A multi-proxy Holocene palaeoenvironmental record of climate change and prehistoric human activity from Lough Cullin,southeast Ireland

Abstract

A multiproxy (pollen, microcharcoal, loss-on-ignition, magnetic susceptibility and geochemistry) sequence from Lough Cullin, southeast Ireland, supported by a high-resolution radiocarbon chronology, modelled using Bayesian approaches, provides a record of environmental change for much of the Holocene. Following the establishment of mixed deciduous woodland, climatic deterioration was likely responsible for pronounced vegetation change and erosion, 7615–6500 cal. BC to 6245–5575 cal. BC, evidence for the ‘8.2 Kyr’ BP climate event. The so-called ‘elm decline’ is dated to 4220–3980 cal. BC and whilst there are possible indications of an anthropogenic cause, clear evidence of woodland clearance with cereal pollen is recorded at 3900–3700 cal. BC, 3790–3580 cal. BC and 3760–3650 cal. BC, during a period of clearance and farming of 320–450 years duration. A reduction in farming/settlement and woodland regeneration during the Middle Neolithic parallels the archaeological record, with low levels of activity during the Late Neolithic/Chalcolithic after 2960–2525 cal. BC, prior to increases during the Bronze Age then woodland clearance and agriculture between 1500–1410 and 1275–1000 cal. BC, corresponding with the archaeological evidence. A subsequent ‘step-wise’ reduction in human activity follows, from the latter date to 815–685 cal. BC, and a brief but pronounced cessation at 690–535 cal. BC. Renewed woodland clearance and agriculture commenced until 415–250 cal. BC. From the latter date until cal. AD 390–540, the Late Iron Age/Early Medieval period, a phase of woodland recovery is attested, followed by renewed landscape disturbance and arable agriculture in particular, continuing to the close of the record at cal. AD 780–1035.

Keywords

archaeology chronology Ireland palaeoecology pollen analysis

Introduction

Understanding the character and chronology of Holocene vegetation development and the respective roles of climatic and anthropogenic impact on patterns and process of landscape change is a key focus of palaeoecological research. There is a long history of such research in Ireland, where the wide distribution of peatland and lake deposits provides the required sampling sites, and investigations continue to provide new insights into environmental change. Various questions concern the timing and character of human activity, climatic change and its relationship to archaeology, continue to be a subject of ongoing debate (see Kelly and O’Carragain, 2021 for a summary). A particular methodological issue concerns the production of tightly constrained chronologies that are now available for the archaeological record (Cooney et al., 2011; McClatchie et al., 2014; McLaughlin et al., 2016) and the utility of formal modelling procedures to generate robust estimates of the tempo of environmental changes such as those around the mid-Holocene ‘elm decline’ (e.g. Kearney and Gearey, 2020; Whitehouse et al., 2014) and the Bronze Age to Iron Age transition (e.g. Gearey et al., 2020).

Recent detailed palaeoenvironmental studies have focussed on the west and north of the island (e.g. Chique et al., 2017; Spencer et al., 2020; Stolze and Monecke, 2021) but there has been relatively little research in the southeast (see Eogan et al., 2015). In this paper, we describe and discuss the results of a multi-proxy palaeoenvironmental analysis of a 7.75 m core from Lough Cullin, Co. Kilkenny, southeast Ireland, which is supported by a high-resolution radiocarbon chronology. Compilation of archaeological evidence from the close vicinity of the sampling site provides an independent record of the relative intensity of human activity through time.

Background

Lough Cullin (52°19′N, −7°06′W) is a small lake (c.5 hectares) located in the catchment of the river Suir, in the south of County Kilkenny, southeast Ireland (Figure 1). The lake is situated in a low-lying landscape (11 m OD), has a maximum depth of 3.4 m and is fed by a series of small streams from the north (with a stream flowing through a channel incised into the Lower Palaeozoic and Devonian rocks at Catsrock), east and south. The outflow is via a small stream to the south-west. The lake is nestled in the centre of a syncline, with the underlying geology of the lake itself being well-bedded pale grey lower Dinantian limestones of the Ballysteen Formation (Tietzsch-Tyler et al., 1994, the Hook Head formation of Keeley, 1983). The slope increases significantly 2.5 km to the east and north of the lake basin, as the geology changes from limestone to Devonian sandstones. The recession of the lake due to 19th century drainage can be seen on the various editions of Ordnance Survey maps produced during the 19th and early 20th centuries. John O’Donovan, who was one of the civilians employed by the Ordnance Survey of Ireland in the 1830s and compiled the name books for the Ordnance Survey, remarked: ‘I remember this lake when it was of considerable extent. It is now nearly drained, and the bog nearly all cut out’ (Ordnance Survey of Ireland, n.d.). There is also sedimentological evidence the lake was once larger, with lacustrine sediments filling an area of 2 km² around the lake. The presence of a glaciofluvial sand and gravel deposit to the north of the lake between it and the channel at Catsrock, suggests the lake may, partly at least, owe its origin to glacial meltwater.

Figure 1.

Location map of Lough Cullin. Inset map indicating the location of selected sites referenced in this paper. 1-Lough Muckno, 2-Lough Arrow, 3-Lough Inchiquin, 4-Lough Dargan and 5-Lough Meenachrinna.

Methods and materials

Core sampling and lithostratigraphy

In June 2012, a 7.75 m sediment core was extracted from the deepest part of the lake using a Livingstone piston corer from a platform secured in the centre of the lake. The core was extracted and wrapped on site, and later transferred to the lab where it was cut in half along its length. One half was used for geochemical analysis, and both halves were subsampled at 1 cm intervals down to 6.33 m (the top of the clays).

Palynological analysis

Sub-samples of 1 cm³ were prepared for pollen analyses following standard techniques including KOH digestion, HF treatment and acetylation (Moore et al., 1991). Pollen concentrations were established by adding a known concentration of Lycopodium clavatum spore (batch number 177745) to the samples before treatment (Stockmarr, 1971). Pollen counts were made using a Leica DM 1000 LED microscope at ×400, ×800 and ×1000 magnification under oil immersion for critical examination of pollen sculpture and measurement of pollen grains. A minimum pollen sum of 400 Total Land Pollen (TLP) grains, excluding spores and aquatics, was employed. Pollen grains were identified mainly using the key from Moore et al. (1991) and Bennett (1995), with reference to Fægri et al. (1989). Pollen and spore identification was made to the lowest taxonomic level possible using the available references and following the nomenclature of Stace (1997), with suggestions from Bennett et al. (1994). The programmes TILIA and TILIA - GRAPH (Grimm, 2013) were used to construct spreadsheets and pollen diagrams. Local pollen assemblage zones (LPAZ) were defined based on visible changes in the pollen record.

Loss on ignition (LoI)

Sediment samples (c.5 cm³) were taken at 2 cm intervals to calculate loss-on-ignition (LoI %). The samples were dried for 24 h at 105°C and subsequently transferred to porcelain crucibles and ashed for 4 h at 550°C (after Bengtsson and Enell, 1986; Heiri et al., 2001).

Geochemical analysis

Geochemical analysis was carried out through non-destructive X-ray fluorescence (XRF) core scanning of the split cores using a Cox Analytical Systems ITRAX XRF Core Scanner located in the School of Geography, University College Dublin. Twenty-eight trace elements were selected for analysis (Mg, Al, Si, P, S, Cl, Ar, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Ge, As, Br, Rb, Sr, Y, Zr, Ba, Nd, Pb, U), of which 10 key elements (Fe, Si, Ti, Ca, K, Sr, Rb, Mn, Cu and Br) and the ratio of inc:coh were chosen for interpretation. Cores were scanned at 600 μm step intervals with a count time of 15 s, using a Mo tube operating at 30 kV and 30 mA.

The elemental data obtained are counts only, and so should be considered as semi-quantitative in nature (Croudace et al., 2006; Weltje and Tjallingii, 2008). The data was normalised using kilo counts per second (kcps) to account for the variation in XRF intensities (Gregory et al., 2019; Jouve et al., 2013; Turner et al., 2015). Relative elemental concentrations within a core can provide valuable information on the sedimentology and palaeoclimatic history of an area (Guyard et al., 2007), particularly when coupled with data from other methodologies.

Along with the geochemical data, the ITRAX scanner returns a profile of the magnetic susceptibility (MS) measurement of the core at 4 mm resolution. MS is the amount of magnetisation acquired by the sediments of the core due to the application of a weak magnetic field. MS is related to the amount of dia- para- and ferrimagnetic minerals within the core (Støren et al., 2016), and changes in MS can be indicative of sediment flux and erosion in lake catchments (Evans and Slaymaker, 2004).

