An Investigation of the History of Vegetation Change …€¦ · An Investigation of the History of Vegetation Change on Ballynahone Bog, County Londonderry using Pollen Analysis

An Investigation of the History of Vegetation Change on

Ballynahone Bog, County Londonderry using Pollen

Analysis.

Aerial photo taken from the South of Ballynahone Bog and the Moyola River.

Source: Friends of Ballynahone Bog (1991).

Megan Noble

BSc Environmental Science with DPP School of Environmental Science

University of Ulster, Coleraine

Abstract

A pollen diagram from a typical lowland raised bog in County Londonderry is presented. The

recorded vegetation is assessed relative to the dating of zones of climatic/vegetation phases

at Sluggan Bog, Co. Antrim. Peat cores were taken from two sites. Site 1 was an area of

cutover bog and two cores were extracted from here. Five cores were taken from the dome

of the bog which was site number two. The first core from site 1 reached the basal peat and

the underlying lake sediments below the surface, the second core was taken above this at a

depth of 2m. Betula (birch), Pinus (pine) and Alnus (alder) woodland started to colonise

early in this sequence; around 12350 BP. However Calluna (heather) and Sphagnum grains

were also present in these deep cores, and these species now grow on the surface of this

area of the bog. Betula (birch) woodland also developed early in the sequence; around

12350 BP (Older Dryas period). The end of the Thermal Maximum, around 12200 BP, caused

the decline of woodland and this is discussed. During the Woodgrange interstadial, Betula

(birch) was susceptible to drought and therefore started to decrease as the peat dried out.

Corylus (hazel) disappeared during this period representing a turning point in woodland

development. During the Late Boreal period, Betula (birch) returned to the mire. The

evidence of human activity and the impact it had to vegetation during the Boreal-Atlantic

transition is considered. The first elm decline (Early Faming period) is suggested to have

been caused by Neolithic forest clearance activity, the second by major forest clearances

during the Bronze Age. The greatest impact on the bog happened during Viking to Late

Anglo-Norman times. The changes caused on the bog by present human impacts are also

discussed and why development of certain species has happened at the two sites.

Key words: raised bog/mire, pollen, vegetation history, climatic change, human impacts.

Acknowledgements

I would like to express many thanks to everyone who has helped me throughout the course

of this project, especially my family who have had to listen to me talk about bogs every day,

and my boyfriend Philip Leckey who constantly checked to make sure I was on track with my

timing to complete my dissertation.

I would firstly like to thank my dissertation supervisor, Dr. Peter Wilson for his advice,

guidance and hands on approach to my topic.

I would also like to thank Claire Mulrone from the Science Shop for helping me to find a

topic of my interest. Thanks to the Ulster Wildlife Trust for granting me permission to take

core samples from Ballynahone Bog. And a special thanks to Pól Mac Cana for the help he

gave out in the field coring the bog.

Thanks especially to Joerg Arnscheidt for helping set up the camera on the microscope to

allow me to take pictures of my pollen grains.

To Thomas Beattie, many thanks for carrying out the laborious task of writing out my

sample bags and for keeping me company during my lab time, whilst being volunteered to

be designated washer of my used apparatus.

Table of Contents

Abstract ………………………………………………………………………………………………………………………… I Acknowledgements ……………………………………………………………………………………………………… II

Chapter 1: Introduction ……………………………………………………………………………………………….. 1 Study Rationale ………………………………………………………………………………………………….. 2 Study Objectives and Aims…………………………………………………………………………………… 4

Chapter 2: Literature Review …………………………………………………………………………………….. 5 Raised Bogs in Northern Ireland …………………………………………………………………………. 5 Peat-land system: an important ‘proxy; of paeloenvironmental data ………………….6 Tephra ………………………………………………………………………………………………………………… 7 The use of pollen analysis …………………………………………………………………………………. 9 Sample collections ………………………………………………………………………………………………. 10 Treatment of samples …………………………………………………………………………………………. 11 Interpreting pollen data: History of Raised Bog Vegetation …………………………………. 12 Restoration and Conservation of Raised Bogs ……………………………………………………… 14

Chapter 3: Site Description …………………………………………………………………………………………..16 Geology ………………………………………………………………………………………………………………. 16 Definition of Raised mire……………………………………………………………………………………… 17 Peat…………………………………………………………………………………………………………………….. 17 Hydrology …………………………………………………………………………………………………………… 18 Climate ……………………………………………………………………………………………………………….. 18 Vegetation ………………………………………………………………………………………………………….. 18 Site History …………………………………………………………………………………………………………. 19 Chronological sequence of events in the conservation history of Ballynahone Bog 20

Chapter 4: Methodology ……………………………………………………………………………………………… 22 Fieldwork………………………………………………………………………………………………………………………….22 Study Area ……………………………………………………………………………………………………………………… 22 Coring …………………………………………………………………………………………………………………………..... 22 Risk Analysis …………………………………………………………………………………………………………………… 26 Description and preparation of cores ……………………………………………………………………………… 26 Treatment of samples …………………………………………………………………………………………………….. 28 Microscopy work ……………………………………………………………………………………………………………. 29 Pollen diagram ………………………………………………………………………………………………………………. 29

Chapter 5: Results ………………………………………………………………………………………………………… 30 Description of Cores ……………………………………………………………………………………………. 30 Sampling ……………………………………………………………………………………………………………… 39 Identified Pollen Grains ………………………………………………………………………………………. 40 Pollen Count, Site Results ……………………………………………………………………………………. 40 Figures of Sampled Pollen Grains ……………………………………………………………………….. 49 Pollen Diagram ……………………………………………………………………………………………………. 56

Chapter 6: Discussion ………………………………………………………………………………………….. 58 Peat deposits ………………………………………………………………………………………………………………….. 58 Pollen diagram; change in vegetation …………………………………………………………………………….. 59 Human or Climatic impacts? ………………………………………………………………………………………….. 62

Chapter 7: Conclusion ………………………………………………………………………………………………….. 66

References …………………………………………………………………………………………………………… 67 Appendices Appendix One Bogland ………………………………………………………………………………………………………………. 78

List of Figures Figure 1.1 – page 2 Figure 2.1 – page 6 Figure 2.2 – page 8 Figure 2.3 – page 10 Figure 2.4 – page 11 Figure 3.1 – page 16 Figure 3.2 – page 19 Figure 3.3 – page 20 Figure 4.1 – page 23 Figure 4.2 – page 24 Figure 4.3 – page 25 Figure 4.4 – page 25 Figure 4.5 – page 27 Figure 4.6 – page 27 Figure 5.1 – page 31 Figure 5.2 – page 32 Figure 5.3 – page 33 Figure 5.4 – page 34 Figure 5.5 – page 35 Figure 5.6 – page 36 Figure 5.7 – page 37 Figure 5.8 – page 50 Figure 5.9 – page 51 Figure 5.10 – page 52 Figure 5.11 – page 53 Figure 5.12– page 54 Figure 5.13 – page 55 Figure 5.14 – page 57

List of Tables Table 4.1 – page 22 Table 5.1 – page 39 Table 5.2 – page 41 Table 5.3 – page 42 Table 5.4 – page 44 Table 5.5 – page 45 Table 5.6 – page 46 Table 5.7 – page 47

Table 5.8 – page 48

Abbreviations EHS – Environmental and Heritage Service for Northern Ireland UWT – Ulster Wildlife Trust NNR – National Nature Reserve KOH – Potassium hydroxide

Chapter 1: Introduction

Ballynahone is an example of a raised bog located at the eastern foot of the Glenshane Pass.

It is situated 54°49’17”N, 06°39’43”W, lying north of the Moyola River, 3km north-east of

Tobermore and 3km south of Maghera in County Londonderry (Fig. 1.1). In 1987 Bulrush

Peat Company Limited applied for planning permission to extract peat from Ballynahone.

Although there were some objections raised against this scheme planning permission was

granted in 1988 by the Department of the Environment. Shortly after this decision was

made the Ulster Wildlife Trust invited its members to take a last walk on the bog now the

fight to retain its ancient flora and fauna had been lost. The group ‘Friends of Ballynahone

Bog’ (FBB) was launched as a result of this walk. By 1991 Bulrush had already dug 13 miles

of drains on the southern half of the bog, and flora in close proximity to the drains, began to

come under threat. Two years after this FBB started the process of declaring Ballynahone a

National Nature Reserve. Planning permission was revoked from Bulrush and they dammed

their drains in December 1993. By 1995 the bog was declared an Area of Special Scientific

Interest (ASSI). Ballynahone Bog is currently the largest nature reserve at 244 hectares,

incorporating the second largest area of intact raised bog in Northern Ireland. It is an Area

of Special Scientific Interest (ASSI), as-well as a designated National Nature Reserve (NNR).

The vegetation on the bog is extremely interesting, species include; rare sphagnum mosses,

liverworts and bog rosemary. The bog and surrounding birch woodland also support a

variety of birds, butterflies and dragonflies. The remaining drains were dammed by the end

of 1994.

Figure 1.1: Ordnance Survey map showing the location of Ballynahone Bog

Study Rational

The value of pollen analysis as a tool for the reconstruction of past vegetation and

environments, and its applications in such areas as climate change studies, archaeology,

geology, honey analysis and forensic science, is now widely known (Moore et al., 1991).

One of the most highly exploited uses of palynology is the investigation of vegetation history

(Godwin, 1975; Bryant and Holloway, 1985). Most effort has certainly been expended on

the reconstruction of changes during the last 11,000 years (the Holocene) during which the

Earth has recovered from the last glaciation, and human pressures upon global vegetation

have become increasingly intense (Moore et al., 1991). Peat extraction at Ballynahone Bog

never came to completion and extraction of peat was never taken from the surface of the

dome. Therefore a full reconstruction of the history of vegetation change as Ballynahone

Bog developed can be carried out from pollen retrieved from the dome.

© Crown Copyright

The use of pollen analysis helps to understand the environmental setting, the economy and

the way of life of prehistoric human cultures (Dimbley, 1985). Further study of modern

agricultural communities and the pollen rain may assist in understanding the effect that

mankind had on the vegetation in the past (Moore et al., 1991). Studies have been carried

out on numerous raised bogs. According to Habitas (2010), over the last thirty five years, no

lowland raised bog in N. Ireland has been the subject of more palaeoenvironmental study

than Sluggan Bog, Co. Antrim. Ballynahone Bog has not had the same amount of research

carried out on it than other bogs in Northern Ireland. This presents an opportunity to study

the change in past vegetation on this bog using pollen analysis.

Study Objective and Aims

Study Objective

The objective of this project is to investigate the history of vegetation change that has taken

place on Ballynahone Bog, Co. Londonderry, as well as finding out if these changes are

significant.

