, wood clearances perfected, and the bulk of the furry marauders was quickly extinguished. A few straggling remnants survived through the eighteenth century and it would appear that the last of the wolves was killed in Co. Carlow in 1786.³¹

Wolves were present in Ireland from prehistoric times, as shown by remains found in caves in Waterford, Sligo and Cork.³⁵ In those Arcadian days the hungry lupines did not have to cover kilometres to find prey, as the countryside was teeming with giant deer and reindeer. Later, when the giant deer became extinct and man appeared, the beginning of farming meant a renewed diet of cattle and sheep. Fortified settlements such as raths or ring forts dating between 500 BC and AD 1000 are evidence of the necessity to protect domestic animals from thieves and wolves during the night.

From the early days of colonisation, the English authorities were concerned that if Ireland were to be fully civilised, the wolves had to be eradicated. The species had disappeared from England and Wales around 1500 and Scotland was in the process of being rid of it (the last Scottish wolf died in 1740). There is no doubt, however, that, prior to English rule, it had been a sport of the Irish chieftains to hunt the wolf – known as fael or bréach and sometimes occurring under the name ‘son of the country’ (mac-tire).³⁶ For that purpose they were assisted by dogs of gigantic proportion, great swiftness and indomitable courage, variously called ‘Wolf-dogs’ or ‘Wolf-hounds’ and not to be confused with greyhounds – although historical research is vague on the origin of the wolfhound as a specific breed and confusion is often noticeable.

Wolf from the Book of Kells (c.800 AD). (The Board of Trinity College, Dublin).

The habit was to kill the wolves by trailing a dead horse through the woods before dropping it in a clearing. When the wolves came to feed at night, the hounds were let slip and quickly dealt with the famished guests. As farming developed and more of the country was put under pasture, the wolf became an increasing nuisance and hunting was promoted through various edicts and bills. In a ‘Book of Information’ compiled in 1584 it was recommended that ‘some order might be had, as when the lease is granted to put in some clause that the tenant endeavour himself to spoil and kill Wolves with traps, snares, or such devices as he may devise’.³⁷ No doubt, the species in the sixteenth century was still very widespread and numerous. An entry in the diary of William Russell, Lord-Deputy of Ireland, in 1596 indicates that there were wolves in the woods just outside Dublin. Further action was encouraged under James I and in 1611 it was decided that an ‘Act for killing Wolves and other vermin’ was necessary – though it was never passed. The text of the proposed Bill cautioned the Lord Deputy or Principal Governor to call off the hunt if they thought that the hunters (requisitioned peasants mostly) were using it as a ploy to get armed – a clear case of wolves in sheep’s clothing.

In a subsequent attempt to civilise Ireland, Cromwell brought out a Bill in 1653 spelling out the necessity to hunt and destroy the plunderers he called ‘doggie wolves’. Some organisation was required – ‘daies and tymes for hunting the Wolfe’ had to be appointed – and money was to be paid on presentation of the heads of male, female or infant wolves, a different rate applying to each specimen. Settlers and natives therefore actively engaged in a renewed bout of destruction, which in 1683 enabled an observer to say about Co. Leitrim: ‘The wolves, which were very numerous, are now very scarce…’. By the close of the seventeenth century the battle was nearly won and Ireland’s reputation as ‘Wolf-land’ could no longer be literally sustained. But the saga of the ‘last’ wolf continued through the eighteenth century with some counties being entirely cleared while in others, like Kerry, more hunting was required. But as the woods dwindled the wolf was left with straggly pockets of trees, which made it even more vulnerable. Eventually silence fell: there was no more ‘panting, lolling, vapouring’³⁸ outside farmyards and no more howling.

European frogs and natterjack toads

The history of the European frog in Ireland has perplexed biologists for several centuries. Was it introduced in 1699, or does its lineage stretch back into the mists of time, to the postglacial period at least 10,000 years ago? The story begins with early categoric statements regarding the frog’s absence. Donatus, the ninth century Irish monk, appears to have been the first to speak:³⁹

Nulla venena nocent, nec serpens serpit in herba

Nec conquesta canit garrula rana lacu.

No poison there infects, no scaly snake,

Creeps through the grass; nor croaking frog annoys the lake.

Cambrensis echoed these sentiments in Topographia Hiberniae, written in the 1180s:⁴³ ‘Of all kinds of reptiles, only those that are not harmful are found in Ireland. It has no poisonous reptiles. It has no serpents or snakes, toads or frogs, tortoises or scorpions.’ But Cambrensis contradicts himself a few pages later when he speaks of the discovery of at least one European frog, found near Waterford: ‘Nevertheless in our days a frog was found near Waterford in some grassy land, and was brought to Robert Poer…’. It was seen by many people including Duvenaldus (Domhnall), King of Ossory, ‘who happened to be there at the time, with a great shaking of his head and great sorrow in his heart at last said (and he was a man of great wisdom among his people and loyal to them): “that reptile brings very bad news to Ireland”.’ So what are we to make of this? What is the real truth about the frog’s pedigree in Ireland?