Chronology

Radiocarbon dating

Thirty-three samples (52 measurements in total) were dated by Accelerator Mass Spectrometry at the Scottish Universities Environmental Research Centre (SUERC-), Queen’s University Belfast (UBA-) and Beta Analytic (Beta-). All measurements were obtained from organic sediment samples except for UBA-22422, which was obtained from a branch fragment of Salix sp. (willow). Where possible, duplicate measurements on the humin (the acid and alkali-insoluble) and humic (alkali-soluble, acid insoluble) fractions (Cook et al., 1997: 21) were obtained to test the reliability of sediment derived radiocarbon determinations (cf. Brock et al., 2011) and the statistical consistency (Ward and Wilson, 1978) of each paired date assessed using the OxCal (Bronk Ramsey, 2009a) programme.

The resulting radiocarbon determinations are presented as conventional radiocarbon ages (Stuiver and Polach, 1977) quoted in accordance with the international standard established by the Trondheim Convention (Stuiver and Kra, 1986). The calibrations have been calculated using the published datasets, IntCal20, (Reimer et al., 2020) and the computer program OxCal v4.3 (Bronk Ramsey, 2009a) and are cited with the end points rounded outward to 10 years. The calibrated date ranges have been calculated using the maximum intercept method (Stuiver and Reimer, 1986) and the graphical distribution of the calibrated result derived from the probability method (Stuiver and Reimer, 1993). All radiocarbon dates are cited at 95.4% confidence, unless stated otherwise.

Bayesian modelling

In order to refine the chronology of palynological features and extend the chronological framework to changes which fall between dated horizons, a Bayesian approach was employed to the modelling of the radiocarbon dates (Buck et al., 1992). The Bayesian approach has been widely discussed in the literature (e.g. Blaauw and Christen, 2005; Blaauw et al., 2007a, 2007b; Bronk Ramsey, 2008). The approach taken here uses the software OxCal v4.3 program (Bronk Ramsey, 2009a), and the P_Sequence function (Bronk Ramsey, 2008) was chosen to allow for a Poisson process, or a potentially random rate, of sediment formation. The prior information for the deposition rate was defined as log_10(k/k_0) where k_0 = 1. This allows k to take any value from 0.01 to 100. This value used was estimated from the radiocarbon dates following the approach outlined in Blockley et al. (2007, 2008)

The command Outlier() was used in OxCal (Bronk Ramsey, 2009b) to identify any measurements that were statistically defined as outliers at a 0.05 probability (1 in 20 chance). The model has been constrained using Boundaries, the depths of which have been defined based on stratigraphic changes (see below). The ranges quoted in italics are posterior density estimates, derived from this Bayesian modelling of the radiocarbon chronology (Bayliss et al., 2007) and are cited at 95.4% probability, unless stated otherwise.

Whilst it has long been largely common practice to use ‘single point’ estimates to describe palaeoenvironmental chronologies, largely for reasons of perceived clarity of data presentation, we utilise posterior density estimates, as these reflect the inherent probabilistic uncertainty associated with radiocarbon dates. It is now usual in much archaeological research to present chronological information in this way (Whittle et al., 2011). In order to allow meaningful, robust comparisons between archaeological and palaeoenvironmental datasets, it is essential we standardise chronological ‘currencies’ and hence develop a ‘best practice’ approach.

Results

Stratigraphy

The core lithology was (from top to bottom) light grey, organic-rich sediment (0–1.75 m); dark brown gyttja (1.75–6.26 m), with a layer of sandier gyttja between 5.55 and 5.74 m. The gyttja lies above 6 cm of sand (6.26–6.32 m). At the base of the sequence was 1.65 m of laminated grey-brown silty clay, with an angular pebble within the sediment at 7 m.

Palynological analysis

A total of forty-nine different taxa, including spores, were recorded across the Lough Cullin pollen profile. The data is presented in Table 1, the percentage pollen diagram LC (Figure 2) and pollen concentration diagram (Figure 3). The pollen diagrams have been divided in 13 local pollen assemblage zones (LPAZ). LPAZ boundaries are given as posterior density estimates derived from the age-depth model shown in Figure 5. In addition, a curve for ‘anthropogenic indicator’ (sensu Behre, 1981) taxa has been calculated (comprising Cerealia-type, Artemisia-type, Asteraceae undif., Caryophyllaceae, Plantago lanceolata, Plantago major/media, Rumex, Trifolium-type and Urtica dioica).

Table 1.

Summary of pollen and loss on ignition data from Lough Cullin (LC).