Aims

A number of aims need to be fulfilled to meet this objective:

To take cored samples to from Ballynahone Bog and to use pollen analysis to

reconstruct the vegetation change of the bog

Analyse any significant relationships that could have occurred between the

environment and past vegetation.

To reciprocate feedback from my data and findings.

Increase personal taxonomic knowledge of raised bog vegetation species; past and

present.

To familiarise myself with identification of specific pollen grain types.

Chapter 2: Literature Review

This section is dedicated to providing on overview and synopsis of the reconstruction of

Quaternary environmental change using biological evidence in the form of plant and animal

remains. Particular emphasis will be put on the use of pollen analysis regarding the

identification of historical vegetation transformation. Discussion will also include the

current condition and status of raised bogs within Northern Ireland. A brief insight into the

growing interest of tephra and how volcanic eruptions could have affected local vegetation

will also be explored. Further investigation will consist of additional scrutiny of restoration

and conservational ideas within these fragile landscapes.

Raised Bogs in Northern Ireland

Many past surveys of lowland raised bogs in Northern Ireland have been carried out

(Hammond, 1979; Leach and Corbett, 1987; Cruickshank and Tomlinson, 1990). One of

these surveys showed that raised bogs are concentrated along the valleys of the Main

(Antrim), Bann (Antrim/Londonderry), Fairy Water (Tyrone), and Arney (Fermanagh) and to

the north of Ballymoney (Antrim). Figure 2.1 shows that almost all peatland areas in

Northern Ireland lie to the west and on the uplands of the north-east, in close association

with wet, gleyed mineral soils (Hammond, 1979). The Environmental and Heritage Service

(EHS) developed a policy statement in 1993 that estimates that over a quarter of the United

Kingdom’s resource of lowland raised bogs may be found in Northern Ireland. About 9%;

2,270 hectares is still intact. Many plant species that are found on peatland systems are

unique, however certain species that are found on raised bogs can also be found within

other habitats. There is a strong set of interactions that take place between the physical

and chemical environment that controls the development of peatland ecosystems and

vegetation (Bedford, 1992). The natural species type of many lowland raised bogs is seen to

be Sphagnum (Money, 1995; Wheeler and Shaw, 1995). Sphagnum also plays an important

role in successful restoration of bogs (Money, 1995). Heterogeneous surface micro-

topography such as pool complexes and hummocks can also be found on raised bogs

(Dierssen, 1992). Vegetation composition studies are a good way to discover what effect

environmental conditions have had on different types of vegetation species.

Figure 2.1: A simplied map of Northern Ireland showing the positions of peatlands.

Source: Hammond (1979). The peatlands of Ireland.

Peat-land systems: an important ‘proxy’ of palaeoenvironmental data

Peat archives have been widely employed to examine changes in climate over the Holocene

in northwest Europe by numerous researchers e.g. Blundell et al., (2007). The search for

reliable records of climatic change during the Holocene has involved much usage of proxy-

records e.g. Barber et al. (2003). All proxies have their advantages and disadvantages

(Barber et al., 2003). Single proxy studies examining plant macrofossils have been

examined greatly (Barber, 1981; Barber et al., 1994). However there are only a few

multiproxy records from peat archives even in well studied regions (Charman et al., 1999;

Chiverrell, 2001) and substantially fewer from Ireland e.g. Caseldine and Gearey (2005).

Plant and animal remains can sometimes be used to sub-divide the Quaternary record

(biostratigraphy). Applications that are related to peat systems are also applicable to lake

sediments, palaeosols, as well as marine and estuarine materials. With respect to

radiocarbon dating, tephra and dendrochronology, peat systems are extremely valuable.

The rather small body of evidence for Ireland’s ancient fauna contrasts markedly with the

wealth of evidence for Ireland’s past vegetation (Hall, 2011). Britain and Ireland’s earliest

mires began forming after the last glaciation, around 15,000 BP. Most mires developed

during the Holocene: since 11,700 BP; however blanket mires started to develop at different

times. Local conditions were affected when these mires started to form. Evidence for

environmental change is often found in ombrogenous mires by examination of peat

stratigraphy. Climate played an important role as an allogenic forcing factor in bog growth

and therefore in peat stratigraphy as a proxy climate record (Barber et al., 1994; Chambers

et al., 1997; Charman et al., 1991; Chiverrell; 2001). Often found in Irish bogs are rather

abrupt changes from dark peat found at the bottom of the mire to less well humified light

peat at the top. These are known as recurrence surfaces. They are potentially useful as

palaeoclimatic indicators if, the recurrence surfaces are synchronous over various areas,

meaning a climatic origin may be valid. What were also found at the bottom of Ballybetagh

Bog in County Wicklow were the bones of the now extinct Great Irish deer (Megaloceros

giganteus) (Hall, 2011).

Tephra

Tephra is volcanic ash. It is the product of a volcanic event (Hall et al., 1994).

Tephrostratigraphers and tephrochronologies are used by Quaternary scientist; mostly in

areas where tephra layers are visible to the naked eye (Hall et al., 1994). Using layers of

micro-tephra as an isochrone marker has only recently been considered. (Persson, 1971;

Buckland et al. 1981). According to Hammer (1984) laborious work needs to be carried out

to trace fine tephra from peat bogs. Tiny particles of volcanic ash from volcanoes that have

erupted almost entirely in Iceland are carried to Ireland by weather systems that originate in

the Icelandic region, only small traces of volcanic ash or tephra have been found in Irish

boglands (Hall, 2011). Tephra is present in Holocene peats and lake deposits. Figure 2.2

shows where these tephra layers have been found in Ireland (Hall et al. 1994). Not all

tephra is colourless (Hall et al., 1993). Found in Sluggan Bog, Fallahogy Bog and Ballynahone

Bog was a layer of flaky light brown volcanic glass found above the Hekla 4 layer of these

peats (Pilcher and Hall, 1992). This layer was also found in Garry Bog along with a number

of other well defined layers (Hall et al, 1993). It is only recently that replicated studies of

tephrostratigraphy in lowland raised bogs in the north of Ireland have been published (Hall

et al., 1993).

Figure 2.2: Sites in Ireland at which tephra layers have been found in peat.

Source: Hall et al. / The Journal of the Association for Environmental Archaeology 11,

(1994) pp. 17 – 22

These show that although tephra events occurred throughout the Holocene, their

frequencies have increased within the past 4000 years (Thorarinsson, 1981). Ash was found

to be present in lowland peats from Sluggan Bog; it was linked geochemically to eruptions of

Hekla in AD 1104 and Öræfajökull in AD 1362 (Hall et al, 1994). Local vegetation may have

been impacted from the eruption of Hekla 4 (Bennet et al. 1992; Blackford et al. 1992;

Hanna, 1993; McVicker, 1993; Hall et al. 1994.) The loss of native pines in Ireland was

hastened by very poor weather after a volcanic eruption far from Ireland (Hall, 2011). This

area of research is growing in interest, palynologists now investigate what influence past

volcanic activity could have had on vegetation (Hall et al. 1994). Evidence that volcanic

eruptions in Iceland have affected the weather in Ireland have even been evident more

recently with mass disruption caused by eruptions from Eyjafjallajökull in 2010.

The use of pollen analysis

Levels of diversity, or differences in the number of organisms between areas, can be used to

indicate the nature of past environments where high diversity and endemism are facilitated

by relative environmental stability (Fjeldså and Lovett, 1997). Various pollination strategies

influence and decide the number of pollen grains ultimately at disposal for analysis, and

their distribution (Faegri and Iverson, 1989). One of the main ways to reconstruct the

environmental past is through data produced by pollen analysis. The composition and

distribution of past vegetation, and changes that may have happened can be determined by

the pollen that has been preserved within mires or sedimentary basins. Palynology is one of

the most widely used research tools in Quaternary studies (Edwards, 1983). It can be

defined as ‘a technique for reconstructing former vegetation by means of the pollen grains

it produced’ (Faegri and Iverson, 1989). Palynology is concerned with both the structure

and the formation of pollen grains and spores, and also with their dispersal and their

preservation under certain environmental conditions (Moore et al., 1991). Pollen analysis

was first developed in Sweden by a botanist, Professor Lagerheim, however it was the

success of von Post’s pioneering experiments in 1916, which enabled pollen analysis to

become recognized and used to document long-term vegetation dynamics. (Birks, 1993). It

was introduced to Ireland in the 1920’s and 1930’s by the Danish scientist, Knud Jessen, who

worked on tracing Irish woodland development since the end of the last glaciation (Hall,

http://www.york.ac.uk/res/kite/research/palaeoecology/pollen-veg%20relationships.pdf

http://www.york.ac.uk/res/kite/research/palaeoecology/pollen-veg%20relationships.pdf

2011). It has also been used in a wide variety of Quaternary applications including

chronostratigraphic correlation, palaeoecology, palaeoclimatology and archaeology

(Macdonald, 1988). Pollen analysis is an extremely versatile method; inferences can be

made about changing vegetation patterns over broad, spatial and temporal scales. The

influences that man had on the landscapes can also be detected.

Sample collection

Many applications of pollen analysis depend upon the sampling of stratified sequences of

peat, lake sediments or soil. These samples can be taken from exposed surfaces e.g. cliff or

peat erosion faces (Moore et al., 1991). Where exposed sections of a deposit are not

available, cores must be extracted from the surface of the site. Figure 2.3 shows the various

types of coring equipment that have been devised to suit the different situations and the

types of sediment (Moore et al., 1991).

Figure 2.3: Different types of samplers that can be used to core section of sites.

Source: Moore et al. (1991). Pollen Analysis.

Diagram (a) is a chamber sampler known as a Hiller, it is fitted with an auger head, allowing

it to be twisted as it penetrates the sediment (Moore et al. 1991). Diagram (b) is a Russian,

it is widely used for peat stratigraphic work because of its clean action and its speed of

operation and cleaning. It also has a great advantage in that the sediment that it passes

through is not disturbed (Moore et al., 1991). Diagram (c) is a Dachnowski and (d) is known

as a Livingstone (Moore et al., 1991). The field work provides not only the material basis for

the work that is to follow, but also the foundation upon which conclusions are built (Faegri

and Iverson, 1989).

Treatment of samples

The various chemical processes developed for the treatment of pollen samples relate to the

different matrix materials in which the pollen may be embedded (Moore et al., 1991).

Treatment with Potassium hydroxide digestion on its own can produce a reasonable

concentration of pollen from certain peats. To remove the cellulose; which is a

polysaccharide, effectively, acid hydrolysis should be used (Moore et al., 1991).