Noxious animals and their evil associations were an obsession of early Christian commentators who placed the frog in the same category as toads, snakes and lizards because of a superficial similarity. Thus when St Patrick, in one generous swing of the crozier, drove all the pernicious creatures away, the frog left the country – or so Christian mythology claims. Another story concerns a certain Dr Gwithers, Fellow of Trinity College, Dublin, labelled ‘frog introducer to Ireland’ who is supposed to have performed his sly deed in 1699.⁴⁰ One snag is that there is no Dr Gwithers recorded on the books of Trinity College, although there was a Dr Gwithers who was one of William Molyneux’s network of correspondents gathering information for the English Atlas, an ambitious and ill-fated project launched by the London bookseller Moses Pitt in 1682 (see here). Dr Gwithers, in his notes supplied to Molyneux, now lodged in the library of Trinity College, Dublin, categorically states that the frog was absent from Ireland. But his zoological credentials were seriously compromised when he noted that both the stag and otter were also absent which, of course, was not true.⁴¹

Another chapter in the mystery of the frog’s antiquity was unravelled some 355 m up on the side of Keishcorran Hill as the present century dawned. Here, at one of the southern outposts of the limestone region in Sligo and Leitrim, at about 90 m above the base of the hill, on the southwestern side, is a line of low cliffs some 15–30 m high punctured by a series of cave entrances. The caves provided refuge and shelter to many animals during the late glacial period some 12,000 years ago. Bones of brown bear, red deer and wolf from this period have been found buried in the earthen floors under more recent material. Other animals came as prey brought by others. During the excavation of one of these caves, the Plunkett Cave, in 1901, a large number of frog bones were found in the upper stratum of soil extending to a depth of some 30 cm on the cave floor. No doubt this stratum was of recent origin, but below were much older layers of soil that revealed more frog bones, associated with Arctic lemmings. Lemmings were present in the Irish landscape some 10,000 years ago as evidenced by the radiocarbon dating of bones found in the Edenvale Cave, Co. Cork, but probably not much longer after that as the rise in temperatures made habitats unsuitable for them. In other words, if frogs were contemporary with the lemmings they had to date back about 10,000 years.

Some of the fossilised frog bones recovered from Plunkett Cave lay in the clay stratum nearly 2 m below the surface layers. Such depth ruled out any likelihood that frogs from more recent times had burrowed down through this overburden, or were deposited there by other animals digging up holes, or had been displaced by soil shifts caused by running water coursing through the cave systems. Moreover the bones were blackened and filled with clay showing that they had not arrived recently. The evidence was enough to convince Scharff that the frog was indeed a member of the ancient fauna of Ireland.^24,42 But there are other opinions about the bones’ antiquity and the argument can only be settled with a radiocarbon date. That this task has not yet been undertaken is quite astonishing. As the European frog lives quite happily throughout Europe and within the Arctic Circle there is no reason why low temperatures in Ireland, at the end of the last glacial phase some 10,000 years ago, would have cramped their style or inhibited their spread throughout the country.

The natterjack toad’s history in Ireland is equally controversial without any definitive conclusion as to its antiquity. However, the somewhat slender evidence would point to it being a more recent arrival in the country than the frog.

View from Keishcorran Cave, Co. Sligo, where ancient frog bones were discovered.

Although Cambrensis observed that there were no toads in Ireland in the twelfth century⁴³ there is no evidence in his texts that he went to west Kerry or had any informants from the region. There was no written reference to toads until 1836, when J.T. Mackay, botanist and author of Flora Hibernica, reported seeing them in 1805 in Callanafersy, a large district between the lower parts of the Rivers Laune and Maine adjacent to the eastern end of Castlemaine Harbour.⁴⁴

How did these toads come to Ireland and why are they restricted to a relatively small sandy coastal area in west Kerry? Are they relicts of a once more widely spread population from a warmer and drier period? What do we make of Chute, writing from Blennerville on 31 March 1846, to Thompson, author of The Natural History of Ireland, ‘I believe the Natter-jack is indigenous to Kerry, though there is an old tradition that a ship at one time brought a lot of them and let them go at the head of Dingle Bay. This is born out by the fact that this is the only part of Kerry that they are met in: a district extending from the sandhills at Inch at Rosbegh at the head of the bay (where they are most numerous) to Carrignaferay, about ten miles in length in low marshy ground, and about the same number in breadth.’⁴⁵ A century later, Praeger spoke contemptuously of this invasion hypothesis: ‘Could misdirected ingenuity go further than to suggest the importation or shipwreck of a cargo of toads on that lonely and harbourless coast!’²⁰

Beebee says of natterjack toads in Ireland: ‘It seems much more likely that they are truly indigenous’ and he argues that they are part of the Lusitanian biota of the Iberian peninsula which is well known in southwest Ireland.⁴⁶ However, the natterjack can hardly be considered Lusitanian with a European distribution stretching northwards to southern Sweden and into western Russia.

Their indigenous status is also supported by Praeger who wrote ‘There is no doubt that in spite of its extremely restricted range the animal is indigenous in Kerry – a relict species like some of the Kerry plants.’²⁰ The only real evidence to support the indigenous status of the toad comes from the discovery of their bones from a megalithic cemetery at Carrowmore, Co. Sligo, during the 1970s.⁴⁷ But the status of these bones is not clear. Were they contemporary with Neolithic man or did they arrive much later and end up buried in the soil at the same spot? Whatever the explanation, this would be the first evidence of the natterjack existing outside its very restricted Kerry range.