LPAZ/top depth (m)	Posterior density estimate (95.4% probability)	Posterior density estimate (68.2% probability)	Cultural period	Main pollen features	LoI
LC13 2.15	780–1035 cal. AD	810–940 cal. AD	Early Medieval	Reductions in AP (c.55%) across zone, especially Corylus (c.20%), Quercus (c.10%) and Alnus (c.10%) towards top of zone. Increase in NAP (c.45%), especially Poaceae (c.20%), Cyperaceae (c.15%), P. lanceolata (c.4%) and Rumex (2%). Cerealia-type recorded across zone. Rise in Pteridium (c.10% TLP+S), Charcoal increases to peak midway through zone.	OM increasing c.40% at base to c.47% at top LPAZ. Average c.43%
LC12 2.36	390–540 cal. AD	395–470 cal. AD	Late Iron Age	Pronounced increase in AP (c.95%), especially Corylus (c.50%) and Quercus (c.30%), other arboreal taxa remaining steady. Falls in NAP predominantly Poaceae and Cyperaceae, P. lanceolata low and sporadic. Increase in charcoal towards top of zone.	OM increasing from c.36% to c.41% at top LPAZ. Average c.39%
LC11 2.64	415–250 cal. BC	405–355 cal. BC	Iron Age	Steady reduction in AP across zone (c.70%), primarily Corylus and following an initial increase, Quercus. NAP increase, Poaceae rises (c.15%), also P. lanceolata (c.8%), Lactuceae (2%) and sporadic Filipendula. Cerealia-type recorded 2.65 m. Charcoal low.	OM ranges c.34% at base to c.29% across LPAZ. Average c.31%
LC10 2.82	690–535 cal. BC	630–555 cal. BC	Iron Age transition	Increase in AP (c.90%), mainly Corylus (c.45%), other arboreal taxa remaining steady. Reductions in NAP, primarily Poaceae, P. lanceolata consistently present, at certain points higher values than the former. Charcoal low and sporadic.	OM increasing from c.33% to 37% across LPAZ. Average c.34%
LC9 2.925	815–685 cal. BC	795–740 cal. BC	Late Bronze Age	Both AP (between 70% and 85%) and NAP (30–15%) fluctuate cross the zone; former mainly due to changes in Corylus but Quercus also involved and the latter Poaceae; P. lanceolata remaining steady. Two Cerealia-type grains recorded at 3.08 m, Pteridium peaks at c.15% and charcoal also shows increase above (3.04 m).	OM ranges c.28% at base to c.35% at top of LPAZ. Average c.30%
LC8 3.14	1275–1000 cal. BC	1225–1080 cal. BC	Middle Bronze Age	Pronounced fall in AP (c.55%), especially Corylus (c.15%) and Quercus (c.10%) towards close of zone. Sharp increase in Poaceae and P. lanceolata, reaching highest values for diagram (c.28% and 7% respectively) also Cyperaceae (7%) and Succisa-type (2%), low values for Chenopodiaceae and Filipendula. Increase in Pteridium aquilinum (11% TLP+S) and Pteropsida monolete (indet.) (9% TLP+S) towards close of zone. Charcoal values very low.	OM increases from c.34 % to c.37% at 3.20 m, decreasing to c.29% by top of LPAZ. Average c.32%
LC7c 3.34	1500–1470 cal. BC (28.1%) 1465–1410 cal. BC (67.3%)	1495–1480 cal. BC (17.5%) 1455–1420 cal. BC (50.7%)	Middle Bronze Age	AP remaining steady (c.80%), Corylus increasing (c.45%) towards top of zone. NAP increases initially (c.20%), mainly Poaceae and P. lanceolata, followed by reduction in former (c.10%). Charcoal increases slightly to peak at top of zone.	OM ranges c.34% to c.36% across LPAZ. Average c.35%
LC7b 3.56	1880–1740 cal. BC	1875–1840 cal. BC (30.0%) 1820–1800 cal. BC (14.1%) 1780–1750 cal. BC (24.2%)	Chalcolithic & Early Bronze Age	NAP remaining steady (15%); the latter mainly represented by Poaceae, low values for P. lanceolata. Charcoal remains low.	OM ranges from c.30% at base to c.40% at top LPAZ. Average c.33%
LC7a 3.90	2620–2240 cal. BC	2505–2320 cal. BC	Late Neolithic	Ulmus remains low, Corylus values fall mid-way to c.25%. Other trees at similar values to previous zone. Increased NAP (c.15%), a second continuous P. lanceolata curve (c.3%) from start of zone, Poaceae also increases, Asteraceae, Apiaceae, Filipendula and Ranunculaceae present. Single grain Cerealia-type (4.02 m) alongside Artemisia-type. Pteropsida (monolete) indet. increases to 8% TLP+S. Charcoal values show very slight increase.	OM ranges c.33% to c.35% across LPAZ. Average c.33%
LC6 4.08	2960–2525 cal. BC	2845–2630 cal. BC	Middle Neolithic II	Steady reduction in Ulmus (c.2–3%), Alnus increases (c.25%) and Salix also present in slightly greater values (c.3%). NAP steady at c.7%, predominantly Cyperaceae, continuous Ranunculaceae, sporadic Filipendula, P. lanceolata, Succisa-type. Charcoal remains steady.	OM ranges c.35% to c.37% across LPAZ, dropping to c.30% at top. Average c.34%
LC5 4.38	3355–3120 cal. BC	3275–3150 cal. BC	Middle Neolithic I	AP values increase overall (c.95%), primarily Corylus (c.30%), Quercus (c.25%) and Ulmus (c.8%) and Alnus (c.20%). NAP values decline, only sporadic records of P. lanceolata. Slight increase in Polypodium (6% TLP+S). Charcoal remains steady.	OM ranges from c.35% to c.37% across LPAZ. Average c.36%
LC4c 4.71	3685–3530 cal. BC	3650–3555 cal. BC	Early Neolithic II	Quercus (c.25%) and Ulmus (c.4%) values recover, Corylus remaining c.30%. NAP values are reduced (c.5%) although a continuous but reduced curve for P. lanceolata (c.1% max) is exhibited, Cerealia-type pollen recorded (2 grains 4.77 and 1 grain 4.75 m); other herbs similar to previous zone. Charcoal also remaining at similar levels.	OM ranges from c.31% at base to c.36% at the top of LPAZ. Average c.34%
LC4b 4.82	3860–3650 cal. BC	3815–3710 cal. BC	Early Neolithic I	Quercus (25–15%) and Corylus (40–30%) decreasing across zone; NAP increases to c.20%, predominantly Poaceae (10%), continuous presence of P. lanceolata (c.5%) and Ranunculaceae (c.1–2%), Artemisia-type, Asteraceae, Rumex acetosella/acetosa, Filipendula and Urtica dioica recorded at lower values. Single grain of Cerealia-type (4.85 m). Charcoal increases at top of the zone.	OM ranges c.10% at 4.90 m to c.31% at top of LPAZ. Average c.29%
LC4a 5.01	4050–3960 cal. BC	4040–4010 cal. BC (25.8%) 4005–3975 cal. BC (42.4%)	Late Mesolithic	Ulmus values decrease at the start of zone (c.10–c.3%) and thereafter remain very low; a temporary reduction in Corylus (c.25%), followed by recovery (c.40%). NAP values increase to c.10%, consisting of Poaceae (c.6%) and other herbs recorded include Asteraceae, Caryophyllaceae and Plantago lanceolata. Pteropsida (monolete) indet. increases to 9% TLP+S. Charcoal remains low.	OM ranges c.30% to c.25% at top of LPAZ. Average c.27%
LC3 5.09	4320–4020 cal. BC	4225–4070 cal. BC	Late Mesolithic	Corylus recovers (c.40%), while Alnus increases steadily to a peak (c.25%), Quercus and Ulmus stable (20% and 10% respectively). The initiation of low but continuous Ilex curve is recorded at top of zone. NAP values remaining low. Slight if sporadic increases in charcoal.	OM ranges from c.29% to c.38%. Average c.34%
LC2 5.84	6245–5575 cal. BC	6120–5780 cal. BC	Early Mesolithic	Temporary reduction in both Corylus (c.30%) and Quercus (c.20%) corresponding with spikes in Betula (c.15%) and Pinus (c.20%), followed by recoveries in the former. Alnus increases abruptly at top of zone to c.15%. NAP remaining low (c.4%). Charcoal remaining very low.	OM ranges c.35% to c.33%. across LPAZ. Average c.34%
LC1 6.03	7615–6500 cal. BC	7320–6745 cal. BC	Early Mesolithic	Dominated by AP, high values of Corylus (c.50%) and Quercus (c.30%), Ulmus (c.8%), Pinus, and Betula present (2–4%). A continuous but low presence of Hedera helix (2%) and Salix (1%). NAP values very low, traces of Poaceae, Cyperaceae and Filipendula. Charcoal very low.	OM ranges from c.35% to c.40% across the LPAZ. Average c.37%

Figure 2.

Pollen percentage diagram from Lough Cullin.

Figure 3.

Selected taxa pollen concentration from Lough Cullin.

Loss on ignition (LoI), magnetic susceptibility (MS) and geochemistry

The results of loss on ignition are presented in Table 1 and, with the results of geochemistry and magnetic susceptibility analyses, shown in Figure 4. Zonation for LoI data follows the LPAZ used in the pollen diagram. LoI results are relatively stable throughout the sequence, with some generally minor fluctuations. However, there is a marked decrease in LoI values at 5.09 m, with a significant and more sudden decrease at 4.90 m, possibly indicating accelerated minerogenic sedimentation into the lake. LoI begins to increase at 3.14 m to a peak at 2.15 m, from where it decreases to the top of the core.

Figure 4.

Loss-on-ignition (LoI), geochemistry and magnetic susceptibility (MS) diagram from Lough Cullin.

The geochemical data, given the high resolution, is ‘noisy’ and must be interpreted with some caution. These data do not always track the changes in LoI, but there are observable patterns which may be hypothesised as reflecting weathering and erosion of different areas of the catchment: in particular, increased values for Calcium (Ca) may derive predominantly from the limestone bedrock areas (see above, Section 2), with Iron (Fe) from the sandstone areas. The latter element does not consistently track the MS curve, possibly because of the dissolution of magnetic minerals.

Chronology

Radiocarbon dating and Bayesian modelling

The measurement on the humic fraction GU43402 from 2.61 m failed, therefore the humin measurement (SUERC-72571) from this depth was used in the model. Four pairs of measurements from 2.65 m (SUERC-70823 and SUERC-70824), 2.71 m (SUERC-70825 and SUERC-70826), 3.26 m (SUERC-76326 and SUERC-76666) and 5.34 m (SUERC-70843 and SUERC-70844) are not statistically consistent (see Table 2). In all instances the humic fraction is younger than the humin fraction; this is likely caused by the downwards penetration of humic acids from above, therefore the humin fractions (SUERC-70824, SUERC-70826, SUERC-76666 and SUERC-70844) have been used in the modelling process for these depths. Measurement UBA-22422, a fragment of Salix (willow) twig, was identified as a possible outlier and has been excluded from the model; this determination was considerably older than those below it, suggesting that reworked material had been incorporated into the profile.

Table 2.

Radiocarbon dates for core LC (Lough Cullin). Radiocarbon dates were calibrated using the datasets published by Reimer et al. (2020) and the computer program OxCal 4.4 (Bronk Ramsey 2009).

