Woodland Decline Research Articles

From the Holocene to the Anthropocene: A historical framework for land cover change in southwestern South America in the past 15,000 years

The main forest transitions that took place in south-central Chile from the end of the last glaciation to the present are reviewed here with the aim of identifying the main climatic and socio-economic drivers of land cover change. The first great transition, driven primarily by global warming, is the postglacial expansion of forests, with human populations from about 15,000 cal. yr. BP, restricted to coastlines and river basins and localized impact of forest fire. Charcoal evidence of fire increased in south-central Chile and in global records from about 12,000 to 6000 cal. yr. BP, which could be attributed at least partly to people. The subsequent expansion of agriculture led to much clearing of forests and the spread of weeds and other indicators of open habitats. The Spanish colonial period in America may have been followed by a transient expansion of forest cover into abandoned land, as indigenous population declined rapidly due to disease and slaughter. The 18th and 19th centuries brought about extensive loss of forests due to the massive impact of lumber extraction for mining operations both in central Chile and in western North America. Two centuries of intensive deforestation, coupled to grazing by cattle and extremely variable rainfall had long-lasting effects on forest cover in south-central Chile, which persist until today. The transition from a preindustrial to an industrial society brought about the “golden age” of timber harvest, assisted by mobile sawmills and railway transportation since the late 1800s. These advances led to the exhaustion of native commercial timber by the late 20th century in south-central Chile. In North America, harvestable stands were exhausted in New England and the Midwest around 1920. Settlement of the independent territories in the late 1800s and early 1900s implied vast burning and clearing of land and mounting soil erosion. Industrial forestry, based on government-subsidized massive plantations of short-rotation exotic trees, developed in the late 20th century, in connection with postindustrial displacement of exploitative activities from developed to third-world nations. In the last two decades, economic globalization and free trade promoted the expansion of new crops and further decline of woodlands, despite modest increases in forest cover. These patterns are repeated in many Latin American countries. To prevent further depletion of native forest resources and to provide an insurance against climate change, in the 21st century developing nations should aim at: (1) relocating subsidies from fiber farms to restoring diverse forest cover, (2) promoting ecosystem management of diverse forest and crops within landscapes, and (3) fostering diverse cultural relationships between people and their land.

Charcoal and fossil wood from palaeosols, sediments and artificial structures indicating Late Holocene woodland decline in southern Tibet (China)

Charcoal and fossil wood taken from palaeosols, sediments and artificial structures were analysed in order to evaluate the regional pedoanthracological potential and to obtain information on Holocene environmental changes, particularly on possible past tree occurrences in southern Tibet. This research was initiated by the question to what extent this area is influenced by past human impact. Even recent evaluations have perceived the present treeless desertic environment of southern Tibet as natural, and the previous Holocene palaeoenvironmental changes detected were predominantly interpreted to be climate-determined. The material analysed – comprising a total of 53 botanical spectra and 55 radiocarbon datings from 46 sampling sites (c. 3500–4700 m a.s.l.) – represents the largest systematically obtained data set of charcoal available from Tibet so far. 27 taxa were determined comprising trees, (dwarf-) shrubs and herbs as well as grasses. The predominant tree taxa were Juniperus, Hippophae, Salix and Betula. According to their present-day occurrence in the region, the genera Juniperus and Hippophae can be explicitly attributed to tree species. Further, less frequently detected tree taxa were Populus, Pinus, Quercus, Taxus and Pseudotsuga. Charcoal of Juniperus mainly occurred on southern exposures, whereas Betula was associated with northern exposures. In contrast, the (partly) phreatophytic taxa Hippophae and Salix showed no prevalent orientation. The distribution of radiocarbon ages on charcoal revealed a discontinuous record of burning events cumulating in the Late Holocene (c. 5700–0 cal BP). For southern Tibet, these results indicated a Late Holocene vegetation change from woodlands to the present desertic pastures. As agrarian economies in southern and south-eastern Tibet date back to c. 3700 and 5700 cal BP, respectively, and the present-day climate is suitable for tree growth up to c. 4600 m a.s.l., we concluded that the Late Holocene loss or thinning out of woodlands had been primarily caused by humans.