Hydrochloric acid treatment can be used if there is an abundance of calcium carbonate in

the sediment. However if there is an abundance of silica present in the sample then

Hydrofluric acid treatment can be used. The removal of silica is essential to avoid the pollen

being obsured when mounted (Moore et al., 1991). When the pollen is mounted, the most

appropriate magnification for routine scanning and counting is X400, i.e. X40 objective and

X10 eyepiece (Moore et al., 1991). This provides sufficient magnification for the

identification of many pollen grains. Figure 2.4 shows some of the pollen grains that can be

seen through the microscope.

Figure 2.4: Different types of pollen grains; from left to right: Betula (birch), Ulmus (elm),

Alnus (alder), Pinus (Pine) and Poaceae (grass)

Source: Faegri, K. and Iverson, J. (1989). Textbook of pollen analysis.

Interpreting pollen data: History of Raised Bog Vegetation

It is useful to think of pollen analysis as a remote sensing technique, which records the past

and present composition of vegetation (Webb et al., 1978). By accessing lake or bog

sediments; that preserve pollen, it is possible to reconstruct plant communities of the past.

The long story of Ireland’s past landscape is not in history’s pages but locked away within

the peat bogs and lake sediments in which Ireland abounds (Hall, 2011). Each individual

plant species is enclosed within a specific environmental envelope; temperature, moisture,

seasonality, soil type and other factors that support the plants growth and reproduction, if

the environment changes (Jolly et al., 1997). Radiocarbon dating can be used on these

pollen grains, so that a reconstruction can be determined of how vegetation has changed

over time. For example Ireland’s changing landscape took 14,000 years to unfold, beginning

with an account of happenings as the last glaciation terminate (Hall, 2011). There are

difficulties with representation of different species as some taxa produce greater amounts

of pollen that can be more widely dispersed (Birks and Birks, 2005) therefore many plants

may be under represented. Pollen stratigraphy provides a record of the changing

vegetation of the past; it supplies information on past climates and land use history (Moore

et al., 1991). The interpretation of peat diagrams allows past vegetation types to be

reconstructed. It consists of two steps: (1) establishing the composition of the vegetation

that delivered the pollen, and reconstructing it; (2) drawing inference from the vegetation

data back to the agents behind them e.g. climate, ecology and human interference (Faegri

and Iverson, 1989). However careful interpretation of pollen diagrams can be tricky, it

requires knowledge of differences in pollen production and dispersal, source areas,

differential preservation and relationships between pollen and former plant communities

(Faegri and Iverson, 1989). The reconstruction of the history of human vegetation

management has proven to be just as difficult as reconstructing climate history (Moore et

al., 1991). Interpretation is therefore dependent on the use of indicator species whose

ecology can be linked to man-induced aspects of the environments, such as fire, disturbed

soils, open canopies, nitrogen and phosphorus flushing, to name but a few (Moore et al.,

1991). Almost everything known about the arrival of the trees to Ireland comes from pollen

analytical studies (Hall, 2011). The early Boreal Period (9200-8570 BP) was a time of real

vegetation significance. The birch woods of the early post-glacial were subject to a set-back

at approx. 9400 BP due to unstable soil characteristics of earlier times. Woodland

development went through a turning point because of a decline of hazel at approx. 8600 BP

(Smith and Goddard, 1990). The spread of vast birch and oak woodland and later the

subsequent spread of agriculture may be traced by pollen analytical studies (Hall, 2011).

Studies carried out on pollen show that the Irish climate entered a period of reduced rainfall

about 8,300 years ago, causing the water table in the boglands to fall and bog surfaces to

dry up enabling pine seeds to germinate. (Hall, 2011). In Sluggan Bog, a densely packed

layer of fossilised timber gives the impression of a great pine wood. Trees began to spread

on the bog surface around 8361 BP. (Hall, 2011). The presence of pine stumps in the peat

suggests a dry phase in the bog development (Smith and Goddard, 1990). Around 8,200

years ago the weather in Northern Ireland deteriorated. The Northern Hemisphere cooling

event is believed to represent the last known major freshwater pulse into the North Atlantic

(Head et al., 2005). Because of this collapse of the North American ice sheet that had

covered much of eastern Canada, the North Atlantic region, the next 40 to 50 years

experienced a period that was cold and wet (Hall, 2011). Using the peat sequence at

Dooagh, Achill Island on the west coast of Ireland, clear evidence is found for a climatic

oscillation in the early Holocene using various measures of pollen, indicating a disruption in

the vegetation leading to a grassland dominated landscape, which is probably due to the

climatic shift to drier and probably colder conditions which lasted for several hundred years

(Head et al., 2005). Conversely there is a lack of peat-based palaeoclimatic studies from

Ireland (Blackford and Chambers, 1995; Barber et al., 2003). Blackford and Chambers (1995)

noted a shift from drier to wetter conditions in Ireland during AD 1300’s from humification

data covering the last thousand years. The decline of birch woodland in 12200 BP

represents the end of the thermal maximum of the late glacial inter-stadial (Smith and

Goddard, 1990). Following pine, the tree species that found a new niche on bog surfaces

was oak, dating from the period 7200-2200 BP (Hall, 2011). Pollen records from Irish

lowlands show that around 7000 years ago, increasing amounts of alder pollen was

preserved in peat (Hall, 2011). Pollen analysis and radiocarbon dating have also assisted in

showing that there is less than 6,000 years since farming and agriculture was introduced to

Ireland. Cereal grains that have been dated show that between 6800-6500 BP the first

cereals were grown in Ireland and Britain (Hall, 2011). According to Chiverrell et al. (2004),

pollen data and archaeological evidence reveals a complicated pattern of human activity

and associated vegetation change during what are conventionally termed the Bronze Age

times (5500-3200 BP). During this period several temporary woodland clearances were

recorded in Northern Ireland (Chiverrell et al., 2004). The Bronze Age was an important

period of landscape evolution in regards to an increase in settled mixed farming and

associated woodland removal, soil erosion, blanket bog development and heathland

expansion all of which caused significant and permanent changes (Chiverrell et al., 2004).

The precision with which human influence can be detected from the pollen record is greatly

facilitated by the practice of agriculture (Moore et al. 1991). In agricultural communities

one expects to find elements of destruction of the natural vegetation, the introduction of

crop species and the presence of weed species associated with arable and pastoral activities

(Behre, 1981). An event known as the elm decline happened around 5840 BP. Pollen

diagrams have recorded these vegetation changes. The decline in elm might be linked to

the new farming practices (Hall, 2011). As agriculture expanded and climate worsened,

woodland depleted further, soils became damaged and drainage became impeded (Hall,

2011). Neolithic forest clearance activity on a minor scale is attested at the elm decline

which at Sluggan, falls rather late in the usual range for this horizon at around 4900 BP.

(Smith and Goddard, 1990). The early farming period (4900 BP) ends with the final decline

of Pine, which coincides with the onset of the Bronze Age clearances on Sluggan. The

Bronze Age was an important period of landscape evolution in regards to an increase in

settled mixed farming and associated woodland removal, soil erosion, blanket bog

development and heathland expansion, all of which caused significant and permanent

changes (Chiverrell et al., 2004). The spread of blanket peat probably owed much to the

effects of human activity and land use (Chiverrell et al., 2004). Around 2,200 years ago bog

woodland had almost disappeared from Ireland, making those that remained north of Lough

Neagh and at Garry Bog in County Antrim the last of their kind (Hall, 2011).

Restoration and Conservation of Raised bogs

The protection of peatlands, especially blanket and raised bogs, is regarded as one of the

top objectives for nature conservation in Northern Ireland. Due to the unique

environmental conditions of bogs, highly specialised plants and animals that are not found

in other habitats are able to colonize here. Blanket and raised bogs are listed as priority

habitats in the EC Directive on the conservation of natural habitats and of Wild Flora and

Fauna. Surveys were conducted for the Environmental Service for Northern Ireland of

raised bogs (Cruickshank and Tomlinson, 1988; Leach and Corbett, 1987) to increase

awareness for the need to protect the peatlands of Northern Ireland for their scientific,

wildlife, landscape and cultural value. These surveys were carried out to establish the

extent of degradation of bogs in Northern Ireland and their potential for conservation. After

1985 the Nature Conservation and Amenity Lands (NI) Order (1989) introduced the ASSI –

Area of Special Scientific Interest designation (Corbett and Seymour, 1997). Restoration of

bogs can have serious problems in terms of the relationship between peat, vegetation,

hydrology and topography due to the complexity of them within bog habitats and how they

are interlinked. According to Wheeler and Shaw (1995) the conservation and restoration of

raised bogs are either mire centred or species centred. Many voluntary groups such as the

Ulster Wildlife Trust (UWT) work to restore and conserve large sections of sites in Northern

Ireland. The aims of groups such as the UWT are to try and maintain or recreate developing

raised bog ecosystems and also to re-establish the populations of species that are typical of

raised bogs. Many species may require human interference however species of Sphagnum

may restore spontaneously. Most interest in peatland systems is with regards to legal

protection of intact bogs. According to Crowley et al. (2003) anthropogenically disturbed

sites including cutover bogs have yet to receive such legislative protection. However in

terms of conservation, research on cutover bogs has now increased.

From the literature it can be seen that pollen analysis is a very effective and versatile

method, in regards to reconstructing past vegetation. It is also widely used; certain bogs in

Northern Ireland have had a lot of work carried out on them to trace their vegetation

history. Knowledge of the past history of mires can also help to restore and conserve these

systems. The next section will describe the sites under investigation as well as their

conditions which make it possible to carry out this study.

Chapter 3: Site Description

Geology

The Landscape Character Area known as the Moyola River Floodplain consists of three ages

of rock strata according to the EHS (1994). The oldest layer is the Carboniferous including

Iniscairn, Altagoan and Desert martin, these clastic and carbonate sediments are around 350

million years old and cover approximately 50% of the south-east area. The Triassic

Sherwood Sandstone Group is 240 million years old, which runs in a strip from east to west.

The Tertiary Lower Basalt Formation is about 55 million years old, covering around 50% of

the north-east area. The drift geology of this area is made up from lacustrine alluvium and

alluvial deposits that were laid down by the Moyola River and underlying glacial deposits.

As last Ice Age ended around 16,000 ago Ballynahone Bog started to develop, Fig 3.1 shows

the development of fen into a raised bog.

Figure 3.1: Transverse section of peatland types. Profile (A) shows fen and (B) shows the

development into a raised bog.

Tephra has been found within the peat column; a layer of flaky light brown volcanic glass

from past volcanic activity (Pilcher and Hall, 1992). On such layer dates to AD1104 from the

eruption of Hekla volcano in Iceland (Hall et al., 1994), tephra from this eruption has been

recorded at many sites within the British Isles.