Lab code	Dated material	¹⁴C Age (BP)	Depth (m)	¹³δC ‰
UBA-22422	Fragment of willow branch	2526 ± 32	1.78	−20.7
SUERC-70812	Organic sediment (humic fraction)	1141 ± 32	2.19	−29.8
SUERC-70813	Organic sediment (humin fraction)	1198 ± 29	2.19	−30.5
Statistically consistent measurements (T’ = 1.9; T’ (5%) = 3.8%; v = 1). Weighted mean 1170 ± 21
Beta-423349	Organic sediment (humin fraction)	1420 ± 30	2.29	−29.6
Beta-423350	Organic sediment (humic fraction)	1500 ± 30	2.29	−29.9
Statistically consistent measurements (T’ = 3.6; T’ (5%) = 3.8%; v = 1). Weighted mean 1460 ± 22
SUERC-70814	Organic sediment (humic fraction)	1661 ± 27	2.37	−29.6
SUERC-70815	Organic sediment (humin fraction)	1635 ± 29	2.37	−30.4
Statistically consistent measurements (T’ = 0.4; T’ (5%) = 3.8%; v = 1). Weighted mean 1622 ± 20
Beta-426773	Organic sediment (humin fraction)	1910 ± 30	2.45	−29.1
SUERC-70816	Organic sediment (humic fraction)	1959 ± 29	2.49	−29.4
SUERC-70817	Organic sediment (humin fraction)	1996 ± 29	2.49	−29.9
Statistically consistent measurements (T’ = 0.8; T’ (5%) = 3.8%; v = 1). Weighted mean 1978 ± 21
SUERC-70821	Organic sediment (humic fraction)	2003 ± 29	2.53	−29.2
SUERC-70822	Organic sediment (humin fraction)	2074 ± 29	2.53	−29.7
Statistically consistent measurements (T’ = 3.0; T’ (5%) = 3.8%; v = 1). Weighted mean 2039 ± 21
SUERC-72575	Organic sediment (humic fraction)	2114 ± 29	2.55	−29.4
SUERC-72576	Organic sediment (humin fraction)	2135 ± 29	2.55	−29.4
Statistically consistent measurements (T’ = 0.2; T’ (5%) = 3.8%; v = 1). Weighted mean 2125 ± 24
Beta-426774	Organic sediment (humin fraction)	2150 ± 30	2.60	−29.1
SUERC-72571	Organic sediment (humin fraction)	2181 ± 33	2.61	−29.9
GU43402	Organic sediment (humic fraction)	FAILED	2.61	–
SUERC-70823	Organic sediment (humic fraction)	2250 ± 29	2.65	−29.4
SUERC-70824	Organic sediment (humin fraction)	2336 ± 29	2.65	−30.1
Statistically inconsistent measurements (T’ = 4.397; T’ (5%) = 3.8%; v = 1).
SUERC-70825	Organic sediment (humic fraction)	2328 ± 29	2.71	−29.4
SUERC-70826	Organic sediment (humin fraction)	2436 ± 26	2.71	−29.8
Statistically inconsistent measurements (T’ = 7.7; T’ (5%) = 3.8%; v = 1)
UBA-22423	Organic sediment (humin fraction)	2413 ± 31	2.77	−25.0
SUERC-70827	Organic sediment (humic fraction)	2467 ± 29	2.81	−29.3
SUERC-70831	Organic sediment (humin fraction)	2506 ± 29	2.81	−29.6
Statistically consistent measurements (T’ = 1.0; T’ (5%) = 3.8%; v = 1). Weighted mean 2489 ± 20
SUERC-70832	Organic sediment (humic fraction)	2446 ± 27	2.915	−29.3
SUERC-70833	Organic sediment (humin fraction)	2514 ± 29	2.915	−29.9
Statistically consistent measurements (T’ = 3.0; T’ (5%) = 3.8%; v = 1). Weighted mean 2478 ± 20
Beta-426775	Organic sediment (humin fraction)	2620 ± 30	2.94	−29.1
Beta-426776	Organic sediment (humin fraction)	2750 ± 30	3.04	−28.9
SUERC-70834	Organic sediment (humic fraction)	2794 ± 26	3.08	−28.9
SUERC-70835	Organic sediment (humin fraction)	2821 ± 29	3.08	−29.7
Statistically consistent measurements (T’ = 0.5; T’ (5%) = 3.8%; v = 1). Weighted mean 2806 ± 20
Beta-423351	Organic sediment (humic fraction)	3050 ± 30	3.18	−28.8
Beta-423352	Organic sediment (humin fraction)	3020 ± 30	3.18	−30.2
Statistically consistent measurements (T’ = 0.5; T’ (5%) = 3.8%; v = 1). Weighted mean 3035 ± 22
SUERC-76326	Organic sediment (humic fraction)	3026 ± 24	3.26	−29.6
SUERC-76666	Organic sediment (humin fraction)	3132 ± 32	3.26	−29.8
Statistically inconsistent measurements (T’ = 7.0; T’ (5%) = 3.8%; v = 1)
SUERC-76327	Organic sediment (humic fraction),	3162 ± 24	3.34	−29.3
SUERC-76328	Organic sediment (humin fraction)	3168 ± 24	3.34	−28.5
Statistically consistent measurements (T’ = 0.0; T’ (5%) = 3.8%; v = 1). Weighted mean 3165 ± 17
SUERC-76329	Organic sediment (humic fraction)	3469 ± 24	3.56	−27.6
SUERC-76667	Organic sediment (humin fraction)	3473 ± 32	3.56	−29.9
Statistically consistent measurements (T’ = 0.0; T’ (5%) = 3.8%; v = 1). Weighted mean 3470 ± 20
UBA-22424	Organic sediment (humin fraction)	3800 ± 36	3.79	−28.2
SUERC-70836	Organic sediment (humic fraction)	4459 ± 29	4.31	−29.7
SUERC-70837	Organic sediment (humin fraction)	4520 ± 27	4.31	−30.1
Statistically consistent measurements (T’ = 2.4; T’(5%) = 3.8; v = 1). Weighted mean 4459 ± 29
UBA-22425	Organic sediment (humin fraction)	4710 ± 39	4.60
SUERC-70841	Organic sediment (humic fraction)	4755 ± 29	4.69	−29.3
SUERC-70842	Organic sediment (humin fraction)	4795 ± 26	4.69	−29.4
Statistically consistent measurements (T’ = 1.1; T’(5%) = 3.8; v = 1). Weighted mean 4777 ± 20
UBA-33721	Organic sediment (humin fraction)	5080 ± 56	4.87
UBA-33722	Organic sediment (humin fraction)	5076 ± 51	4.97
UBA-30917	Organic sediment (humin fraction)	5210 ± 34	5.01
SUERC-70843	Organic sediment (humic fraction)	5675 ± 27	5.34	−29.4
SUERC-70844	Organic sediment (humin fraction)	5788 ± 26	5.34	−30.0
Statistically inconsistent measurements (T’ = 9.1; T’(5%) = 3.8; v = 1).
UBA-22426	Organic sediment (humin fraction)	6154 ± 47	5.46
UBA-30918	Organic sediment (humin fraction)	7358 ± 37	5.91
UBA-22427	Organic sediment (humin fraction)	9057 ± 48	6.21

An age-depth model (Bronk Ramsey, 2008) for the profile was constructed to provide a chronology for the sequence. The P_Sequence model (Figure 5) has good agreement (A_model = 99) and has been used to provide estimates for the boundaries between the local pollen assemblage zones (Table 1). Except for UBA-22422 (the Salix twig) the model shows good agreement, suggesting the sequence is intact below 2.19 m.

Figure 5.

Bayesian age-model of the chronology of the sediment sequence at Lough Cullin (P_Sequence model (k = 0.01–100)) (Bronk Ramsey, 2008). Coloured band showing the estimated date of sediment at the corresponding depth at 95.4% probability.

The pollen sequence can be estimated to cover a period of 8830–9560 years (95.4% probability, distribution not shown), probably 9060–9330 years (68.2% probability, distribution not shown). Estimates derived from the age-depth model suggest an average deposition rate of 4–5 cm/100 year (distribution not shown) between the upper and basal radiocarbon measurements; it can be estimated that 21–23 years (distribution not shown) are represented in every centimetre.

The effectiveness of the model can be seen by considering the radiocarbon determination UBA-22423: this provided a calibrated (unmodelled) date of 750–400 cal. BC. The output on the model (Figure 5) constrained this to 595–445 cal. BC (Figure 6), a significant reduction in the bandwidth, from 350 to 150 years. This reduction was partly achieved through obtaining two determinations that fell on the ‘steep’ part of the radiocarbon calibration curve (SUERC-70824 and Beta-426775) thus helping to constrain the determinations between them, in particular those on the ‘Hallstatt plateau’.

Interpretation

LC-1: 6.25–6.03 m, 9050–8090 cal. BC to 7615–6500 cal. BC

The pollen diagram covers much of the Holocene from 9030–8065 cal. BC to cal. AD 780–1035, the Early Mesolithic to the Medieval period. Quercus (oak) and Ulmus (elm) are well established from the base of the sequence and constitute the main tall canopy trees in the landscape around Lough Cullin. Corylus avellana-type (probably largely hazel) is abundant, comprising a major component of the vegetation, probably as an under-storey shrub, while Betula (birch) and Salix (willow) had minor presences in the landscape. Low values for non-arboreal pollen (NAP), <5%, suggest the woodland had a rather closed structure. The presence of Hedera helix (ivy) and Polypodium vulgare (common polypody) probably indicate the presence of epiphytes (Molloy and O’Connell, 1991).

LC-2: 6.03–5.88 m, 7615–6500 cal. BC to 6245–5575 cal. BC

Zone LC-2 is marked by a decrease in hazel (c.50–30%) and oak (c.30–20%) and corresponding increases in Pinus sylvestris (Scots’ pine) (c.4–20%) and birch (c.4%–15%) between 5.97 and 5.93 m. Hazel falls to its lowest value for the zone at 5.89 m, corresponding to a peak in birch; whilst oak reaches its lowest percentage at 5.93 m, at which point pine demonstrates a clear peak, attaining its highest values for the entire sequence before falling again. There are also reductions in elm and ivy apparent across these levels. Total NAP values do not show any fluctuations, suggesting the vegetation changes involved the woodland canopy taxa. Total pollen concentrations display a marked reduction across these levels, from 232 × 10³ to 155 × 10³ grains cm⁻³, which may reflect fluctuations in relative pollen productivity.