Long-term and millennial-scale climate variability in northwestern France during the last 8850 years

Vegetation and quantitative climate reconstructions from a northwestern France shelf core (VK03-58Bis) show orbital and suborbital climate variability for the last 8850 years in this region. A long-term cooling trend in summer temperatures, marked by gradual temperate and humid forest decline, parallels cooling in Greenland and the decrease of mid-latitude summer insolation reduction until at least 2000 cal. yr BP. At the long-term scale, the lowering in seasonal contrast revealed by vegetation changes follows the increase of precession. Corylus woodlands spread at the expense of deciduous Quercus forest, between 8740 and 8390 cal. yr BP, linked with the high seasonality conditions that, counterbalancing the long-term astronomical forcing trend, were amplified by the north Atlantic high-latitudes winter sea-ice expansion. High seasonality conditions resulted from the Agassiz and Ojibway final outburst episodes and consequent gradual reduction of the Meridional Overturning Circulation (MOC). Between 8390—8060 cal. yr BP, a sudden Corylus woodland decline marks the 8.2 kyr cold event in northwestern France probably triggered by the severe MOC reduction leading to the additional drop in winter temperature over Europe and Greenland. Nonetheless, seasonality remains high during this interval. The high seasonality conditions detected in `VK03-58Bis' between 8740 and 8060 cal. yr BP reflects the multicentennial-scale climate cooling 8.6—8.0 kyr episode of the North Atlantic. Following the Agassiz and Ojibway final outburst episodes, climate became more stable. However, millennial-scale climate cooling episodes are recorded in `VK03-Bis' and are characterized by weak winter cooling and increases in precipitation. Furthermore, dinocyst analysis and benthic gastropod Turritella communis occurrences indicate regional changes such as the southward migration of the Boreal biogeographical zone between 8740 and 8480 cal. yr BP and the subsequent opening of the English Channel at around 8480—8390 cal. yr BP.

THE ETHNOBOTANICAL HISTORY AND HOLOCENE EXTENT OF YEW (TAXUS BACCATA L.) ON THE IRISH LANDSCAPE

The European yew tree (Taxus baccata L.) has been utilized by humans for tens of thousands of years. The Irish saw the yew as a symbol of life and death, used the wood for religious implements, symbolized it in their alphabet, formed laws and stringent fines for harming the trees, and integrated its cultural significance into their lyric prose. There is contradiction in forest history literature as to the extent of this tree on the Holocene landscape, but toponymy, the ancient texts and pollen analysis suggest that yew was historically abundant. Pollen data suggest not only that the tree was abundant in Ireland, but also that it increased during a time of regional woodland decline. The tree became relatively rare on the natural landscape within the last 800 years and religious reverence has waned, but a revived interest in Celtic spirituality and movements by Heritage Council Ireland could serve to prevent further decline.

The Ethnobotanical History and Holocene Extent of Yew (Taxus Baccata L.) on the Irish Landscape

The European yew tree ( Taxus baccata L.) has been utilized by humans for tens of thousands of years. The Irish saw the yew as a symbol of life and death, used the wood for religious implements, symbolized it in their alphabet, formed laws and stringent fines for harming the trees, and integrated its cultural significance into their lyric prose. There is contradiction in forest history literature as to the extent of this tree on the Holocene landscape, but toponymy, the ancient texts and pollen analysis suggest that yew was historically abundant. Pollen data suggest not only that the tree was abundant in Ireland, but also that it increased during a time of regional woodland decline. The tree became relatively rare on the natural landscape within the last 800 years and religious reverence has waned, but a revived interest in Celtic spirituality and movements by Heritage Council Ireland could serve to prevent further decline.