Definition of Raised mire

The Definition of raised mire from the Dictionary of Physical Geography (Thomas and

Goudie, 2000): “An acid peatland dominated by Sphagnum mosses and supplied by

precipitation solely from atmospheric source (rain, snow, fog etc). Raised mires form

characteristic shallow domes of peat where the topography is typically convex, with gently

sloping land away from its centre toward the surrounding moat-like drainage channel or lag

(Swedish terms describing margin of raised bog, typically with a stream and/or

minerotrophic poor-fen or fen woodland) surrounding the bog. This mire type is primarily a

lowland system, and mainly occurs in broad, flat(ish) valleys or basins. Raised mires have a

wide distribution in Britain but predominate in the cooler, wetter north and west. In lowland

Britain raised mires are recorded in basins, floodplains and at the heads of estuaries”.

Peat

Ballynahone Bog has around 60 hectares of uncut bog making it the second largest area of

uncut lowland raised bog in Northern Ireland. The storage of organic matter is greater than

the rate of decomposition, resulting in this area of peat having a positive energy balance

(Dierssen, 1992). According to Bellamy (1986), peat can be scientifically defined as partially

decayed matter consisting mainly of plant origin. Ballynahone Bog is considered to have the

best examples of raised bog habitats in the United Kingdom due to the area of uncut peat

taking the shape of the classic dome profile. Pools, hummock hollows and lawn complexes

can also be found within this area.

Hydrology

The nearest point of the Moyola River to Ballynahone Bog is 150m south of it. The Black

Burn River which is a tributary of the River Moyola is situated approximately 350m from the

bog. However this bog is a rain-fed system despite its close proximity to the river, making

this an ‘ombrotrophic’ bog. Lindsay (1995) states that the wetland conditions of the bog

and consequently the nutrient supply are derived from direct atmospheric precipitation

alone. The hydrological status of the bog is dependent on a number of factors; annual

precipitation, local climate, water movement on and off the body of the bog and also the

amount of human disturbance etc. Bearing the above factors in mind it is understandable

how the hydrology of Ballynahone Bog has been altered in the past by hand peat cutting but

more significantly by the drainage ditch excavation put in place by the Bulrush Peat

Company in preparation for mechanical peat cutting. The EHS in 1994 dammed the drains

using peat in order to restore the hydrological condition of the bog.

Climate

The estimated amount of rainfall needed for peat formation is 475mm annually (Lindsay,

1995). Northern Ireland is ideally suited to provide a climate beneficial to the production of

bog peat; in 2011 the annual amount of rainfall was 1356mm (Met Office, 2012), almost

triple the average for the formation of peat. According to Lappalanien (1995) ombrogenous

mires are entirely dependent on atmospheric inputs for their water and solute supply; they

can only develop in regions which have an annual surplus of precipitation over evaporation,

and not too great a deficit of precipitation during any season of the year.

Vegetation

As mentioned previously a full range of lowland raised bog characteristic structural features

such as the classic domed profile, along with pools, hummocks and lawn complexes are

found on Ballynahone Bog. A further mosaic of habitats have developed on this site due to

past disturbances; Purple Moor-grass grasslands, poor fen, regeneration of the bog and

Downy Birch woodland etc. This structural variation supports a wide range of vegetation,

mainly dominated by Sphagnum mosses. The abundance and composition of vegetation

species is dependent on local edaphic conditions (EHS, 1994). Prominent species found on

the dome of the bog include; Heather, Deer grass, Common cotton grass. Bog Myrtle and

White beaked sedge are also widespread on the bog. Bog rosemary is rare; however it can

be found growing on Ballynahone Bog alongside only one other lowland raised bog in

Northern Ireland (EHS, 1994). Ballynahone Bog is also surrounded by a young Birch

woodland as shown in Figure 3.2.

Figure 3.2: The cut-over part of the Ballynahone Bog surrounded by Birch trees

Site History

Man has exploited Ballynahone Bog in the past through peat cutting by hand, commercial

peat cutting in the 1980s and through drainage in preparation for this. Clay pigeon shooting

that has taken place on the bog has caused ground contamination. Resulting from the peat

extraction that took place on the Ballynahone bog, over 38.5 hectares of the approximately

100 hectare total of the National Nature Reserve were cutover. In the 1990s increased

awareness of raised bog ecology and vulnerability to disturbance resulted in the

government designation of Ballynahone Bog as an ASSI.

Figure 3.3: The cut-over section of Ballynahone Bog

Chronological sequence of events in the conservation history of Ballynahone Bog

Between August and October of 1985, Ballynahone Bog was considered one of the top ten

lowland raised bogs after being surveyed by the Countryside and Wildlife Branch (DOENI).

By 1988 a horticultural company known as Bulrush Peat Company had acquired a large part

of the bog. Despite objections planning permission was granted to Bulrush to extract peat

for commercial use. Drains were put in place on the southern part of the bog in 1991.

During the 6 year period from 1988 to 1994 opposition to the commercial use of peat

extraction came from locals, which then caused Friends of Ballynahone Bog to start a

campaign against Bulrush which drew in a lot of support from local environment groups and

celebrities. Planning permission was then revoked from the site as a result from the local

campaign and also from a further site survey carried out by the EHS; who then bought the

area that was owned by Bulrush. By January 1995 the 244 hectares of Ballynahone Bog was

designated an Area of Special Scientific Interest (ASSI) by the EHS, who then proposed it as a

candidate for designation as a Special Area of Conservation (cSAC) under the EU Habitats

Directive (92/43EEC). During September 2000, 98.5 hectares of the bog was designated as a

National Nature Reserve; 60 hectares as uncut bog and 38.5 hectares as cutover bog. EHS

declares NNRs under the ‘Nature Conservation and Amenity Lands (Northern Ireland) Order

(1985)’. Ballynahone Bog is now managed by the Ulster Wildlife Trust.

Chapter 4: Methodology

This section includes details in each aspect of the investigation including; field work, lab

work, identification of pollen grains and construction of a pollen diagram.

Fieldwork

Study Area

Before samples could be taken from Ballynahone Bog, consent had to be received from

NIEA; Northern Irelands Environment Agency. Permission was granted on the 5th of January

2012 for samples to be collected. On Monday 23rd of January 2012, the process of collecting

primary data began. Seven 50cm cores were taken in total from two different locations of

the bog. Two cores were extracted from the cut-over part of the bog (site 1) and 5 were

taken from the dome of the bog (site 2) (Table 4.2).

Table 4.1: Depth and location of each core.

Co-ordinates Site Core Depth (m)

1H 85299 97886 ± 5m

1 1 2.5

1 2 2

1H85380 97998 ± 5m

2 1 0.5

2 2 1

2 3 1.5

2 4 2

2 5 2.5

Coring

No exposed sections of Ballynahone Bog were available to take samples from therefore

cores had to be extracted from the bog’s surface. The 7 cores were extracted using a

Russian Sampler; the main advantage of using this corer is because “the sediment in which it

passes through is not disturbed by churning action” (Moore, et al., 1991). The only

disadvantage of using this corer is that it is limited to be used in soft materials as it lacks an

auger head. The main blade of the sampler passes the material to be sampled as it pushed

lower in to the bog, the movable chamber rotates 180° and cuts a semi-cylinder of peat

which remains intact as it is pulled up to the surface.” Figure 3.1 shows that to pull the

sampler back up to the surface is a two person job.

Figure 4.1: Removal process of sampler from the bog to extract core.

When the chamber of the sampler is opened, the entire core is in a complete and

undisturbed condition (Fig 3.2). No dismantling of the Russian sampler was needed. The

length of time the cores were exposed to air and pollen rain was limited as they were

quickly cover (put in bags).

Figure 4.2: Intact core taken from site 1, showing the changes in colour from light lake sands

to dark peat.

To keep the cores intact, and to store them, they were transferred into plastic guttering (Fig

3.3) that measured around 60cm in length. The guttering was labelled appropriately so that

the top and bottom ends, respectively, could be easily recognised (Fig 3.4). These were then

wrapped them in thick plastic bags to transport them back to the Laboratory. The whole

coring process was quick and efficient; took around three and half hours.

Figure 4.3: Transferal of core into guttering for storage.

Figure 4.4: Labelling of guttering for easy recognition in the lab.

Risk Analysis

Before starting to core the bog Willie McNaire from the Ulster Wildlife Trust met with us to

see where the cores would be extracted from in order to make sure the location was

feasible. Certain parts of the bog were saturated and would be unable to extract cores

from; these areas had to be identified. Willie then advised where the best places to take

the cores from the dome were (site 2), so that the drains that had been dug by the Bulrush

Company could be avoided. He advised this as he said that “it would be a nasty experience

to fall down one of these.” He made us aware of the drains’ locations so that we were

conscience of their whereabouts. He then left us to do some birdwatching on the bog and

stayed nearby so that if any problems arose he would be on hand to help.

Description and preparation of cores

Due to the decent storage and protective nature of the guttering, descriptions of the cores

were easy to record as the cores remained in an excellent condition. Core logs were drawn

up to describe what could be seen on the surface of each core e.g. the presence of roots and

fragments of wood. The colour of each core was recorded using the Munsell colour scheme.

After the colour was recorded for each core it was visible the change in humification of peat

with increasing depth down the bog.

After each core was described they had to be divided in to 1cm segments (Fig 3.5). This was

done by having a tape measure running the length of the core and using a knife to cut each

section at 1cm intervals. Each segment was put into a labelled plastic bag recording the

location of the core, where it was taken from and the core and site number (Fig 3.6). They

were then stored in the fridge. The cores were cut into these small sections so that when it

came to extracting the pollen, the smaller amounts of peat were easier to digest and break

up, along with humic material being dissolved.

Figure 4.5: Core being divided into 1cm segments.

Figure 4.6: Example of labelled bag with recorded site information, containing 1cm

segment.

Treatment of samples

Peat samples for pollen analysis need chemical pre-treatments in order to concentrate the

pollen, these must be done in a fume cupboard and the reagents handled with great care. A

laboratory coat, safety glasses and rubber gloves must be worn. Plenty of water should be

used for washing away any waste.

The idea for my method is mostly derived from “Pollen Analysis” by Moore, et al., 1991.

There are 3 stages to the procedure. Stage 1 is Peat Digestion. Start by placing 1g of peat

into a boiling tube and add 10ml of 10% KOH. After this test tubes are placed into a water

bath for 30 minutes and continually stirred with a glass rod to break up any lumps. Distilled

water may be added if needed to maintain the volume. This digestion process breaks up the

matrix and dissolves humic materials to produce a dark brown solution. Next, the solution is

filtered through a 100µm sieve, into a centrifuge tube where the pollen will pass through

the sieve thus leaving plant debris to remain. The final part to this first stage is to centrifuge

all 8 tubes for 3 minutes at 3000 rpm. The produced supernatant liquid is then decanted

and this procedure is repeated until supernatant is clear. This should result in the

deposition of a small pellet of material at the base of the tube. Care must be taken when

decanting as this material can easily be lost.