In terms of geochemistry, this zone sees the highest values for Ti, Ca and Mn for the entire diagram, tracking increasing values for MS, although LoI percentages remain fairly steady (c.30%). This pattern may indicate a change in the source of inorganic material eroded from the catchment, with weathering of the soils on the limestone (Ca) as well as the sandstone bedrock (Fe) implied. These fluctuations are closely associated with the changes in woodland composition outlined above. Taken collectively, the data may well indicate the impact of climatic deterioration, with destabilised soils across the catchment associated with pronounced declines in thermophilous arboreal taxa (oak, hazel, elm and ivy), and related expansion in trees/shrubs (pine and birch) tolerant of colder conditions.

Towards the top of LC-2, Alnus glutinosa (alder) percentages begin to rise, implying the establishment of this tree, probably as alder carr at the lake edge. The date for the establishment of alder (5.89 m, 6350–5910 cal. BC, the ‘rational limit’, sensu Smith and Pilcher, 1973) appears to be slightly earlier than elsewhere across Ireland. This spread and expansion of alder post-7000 BP appears to have been erratic in space and time (Bennett and Birks, 1990): for example, alder became established after 5490–5010 cal. BC (6315 ± 110, D-115) at Belle Lake (Craig, 1978), after 5480–5070 cal. BC (6330 ± 80, Beta-65095) at Clara Bog (Connolly, 1999; Crushell et al., 2008), whilst at Lough Kinale (Ballywillin Crannog core) this tree expanded after 5720–5560 cal. BC (6720 ± 40, Beta-173320; Brown et al., 2005; Selby et al., 2005).

LC-3: 5.88–5.19 m, 6245–5575 cal. BC to 4320–4020 cal. BC

By the close of LC-2, oak and hazel recovered as the dominant woodland taxa. Arboreal taxa remain very well represented in LC-3 (minimum 95%) with few other marked changes. However, Ilex aquifolium (holly) is recorded from midway through the zone (5.30 m): this shrub tends to become established in more open conditions (Molloy and O’Connell, 1987), but there is no evidence of significant changes to the woodland structure that might suggest disturbance similar to the previous zone. Indicators of open environments such as Plantago lanceolata (ribwort plantain), are present only sporadically prior to the establishment of holly, but cease during the initial expansion of the latter. The low levels of NAP (<5%) suggest open environments were limited, although the extent of openness will have been greater than implied by the percentages.

The LoI values do not show any marked changes, falling slightly towards the top of the zone. The geochemical data show reductions for Ca and Mn, although there are increases in Mn midway through the zone. Fluctuating values for Fe with pronounced decreases at the top and base of the zone are apparent. These fluctuations are slightly enigmatic but might imply some destablisation of the local soils, albeit not on a similar scale to LC-2.

LC-4a: 5.90–5.01 m, 4320–4020 cal. BC to 4050–3960 cal. BC

Zone LC-4a is defined by a pronounced reduction in elm from 4220–to 3980 cal. BC, accompanied by a temporary fall in hazel, although other arboreal taxa remain steady. NAP increases (c.10%), primarily Poaceae (grass), but with sporadic grains of other herbs including ribwort plantain, Asteraceae (daisies) and Caryophyllaceae (pink family). There are decreases in LoI percentages across the zone coincident with increasing anthropogenic indicators, indicating increased mineral inwash into the lake and/or changes in accumulation rates associated with the reduction in woodland and expansion of open environments. This is supported by the rather abrupt fluctuations in Ti, Fe and Ca, indicating weathering and erosion in the lake catchment, again potentially involving soils on both the limestone and sandstone geologies.

LC-4b: 5.01–4.82 m, 4050–3960 cal. BC to 3860–3650 cal. BC and LC4c: 4.82–4.71 m, 3860–3650 cal. BC to 3685–3530 cal. BC

Further reductions in arboreal pollen (AP), c.80%, specifically oak and hazel are recorded from 4040–3910 cal. BC, with rises in NAP (c.20%) and a greater diversity of ruderal herbaceous taxa including ribwort plantain, Ranunculaceae (buttercups), Rumex (docks), daisies, Artemisia-type (mugwort) and Urtica dioica (nettles). This indicates the expansion of open, pastoral environments, at the expense of deciduous woodland, especially oak but with hazel affected to a lesser degree. The identification of Cerealia-type (cereal) grains at: 3890–3700 cal. BC, 3790–3580 cal. BC and 3760–3560 cal. BC demonstrate arable farming in the pollen catchment. The LoI percentages show an abrupt drop to their lowest values for the entire sequence (4.90 m) corresponding to a peak in total anthropogenic indicators, followed by an equally abrupt recovery, indicating inwash of minerogenic material. There are no clear corresponding changes in the geochemistry, other than some fluctuations in Ti, nor does the MS show any response.

This phase lasted until 3860–3650 cal. BC, at which point AP began to recover (LC-4c). However, although there are reductions in NAP across this subzone, anthropogenic indicators including ribwort plantain and cereal-type are still recorded. The impression is of clearance of woodland and some destabilisation of soils during LC-4b, followed by a less intense period of human activity with some recovery of trees and shrubs in LC-4c. The initial phase lasted for 70–320 years, and the subsequent phase 10–270 years, with the pollen data implying both pastoral and arable land-use.

LC-5: 4.71–4.35 m, 3685–3530 cal. BC to 3355–3120 cal. BC and LC-6; 4.38–4.08 m, 3355–3120 cal. BC to 2960–2525 cal. BC

The overall AP values increase, especially elm, and the ribwort plantain curve is interrupted, reflecting woodland recovery. Elm populations regenerated, although not to their previous extent, while Fraxinus (ash) played an increased role in the arboreal vegetation dynamics, presumably expanding into the gaps created in the woodland in LC-4. This recovery of elm and associated woodland regeneration was sustained until 3310–3090 cal. BC, when a second reduction in elm is apparent, primarily concomitant with increased representation of alder, a slight increase in ash and marginally increased levels of NAP, primarily in wet-loving taxa such as Cyperaceae (sedges) and Filipendula (meadowsweet). This suggests the expansion of wetland environments, probably in the form of alder carr at the lake’s edge, perhaps as processes of hydroseral succession created favourable habitats. The muted response in NAP aside from the wetland taxa, raises questions concerning the cause and process of the decline in elm (see below). LoI values are stable (c.36%) across LC-5 and LC-6 but decline towards the top of the latter zone (c.30%). Some fluctuations in Fe are recorded, possibly indicating changes in the source of the minerogenic input into the lake.

LC-7a: 4.08–3.90 m, 2960–2525 cal. BC to 2620–2240 cal. BC

A small but pronounced reduction in AP and re-establishment of a continuous curve for ribwort plantain and other light demanding ruderal/grassland taxa [including buttercups, daisies, mugwort, Lactuceae (dandelions etc.)] are apparent from 2960–2525 cal. BC, indicating an expansion of open, meadow environments. The woodland regeneration phase in the previous zones (LC-5 and 6) lasted 660–1120 years. The appearance of cereal-type pollen at 2860–2420 cal. BC suggests arable farming around Lough Cullin. After the latter date, NAP continues to increase at the expense of primarily hazel and oak. Charcoal shows a slight increase and loss on ignition values are generally stable (c.30–34%); MS values increase coincident with a spike in Fe at c.4 m, the highest values for anthropogenic indicators for this zone. These data collectively indicate catchment scale disturbance, related to the evidence for woodland reduction and the expansion of open environments.

LC-7b: 3.90–3.56 m, 2620–2240 to 1880–1740 cal. BC and LC-7c: 3.56–3.34 m, 1880–1740 to 1500–1410 cal. BC

Zone LC-7b is primarily defined on the basis of steadily increasing NAP, primarily grasses, with continuing low values of other herbs, suggesting open areas persisted but were of limited extent. Low values of microcharcoal are recorded, indicating restricted burning during this zone. This picture changes at the transition from LC-7b to LC-7c, around the Middle Bronze Age (1880–1740 cal. BC), with increases in ribwort plantain and the appearance of other anthropogenic indicators including dandelions and docks towards the close of the zone, reflecting an expansion in open, pastoral environments. However, percentages of arboreal pollen remain relatively steady, although there are fluctuations in hazel values. Charcoal values do not increase. The overall impression is of some expansion in open grassland environments, but only small decreases in woodland cover. The LoI values are largely stable, rising slightly across LC-7b (from c.30% to 40%) before falling slightly across LC-7c. There are no clear changes in the MS or geochemical data other than a rise in Ca, possibly indicating disturbance on the limestone areas.