In fact, there are two flies in the indigenous ointment. First, the natterjack’s restricted distribution and its failure over its presumed long period of residence to colonise other available habitats and second, the lack of place names incorporating the Irish for ‘toad’.³⁶ Both would argue against its native status. On the other hand, it would be wrong to dismiss completely the possibility of their arrival from a ship at the head of Dingle Bay for two reasons. First, local stories in Ireland are more than often grounded in fact and there is no reason to disbelieve this one. Smith, in his survey of Kerry published in 1756, wrote about Castlemaine Harbour in the mid-eighteenth century: ‘Deep enough for vessels of 50 tons or upwards to sail up to the bridge at high water where they may lie on soft oozy ground to discharge. Some vessels are unloaded here on the bankside which serves as a wharf. These are generally freighted with rock salt from England, and others are laden with iron ore which is carried on horses to the iron foundries.’⁴⁸ Some toads could have been caught up in sand ballast, brought from European ports, and dumped on the shore at any point of the operations described above. The dumping of ballast on both sides of the Dingle Peninsula would explain the toad’s presence at Castlegregory and Castlemaine sites. Secondly, toads would have almost certainly been noticed and commented upon prior to their first recording in 1805 had they been present in the area over the centuries. Also, how could such an astute recorder as Smith overlook them in the 1750s? Finally, the non-indigenous hypothesis is strengthened by the absence in Ireland of the common toad whose European distribution is even more widespread than the natterjack’s, with populations extending much further north and east. It might therefore be suggested that the factors operating against the common toad’s spread westwards were also operating against the natterjack: both were probably prevented from hopping across land bridges connecting Britain and Ireland because those had already been drowned.

The hypothesis of the natterjack’s arrival by boat is also supported by some comments by Cambrensis. When discussing the fate of poisonous reptiles when they arrive in Ireland he states ‘I have heard merchants that ply their trade on the seas say that sometimes, when they unloaded their cargoes at Irish port, they found toads brought in by chance in the bottom of the holds. They threw them out still living on to the land…’.⁴³ One way of throwing more light onto the natterjack’s status would be to investigate biochemical and genetic divergence between the Irish, British and European populations by electrophoresis or more sophisticated genetic techniques. Some historical research into the traffic of boats and the way their ballast and cargoes were handled in Dingle and Tralee Bays might also be helpful. The occurrence of jettisoned ballast on Irish shores is well known: it has been accepted that the large erratics of flint on the foreshore at Kilmore Quay, Co. Wexford, came by boat, while the many small boulders of brown granite found near the entrance of Lough Hyne, Co. Cork, close to a rough disused landing place were the same rocks used to build the lighthouse works on Clear Island, Co. Cork – they came from Cornwall. In Broadstrand Bay, on the west side of Courtmacsherry Bay, Co. Cork, a variety of igneous pebbles and boulders, most of them granite with coloured feldspars, were found in the clefts of an early glacial rock platform as well as in the gullies of small beaches. Farrington was in no doubt, having examined all likely local sources, that the boulders and pebbles in question were ballast, probably deposited 60 years before he recorded his observations in 1965.⁴⁹

Freshwater fish

The first fish to come back to Ireland after the last Ice Age were the euryhaline species (those that can tolerate a wide range of salinity and are encountered in both salt and fresh water). These fish are able to maintain the concentration of chemical salts in their blood and body fluids regardless of the changes in the water around them. Thousands of years ago they almost certainly cruised around the coastline, following the northwards retreat of the glaciers, exploring the unfolding and warming aquatic systems, and penetrating the ice-free rivers and lakes. Maitland considered that the following 12 euryhaline fish colonised the freshwater systems of Ireland in early postglacial times:⁵⁰ sea lamprey, river lamprey, Allis shad, Twaite shad, Atlantic salmon, brown trout, Arctic charr, pollan, smelt, European eel, three-spined stickleback and ten-spined stickleback. The latter, however, is considered by some to have been introduced (see below).

As to the stenohaline species (those that can tolerate only a narrow range of salinity), a question mark prevails over their provenance. The issue is twofold. Firstly, they are non-migratory although some, like the pike, have a capacity to spread rapidly across the land through interconnecting lakes and rivers. Secondly, they were not suited to the salt waters that surrounded all Irish shores from postglacial or earlier times. The four possible explanations for their presence are that they were already present during the last interglacial period and survived the final phase of the Ice Age in sheltered ice-free ponds; that they swam into Ireland, using the waterways in the land bridges between Ireland, Britain and the Continent; that they were once able to tolerate salt water and swam into Ireland across the sea, or that they were introduced by man or by some other agent.

The following species are generally considered to have been introduced to Ireland by man:⁵¹ brook lamprey, pike, carp, gudgeon, tench, bream, minnow, rudd, roach, dace, stone loach, perch and ten-spined stickleback. When were these first brought into Ireland? The weight of expert opinion is that probably most, if not all, were introduced sometime between the Norman invasions and the late nineteenth century. An examination of the Irish names for fish provides some corroborative insights: salmon or brown trout, not in the above list, have at least 30 different Irish names – including many local variants – authenticating their ancient presence in Ireland. By contrast, the dace and tench, both relatively recent arrivals, have only one and two Irish names respectively.⁵² However, this is subject to caution, as the Arctic charr and pollan, both prehistoric but rather scarce species, and not known to many, only carry a few names.

Cambrensis provides clues as to the origin of certain fish. The following translation, quoted by Went, is by Forester from Wright’s The Historical Works of Giraldus Cambrensis.^53,54

‘Sea-fishes are found in considerable abundance on all the coasts. The rivers and lakes, also, are plentifully stored with the sorts of fish peculiar to those waters, and especially three species: salmon and trout, muddy eels and oily shad. The Shannon abounds in lampreys, a dangerous delicacy indulged in by the wealthy.

This country, however, does not produce some fine fishes found in other countries, and some excellent fresh-water fishes, such as the pike, the perch, the roach, the barbel, the gardon [chub], and the gudgeon. Minnows, also, bullheads, and verones [minnows] are not found there, also no loches, or they are very rare.