The second stage is Cellulose Removal. Cellulose is a polysaccharide and can be removed

most effectively by acid hydrolysis (acetolysis). The technique below is basically a replica of

that of Erdtman (1960). The reagents used in acetolysis are concentrated sulphuric acid and

acetic anhydride which are both corrosive and react vigorously with water (Moore, et al.,

1991). Extreme caution needs to be taken at this stage of the procedure as both are

corrosive and irritant to the skin. 10ml of glacial acetic acid is added to the centrifuge tube,

stirred with a glass rod, centrifuged again and then decanted. The added 10ml of acetolysis

mixture is placed in a boiling water bath for one minute. This is then centrifuged and

decanted carefully in to running water. Repeat step one by adding 10ml of glacial acetic

acid and centrifuge and decant once more. Finally add 10ml of distilled water and a few

drops of KOH, centrifuge and decant. Then repeat with more water and KOH.

Microscopy work

The final stage to the procedure is to identify the pollen grains. The residue is mounted

onto a glass slide, a drop of glycerine oil is added and spread out, and the coverslip is placed

on top. Immersion oil is spread on top of the coverslip to seal it to prevent drying to reduce

the degeneration process. The precision with which pollen grains can be identified depends

upon the quality of microscope used for observing them (Moore et al., 1991). According to

Moore et al (1994) the most appropriate magnification for routine scanning and counting is

×400 i.e. a ×40 objective and ×10 eyepiece. This provides sufficient magnification for the

identification of many pollen grains, and an adequate field of view for comfortable counting

in all. A total of fifty pollen grains were counted for each slide, the process for this is to

move from left to right across the slide counting pollen visible pollen grains and stopping

whenever fifty have been counted.

Pollen Diagram

Quaternary palynology originated in temperate regions and was initially a technique for

geological correlation and relative dating. Techniques of absolute dating have become

more available recently and emphasis has switched to vegetation and environmental

reconstruction (Flenley, 1985). From the data compiled after counting pollen grains, a

pollen diagram was constructed, to show the changing proportions of plant species

throughout the history of the mire. This was constructed through POLPAL, which is a

computer system for palynological analysis. Each horizontal line of the diagrams represents

the pollen result from a single slide. Each slide corresponds to a different depth of each

core. The results of the graph are organised in order of depth.

The total land pollen is tallied when the number of pollen grains recorded from each plant

species is converted into a percentage. The increases and decreases in the amount of each

plant species in the diagram shows that environmental conditions have changed over time.

This enables the impact, climate and humans have had on past vegetation to be seen.

Chapter 5: Results

Description of Cores

A description was taken of each core to visually apparent characteristics. The bog is split

into different layers and zones which run from the top of the bog to the base. The top cores

are lighter; reddish brown/dark brown in colour whereas the deeper cores are a darker

colour; black. The change in colours show that the lower darker peat is well humified and

separated by the overlying lighter less humified Sphagnum peat.

KEY:

Silt and Mud

Peat mixed with Silty Mud

Disturbance

Roots

Fragments of wood

Thick woody roots

Key to show different features that are visible

in each core

Figure 5.1: Representation of vertical core arrangement from site 1.

Site 1, Core 1

From top of the core 1cm to 48cm, the peat is all the same colour at: HUE 7.5YR 2.5/1 –

Black (Munsell colour system).

When the peat is cut, the centre of the core is a different colour: 10YR 2/1 Black.

21-22cm – segment in the middle- reddish- brown colour: 7.5YR 2.5/2.5/3 Very Dark Brown.

27-28.5cm – piece of wood below peat.

34-41cm and 44.5cm – wood is very common in the core, fragments can be seen.

43-46cm – peat mixed with silt, can hear a crunching sound when cut.

48-50cm – light sandy mud. 10YR 4/2 Dark Greyish Brown.

Top 0-1cm

Bottom 50 cm

Top 0-1cm

Bottom 50 cm

Site 1, Core 1


Site 1, Core 2

Core same colour throughout: 10YR 2/1 Black.

When core was cut colour changed: 7.5YR 2.5/1 Black.

Fragments of wood throughout core.

21-25cm – chunks of wood running diagonally across peat.

28-31cm- lots of wood, have to cut through it.

42-50 cm alot of wood is visible.

Around 40% of core has visible wood flakes.

Some disturbance to core when moving in from the corer to guttering.

Top 0-1cm

Bottom 50 cm


Site 2, Core 1

Top 0-1cm

Bottom 50 cm

Slight colour change throughout core.

Roots are present throughout whole core, most abundant 26-41cm.

Top 1-10cm- 7.5YR 2.5/2.

Some roots through top part of core.

10-40.5cm –2.5 3/1 Reddish Brown.

Abundance of roots in this part of the core 26-40.5cm; most located in a cluster between 35-40.5cm.

Bottom 40.5-50cm –10YR 2/1 Black.

40.5-43cm and 49-50cm roots are visible.

Max 15% of roots are visible on the surface of the core.

Three colour changes throughout core which are not that obvious. Bottom section is a

darker colour and therefore the change in colour is more noticeable in this section.

0-5cm – darker peat on top: 10YR 2/1 Black.

Hard to cut this core apart as roots ran through it.

5-31cm: 2.5YR 2.5/1 Reddish Black.

31-50cm: 2.5YR 2.5/2.

Very slight variation in colour throughout the core.

32-50cm is disturbed, light brown than the section above it.

Less than 10% of the core had visible roots.


Top 0-1cm

Bottom – 50cm

Site 2, Core 2

0-8cm: 7.5 2.5/2 Very Dark Brown.

8-17cm: 5YR 2.5/1 Black.

17-35cm: 7.5YR 2.5/1 Black.

35-42cm: 10YR 2/1 Black.

42-50cm: 10YR 2/2 Very Dark Brown.

Very slight colour change throughout core.

Most roots down the right side of the core.

Very tough to cut through the roots, hard to separate different samples of the core.

8-10% of core had visible roots.


Site 2, Core 3

Top 0-1cm

Bottom – 50cm

Top 0-1cm

Site 2, Core 3

0-6.5cm – 10YR 2/2 Very Dark Brown.

6.5-50cm – 2.5YR 2.5/1 Reddish Brown.

The middle of 13-14cm is a different colour: 7.5YR 2.5/3 Very Dark Brown.

The middle of 38-39cm is a lighter reddish brown in the middle: 2.5YR 3/2 Dusty Red.

Apart from the first 6.5cm’s the core is intact, smooth.

At a closer glance some roots can be seen at the top 7cm.

Many roots are scattered through the top of the core until 23cm then they are harder to notice.

Some roots visible at the bottom 4cm.


Bottom – 50cm

Top 0-1cm

Site 2, Core 4

Core is the same colour throughout: 7.5YR 2.5/1 Black.

0-8cm – some visible roots.

32cm – core has split so roots are more visible between the peat.

38-50cm - more roots are visible in the section of the core.

39cm onwards – hard to cut sections of the peat due to allot of roots being located here.

43-47cm allot of thick wooden roots.

49-50cm – most of this section of the core is not made up of peat but of soft bark.

Most of the roots are located down the right side of the core.


Site 2, Core 5

Top 0-1cm

Bottom – 50cm

Main Observation

Site 1, core 1 which is from the very bottom of the bog, lake sands were present in

core, is very dark in colour HUE 10YR 2/1 Black, also a lump of wood was found in

this core.

Site 1, core 2 was also dark in colour with lots of wooden roots and flakes

throughout it.

Site 2, cores 1-4 are lighter in colour and have thin roots running through each of the

cores, possibly from Sphagnum and heather etc.

Site 2, core 5 is a lot darker in comparison to the cores above it. There are also a lot

of wooden roots through out this core. This core shows the change in zones of peat,

this core is a lot more humified than the 4 cores above it.

Sampling

The table below records which parts of each core that were used as samples to carry out

pollen grains analysis. Eight random samples from each core were selected from

approximately equal distances down the core. Table 5.2.1 show the location of each of the

samples taken from each core.

Table 5.1: Table showing position of samples taken from each of the seven cores.

Site 1, Core 1 (Depth: 2.5m) Site 2, Core 2 (Depth: 1.0m)

Sample number Location of position of core

Sample number

Location of position of core

Sample 1 4-5cm Sample 1 1-2 cm

Sample 2 15-16cm Sample 2 6-7cm







Site 1, Core 2 (Depth: 2.0m) Site 2, Core 3 (Depth:1.5m)


Sample number










Site 2, Core 1 (Depth: 0.5m) Site 2, Core 4 (Depth: 2.0m)


Sample number








Sample 7 40.5-41cm Sample 7 42-43cm


Site 2, Core 5 (Depth: 2.5m)


Sample 1 2-3cm

Sample 2 11-12 cm

Sample 3 18-19cm

Sample 4 25-26cm

Sample 5 32-33cm

Sample 6 40-41cm

Sample 7 44-45cm

Sample 8 49-50cm

Identified Pollen Grains

Pollen Count, Site Results

The following tables include the number of different pollen grain types that was found on

each single slide. Each of these slides was created using sediment samples taken at regular

intervals along each core. The total amount of pollen grains that was counted for each

species and their total percentages from each sample of the core are noted below. During

the investigation, site 1 had a sufficient number of pollen grains from tree species and these

were prioritised, hence the low number of herb, shrub and spore pollen counts. However

the cores from site 2 were taken from the top of the dome of the bog, where no trees

where present, so herbs, shrubs and spores were counted alongside any tree species that

was found. The result of each species was then turned into a percentage e.g. at 7cm, 21

Sphagnum grains where counted. 50 grains were counted in total. The percentage of the

Sphagnum is shown below:

(21÷50) × 100 = 42%

Therefore 42% of the total pollen at 7cm depth was from Sphagnum.

Site 1, Core 1 = taken from the part of cut over bog at a depth of 2.5m, reached mud from

ancient lake and start of peat formation.

Table 5.2: The total amount of pollen grains for each species, and total percentage that has

been found in different samples taken from Core 1.