LC-8: 3.34–3.14 m, 1500–1410 to 1275–1000 cal. BC

The opening of LC-8 marks the beginning of a period of intensive human impact on the environment, the most pronounced recorded for the entire sequence. This seems to follow a brief period of reduced impact at the opening of the zone with reduced total anthropogenic indicators and increases in hazel, followed by a very pronounced increase in NAP (c.45%), especially grasses, and associated decline in AP demonstrating a significant opening up of the woodland cover. The rising values for ribwort plantain (peaking c.7%) alongside grasses and to a lesser extent sedges, demonstrate the expansion of open, pastoral environments to form the greater proportion of the landscape around the lake. The occurrence of a single grain of cereal-type pollen at 3.20 m (1380–1220 cal. BC) indicates arable farming. There are also reductions in alder, suggesting the alder carr on the wetter soils, probably close to the lake edges, were affected by clearance at this time.

However, a relatively restricted range of herbs is recorded: Chenopodiaceae (fat fen family), buttercups and Succisa (devil’s bit scabious) appear alongside the peak of ribwort plantain, all of which are typical of open grassland/meadow environments. The concomitant increase in Pteridium aquilinum (bracken) across this zone is further evidence for the opening up of the landscape on drier soils, whilst a spike in charcoal demonstrates increased burning. The LoI percentages fall, generally tracking the increase in NAP, whilst in the geochemical data, Fe also shows pronounced peaks at the opening and close of the zone, coincident with small rises in Mn and Ti, and increases in the MS curves.

The combined data seem to indicate a short episode of reduced human activity and the recovery of shrubs, prior to intensive clearance and farming leading to soil disturbance across the catchment. Overall, the period between 1500–1410 and 1275–1000 cal. BC was one of woodland reduction. Most parts of the landscape were affected, from the fertile dryland soils through to the ‘marginal’ wetland contexts. There is evidence for farming, predominantly of a pastoral character, and since cultivation is significantly underrepresented palynologically, arable plots were also present locally.

LC-9: 3.14–2.925 m, 1275–1000 cal. BC to 815–685 cal. BC and LC-10: 2.925–2.82 m, 815–685 cal. BC to 690–535 cal. BC

The previous period of woodland clearance and farming was followed by the recovery of woodland taxa (50–60%), especially hazel, oak and alder, accompanied by reductions in grasses and ribwort plantain (LC-9).However, increased diversity in herbs is recorded, specifically the anthropogenic indicators fat hen family, nettles and dandelions. Micro-charcoal values also increase, whilst a single cereal grain coincides with the peak in ribwort plantain at 1020–915 cal. BC indicating the presence of arable and pastoral habitats.

However, the subsequent zone, LC-10, is notable for a marked fall in ribwort plantain and recovery of AP, especially hazel and oak, but with elm values also forming a low but consistent curve for much of the zone. Elm tends to thrive on fertile, better-drained soils that are often suitable for arable agriculture (as observed in the previous zones), implying that trees and shrubs re-colonised much of the landscape. The almost complete absence of microcharcoal also contributes to the impression of little anthropogenic activity, until the close of the zone. There is a small but sustained increase in LoI across the zone, with Fe values reduced relative to the previous zone, suggesting some stabilisation of the catchment soils related to the recovery of the woodland.

LC-11: 2.82–2.64 m, 690–535 cal. BC to 415–250 cal. BC and LC-12: 2.64–2.36 m, 415–250 cal. BC to 390–540 cal. AD

The landscape changed again at the opening of LC-11, with a fairly abrupt increase in ribwort plantain defining the zone transition, suggesting opening of the landscape. The response from other herbs, grasses included, is slightly muted, although levels of dandelions rise towards the close of the zone and there are occasional records of other grains such as mugwort, fat hen family, meadowsweet and buttercups. There is a steady reduction in hazel across the zone and oak also displays a fall, following a peak at the opening of the zone, contributing to falling AP from c.90% to 70% across the zone. Total anthropogenic indicators reach their highest percentage at the top of LC-11, at which point cereal-type pollen is recorded at 430–360 cal. BC. However, microcharcoal values show only modest increases. The record therefore indicates a resurgence in human activity, which led initially to an expansion in grassland and pasture and the clearance of areas of woodland, with evidence for arable cultivation towards the end of the zone.

Almost immediately following the peak in pastoral and arable farming, there is evidence for what can only be described, on the basis of the pollen record, as the apparent possibly complete cessation of human activity. This is manifested through an abrupt drop in ribwort plantain at the opening of LC-12, and the disappearance of this species for the entire zone. Grasses also display a slight reduction, whilst few other herbs are recorded. Microcharcoal values are minimal and absent from the middle section of the zone, closely parallelling the behaviour of total anthropogenic indicators. AP percentages increase, mainly hazel and oak, but with some recovery in elm and birch. Overall, from around 415–250 cal. BC to 390–540 cal. AD, woodland dominated the landscape around Lough Cullin.

LC-13: 2.36–2.15 m, cal. AD 390–540 to cal. AD 780–1035

The final zone, LC-13, opens with the relatively abrupt resumption of the ribwort plantain curve, a steady rise in grasses and reductions in hazel and subsequently oak. Elm effectively disappears from the record and microcharcoal values also increase. Other herbs reappear including docks, mugworts and daisies etc., all of which form continuous curves. Total anthropogenic indicators demonstrate a marked increase whilst cereal-type pollen is recorded in almost all levels, indicating a significant expansion and persistence of arable cultivation in the pollen source area. Despite this, the maintenance of AP (c.80%) until the close of the diagram, suggests sizable areas of woodland remained locally. The diagram closes at cal. AD 780–1035 with an indication of renewed falls in arboreal taxa suggesting further anthropogenic pressure on the woodland. There is a hint that by this time, clearance of woodland was starting to impact all parts of the landscape again, with alder falling to its lowest values since LPAZ LC-2. The LoI values increase across the zone, with the rising values for Fe that began in LC-12 also continuing.

Discussion

Overview

The Lough Cullin sequence provides a record of vegetation change from the Early Mesolithic (9050–8090 cal. BC) through to the Medieval period (cal. AD 780–1035), a period of 10020–9025 years. A series of phases of expansions and contractions of AP and NAP are apparent: with one exception (see below), these appear to reflect human disturbance, characterised by increases in taxa indicative of open, pastoral environments and disturbed soils (especially ribwort plantain, grasses, docks, dandelions and occasional grains of cereal pollen suggesting arable agriculture) and falls in values of tree/shrub pollen showing contraction in wood/scrubland.

It should be noted total tree and shrub pollen percentages rarely drop below 75% of total land pollen for the entire record, implying that although herbaceous taxa are probably underrepresented palynologically (Caseldine and Fyfe, 2006), wood/scrub cover remained of greater extent than open ground, even during episodes of human impact and woodland clearance (see below). Episodes of intensified human activity seem to have impacted most on the populations of hazel and oak, with elm affected at some points, especially at the start of the Neolithic (4040–3900 cal. BC). The behaviour of Fraxinus (ash) suggests this fast growing and light demanding tree was favoured by the opening up of the woodland canopy during episodes of increased human activity (Caseldine and Hatton, 1996).

The values for microcharcoal, an indicator of the frequency of burning in the landscape around the site (probably mainly from domestic fires, but potentially from natural burns), closely track these phases, with increased values associated with rises in pollen taxa indicating human activity. Microcharcoal falls noticeably during episodes of woodland recovery. The fluctuations in the LoI, MS and geochemical data provide additional information concerning the patterns of inwash and provenance of inorganic material into the Lough during the episodes of landscape disturbance. On the basis of these data, the most pronounced episodes of weathering at the catchment scale by far occurred during LC2, 4a, 7a and 7c, with the first presenting the clearest signal for the entire record.

The 8.2 ka event: Climatic forcing and vegetation change (LC-2)

The earlier Holocene landscape was dominated by deciduous woodland, consisting predominantly of hazel, oak and elm, with some birch and willow probably growing on the damper soils. Scots’ pine was probably growing locally, despite the possibility of long-distance transport of this species’ pollen (Pilcher et al., 1995, cf. Lageard et al., 1999). This limited representation is comparable with records from the east and midlands (e.g. Caseldine and Hatton, 1996; Selby et al., 2005), although Scots’ pine had become established locally at Kelly’s Lough, Co. Wicklow (Leira et al., 2007) by 7450–7070 cal. BC (8220 ± 50 BP, ß-173463).

The abrupt reduction in hazel and oak in LC-2 indicates significant changes in this woodland composition, also reflected by a pronounced fall in pollen concentrations. Hazel pollen production can be adversely affected by climatic shifts such as air frosts, drought or excessive precipitation levels (Tallantire, 2002), while oak is also sensitive to early spring and autumn frosts (Giesecke et al., 2008). On the other hand, pine and birch are tolerant of low summer temperatures and can be rapid colonisers, given suitable conditions (Atkinson, 1992; Paus, 2010; Richardson and Rundel, 1998). The expansion of pine and birch alongside the small increases in NAP, and the fluctuations in the geochemical, LoI and MS data, can be interpreted as the impact of climatic deterioration, possibly a shift to a more continental climate, with colder winters but also lower summer temperatures and a considerably lower annual thermal sum (cf. Huntley, 2012).