On the other hand, the lakes of this country contain three species of fish which are found nowhere else. One is a sort of trout, called the salares, which are longer and rounder than trout, and which are white, close grained and good flavoured. The tymal, commonly called the umber, resembles the former kind of fishes, except that it is distinguished by a larger head. There are others which very much resemble the sea herring, both in shape and quality and in colour and taste. A third sort, exactly resembles the trout, except that it has no spots. The first sort is called Glassans, the second Cates, and third Brits. These three fish make their appearance in the summer only, and are never seen in the winter’.

It would appear from this text that the freshwater fish present in Ireland during the twelfth century included salmon, brown trout, eel, shad (probably both Twaite and Allis), sea and river lampreys, and almost certainly the brook lamprey, as the habitats of the three overlap. Amongst these early settlers, the sea and river lampreys, Atlantic salmon and the brown trout are anadromous, i.e. spend most of their lives in the sea but migrate to fresh water to spawn.

Other anadromous species arrived in Ireland from more southerly seas at the end of the last glaciation. They were the Allis and Twaite shads. Resembling herrings and found in shallow coastal waters and estuaries in western Europe, they run up the lower reaches of the larger rivers during the spawning season. In Ireland, however, the Allis shad has no known spawning site left. In fact, it is not certain whether the species is still here, as its presence is only supported by a few post-1960 records – in the Foyle estuary, Co. Derry, at two north Mayo sites, in the River Corrib, Co. Galway, and at one site in Cork. The Twaite shad shares the same coastal distribution and probably still breeds in a few Irish rivers such as the Nore, Suir and Barrow, all flowing into Waterford Harbour and the Cork Blackwater. When locked away in remote lakes, it developed into different subspecies, the Killarney shad, Alosa fallax killarnensis, being one of the most celebrated. Known locally as the ‘goureen’, it is restricted to Lough Leane and Muckross Lake, Co. Kerry, where it has been preserved for several thousand years. The smelt, also a coastal dweller in western Europe, imitates the anadromous behaviour of the shads. In Ireland it spawns in the rivers Shannon, Fergus and Foyle and perhaps at various sites in rivers Suir, Nore and Barrow. The remaining native euryhaline fish to arrive after the last Ice Age was the European eel, a catadromous species (one that migrates from rivers to the sea to spawn). Eels live in lakes and rivers and spawn in the Sargasso sea, after which the baby eels return to Ireland.

Once in Ireland the brown trout evolved a series of varieties, some of which are collectively known as sea trout (sometimes ascribed subspecific status as Salmo trutta trutta but not fully accepted by all scientists) with anadromous habits, and the darker, landlocked non-anadromous brown trout (sometimes ascribed the subspecific status Salmo trutta fario, again not fully accepted by all scientists). The latter have given rise to many other different varieties. For instance in Lough Melvin, Co. Leitrim, there are three clearly distinct stocks of brown trout: the ferox (Salmo trutta ferox), the gillaroo (Salmo trutta stomachius) and the sonaghan (Salmo trutta nigripannis). They are genetically different and spawning takes place in different parts of the lake.

Arthur Went who, apart from being the scientific advisor on fisheries to the Irish Government, was a specialist in questions concerning the history of fish in Ireland, believed that the pike was an introduced species, basing his arguments on an examination of historical documents including the statement by Cambrensis (see here). Cambrensis had a reasonable knowledge of Irish lakes and rivers. He mentions the pike as absent from Ireland. A further clue as to the late introduction of the species is supplied by the great historian Roderic O’Flaherty, who clearly ascertained that in 1684 the pike was absent from Connacht when he wrote:

‘The water streames, besides lampreys, roches, and the like of no value, breed salmons (where there is recourse to the sea), eels and divers sorts of trouts. There was never a pike or bream as yet engendered in all this countrey, nor in the adjacent parts of Mayo or Galway counteys.’⁵⁵

The pike must have been brought into Ireland some time before 1682, for historical records state the presence of weirs for eels and pike on the River Camoge at the Abbey of Monasternenagh, near Croom, Co. Limerick, at the time of the Abbey’s dissolution.⁵⁶ The Civil Survey of Ireland (1654–6) also noted the River Camoge as well as other tributaries of the River Maigue had pike.⁵⁷ Its widespread distribution today should not be mistaken for a sign of long-lasting presence in the country. As a rapid coloniser, the species was able, once introduced, to spread throughout freshwater systems over a short period of time.⁵³

Went stated that there was no evidence as to whether the perch was a native species or not. However, since the remark by Young in Tour in Ireland that perch first ‘swarmed in the Shannon’ in about the year 1770, the geographic distribution of the species and its numbers have increased considerably.⁵⁸ The roach, often confused with the rudd, was introduced to the River Blackwater, Co. Cork, in 1889. The barbel and ‘gardon’ – almost certainly the chub – referred to by Cambrensis are not present in Ireland today. The gudgeon, however, which the Welshman reported absent in the twelfth century, is now claimed to be a native species as are minnows – also called ‘verones’ by Cambrensis – and the stone loach.

The ‘salares’ of Cambrensis is almost certainly one of the pollan or whitefìsh species, restricted to five of the largest Irish lakes – Lough Neagh, Upper Lough Erne (no records this century), Lower Lough Erne (small but precarious population⁵⁹), Lough Derg and Lough Ree (no recent records). Absent from Britain and elsewhere in western Europe, its presence in Ireland is outlandish, and it is possibly a relict from a once wider distribution. Today it is only found in the coastal areas and lower reaches of arctic rivers in eastern Europe, Asia and western North America. Once thought to be an intermediate between the powan and the vendace – both absent from Ireland – it has the status of an endemic Irish subspecies of the Arctic cisco which lives in Alaska, Coregonus autumnalis pollan. These two ‘conspecifics’, the Arctic cisco and Irish pollan, have probably been separated for about 10,000 years since the first pollan – a cold water species able to withstand life at the edge of ice sheets – are thought to have entered Ireland through the Shannon system at the start of the postglacial period.⁶⁰ Although the pollan are anadromous throughout most of their northern range, in Ireland they are virtually non-migratory, and restricted to fresh waters. The species named the ‘tymal’ by Cambrensis is the grayling which, in fact, is absent from Ireland. Was it ever present or did the observer misidentify the species? It is impossible to say.