Evolution and origin of the Central Grassland of North America: climate, fire, and mammalian grazers1

Grasslands are a widespread vegetation type that once comprised 42% of the plant cover on earth's surface. Features commonly shared among grasslands are climates with periodic droughts, landscapes that are level to gently rolling, high abundances of grazing animals, and frequent fires. World-wide expansion of grasslands occurred 8 to 6 MaBP and was associated with increasing abundance of grasses using the C4 photosynthetic pathway, a decline in woodlands, and coevolution of mammals adapted to grazing and open habitats. Beginning with Transeau's seminal paper on the prairie peninsula in 1935, North American ecologists debated the relative importance of fire and climate in determining the distribution of grasslands. In the 1960's, a major research interest was the response of prairies to fire, especially the productivity of burned and unburned grasslands. Understanding mechanisms for increased productivity on burned prairies began in the late 1960's and continued into the middle 1980's. During the past 20 to 25 years, grassland research has focused on the coevolution of grasses and mammalian grazers and fire-grazing interactions that affect habitat heterogeneity and diversity across trophic levels. While this paper does not follow a chronological development of our understanding of grasslands, all of these major research interests are considered.

Interpretation of charcoal and pollen data relating to a late Iron Age ritual site in eastern Ireland: a holistic approach

The study of charcoal produced by five burning episodes that occurred in a rapid succession within a ritual pit dating to the late Iron Age at Raffin Fort, Co. Meath, Ireland, reveals considerable variation in the charcoal assemblages resulting from each burning episode. Wood selection processes are considered against the background of information on woodland composition and land-use history provided by a detailed pollen diagram from nearby Emlagh Bog, the chronology of which is based on both AMS 14C dates and tephra analysis. A human skull fragment lay on top of the charcoal layers but the radiocarbon evidence indicates that the skull predated the burnings by at least a century. This and other evidence indicate a ritual pit with the skull as a human relic. It is suggested that, in this instance, wood selection was neither random nor determined solely by availability or combustibility, but instead may have been informed by socio-religious belief systems pertaining to trees and wood. Early Irish documentary sources, which reveal a complex ethnography of wood and trees in later prehistoric and early historic Ireland, are reviewed. The results shed fresh light on aspects of late Iron Age archaeology in a part of Europe that was outside the direct influence of the Roman world. New information is provided on a distinctive feature in late Holocene Irish pollen records namely the Late Iron Age Lull (ca. a.d. 1–500). During this time, widespread regeneration of woody vegetation took place. In the subsequent early Medieval period renewed farming activity resulted in substantial decline in woodland, a pattern also seen at many other locations in Ireland.

Random and systematic land-cover transitions in northern Ghana

Abstract The objective of this paper is to detect the dominant landscape changes in a 5400 km 2 area in northern Ghana. An in-depth analysis of the conventional transition matrix was used to separate landscape transformations to random and systematic transitions. A landscape transition is random if a land-cover category gains from other categories in proportion to the availability of those other losing categories, or if a category loses to other categories in proportion to the size of those other gaining categories. Any large deviation from those proportions is referred to as systematic transition. The highest systematic transition involved the conversion of about 12% of landscape from grassland to cropland. Other systematic landscape transitions included degradation of closed woodland to open woodland (11% of landscape), gain in biomass from open woodland to closed woodland (8% of landscape), and the degradation of open woodland to grassland (6% of landscape). The vulnerability of grassland to transition to cropland probably reflects the ease of clearing grassland compared to other natural vegetation. Cropland systematically avoided gaining from woodland and woodland systematically avoided losing to cropland, suggesting that woodcutting for charcoal and firewood collection is the major proximate cause of decline in woodland. Most of the random landscape transitions occurred in areas affected by spontaneous occupation by migrants, peri-urban cropland expansion as a result of displacement of farmers, and the resettlement of households along the White Volta River after the eradication of water-borne diseases. It is essential to combine systematic and random landscape change analyses for improved understanding of the processes of land use change. This will help in linking patterns to processes and in designing policy interventions aimed at reducing the unfavorable effects of dramatic land change.