Slide 1 4-5cm Slide 2 15-16cm

Pine (Pinus) 30 = 60% Pine (Pinus) 20 = 40%

Birch (Betula) 10 = 20% Alder (Alnus) 20 = 40%

Alder (Alnus) 8 = 16% Birch (Betula) 5 = 10%

Elm (Ulmus) 1 = 2% Hazel (Corylus) 3 = 6%

Oak (Quercus) 1 = 2% Elm (Ulmus) 2 = 4%




Alder (Alnus) 10 = 20% Birch (Betula) 9 = 18%

Hazel (Corylus) 3 = 6% Hazel (Corylus) 1 = 2%


Birch (Betula) 20 = 40% Birch (Betula) 19 = 38%

Pine (Pinus) 17 =34% Pine (Pinus) 18 = 36%

Alder (Alnus) 11 = 22% Alder (Alnus) 11 = 22%



Birch (Betula) 24 = 48% Pine (Pinus) 28 = 56%

Pine (Pinus) 19 = 38% Birch (Betula) 13 = 26%

Alder (Alnus) 7 = 14% Alder (Alnus) 9 = 18%

Site 1, Core 2 = taken from cut over bog at a depth of 2.0m.


been found in different samples taken from Site 1 Core 2.



Pine (Pinus) 10 = 20% Sphagnum 17 = 34%

Sphagnum 8 = 16% Pine (Pinus) 5 = 10%

Elm (Ulmus) 5 = 10% Elm (Ulmus) 3= 6%

Oak (Quercus) 4 = 8% Ling Heather (Calluna) 1 = 2%

Ling Heather (Calluna) 4 = 8% Oak (Quercus) 1 = 2%



Sphagnum 12 = 24% Sphagnum 10 = 20%


Elm (Ulmus) 3 = 6% Elm (Ulmus) 8 = 16%

Ling Heather (Calluna) 2 = 4% Ling Heather (Calluna) 2 = 4%



Pine (Pinus) 13 =26% Pine (Pinus) 13 = 26%


Elm (Ulmus) 2= 4% Elm (Ulmus) 7 = 14%






Elm (Ulmus) 3 = 6% Alder (Alnus) 5 = 10%

Alder (Alnus) 1 = 2% Elm (Ulmus) 4 = 8%


Main Observations – Site 1.

Site 1’s results shows of a mixed forest made up mostly of Pinus (Pine).

The results of the pollen count of site 1 show that Pinus (Pine) usually makes up half

of the pollen found there.

Pine is not a dominant species of site 2; however it still exists in quite high quantity.

The general trend from the bottom of the bog; slide 8 from site 1 to slide 1 of site 2

shows a gradual decrease in Pinus (Pine).

Sphagnum and Calluna (Ling Heather) become present in site 2.

The further up core 2 Alnus (Alder) disappears. It is found is slide 7 and 8 but in very

low percentages.

Site 2, Core 1 = taken from the top of the dome at a depth of 0.5m.




Ling Heather (Calluna) 18 = 36% Sphagnum 19 = 38%

Sphagnum 16 = 32% Ling Heather (Calluna) 15 =30%

Oak (Quercus) 6 = 12% Fern (Filicales) 5 = 10%

Hazel (Corylus) 4 = 8% Oak (Quercus) 4 = 8%

Fern (Filicales) 3 = 6% Sedge (Cyperaceae) 4 = 8%

Sedge (Cyperaceae) 3 = 6% Birch (Betula) 3 = 6%





Sedge (Cyperaceae) 4= 8% Sedge (Cyperaceae) 5 = 10%

Fern (Filicales) 3 = 6% Fern (Filicales) 4 = 8%



Sphagnum 20 = 40% Ling Heather (Calluna) 20 = 40%


Oak (Quercus) 8 = 16% Oak (Quercus) 10 = 20%

Sedge (Cyperaceae) 2 = 4% Sedge (Cyperaceae) 2 = 4%

Birch (Betula) 2 = 4% Fern (Filicales) 2 = 4%

Fern (Filicales) 1 = 2% Birch (Betula) 1 = 2%




Oak (Quercus) 6 = 12% Oak (Quercus) 10= 20%





Site 2, Core 2 = taken from the dome of the bog at a depth of 1.0m.






Birch (Betula) 9 = 18% Oak (Quercus) 6 = 12%

Elm (Ulmus) 6 = 12% Sedge (Cyperaceae) 4 = 8%




Sedge (Cyperaceae) 1 = 2% Elm (Ulmus) 1 = 2%






Elm (Ulmus) 4 = 8% Sedge (Cyperaceae) 4 = 8%



Sedge (Cyperaceae) 1 = 2% Elm (Ulmus) 1 = 2%




Fern (Filicales) 5 = 10% Sedge (Cyperaceae) 8 = 16%



Sedge (Cyperaceae) 3 = 6% Birch (Betula) 1 = 2%

Birch (Betula) 1 = 2% Hazel (Corylus) 1 = 2%






Fern (Filicales) 2 = 4% Oak (Quercus) 2 = 4%






Elm (Ulmus) 16 = 32% Elm (Ulmus) 19 = 38%




Pine (Pinus) 3 = 6% Fern (Filicales) 3 = 6%

Ling Heather (Calluna) 3 = 6% Pine (Pinus) 2 = 4%

Fern (Filicales) 3 = 6% Hazel (Corylus) 2 = 4%

Alder (Alnus) 2 = 4% Ling Heather (Calluna) 1 = 2%

Hazel (Corylus) 2 = 4% Alder (Alnus) 1 = 2%


Elm (Ulmus) 20 = 40% Sphagnum 17 = 34%

Oak (Quercus) 8 = 16% Elm (Ulmus) 13 = 26%

Birch (Betula) 6 = 12% Oak (Quercus) 11 = 22%

Sphagnum 6 = 12% Birch (Betula) 4 = 8%

Ling Heather (Calluna) 6 = 12% Hazel (Corylus) 2 = 4%


Hazel (Corylus) 1 = 2% Ling Heather (Calluna) 1 = 2%



Elm (Ulmus) 23 = 46% Birch (Betula) 15 = 30%

Oak (Quercus) 12 = 24% Sphagnum 12 = 24%

Birch (Betula) 5 = 10% Elm (Ulmus) 9 = 18%


Fern (Filicales) 3 = 6% Alder (Alnus) 5 = 10%

Hazel (Corylus) 1 = 2% Fern (Filicales) 2 = 4%

Sphagnum 1 = 2% Hazel (Corylus) 1 = 2%

Alder (Alnus) 1 = 2% Ling Heather (Calluna) 1 = 2%


Elm (Ulmus) 20 = 40% Birch (Betula) 12 = 24%

Sphagnum 14 = 28% Elm (Ulmus) 10 = 20%


Pine (Pinus) 3 = 6% Sphagnum 7 = 14%










Sphagnum 8 = 16% Elm (Ulmus) 7 = 14%



Hazel (Corylus) 2 = 4% Oak (Quercus) 2 = 4%

Oak (Quercus) 1 = 2% Alder (Alnus) 1 = 2%


Sphagnum 15 = 30% Birch (Betula) 20 = 40%



Hazel (Corylus) 5 = 10% Elm (Ulmus) 4 = 8%

Birch (Betula) 4 = 8% Hazel (Corylus) 4 = 8%






Elm (Ulmus) 7 = 14% Ling Heather (Calluna) 5 = 10%

Ling Heather (Calluna) 6 = 12% Elm (Ulmus) 4 = 8%

Hazel (Corylus) 4 = 8% Alder (Alnus) 4 = 8%

Fern (Filicales) 4 = 8% Hazel (Corylus) 3 = 6%





Elm (Ulmus) 7 = 14% Ling Heather (Calluna) 7 = 14%

Ling Heather (Calluna) 5 = 10% Alder (Alnus) 7 = 14%

Fern (Filicales) 2 = 4% Elm (Ulmus) 6 = 12%


Oak (Quercus) 1 = 2% Hazel (Corylus) 3 = 6%






Hazel (Corylus) 9 = 18% Sphagnum 11 = 22%

Sphagnum 8 = 16% Alder (Alnus) 7 = 14%

Elm (Ulmus) 7 = 14% Pine (Pinus) 7 = 14%

Ling Heather (Calluna) 4 = 8% Fern (Filicales) 6 = 12%

Pine (Pinus) 4 = 8% Elm (Ulmus) 3 = 6%

Fern (Filicales) 2 = 4% Ling Heather (Calluna) 3 = 6%






Ling Heather (Calluna) 5= 10% Fern (Filicales) 6 = 12%

Fern (Filicales) 2 = 4% Alder (Alnus) 3 = 6%

Pine (Pinus) 1 = 2% Hazel (Corylus) 1 = 2%





Ling Heather (Calluna) 7 = 14% Fern (Filicales) 6 = 12%


Fern (Filicales) 3 = 6% Alder (Alnus) 5= 10%




Fern (Filicales) 5= 10% Ling Heather (Calluna) 7 = 14%


Alder (Alnus) 5= 10% Hazel (Corylus) 3 = 6%


Ling Heather (Calluna) 4 = 8% Alder (Alnus) 1 = 2%

Main Observations – Site 2

Sphagnum and Calluna (Ling Heather) are the dominant species of core 1.

Core 1 is mainly made up of shrubs (Hazel), Herbs (Sedge) and spores (Ferns and

Sphagnum).

Only two tree species found in core 1, in very low percentages; Oak- less than 16%

and Birch – less than 8%,

Core 2 has the same species being dominant as core 1. The species have also been

found in core 2 as in core 1.

However Ulmus (Elm) has also been found in core 2 which is the only addition

species found.

Core 3 differs from the two previous cores. Ulmus (Elm) is now the dominant

species.

There is a more varied amount of species in core 3, more tree species have been

found.

Vegetation found in core 3 indicates a woodland as Ulmus (Elm) Quercus (Oak) and

Betula (Birch) have the highest percentages.

Pinus (Pine) and Alnus (Alder) are now present in core 3.

In core 4 the amount of pollen grains found for Quercus (Oak) has decreased.

Ulmus (Elm) has also decrease in numbers found.

Betula (Birch) is now the dominant species of core 4

The amount of Sphagnum has also increased.

Pinus (Pine) has completely disappeared, no pollen grains were found in this core.

In core 5 Betula (Birch) and Sphagnum are still the dominant species of this, same as

core 4.

Core 5 has similar species and percentages as core 4, only difference is Pinus (Pine) is

now present

Figures of sampled pollen grains

The following six figures show pollen grains of the following species; Betula (Birch), Pinus

(Pine), Calluna (Ling Heather), Sphagnum, Quercus (Oak) and Cyperaceae (Sedge). These are

actual samples that I have collected from the cores.

Figure 5.8: Pollen grain (circled) of Betula (Birch).

Figure 5.9: Pollen grain (circled) of Pinus (Pine).

Figure 5.10: Pollen grains (circled) of Calluna (Ling Heather).

Figure 5.11: Pollen grain (circled) of Sphagnum.

Figure 5.12: Pollen grains (circled) of Quercus (Oak).

Figure 5.13: Pollen grain (circled) of Cyperaceae (Sedge)

Pollen diagram

The data from the above tables was used to produce a pollen diagram (Fig 5.14). This pollen

diagram will allow us to visualise how the abundance of different pollen grains has changed

over time , which then in turn gives an indication of how the abundance of the different

plant types, that produced these pollen grains, has changed over time.