The ‘spotless’ fish referred to by Cambrensis is the Arctic charr, whose name is derived from the Gaelic ‘tarr’, meaning belly. The male belly colour ranges from pink to bright vermilion, as pointed out in two Irish names, tarr-dhearg, meaning ‘red-bellied’, and ruadh bhreac, meaning ‘red trout’.⁵² The female is drabber than her male counterpart whose bright red colour plays an important role both in courtship and defence of the breeding territory. Charr, more than most other freshwater fish, excite the imagination of naturalists who know them as ‘glacial, or Ice Age relicts’, i.e. survivors of the Ice Age. They inhabit the deep dark, oligotrophic (nutrient-poor) formerly glaciated lakes which they invariably share with brown trout – although in Ireland, they often break from their austere habitats and are found in shallow and eutrophic (nutrient-rich) waters. The Arctic charr is distributed throughout the northern hemisphere with both anadromous and non-anadromous populations. In Ireland, it is non-anadromous. Like the smelt and Twaite shad, it is classified as an ‘endangered and vulnerable’ species – the pollan, Killarney shad and Allis shad are ‘endangered’ species while the sea lamprey, river lamprey and brook lamprey are ‘threatened’ species.⁶¹

In an exercise of species-splitting much practised once, Regan examined various charr from Ireland and identified six ‘species’ living in different Irish lakes.⁶² They were: Cole’s charr, Salvelinus colii, (Loughs Eske and Derg, Co. Donegal, Lough Conn, Co. Mayo, Loughs Mask and Inagh, Co. Galway, Counties Clare and Kerry); Grey’s charr, S. grayi, (Lough Melvin, Co. Fermanagh); Trevelyan’s charr, S. trevelyani, (Lough Finn, Co. Donegal); Scharff’s charr, S. scharffii, (Loughs Owel and Ennell, Co. Westmeath); Coomasaharn charr, S. fimbriatus, (Coomasaharn Lake, Co. Kerry) and blunt-nosed charr, S. obtusus, (Loughs Tay and Dan, Co. Wicklow, and Loughs Leane and Acoose, Co. Kerry). Today these are regarded as different local forms of the single species Arctic charr.⁶³ Since 1930, the Arctic charr has been recorded in 32 lakes in western Ireland ranging from Lough Fad, Co. Donegal, to Lough Inchiquin, Co. Kerry, together with Lough Dan, Co. Wicklow. Several other lakes, especially those suffering from eutrophication, have lost their populations of this pollution-sensitive salmonid.⁶¹

The freshwater fish that have been indisputably introduced to Ireland, and for which there are reasonably good historical records, include the following five species.

1. RAINBOW TROUT

Introduced to Ireland from western North America in 1888 when eggs were sent to hatcheries at Inishshannon and the River Bandon, Co. Cork, and Ballymena, Co. Antrim.⁶⁴ Spawning takes place at about 40 sites in Britain and Ireland but the populations are self-sustaining at only six, including three in Ireland. One site was at Lough Shure, Aran Island, Co. Donegal, where they were recorded present in 1940, and the second was at White Lough, Co. Westmeath, where they were introduced by the Inland Fisheries Trust in 1955.⁶⁴ Breeding was recorded at the third site, Lough na Leibe, Ballymote, Co. Sligo, in 1971 (originally stocked in 1955 by the Inland Fisheries Trust). In all cases their present status is unknown.^65,66 Elsewhere most populations are maintained by the continued introduction of hatchery-reared fish.

Rainbow trout. There are only two self-sustaining populations in Ireland (J. Barlee).

2. CARP

Originally a central Asian species, carp was brought to England in the first quarter of the sixteenth century and to Ireland some time around 1634 on account of its potential as a food fish. Originally introduced to Ireland by Richard Boyle, Earl of Cork, as announced by his son Robert to the Royal Society in April 1663.⁶⁷ Diary entries in the autumns of 1640 and 1643 record orders given by the Earl to send both carp and tench to his friends.⁶⁸ Smith claims that both carp and tench were in the River Awbeg, Co. Cork, during the reign of James I (1603–25).⁶⁹ Like tench, carp can live in stagnant waters with very low oxygen levels (down to 0.7 mg/1) but require a water temperature of at least 18°C before they can spawn either in spring or late summer.

3. TENCH

Since its introduction in the seventeenth century noted above there have been selective introductions to Ireland during the past 40 years.