Lateglacial and Holocene vegetation history at Nisi Fen and the Boras mountains, northern Greece

New pollen data from three contrasting sites in northern Greece allow an analysis of spatial and temporal patterns of vegetation change during the Holocene and Lateglacial in northern Greece. At the principal site, Nisi Fen, six cores from the thickest surficial peat deposits have yielded a detailed, composite, AMS 14C-dated pollen record covering the period from 20000 cal. BP almost to the present-day. Cores Kp-4 and Bor-3 were taken from small mires at high elevations in the Boras mountains, a few kilometres to the north of Nisi, in which peat has been accumulating since the mid-Holocene. Our results show that only Pinus expanded significantly during the Lateglacial Interstadial, although small thermophilous tree populations were present in the region. The Younger Dryas chronozone is at best marked by subtle vegetational change in favour of steppe taxa. Tree cover increased rapidly at the beginning of the Holocene, with deciduous woodland probably expanding above its present-day altitudinal limits. There is evidence for drier and/or warmer summers, and mild winters, between c. 10500 and 7500 cal. BP, although the vegetation was not as markedly sclerophyllous as at many sites elsewhere in Greece. The mid-Holocene saw a reorganization of the woodland, with first Abies and then Fagus becoming important at high altitudes, and an increase in the diversity of deciduous woodland at medium elevations. The suggestion of human impact in the form of a decline in woodland and the appearance of crops in the pollen record can be found at all altitudes in the later Holocene.

Early land-use and landscape development in Arisaig

Re-alignment of a 6km section of the A830 road in Arisaig (NGR: NM 6714 9054) provided an opportunity to investigate the archaeology of this poorly understood area of the West Highlands. A combination of archaeological and palaeoenvironmental techniques were used to investigate the road corridor. Archaeological survey, followed up by selected excavations, identified a previously unrecorded Bronze Age kerb cairn and two areas of shieling huts. Investigation of the shielings obtained evidence for repeated reuse of sites and reconstruction of structures through the medieval and post-medieval periods. In both cases, Bronze Age deposits were also recorded at the base of the medieval sequence. Analysis of a long peat core from a basin close to one of the shielings revealed a history of continuous but gradual decline in woodland, starting in about 3200 BC and continuing to the present day. Collation of archaeological and palaeoenvironmental data from the present project and previous investigations in the area have allowed the creation of a tentative model of landscape evolution for Arisaig.

Early land-use and landscape development in Arisaig

Re-alignment of a 6km section of the A830 road in Arisaig provided an opportunity to investigate the archaeology of this poorly understood area of the West Highlands. A combination of archaeological and palaeoenvironmental techniques were used to investigate the road corridor. Archaeological survey, followed up by selected excavations, identified a previously unrecorded Bronze Age kerb cairn and two areas of shieling huts. Investigation of the shielings obtained evidence for repeated reuse of sites and reconstruction of structures through the medieval and post-medieval periods. In both cases, Bronze Age deposits were also recorded at the base of the medieval sequence. Analysis of a long peat core from a basin close to one of the shielings revealed a history of continuous but gradual decline in woodland, starting in about 3200 BC and continuing to the present day. Collation of archaeological and palaeoenvironmental data from the present project and previous investigations in the area have allowed the creation of a tentative model of landscape evolution for Arisaig.