The date range at Lough Cullin (7120–6230 cal. BC to 6350–5910 cal. BC) correlates with climate anomalies in the Greenland ice-core records (Rasmussen et al., 2007; Thomas et al., 2007) between 8.5 and 7.9 kyr BP (Rohling and Pälike, 2005). This climatic deterioration might have resulted from changes in the strength of the Atlantic meridional overturning circulation (cf. Alley and Ágústsdóttir, 2005; Alley et al., 1997; Ellison et al., 2006; Hede et al., 2010), leading to colder and drier conditions in the North Atlantic region (Alley and Ágústsdóttir, 2005; Alley et al., 1997; Barber et al., 1999; Wiersma and Renssen, 2006). The clear palaeoenvironmental signature at Lough Cullin provides persuasive evidence for the impact of this climatic ‘event’ on the eastern as well as western seaboards of Ireland, with the chronology of the increase in Scots’ pine overlapping with dendrochronological evidence for expansion in this tree after 6250 BC (Torbenson et al., 2015).

Similar reductions in thermophilus taxa coincident with increases in cool-tolerant trees are exhibited in other Irish pollen records: Cooney Lough, County Sligo showed a marked reduction in pollen from hazel and oak, synchronous with expansion of pine and birch (Ghilardi and O’Connell, 2013a). Fluctuations in the frequency of juniper at An Loch Mór, Inis Oírr (Molloy and O’Connell, 2004) and increased representations of pine at the expense of hazel are recorded during a period of erosion at Lough Maumeen, Connemara (Huang, 2002).

The ‘Elm Decline’: Neolithic woodland clearance and agriculture

Mesolithic impacts on the environment have been identified in pollen records from the UK and Ireland (e.g. Simmons and Innes, 1996; Smith, 1970; Warren, 2020; Warren et al., 2014), but there is little evidence for such ‘disturbance events’ in the Lough Cullin record, although the archaeological record indicates Mesolithic activity (Gleeson and Breen, 2006a, 2006b; Russell, 2010; Wren, 2006a, 2006b). A continuous ribwort plantain curve and increased values for NAP (especially ruderal taxa) are evident from the Early Neolithic around 4040–3900 cal. BC, and some 10–260 years after the initial decline in elm at 4220–3980 cal. BC. This may indicate the ‘elm decline’ was unrelated to human activity, although rising values for grass and trace values for anthropogenic indicators are coeval with reductions in this tree. However, this might equally reflect open environments resulting from the mortality of elm trees due to disease (Caseldine and Fyfe, 2006). The fluctuations in the geochemical data, LoI and MS are distinct, if not as pronounced as in LC-2, indicating the decline in elm was coeval with disturbance to local soils and inwash of minerogenic matter into the Lough. Other Irish records (Ghilardi and O’Connell, 2013b; Kearney and Gearey, 2020; McClatchie and Potito, 2020; Molloy et al., 2014; O’Connell and Molloy, 2001), also indicate a ‘gap’ between the ‘Elm Decline’ and clear palynological evidence for human disturbance. Overall, this may refute an anthropogenic cause for the reduction in elm, although the chronological disparity could also reflect increased stimulation of arboreal pollen production resulting from openings to the woodland canopy (cf. Aaby, 1986).

The Early Neolithic (LC-4a) is marked by the continuous presence of ribwort plantain from 4040–3900 cal. BC until 3720–3540 cal. BC, a duration of 220–450 years. During this period, there was a substantial opening up of the woodland and expansion in open habitats, presumably relatively close to the lake, although this is considerably earlier than the estimated date (3720–3680 cal. BC) for the Neolithic ‘house horizon’ and the first cereal cultivation in Ireland (Cooney et al., 2011; McClatchie et al., 2014; McLaughlin et al., 2016; McSparron, 2008; Whitehouse et al., 2014). Overall, the impact of Early Neolithic agriculture in Irish pollen records is rather variable (Connolly, 1999; Crushell et al., 2008; O’Carroll, 2012), perhaps reflecting the fact that Early Neolithic agriculture was spatially heterogeneous (Whitehouse et al., 2014) with varying levels of intensity, and the relative proximity of activity to sampling sites would further attenuate the signal.

Cereal-type pollen is recorded at 3900–3700 cal. BC, an estimated 50–290 years after the start of clearance and again from 3790 to 3580 cal. BC. Palynological evidence from Newrath, south of Lough Cullin (Timpany, 2009) also strongly suggests Neolithic arable agriculture at this time. The most reliable evidence is the presence of charred cereal grain in Neolithic archaeological contexts (e.g. Hughes, 2006; McKinstry, 2010; Monteith, 2009, 2011). The chronological model estimates farming continued for 220–450 years, implying Early Neolithic farmers did not engage in shifting cultivation contra Iversen’s (1941) Landnam model, but rather longer-term, fixed-plot agriculture (McClatchie and Potito, 2020; Whitehouse et al., 2014).

This phase of agriculture was followed by woodland regeneration and a decline in anthropogenic indicators from 3720–3540 cal. BC. A similar pattern of re-afforestation is implied during the Middle Neolithic in other parts of Ireland (e.g. Chique et al., 2017; Ghilardi and O’Connell, 2013b; Molloy et al., 2014; Stolze and Monecke, 2021). It has been suggested the Middle Neolithic saw a reduction in human activity overall (Whitehouse et al., 2014), rather than a shift in location, as reflected by the archaeological record: the number of confirmed Middle Neolithic archaeological sites in the region is substantially lower than in the preceding Early Neolithic, also in keeping with the archaeological evidence from across Ireland. This has also been linked to climatic change, dubbed the ‘5.2 ka event’ (Roland et al., 2015), although the precise nature and timing of this remains unclear (Plunkett et al., 2020).

Evidence for sustained human activity is subsequently absent until 2960–2525 cal. BC, a period of woodland regeneration of estimated 660–1120 years, followed by a renewal of arable and pastoral activity. The reappearance of agricultural activity during the Late Neolithic is indicated in other pollen records (Molloy and O’Connell, 2004; Molloy et al., 2014; Stolze and Monecke, 2021) whilst the archaeological record also suggests a limited Late Neolithic presence in south-east Ireland (Monteith, 2011; Tierney, 2005; Wren, 2006b).

The reduction in Scot’s pine from 2620 to 2240 cal BC, probably coincides with the beginnings of the ‘Pine Decline’ in the region. The decline of Scot’s pine has been well documented across much of Ireland, northern Scotland and England (e.g. Bennett, 1984; Bridge et al., 1990; Gear and Huntley, 1991; Lageard et al., 1999; Mighall et al., 2004; Pilcher et al., 1995), although recent studies have suggested the persistence of the taxa in certain regions (McGeever and Mitchell, 2016; Sassoon et al., 2021). Numerous competing hypotheses have been proposed for the cause of this reduction, from climate (Bradshaw and Browne, 1987; Mighall et al., 2004) to anthropogenic activity (Tipping et al., 2008), however Lough Cullin provides no conclusive evidence for the cause of this at the site.

Human activity from The Bronze Age to early Medieval period

Relatively low levels of human activity are indicated during the Late Neolithic (LC-7a) through to the Chalcolithic/Early Bronze Age (LC-7b), followed by resurgence into the Middle Bronze Age (LC-7c), peaking in the Middle to Late Bronze Age (from 1500–1410 cal. BC to 1275–1000 cal. BC). Excursions in the geochemical data, especially Ca during LC-7c, followed by increases in Fe and associated peaks in MS towards the top of LC-8, support the picture that the Middle Bronze Age saw significant scrub/woodland clearance, farming and associated destabilisation of soils. Following this, human activity then seems to have decreased in two ‘steps’: an initial reduction, which may be described as a contraction, during the Late Bronze Age from 1275–1000 cal. BC to 815–685 cal. BC (LC-9) followed by a pronounced ‘collapse’ from 815–685 cal. BC until 690–535 cal. BC (LC-10), the Bronze Age to Iron Age transition. Human impact on the landscape seems to have almost completely ceased, quite abruptly in this latter period.