4. ROACH

Accidentally introduced to the River Blackwater, Co. Cork, in 1889, then introduced to a small ornamental lake on the River Foyle system in the mid 1920s, from where it soon escaped to colonise the river system. In the early 1970s it was illegally introduced to the Erne waterways and within ten years had colonised this large river system up to its headwaters. Since then it has been introduced to the rivers Boyne, Shannon, Corrib, Liffey, Barrow and Nore.^70,71

5. DACE

Accidentally introduced to the River Blackwater at the same time as the roach. Apparently two tins of each species were brought over from England as pike bait and were washed away in a flood.⁶⁵ In the late 1980s and early 1990s they were illegally introduced to Doon Lake, Co. Clare and to the lower end of the River Nore.⁷²

Many of these introductions have upset the ecology of rivers and lakes, and led to the displacement of native species such as trout. The roach, one of the most recent interlopers and a prolific breeder, has rapidly spread from its initial area of introduction in Co. Cork some hundred years ago to colonise many river systems. It has displaced the rudd and hybridised with it, and also with bream. Apart from interspecific competition for food resources, introduced fish can bring with them fungal, viral, bacterial and other diseases. Cross-breeding with closely related species will cause genetic disruption to the disadvantage of resident species. However, fish, like other animals, are able to share out food and habitat resources. As a general ecological principle, coarse fish tend to occupy warmer, calmer and muddier waters, leaving the more turbulent, oxygen-rich and cooler areas to the native salmon and sea trout.

The heathers

The Ericales or heathers are to many people the most typical and interesting group of peatland plants in Ireland. They are pretty and colourful, and five species are of particular biogeographical and botanical interest. Not only do they have a restricted distribution in Ireland but they exhibit a discontinuous or relict distribution in Europe, suggesting a more widespread earlier dispersion. Such issues raise many difficult questions such as when and how did they travel to Ireland, or have they been resident here since Gortian times? Why are four of the species concentrated in a relatively restricted bogland area of west Galway and Mayo? Together with five other plant species – large-flowered butterwort, St Patrick’s cabbage, kidney saxifrage, the strawberry-tree and the Irish orchid – they form the central core of the so-called Mediterranean-Atlantic element of the Irish flora. These are the species found generally in the west and southwest of Ireland, western France, Spain, Portugal and in some western Mediterranean locations. The presence of the five heaths in Ireland, and how they accomplished and survived the transition from quite different ecological circumstances are puzzling questions. If they entered Ireland on a land bridge from north Spain during an interglacial period, why did none of them lodge in Cork and Kerry? Why did they all congregate in western Galway and Mayo?

As the five species of heath are such special members of the Irish flora, additional information is presented on their discoveries and general ecology.

1. DORSET HEATH

Originally discovered in 1846 by Thomas Bergin at one very small site, close to a bog road, some 6 km southeast of Clifden, Co. Galway. Bergin presented an annotated herbarium specimen to Trinity College Dublin.⁷³ It was reported again from the same location in 1852 and then remained elusive until it was rediscovered by Lambert in 1965. Its site is a damp hollow, close to the road, and it has been suggested that the location indicates introduction by the agency of man.⁷⁴ Its growth is low and straggly, and seems at a disadvantage in relation to the nearby and taller vegetation of purple moor-grass and soft rush. The site extends no more than a few square metres with approximately five plants.⁷⁴ Its bell-like deep pink flowers are large, up to 8–10 mm, with leaves in whorls of three. The population here is unique in that there are no glands on the tips of the stout marginal hairs of the leaf.⁷⁵ It is sterile, never setting any seed of its own, but a hybrid with cross-leaved heath has been found here by Scannell. Outside Connemara it only occurs in Cornwall, Devon and further east in Dorset. In Britain it hybridises with cross-leaved heath. On the Continent it occurs in central France, Spain, Portugal and in heathy woodland in northwest Morocco. Dorset heath was present and growing in Ireland during the warm interglacial Gortian period some 428,000–302,000 years ago (see below).¹

2. MACKAY’S HEATH

Confined to Counties Donegal and Galway until it was recently discovered in northwestern Mayo in 1990 by van Doorslaer in a small area of raised bog near Bellacorick. The natural hybrid Erica mackaiana x tetralix (a cross between Mackay’s and cross-leaved heath) was growing nearby. In Donegal, Mackay’s heath grows on blanket bog on the shore of Lough Nacung Upper near Dunlewy, while in west Galway there are two stations – one small colony 1.5 km southeast of Carna and the other, more extensive (about 3 km²), around Lough Nalawney on the lowland blanket bog stretching southeast from Clifden to Errisbeg. The species was first discovered, prior to 1835, by schoolmaster William McAlla, who was born at Roundstone. It has shorter, broader, darker green leaves than Dorset heath, but like the latter it is sterile, for reasons not yet understood. It spreads vegetatively and the population would therefore seem to consist of a single clone from the original plant or plants. It hybridises with cross-leaved heath. The hybrid is now known as E. x stuartii. Outside Ireland it is found only in the province of Oviedo in northwest Spain, in the mountains of Castile and Asturia. Remains of leaves of E. mackaiana have been recorded in postglacial deposits from a blanket bog near Roundstone, Co. Galway⁷⁶ and from the much earlier interglacial Gortian deposit. Remains of Mackay’s, Dorset and Cornish heath have all been found in the Gort deposits as they have been in other interglacial deposits raising the possibility that they may have survived the final stages of the Ice Age and that they may not be of recent origin.^2,77

Mackay’s heath at Lough Nacung Upper, near Dunlewy, Co. Donegal. Very similar to crossleaved heather but has a stronger and bushier habit.

St. Dabeoc’s heath with its urn-shaped corolla.

3. ST DABEOC’S HEATH

Confined to but very numerous in some locations in west Galway and in south and west Mayo from near Cong and Partry to the Killary Harbour and Croagh Patrick, and at Corraun on Achill Island. It was first unwittingly discovered by Edward Lhwyd, the great Welsh naturalist and antiquarian, who found it growing in most of the mountains of Galway and Mayo during a visit, probably mid May 1700. At the time he did not know it was St Dabeoc’s heath, describing it as ‘…an elegant sort of Heath, bearing large Thyme-leaves, a spike of fair purple Flowers, like some Campanula, and various stalk…’. He brought his specimens back to London and presented several to his friends there, including the botanist Petiver who later identified and described it in 1703.⁷⁸ It is a small undershrub with straggly branches, often growing up through heather or gorse. Its leaves are narrow, elliptical, shiny green on top and whitish underneath. The large purplish corolla is about three times the size of those of bell heather. It is absent in Britain but found in southwest France as far north as the River Loire, and especially in the Cantabrian mountains, in the Spanish peninsula and the Azores. In the Pyrenees it survives quite happily under a snow covering for five months each year, belying the notion that it is a tender Mediterranean plant.