Incidence of Perenniporia fraxinophila and its effects on green ash ( Fraxinus pennsylvanica) woodlands in eastern Montana, USA

Green ash ( Fraxinus pennsylvanica) woodlands are declining throughout the Northern Great Plains of North America. The heart rot disease of ash caused by Perenniporia fraxinophila is common in these woodlands, but its importance in woodland decline is not known. We sampled the visible incidence of P. fraxinophila stem decay on green ash in 17 native woodland stands in east-central Montana, USA. Randomly chosen trees with and without P. fraxinophila sporocarps were measured for age, height and girth. Incidence of sporocarps on green ash trees ranged from 0 to 67% within stands with a mean of 38%. Sporocarps of other wood-rotting basidiomycetes were not observed in sample stands. P. fraxinophila sporocarps were more frequent on larger, faster growing trees. Rot was detected in basal cores from 23% of the sample trees; 74% of these also had sporocarps. Trees originating from multiple-stump sprouts were not more likely to have sporocarps, suggesting that P. fraxinophila does not usually enter sprouting trees directly from infected stumps. Mean canopy dieback ranged from 22 to 50% and averaged 54% for trees with sporocarps compared with 37% for trees without sporocarps. However, 27% of ash trees lacking both sporocarps and rotten cores had mean canopy dieback ≥50%, indicating that P. fraxinophila is not the primary cause of canopy dieback. Growth rates of ash trees with P. fraxinophila sporocarps declined as the number of sporocarps increased. The incidence of P. fraxinophila is associated with a decline in mean annual precipitation across Nebraska and eastern Montana. These results suggest that this disease may contribute to the decline of ash woodlands, especially where drought stress is common.

Eight years of integrated monitoring in Alpine forest ecosystems of Trentino and South Tyrol, Italy

After the acute emergency of decline in European woodland at the beginning of 1980’s, forest health was the subject of several studies in Trentino and South-Tyrol. Since 1992 investigations focused on an integrated monitoring under the UN-ECE-ICP programme in 4 selected areas, 2 in subalpine Norway spruce woodland (Lavazè Pass and Renon), and 2 in thermophilous Pubescent oak woodland (Pomarolo and Monticolo). The interdisciplinary programme of integrated monitoring aimed to investigate the state of alpine semi-natural forests in relation to air pollution, anthropogenic stresses, climate changes and trophic-energetic balances. Assessment of forest health by means of crown conditions showed very low levels of defoliation and discoloration in the subalpine areas, while in the other ones the same parameters had slightly higher values. Every year and in all the sites the mean percentages values were always in class 0 and class 1, hence indicating no danger. Weather patterns showed the presence of occasional water deficit, albeit general trends were not observed. High level of pollution were never detected while the level of acidity in rainfall has been slightly decreasing in all the investigated plots. Only ozone showed higher values than normal but there was no correlation with any damage. Foliar mineral nutrient contents ranged quite always within the threshold level. Because of the few years of observation and the absence of relevant stress, it is not possible to get any indication about the relationship between the forest health status and the fungi community composition. The presence of some anomalous data and the growing concern on climate change give reason to the importance of a continuous monitoring action acquiring of comparable set of data, in order to get a better understanding of forest ecosystems response to stress and make progress in general ecological knowledge.

Holocene palaeoenvironments of salt lakes in the Darling Anabranch region, south-western New South Wales, Australia

Abstract Aim Fossil pollen preserved within small salt lake basins in the Australian interior is used to reconstruct mid- to late Holocene vegetation. The study aims to identify the origin of problems such as woodland decline and salinization within present ecosystems. Location Warrananga and Tooperoopna salt lakes, south-western New South Wales, Australia. Methods Pollen, carbonized particle and sedimentological analyses of cores taken from salt lakes. Results Prior to c. 4500 years ago, the region supported a dense cover of Casuarinaceae woodlands. It is possible that the subhumid zone species Allocasuarina luehmannii comprised some of the Casuarinaceae element. In the late Holocene, A. luehmannii disappeared from the record and chenopodiaceous low shrublands expanded. About 2000 years ago, Callitris representation decreased. Woodland contraction also occurred after European settlement. Main conclusions Increasing aridity or greater seasonal variation in the climate during the late Holocene caused a contraction of woodland vegetation. Increased proportions of Chenopodiaceae may indicate soil salinization around the basins. A decrease in Callitris was possibly due to heightened severity or frequency of drought events after 2000 years ago. Decline in woodland pollen in the uppermost samples is explained by the preferential clearing of Callitris glaucophylla, Callitris gracilis and Casuarina pauper for timber and their limited regeneration because of browsing by stock and rabbits.