The following factors that may have impacted on the past vegetation:

Depositional environments.

Palaeoclimate.

Human impact – pollen provides a record of land use change e.g. woodland

expansion, deforestation or arable agriculture.

The information about the ecology of these different plants can be used to chart changes in

environmental conditions over time. The plant species with the highest abundance in a

pollen diagram shows that their ecological requirements are being met by the prevailing

environmental conditions at that time. By referring to the ecological requirements of these

species, then the environmental conditions can be reconstructed

Figure 5.14: Pollen diagram of percentage of pollen grains found at Ballynahone Bog

Pollen diagram

0 40

0 50

0 60

0 25

0 40

0 50

0 20

0 20 0 15

0 45

(cm)

Chapter 6: Discussion

In this section the aim is: (1) incorporate the findings illustrated by pollen diagram and to discuss

how and why vegetation has changed the way it has. (2) To determine if there are any correlations

regarding human impacts on the land and the disappearance of some species or whether climatic

factors were solely responsible for vegetation change, or was it a contribution of both that caused

the vegetation of Ballynahone Bog to change over time.

Peat deposits

The development of peat mires has a very large autogenic component. Assuming that organisms

colonize a relatively fertile lake soon after it is formed; the first layers of the sediment will probably

include much inorganic matter derived by soil disturbance in the catchment, as well as organic

remains from algae and small animals (Burrows, 1990). The basal deposit of site 1 was a sticky black

peat with sandy mud at the bottom of the core. This was extracted from the cutover part of the bog

at co-ordinates H 85299 97886 ± 5m. This core was taken from a depth of 2.5m and reached the

bottom of the bog and into the former lake sediments below. A second core was taken from this

site at 2m depth, which was generally the same colour as the previous core. In the centre of the

basin above the basal peat, telmatic deposits of moss and wood peat accumulated: the basis of fen

development. The samples for pollen analysis show that a Betula (birch), Pinus (pine) and Alnus

(alder) woodland started to accumulate at this point. The vegetation species that now grow on the

surface of the bog are Calluna (heather) Sphagnum, Filicales (ferns), Cyperaceae (sedge) and some

different types of grass.

On the dome of the bog which was located at co-ordinates H85380 97998 ± 5m, was Sphagnum

dominated peat. The degree of humification in these five cores was variable. The upper cores were

less humified whereas the lower cores contained different types of vegetation species and therefore

were more humified. The lower cores of this section of the bog had a lot of very wooden roots and

fragments of bark throughout them. This could possibly be from stumps of pine that are rooted in

the lower sections of the peat. The presence of pine stumps suggest a relatively dry phase in the

bog development (Smith and Goddard, 1991). The results from the pollen diagram show that

Sphagnum starts to develop when Pinus (pine) starts to decline, which is at 3.5m depth and then

disappears completely at 1m depth. Alnus (alder) starts to decline at around 4m depth to then

slowly start to increase in quantities until 1m depth, when it is no longer found within the samples.

Betula (birch) is the dominant tree species throughout the bog history, as it has always been present

in all the samples. A Betula (birch) woodland still surrounds the bog today, which is why many grains

have been found in the cores near the top of the bog as these pollen grains have probably been

transported by the wind and incorporated into the upper peat layers.

Pollen diagram; change in vegetation

To begin with the Ireland of 11,000 years ago was not the same shape as modern Ireland, seal level

were still rising, resulting in changes in the coastal outline. Soils were sandy to begin with. Former

lakes developed into fens and then woods, Sphagnum grew on the moist floor of these new

woodlands. All of the tree species that came to the British Isles appear to have done so from Europe

(Hall, 2011).

Pinus (pine), Alnus (alder) and the tiny amount of Corylus (hazel) pollen grains which were present in

the bottom sample can be dated back to the Older Dryas period as the results are similar to that of

Sluggan Bog. These pollen grains may have been transported long distances by wind. Pollen grains

of other species are very sparse; productivity on the bog was obviously low. As conditions started to

get warmer Betula (birch) started to develop (Smith and Goddard, 1991), quite abundantly alongside

Pinus (pine). Almost 50% of the total pollen in one of the samples was made up of Betula (birch).

According to Smith and Goddard (1991) the Woodgrange interstadial occurred around 12350-11000

BP. During this stage Betula (birch) starts to decrease on the bog. Deciduous Betula (birch) soon

expanded across to cover the majority of Ireland as soon as the Holocene started. Betula (birch)

trees may have survived during the previous cold period in sheltered places on the Dingle Peninsula

in Co. Kerry. Betula (birch) seeds are light and readily spread by the wind and the trees can grow on

a range of soils (Hall, 2011). Betula (birch) is susceptible to drought and needs soils that are

sufficiently mature to hold water (Hall, 2011). Pinus (pine) and Alnus (alder) are also still abundant

in numbers. Alnus (alder) is a tree that favours waterlogged soils on the banks of lakes and rivers.

Oxygen-depleted, saturated soils which are low in nutrients; Alnus (alder) can grow in. Quercus

(oak) and Ulmus (elm) are staring to develop whereas Corylus (hazel) disappears during this period.

There is now less tree cover than before, allowing conditions to become more open. The water

table may also have risen making conditions suitable for bog-bean comparable to that of Sluggan

(Smith and Goddard, 1991).

Around 970O-9200BP (the Early post-glacial period) Betula (birch) is an important taxa during this

phase. As at Sluggan Bog, Pinus (pine) and Alnus (alder) have declined in numbers. This reduction

may have been due to a rise of the water table (Smith and Goddard, 1991).

Within the Early Boreal Period (9000 BP) Corylus (hazel) started to rise, around the same time Ulmus

(elm) is increasing in numbers again, marks a turning point of real vegetation significance (Smith and

Goddard, 1991). The Irish climate entered a period of reduced rainfall, bogland water tables fell

and bog surfaces dried enough to let pine seeds germinate (Hall, 2011). Calluna (ling heather)

started to expand during this period, it occupies a distinct ecological niche were soils are drier, with

better drainage. Boreal Corylus (hazel) had a greater development in the north of Ireland than

anywhere else in northern Europe (Jessen, 1949). Betula (birch) is in decline and has been replaced

with Corylus (hazel) and Ulmus (elm) which are now the dominant species. Soils may have become

more fertile (Smith and Goddard, 1991) however Quercus (oak) was absent during this phase even

though soil and climatic conditions at this time would have been suitable for its growth. The local

changes in the herbaceous flora seen from the diagram suggests that characteristics of the

vegetation were similar to before but with a gradual invasion of forest trees.

The Late Boreal Period lasts about 1600 years (8570 – 7020 BP) (Smith and Goddard, 1991), during

this period high values of Betula (birch) are found in the bog. These grains could possibly have been

deposited from surrounding woodland nearby. Pinus (pine) is also present but continues to

decrease in quantity, which is possibly a result of being unable to compete with Ulmus (elm) and

Betula (birch) and against Quercus (oak) which was starting to expand. Pinus may have invaded the

mire or it could have been growing on surrounding soils. This change differs to that at Sluggan Bog;

Pinus (pine) did not start to decrease in value until around 7020-4900 BP (Smith and Goddard, 1991).

Ulmus (elm) also continues to rise in numbers alongside the growing numbers of Quercus (oak).

Ulmus (elm) now shades out Corylus (hazel).

Sphagnum spores start to become very abundant during the Atlantic period (7020-4900 BP). This

period reflected a change in the surface conditions of the mire which at this stage would have

possibly been highly humified. The bog surface, if similar to Sluggan at this period, would have been

relatively dry (Smith and Goddard, 1991). However an increase in Sphagnum indicates wetter

conditions; Ballynahone Bog was becoming wetter. Sphagnum is a highly specialised plant which

requires a strict set of environmental conditions in order to survive. It is very sensitive to change

and is therefore a good indicator of changing environmental conditions across the bog. Around this

time Neolithic people had arrived in Ireland; however no distinct sign of interference with the

vegetation has been detected at this stage. Some similarities to Sluggan Bog as both have

exceptionally low values for Ulmus (elm) and Pinus (pine) which date to around 5050 BP. Quercus

(oak) values begin to increase within this period, as conditions around the edge of the bog became

suitable for Quercus (oak). Bog oaks demand more nutrients than Pinus (pine) and therefore their

development was restricted. There is no erratic increase in non tree pollen or appearance of weed

to suggest human interference.

Between 4900-3880 BP was the Early farming period, during this phase the Ulmus (elm) decline

happened. Ulmus (elm) recovered after the first decline, but then a second decline was recorded.

Research carried out by Smith, (1985, 1961) and Hirons and Edwards, (1986), show that this pattern

is common in pollen diagrams in Northern Ireland. The Ulmus (elm) decline is followed by the loss of

Pinus (pine); Quercus (oak) values do start to rise but start to decline again. During this period

agriculture was introduced to the landscape. Agriculture and the Ulmus (elm) decline belonged to

the Neolithic times. The period of low values of Ulmus (elm) lasted around 250 years, which

confirms that agriculture that took place during this period was more than a single episode of ‘slash

& burn’. There is a slight forest clearance but Ulmus (elm) starts to recover and Calluna (ling

heather) starts to increase allowing the bog to become healthier, with drier conditions.

The Late Prehistoric Period (3880-1560 BP) began with the final Ulmus (elm) decline (Mitchell,

1956). However the high Betula (birch) values indicate that there may have been a secondary

nature to this woodland. Certain areas of the mire may have been returned to woodlands which

existed before human interference.

From 1560 BP to the Present day is known as the Historic period. The decline of Ulmus (elm) and

Quercus (oak) may have been due to clearance which then resulted in an increase of shrubs, spores

and ferns. Afforestation of Quercus (oak) may have been for hardwoods; this usually occurred

alongside the establishment of estates. Mitchell (1956) and McCracken (1971) suggest that during

the eighteenth Century there was a lot of heavy agricultural usage. Also the change in the

abundance of heaths is associated with the local drains.

Human or Climatic impacts?

The late glacial vegetation is demonstrated to be heterogeneous. Ballynahone Bog had an

abundance of Betula (birch). The first decline in Betula (birch) which can be seen in Fig 5.14 may

have been connected to changes in the water level. Climate is thought to have deteriorated at

around 12000 BP. The decrease in Betula (birch) pollen is similar to the results of Sluggan Bog. The

decline at Sluggan is thought to be the equivalent of the Betula (birch) assemblage zone of the

Windermere Interstadial (Pennington, 1997). Pennington (1997) speaks of an environmental

regression at Windermere and the interstadial vegetation as having suffered only a minor regression

during the climatic deterioration.