4. IRISH HEATH

First found by Mackay in 1830 on Errisbeg, near Roundstone, Co. Galway, and later in other localities in west Co. Galway. In Co. Mayo it is present at the mouth of Killary Harbour, on Clare Island, at Bellacragher Bay (north of Mallaranny), northwards to the Mullet peninsula and eastwards to Lough Conn (west and eastern shores). It is absent from Britain. The single station northwest of Bordeaux in southwest France is probably extinct.⁷⁵ It occurs in good quantity in Portugal and in northwest Spain. Unlike the other heaths in Ireland, it may start flowering in January with the blooms at their finest in April, producing one of most magnificent botanical sights in the country. This hairless shrub forms dense stands, sometimes as high as 3 m, both at sea level (Praeger once observed it adorned with seaweed thrown up during storms) and on the mountainside (up to at least 155 m) rising up from the head of Bellacragher Bay. The sight of it here in early spring is a truly remarkable botanical feast.⁷⁹ On the Bellacragher Bay mountainside the heather tracks the snaking pathways of small streams and rivulets that provide the plant with extra nutrients and moisture. Irish heath is also found further south, in the remarkable area of lowland blanket bog between Roundstone and Clifden, Co. Galway, that was covered with woods in the aftermath of the last glaciation. Jessen showed from the analysis of pollen remains found in the muds that Irish heath was growing in those woods, as it does in northwest Spain today.⁷⁷ How it successfully survived the transition from a protective woodland environment to the barren, bleak and windswept blanket bog habitats in the west of Ireland is a tribute to its adaptive capabilities. Unlike the two other rare heaths, Dorset heath and Mackay’s heath, it is fertile and reproduces by seed. It has been argued by Foss & Doyle that it could have been introduced to Ireland by man some 500 years ago, at a time when there were direct trade links between Ireland, Spain and Portugal. Irish heath is found growing close to many pilgrimage shrines and abbeys in Portugal, Spain and France and it is postulated that it could have been carried by pilgrims.⁸⁰

5. CORNISH HEATH

Originally found by Major Dickie of Enniskillen, but first reported by Praeger in 1938.⁸¹ It was growing on an isolated blanket bog near Belcoo, Co. Fermanagh, with white flowers (normally lilac-pink), and Praeger sided with those who considered the plant indigenous in a native habitat. Webb visited the bog in 1954 and reckoned that ‘the force of arguments were in favour of regarding it as native’.⁸² The site, close to a mineral flush, was visited in 1965 and 1966 by McClintock when about 1,000 plants were recorded.⁸³ Another historical site was reported by Robert Burkitt in the 1850s, on the cliffs of Islandikane townland, west of Tramore, Co. Waterford, but the species has not been seen there since, despite repeated searches. It was naturalised on the sand hills at Dundrum, Co. Down, where it was discovered by Swanston in 1899, and was still present in 1978.⁸⁴ It also grows on the rocky shore at Shane’s Castle, Co. Antrim. Outside Ireland it occurs in heaths in south Cornwall, and elsewhere in western Europe. It is a short to medium hairless undershrub with flowers ranging from white to pink to lilac. No evidence has yet been produced to show that Irish heath was a member of the Irish interglacial flora. Their seeds are consistently larger (c.0.7 mm) compared with c. 0.5 mm of other Erica species, so it would have been difficult to overlook them in samples of interglacial deposits.⁸⁵

Irish heath with western gorse at Ballacragher Bay, Co. Mayo.

The Connemara and Burren plant assemblages

The congregation of the above ericaceous species in western Connemara is one example of apparent geographical plant madness, but the eclectic agglomeration of rare flowers in the Burren, Co. Clare, with representatives of arctic, alpine and Mediterranean floras also begs explanations. What could be the origin of such an unlikely association?

One interpretation postulates that these species originally had a more widespread range in Ireland. Although the Pleistocene glaciers probably wiped much of the landscape clean of living resources, some plants may have been able to avoid the ice blanket by moving up to the highest mountain peaks or sheltering in other refugia. Others, however, possibly shifted westwards to ice-free offshore islands and peninsulas. The sea level started to drop around 35,000 years ago, reaching its maximum fall of some 130 m below present day levels around 15,000 years ago. The west Clare and Connemara coastlines could then have extended perhaps some 45 and 10 km respectively west of today’s shorelines.² Admiralty charts show commodious areas off the Burren coast stretching beyond the Aran Islands which would have been uncovered and well above water during the Ice Age. Assuming that the North Atlantic Current exercised some warming influence, the glaciers could not have impacted those areas. It is therefore possible that the plants may have survived in isolation on mist-shrouded, ice-free banks. As the glaciers withdrew and the sea started to rise again, the plants would have had to move back to the mainland. Despite the vegetative reproduction of most alpine species and presumed slow migration rates, the long time spans associated with the waxing and waning of the glaciers would have been sufficient to permit the relatively short migrations from the Burren and Connemara to those western tips and back again. Survival of plants during the first glacial epochs of the Ice Age on the summits of the Burren hills can probably be ruled out as all of them are too low to have escaped a scouring of the ice sheets (the highest is Slieve Elva at 344 m). However, several Burren hills were glacier-free during the last Midlandian glacial phase, towards the end of the Ice Age.