A Scottish speleothem record of the H-3 eruption or human impact? A comment on Baker, Smart, Barnes, Edwards and Farrant

Studies of a stalagmite sample from Sutherland, Scotland, have identified a period of enhanced growth that lasted for four years and has been dated to 1135 ± 130 BC (Baker et al., 1995). This episode is unique within this sample and has not been observed elsewhere. The authors correlate it with the Icelandic volcanic eruption at 1021 + 130/-100 Bc that produced the Hekla-3 (H-3) tephra. There is, however, no direct evidence for a causal relationship between volcanic activity in general, or the H-3 eruption in particular, and the growth patterns of the stalagmite. As an alternative to the volcanic explanation of enhanced growth, we suggest that the speleothem could reflect environmental changes associated with woodland decline and the spread of blanket peat.

ELEPHANT DENSITY AND IMPACT ON KALAHARI WOODLAND HABITATS

SUMMARY Over-abundance of elephants could result in a decline of woodlands and tall canopied trees. Elephant carrying capacity of woodlands can be defined as the subsistence of a threshhold number of elephants in woodlands where the growth of tall trees is not impaired. The aim of this study was to assess elephant damage in three woodland types dominated by Acacia erioloba, Baikiaea plurijuga and Colophospermum mopane which were monitored in plots distributed throughout northern Botswana. Contemporary densities of woody plants of nine height classes were compared with the associated local elephant densities and fire occurrences. Woodland types differed with respect to structure, extent of elephant damage and the occurrence of fire. It seems that woodlands sustaining high elephant impact, such as C. mopane can carry more elephants because of a healthy age structure. Inherently low seedling recruitment rates and high occurrences of fire preclude the carrying capacity of A. erioloba and B. plurijuga for elephants, although elephant-induced damage to trees is low.

Late Quaternary vegetation history of the Western Isles of Scotland.

Palacoecoiocical investigations of two lake sediment sequences are used to reconstruct the vegetation history of the Western Isles. Pollen records begin in the late glacial and show a clear progression From herb-rich grassland with abundant Salix, Rumex and Poly-podium to widespread Empetrum nigrum heath. Woodland developed widely in the early Holocene, and regional vegetation patterns emerged. Western Lewis supported extensive areas of birch woodland with Corylus avellana, Salix, Populus and Sorbus aucuparia. Open birch-hazel woodland dominated other lowland regions. Regional variation was accentuated when woodland underwent a sudden decline in western Lewis at about 7900 BP. Trees were replaced by blanket peat and woodland failed to recover on a regional scale after the decline- Woodland continued to diversify in central and eastern regions and, by 6000 BP, Quercus, Ulmus, Pinus sylvestris, Alnus glutinosa and Fraxinus excelsior had become established. Open mixed woodland persisted until the second major decline began between 5200 and 4000 UP. Woodland contracted gradually as blanket peat expanded. The Western Isles were predominantly treeless at 2500 BP. Blanket peat started to form in localized areas on the Western Isles between 9000 and 8000 BP; two main expansion phases are associated with periods of woodland decline. Sublossil wood or macrofossils are reported from a total of 40 sites. Radiocarbon ages are presented for 13 samples of these.