This pattern is parallelled by the changes in archaeological site distributions across this entire period (cf. Armit et al., 2013; Becker et al., 2017); extensive landscape utilisation until the beginning of the Hallstatt plateau, followed by a marked contraction. This characteristic pattern can also be traced in the archaeology in the southeast (Eogan et al., 2015). Comparison with data from recently published Irish pollen records indicates a broadly coherent pattern during the Early to Middle Bronze Age of consistent and increasing woodland clearance and agriculture, followed by fluctuating human activity during the Late Bronze Age (Chique et al., 2017; Spencer et al., 2020; Stolze and Monecke, 2021). Plunkett (2009) has previously drawn attention to a similar pattern, suggesting a link between increased archaeological visibility during the Late Bronze Age and palynological evidence for intensified pastoral activity, and indicating that the end of this period may have been characterised by consolidation of settlement and agriculture.

Climate change and human activity during later prehistory

It has long been suggested there is an apparent coincidence between the ‘end’ of the Bronze Age (c. 1150–800/600 cal. BC) and evidence for climatic deterioration (wetter/colder conditions) across northwest Europe; the period known as the ‘Sub-Boreal to Sub-Atlantic transition’ or the ‘2.8 Ka event’ (see Gearey et al., 2020 for a recent review). Some scholars have suggested a direct causal link, with the onset of wetter/colder conditions, impacting directly on Bronze Age settlement and agriculture. However, Armit et al. (2014) have presented combined palaeodemographic (Armit et al., 2013) and hydroclimatic data (peatland Bog Surface Wetness/BSW records; Swindles et al., 2013) from Ireland, arguing a ‘peak’ in human activity c.1050–900 BC, was followed by a reduction to c.800 BC and a rapid ‘collapse’ to c.750 BC. The combined BSW data indicate climatic deterioration c.750–550 BC, which may suggest that this ‘event’ can be causally ‘disconnected’ from the ‘end’ of the Bronze Age, at least as indicated by the proxy demographic data.

There are few comparative palaeotemperature datasets for this period; although a recent chironomid-based reconstruction (expressed as mean July air temperature, referred to as Chironomid-inferred temperatures: C-ITs) is available from Lough Meenachrinna, Co. Donegal (Taylor et al., 2018). These data indicate C-ITs of 11.5℃ during the Early Bronze Age (c.1390 BC), rising into the Middle Bronze Age (c.1310–1100 BC) to peak at 13.5℃ (c.1260 BC), then falling to c.12℃ at the beginning of the Late Bronze Age (c.1150–960 BC). Slight increases in C-ITs to 12.8°C are recorded from the end of the Bronze Age into the Iron Age (c.920–620 BC), later dropping to 11.4℃ (c.660–480 BC). The range of palaeotemperature fluctuations in this record are relatively small and their potential significance for human activity hard to assess (K. Taylor, personal communication).

However, ‘events’ in the Lough Cullin pollen record can be described as chronologically ‘imbricated’ with the palaeoclimatic ‘events’: a clear peak in human activity during the Middle Bronze Age, followed by contraction or consolidation during the Late Bronze Age and a pronounced fall into the Iron Age. The initial reduction (LC-9) also overlaps with the beginning of the palaeodemographic drop (Armit et al., 2014) and the subsequent ‘collapse’ (LC-10) with the postulated climatic deterioration in the BSW records (see also Plunkett et al., 2020 who point to a gap in germination in the bog oak record between 751–713 BC and 709–668 BC). Correlations are hampered by the variable chronological precision of the different records; even with the improved chronological precision of the Cullin record, the ranges for the palynological ‘events’ are still ‘smeared’ over several centuries. Nevertheless, the chronological correspondence between the postulated climatic downturn (c.750 BC) in the BSW records and the contraction of human activity during the Bronze Age-Iron Age transition (690–535 cal. BC) at Lough Cullin can be noted; at the very least leaving open the possibility of a link between the two. Further analysis is also hampered by a general lack of detailed knowledge of the precise nature or severity of climatic changes, and an associated lack of clarity concerning pattern and process of social-cultural changes from Bronze to Iron Age (see Coyle-McClung and Plunkett, 2020; Gearey et al., 2020 for further discussion).

Whatever the cause/s of the decline in anthropogenic activity during the transitional period between Bronze and Iron Ages, two ‘steps’ can be defined: a rapid recovery following the previous ‘collapse’ and marked expansion in woodland clearance and farming very soon afterwards, between 690–535 cal. BC and 415–250 cal. BC (LC-11). This was followed by another phase of woodland recovery from the latter date until 390–540 cal. AD (LC-12). A marked period of woodland regeneration is a feature of many Irish pollen records during later prehistory, sometimes referred to as the ‘Late Iron Age Lull’ (Mitchell and Ryan, 1997) although the reduction in activity dates to the Developed Iron Age at Lough Cullin. The timing of woodland regeneration and reduced human activity generally varies between records, from the final centuries BC to the early centuries AD (Chique et al., 2017). In some locations, human activity continued, albeit at fairly low levels, across the Late Iron Age (e.g. Ghilardi and O’Connell, 2013b). There are indications of drier/warmer conditions in Ireland from c.300 BC to 400 AD (Coyle-McClung and Plunkett, 2020), corresponding broadly with the woodland regeneration phase (LC-11) in the Cullin record.

Figure 6.

Unmodelled (light grey) and modelled (dark grey) dates across the ‘Hallstatt’ plateau. Modelled dates are derived from the Bayesian age-model shown in Figure 5.

At Lough Cullin, human activity seems to have ceased almost completely until cal. AD 390–540, when there was a relatively abrupt resumption of the ribwort plantain curve, a steady rise in grass and reductions in hazel and oak (LC-13). Anthropogenic indicators demonstrate a marked increase and cereal pollen is recorded in almost all the samples across the zone, indicating a significant expansion of arable cultivation locally. In comparison to the sporadic record of cereal pollen from the rest of the sequence, the Early Medieval period saw the most extensive period of arable cultivation in the Lough pollen catchment. A steady rise in Fe and Ca towards the close of the zone, a peak in MS track rising NAP; the increasing LoI values are contrary to the evidence for increased mineral input, but may reflect increased eutrophication of the lake due to the input of organic material from intensified arable and pastoral farming; the record terminates at cal. AD 780–1035 with increasing anthropogenic indicators and NAP and associated reductions in AP.

Conclusions

The Lough Cullin sequence provides a nuanced and detailed multi-proxy (pollen, loss-on-ignition, geochemistry and magnetic susceptibility) reconstruction of Holocene environmental and landscape change from 9050–8090 cal. BC to 780–1035 cal. AD, the Mesolithic to the Early Medieval Period; the provision of a high resolution radiocarbon chronology has allowed a comparatively high level of chronological precision for the later prehistoric period in particular, using Bayesian approaches permitting formal, robust estimates of the timing and duration of particular events, avoiding potentially misleading precision resulting from other approaches to age-depth modelling of palaeoenvironmental records. The data provide clear evidence for the impact of the ‘8.2 Kyr’ BP climate event on the environment of the southeastern seaboard of Ireland. Certainly, on the basis of the geochemistry and magnetic susceptibility datasets, the ‘signature’ of the 8.2 ‘event’ is very pronounced, which is interpreted as reflecting the impact of this colder/drier period across the entire catchment. Later alleged prehistoric climatic ‘events’ are largely obscured or overlain by human impact, reflecting woodland clearance, settlement and agriculture which began during the Early Neolithic, slackened during the Middle Neolithic before intensifying in the Middle-Late Bronze Age. The compilation of archaeological data has allowed a qualitative comparison of the palaeoenvironmental record with spatially delimited evidence of human activity and taking account of the uncertainties associated with the interpretation of both records, broad correspondence in terms of implied intensities of human activity are indicated. A steady ‘demise’ of human activity during the Late Bronze Age-Iron Age is apparent, although there is no clear evidence to illuminate the cause/s of this, there is chronological correspondence with alleged national climatic deterioration around the mid-8th century BC. There is also unambiguous evidence for a reduction in human activity during the Iron Age until the Early Medieval period, providing further indication of the spatial and chronological variability of settlement and agriculture in Ireland across these periods. Despite ongoing archaeological and palaeoenvironmental investigation of the later prehistoric period in particular, uncertainties concerning data interpretation and variations in the chronological resolution, precision and robustness of different proxy climate records, hamper the formulation of mechanistic models linking environmental and cultural processes. The development of new methods and the generation of further, high resolution palaeoenvironmental records are one key to future progress, but this must include further research into archaeological data on regionally specific scales.

Footnotes

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: The authors would like to acknowledge funding from the Irish Research Council, under the Government of Ireland Postgraduate Scholarship Scheme, the Heritage Council and Transport Infrastructure Ireland (TII) for the project ‘Seeing beyond the site: Settlement and landscapes in Later Prehistoric Ireland’ (AR04557/AR006241) under the INSTAR (Irish National Strategic Archaeological Research).

ORCID iDs

Kevin Kearney

Susan Hegarty

Carla Ferreira

Meriel McClatchie

Ian Armit

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