An alternative hypothesis regarding the survival of plants put forward by Mitchell & Ryan envisages a general migration of the various Burren and Connemara curiosities as well as other Lusitanian plant species up and down the western Atlantic seaboard from the Irish west coast to the shores of Spain and Portugal. In support of their western seaboard migration route hypothesis they quote the present known distribution of the shore-living bug Aepophilus bonnairei in Ireland, southern England, west Wales and the Isle of Man. Its modern day distribution centre is the Atlantic coast from Morocco to Portugal. If the bugs had been present in Ireland historically, they would not have survived the cold Nahanagan snap and must have ‘marched’ up along a western seaboard land bridge as temperatures rose some 10,000 years ago. Additional support for the southern route to Ireland for Lusitanian species comes from detailed pollen studies carried out by Fraser Mitchell,² which show that pine, oak and alder followed the proposed route taken by Aepophilus across the ‘dry’ Bay of Biscay to the Celtic Sea and then into southern Ireland. However, the question of sea barriers and the long distances involved make this hypothesis less convincing. The introduction of seeds by migrating birds travelling northwards from Spain and Portugal is also improbable as most seeds of the Burren and Connemara curiosities are not eaten by birds.

Western Connemara, Co. Galway, the location of rare plant assemblages.

Devoy has discussed five possible land bridge connections between Ireland and Britain, including the Continental shelf, across which flora and fauna could have moved into Ireland when the country was released from the grip of ice during the late Ice Age.⁸⁶ Devoy considered that the route from the south, across the Continental shelf, along which the southern Lusitanian species would have travelled, would have been problematical. An interconnected series of channels and troughs off the south coast of Ireland led west and southwest into canyons lying at a greater depth than 100 m below today’s sea level. The movement of meltwaters and sediments over this area at the time even when sea levels were much lower than today would have created adverse conditions (pools, channels, rivers, etc.) for species sensitive to water, and made it very difficult, if not impossible, for plants to move dry-shod from Portugal, northern Spain and western France into Ireland. Thus the southern entry route for the so-called Lusitanian and other Mediterranean species now present in the Burren and in Connemara seems to be ruled out. Entry into Ireland of these species across the other four land bridges traversing what is now the Irish Sea is not supported by any historic or present day evidence. Survival of these species, many of which were already present in Ireland, in ice-free areas or refugia (off the west coast) thus appears to provide the most plausible explanation to account for the curiosities of Clare and Connemara.

The oceanic flora

The lowlier plants – ferns, mosses, liverworts and lichens – reproducing by minute, wind-blown spores, have less difficulty in crossing expanses of sea, and the mild, oceanic climate of Ireland has been particularly favourable to their colonisation. Especially in the extremely humid west, the profusion and luxuriance of these plants is a striking and important feature of the vegetation. In many of the western woods, communities of fìlmy-ferns, mosses and liverworts cover the rocky woodland floor and lower tree trunks, while lichens are most conspicuous on the upper trunks and branches. Many of these species have an extremely restricted European and even world distribution, confined to the far western seaboard and the Atlantic Isles of the Azores, Madeira and the Canaries (Macaronesia).

The most famous is the Killarney fern, much the largest and finest of our three fìlmy-ferns, once locally abundant along the rocky streams and in the lower corries of the southwestern mountains, but reduced to rarity by indiscriminate collecting. The moss-like Tunbridge and Wilson’s fìlmy-ferns are in amazing quantity in many rocky woodlands and shady block screes, while the hay-scented buckler-fern, with its distinctive crinkly fronds, grows large and in unusual quantity. Visitors from Britain are struck by the general abundance in western Ireland of the royal fern, often to be seen in great dense patches on peaty ground. The fern collectors made less impression on it here than in western Britain, where it was once also abundant in places. The Irish spleenwort is a very rare and beautiful fern of exposed dry rocks and banks in southern Ireland and is unknown in Britain, but another Mediterranean-Atlantic fern of similar habitats, the lanceolate spleenwort, is more frequent in western Britain than Ireland. The delicate maidenhair fern, a widespread species in warmer parts of the world, grows luxuriantly on limestone, especially in crevices of the Burren pavements. Also of interest are the liverworts Cephalozia hibernica, Lejeunea flava, L. hibernica and Radula holtii, found in Ireland but not in Britain (see Appendix 1).

The profusion of ferns, mosses and liverworts, including many oceanic species, extends up the mountains. In the extreme west, the shady corries and slopes facing between north and east have communities of leafy liverworts amongst or below heather or other dwarf shrubs and on rock ledges. These are virtually identical to liverwort carpets in similar situations on the equally wet mountains of the western Scottish Highlands. They contain species notable for their highly discontinuous world distribution in humid mountain regions as far apart as southwest Norway, British Columbia, Alaska, the Himalayas and Yünnan (e.g. Mastigophora woodsii, Herbertus aduncus and Pleurozia purpurea). The abundance of the woolly fringe-moss on stable block screes, bog hummocks and peat hags, and its dominance on many high mountain tops, is another feature of the oceanic climate.

Many plant introductions from warmer regions have flourished in the mild Irish climate. The luxuriant and colourful hedges of fuchsia are one of the most distinctive features of the west, while the invasion of woodland by rhododendron has created a conservation problem. The southwest, with lowest incidence of frost, has well-established growths of escallonia, New Zealand flax, giant rhubarb, the hedge veronica Hebe elliptica and the cabbage palm tree.