In order to quantify palaeoclimates from the pollen spectra, there must be a relationship between

contemporary climate and pollen grains which can be applied by a multivariate transfer function

down the core (e.g. Birks and Birks, 1980; Webb 1980; Heusser and Streeter, 1980).

The beginning of the Thermal Maximum is more problematic to date. The work of Coope et al.

(1977) shows that the thermal maximum in Great Britain began well before the establishment of

shrub or tree cover and had probably been reached by about 13000 BP (Coope, 1977; Bishop and

Coope, 1977). The speed Betula (birch) cover developed at Ballynahone Bog suggests that it may

have sparsely been present and some factor may have been unsuitable for the growth of trees, once

this factor was removed, trees were able to then grow.

If tree growth was not prevented by some seasonal aspect of climate then there must have been

some other reason e.g. soil stability, plant cover or grazing pressures (Watts, 1977; Craig, 1978).

Records from the Meteorological Office confirmed that Ballynahone Bog is one of the areas of

Northern Ireland that has the lowest amount of rainfall and longest growing season (Smith and

Goddard, 1991).

The Betula (birch) curve declines during the Woodgrange period. The behaviour of the curve is the

same as the results from Roddansport, Co. Down (Morrison and Stephens, 1965). Nonetheless

Ballynahone Bog differs from other Irish pollen diagrams, as no other peaks of Betula (birch) are

present in these. The inward peak of declined Betula (birch) values took place around 9500 BP

(Smith and Goddard, 1991), and lasted no more than 200 years. These results are remarkably similar

to that of Hoydalar in the Fosroe Islands (Johansen, 1975). Johansen (1975) also suggests that the

decline in Betula (birch) could possibly be due to a change from continental to a more oceanic

climate.

The peak in Pinus (pine) during this period in time was noted by Behre (1967) at Westranderfehn in

Friesland, pine at this time covered a fairly wide region of N.W Germany, Holland and Belgium. The

climate oscillation responsible for the decline in Betula (birch) and peak in Pinus (pine) is dated to

1050-9850 BP. The rise in Alnus (alder) and decline of Pinus (pine) during the Boreal and Atlantic

periods was due to climate and increasing wetness. Soon after the first bog Pinus (pine) forest

became established the weather worsened, this was the coldest phase of weather since the Ice Age

ended which may have been the result of the final collapse of the ice sheet that covered much of the

eastern Canada; allowing a final flush of fresh water into the North Atlantic Ocean (Hall,2011).

The Early Farming period began with the Ulmus (elm) decline and ended with the final decline of

Pinus (pine). The needs of animals and plants placed new pressures on the landscape. Early Irish

settlers followed a similar practice to the pioneer American farmer, rather than invading grasslands

for farms, clearings were made by deadling the trees and clearing litter by occasional burning

(Neeson, 1991). The amount of open land was expanding and levels in Ulmus (elm) pollen were

decreasing across the British Isle and Europe (Hall, 2011). Explanations for the fall in Ulmus (elm)

values could be that people may have cut the young branches of Ulmus (elm) to feed their cattle.

However the decline in Ulmus (elm) was widespread and it seems to have happened simultaneously

in all area suggested a climatic cause e.g. late springs killing the young flowering buds. An

alternative explanation could be the trees were devastated by the ravages of a fungal infection:

Dutch elm disease. The final decline in Pinus (pine) may have been a result of clearances made

during the Bronze Age period. However evidence of agriculture is virtually absent at Ballynagilly, Co

Tyrone (Pilcher and Smith, 1979). This final Pinus (pine) decline may then be a result of climatic

changes and the connection with the Bronze Age clearances may be coincidental. A decrease in

Pinus (pine) trees meant that less water was removed by transpiration through the needle-shaped

leaves; soils became increasingly waterlogged and the bog’s surface became wetter. The decline

took place at Sluggan around 4200BP; it was probably around this date that it happened at

Ballynahone Bog. It is possible that the loss of pine could be due to the hastened poor weather

conditions after volcanic eruptions from Iceland.

The vegetation that happened in the Late Prehistoric period appears to be attributable entirely to

the hand of man, which seems to be the dominant ecological factors. Woodland depleted further by

agricultural expansion and a worsening climate. It is not possible to identify any significant climatic

change. Despite episodes of clearance, tree pollen at Ballynahone remained high. The Late Bronze

Age was responsible for the majority of clearance with economic prosperity found in this period.

Within this period Mitchell (1976) found there was an intensification of agriculture.

During the Historic period the final decline in elm takes place. This may be a result if the onset

agricultural phase. However no cereal grains have been found so, emphasis on cultivation must

have been put on vegetable growing. Neolithic, Bronze Age, Iron Age, Celtics, Romans, Saxons and

Vikings all had an effect before 500 BP; their activities resulted in accelerated erosion and

deforestation (Higgitt and Mark Lee, 2001). However the greatest impact put on the land during this

period was during the Viking period right up until the Late Anglo Norman Period.

Drains were placed along the southern part of Ballynahone Bog in 1991. These drains play a role in

the position of where species germinate and expand. The percentage of Sphagnum, with increasing

distance to the drains, decreases. Sphagnum needs very wet condition to survive, whereas Calluna

(ling heather) increases in value with closeness to the drain. The ecology of the drains played a large

role in the environment conditions of the bog regarding vegetation change. Now that the drains are

dammed on the bog starts to become wetter, Sphagnum may start to expand in values, Calluna (ling

heather) then in turn may decrease.

Vegetation change has happen throughout time on Ballynahone Bog, as a result of human and

climatic factors. However Ballynahone Bog has managed to restore itself each time through the

growth of various species. The bog now appears to be restoring by recolonizing of desirable

vegetation. This trend should continue, however hydrological and biological monitoring should be

ongoing practices.

Chapter 7: Conclusion

The findings of this investigation have indicated that climatic changes have caused the

vegetation of the Ballynahone Bog to change, however human pressures have also affected

the composition of the vegetation.

Acid bogs are ombrogenous in nature; they depend upon precipitation reaching them and

are therefore sensitive to changes in rainfall and evaporation (Godwin, 1981). The climate

had an unfavourable effect on some of the species that once grew on the bog. The early

colonisation by Pinus (pine) and Betula (birch) indicate a warmer climate in the north of

Ireland and causing the drying of Ballynahone Bog. Calluna (ling heather) started to expand

on the bog during the Boreal period indicating a period of reduced rainfall within the Irish

climate. The rapid growth of Sphagnum during the Atlantic period indicates the bog

becoming much wetter.

Humans had a detrimental effect on the amount of species that was present on the bog; the

loss of woodlands and the creation of open spaces in which crops grew or animals graze

were the first indicators of human impacts on the bog which continued up until the 1990’s.

The Ulmus (elm) decline was probably linked to the framing practices that were carried out

in Neolithic times. Where Ulmus (elm) grew may have been attractive to humans for

settlement, as elm grows on good soil. Woodland was further depleted by agriculture and

the worsening climate. An increase in the amount of trees that were cut down took place to

open up more areas for farmlands. The expansion of Sphagnum can be assumed to have

occurred as the bog surface became wetter and caused the decline of Pinus (pine).

The upper cores taken from the dome of the bog were recorded as light less humified

Sphagnum peat, the results supported this observation, and the lower cores of the dome

have been noted as a darker colour to represent this peat being more humified. A variety of

species have been recorded to be growing on the bog at this time. However the pollen

diagram shows a lot of Sphagnum to be present as the bog developed. A reason behind so

much Sphagnum being present is that site 1 was taken from the cutover part of the bog.

After the peat cutting of Ballynahone Bog stopped, sphagnum has probably colonized this

bare area.

Betula (birch) was constantly present on the bog in significant values; Betula (birch) was

present on cores taken from the dome of bog even though it no longer grows on this area of

the bog. As a Betula (birch) wood surrounds Ballynahone Bog, pollen grains from these

trees have probably be transported by the wind to become incorporated in these upper

layers.

As with all investigations, human sampling error must be considered such as a limited

taxonomical knowledge e.g. pollen grain of different species could be more correctly

identified. Although the relationships that exist between plant species was not the aim of

the study, to explore these relationship further could be advantageous. This may develop

further ideas on environmental change; how species that occupy similar niches reacted to

each other.

Further to this a study should be carried out on Coleoptera (beetles). Beetles possess a

highly robust exoskeleton (chitin), which can survive with sufficient detail reserved after

thousands of years to enable identification. Many species are stenotypic and show a

marked preference for a particular environment and are therefore very valuable

palaeoecological/ environmental indicators. During the Quaternary beetles seem to have

not undergone evolution; this is extremely useful for environmental reconstruction as

fossilized beetles represent the same species as the living. So by identifying species from

peat and knowing the modern climatic range of that species; palaeoclimate can then be

deduced.

The findings of this study support the research that has been carried out on various bogs in

Northern Ireland regarding vegetation change; specific species have increased/decreased

during the same periods. This project provides a basis for discussion of further historical

ecology on Ballynahone Bog and a comparison between the bogs in the north of Ireland.

More specifically it has implied the change that will potentially take place on the bog.

Further studies are needed to explore changes that may have taken place on different

locations of the bog e.g. the edge, and to precisely date pollen grains found. Radiocarbon

dating will provide a more dynamic approach to the study of vegetation history. Exploration

of the extent the impacts humans may have had on the landscape as wells their interactions

e.g. looking for cereal grains in the cores. The Irish landscape will continue to change in the

future, by natural forces and human hands. Together they will shape and reshape parts of

the landscape. Ireland’s landscape has been and will continue to be influenced by

persistent change. With an understanding of how the landscape of Ballynahone Bog

developed, insight is gained of how to care for it.

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Barber, K.E., Chambers, F.M. and Maddy, D. (2003). ‘Holocene palaeoclmates from peat stratigraphy:

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BOGLAND By Seamus Heaney We have no prairies To slice a big sun at evening Everywhere the eye concedes to Encroaching horizon, Is wooed into the cyclops' eye Of a tarn. Our unfenced country Is bog that keeps crusting Between the sights of the sun. They've taken the skeleton Of the Great Irish Elk Out of the peat, set it up An astounding crate full of air. Butter sunk under More than a hundred years Was recovered salty and white. The ground itself is kind, black butter Melting and opening underfoot, Missing its last definition By millions of years. They'll never dig coal here, Only the waterlogged trunks Of great firs, soft as pulp. Our pioneers keep striking Onwards and downwards, Every layer they strip Seems camped on before. The bogholes might be Atlantic seepage. The wet centre is bottomless.

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An Investigation of the History of Vegetation Change …€¦ · An Investigation of the History of Vegetation Change on Ballynahone Bog, County Londonderry using Pollen Analysis