Holocene vegetation history and human impact at Bryn y Castell, Snowdonia, north Wales

summaryThree radiocarbon‐dated pollen diagrams are presented from Holocene peat and lake deposits in Snowdonia, close to the Late Iron Age/Romano‐British ironworking hill‐tort of Bryn y Castell, Gwynedd, in upland north Wales. This paper discusses pollen, charcoal and peat‐stratigraphic evidence for major local vegetation changes and for the development of the surrounding cultural landscape during the last 10000 radiocarbon yr. Pollen data from one of the sites (BYC 2) provided a vegetational record for most of the Holocene. The early part of the sequence suggests an oligotrophic lake in a landscape that is being colonized by birch‐pine woodland; later, mixed deciduous woodland surrounds an infilling lake basin. Dating of peat deposits at two of the sites (BYC, BYC H) indicated that their pollen records commenced between 5500 and 5000 yr BP. By this time, the lake basin was fringed by alder carr. There followed a gradual and then, c. 2700 yr BP, a more abrupt decline in woodland, such that, by the end of the Bronze Age and with the basin largely terrestrialized, the local landscape became dominated by mire vegetation communities, which have persisted to the present. Human activity seems to have been a major factor in the loss of woodland cover. Although there is some circumstantial evidence for earlier phases of human disturbance at BYC 2, human activity becomes increasingly apparent from c. 5000 yr BP. During the mid Holocene, the impact of Neolithic and early‐ to mid‐Bronze Age cultures appears to be characterized by temporary woodland clearances, for arable and pastoral agriculture. By c. 2700 yr BP the majority of woodland cover seems to have been permanently removed from the landscape, but as there is scant archaeological evidence for late Bronze Age cultures in this part of Snowdonia, other factors, especially climate change, could be implicated. During the late Holocene, especially during part of the late Iron Age and Romano‐British period, remaining local stands of woodland seem to have been exploited for iron smelting, although the overall impact of ironworking was limited.

Vegetation history of Orkney, Scotland; pollen records from two small basins in west Mainland

summaryPollen analysis was carried cut on sediment sequences from two small basins situated 6 km apart in the hills of west Mainland, Orkney, At both sites, vegetation development from the late glacial until after the arrival of Neolithic people is recorded. An initial late glacial heath, interrupted by a herbaceous phase indicating the Younger Dryas, was replaced by tallherb and grassland vegetation. The Saksunarvatn ash layer was recorded, coinciding with the arrival of Corylus avellana in the islands at around 9.2 ka BP. Extensive woodland developed at about 8000 yr BP, predominantly Betula–Coryhus with Salix, alnus glutinosa. Quercus and Pinus sylvestris occasionally present. The woodland was locally affected by Mesolithic human activity and finally lost at around 5kaBP, partly as a consequence of Neolithic human activity. Mire development was actively proceeding in both basins after the woodland decline. The records illustrate the importance of human activity in the development of the treeless, varied landscape seen in Orkney today.

A history of vegetation and fire, 6,600 B.P. to present, County Sligo, western Ireland

Dodson, John R. & Bradshaw, Richard H. W. 1987 06 01: A history of vegetation and fire, 6,600 B.P. to present, County Sligo, western Ireland. Boreas, Vol. 16, pp. 113–123. Oslo. ISSN 0300–9483.Two lake sites on metamorphic rocks with small catchments and one mor humus deposit have been analysed to assess the relative influences of fire, man and climate upon the regional and local vegetation of the Lough Gill region of County Sligo. The vegetation of the area was dominated by mixed woodland from 6,600 B.P. to 600 B.P. The first evidence of human impact on the forests was around 5,400 B.P. in the form of clearance for pasture. The intensity of human impact varied between sites, and there were periods of forest recovery as well as decline. From 600 B.P. widespread forest destruction took place, and pasture with heathland became predominant. Pinus sylvestris had a major presence until about 5,400 B.P. It declined from this time and had a patchy distribution by 2,000 B.P. The decline of Pinus was linked with the expansion of treeless peatland in what are presumed to be wet periods, and Pinus recovery in drier periods. Fire may have encouraged the spread of heathland at the expense of Pinus. Arbutus unedo pollen was found at Slish Lake as early as 1,900 B.P., suggesting that it is native to this area. Isolated trees survive today at woodland edges. Charcoal particles occurred in all the profiles. Fire was particularly associated with heathland communities, and may have been used as a management tool to improve grazing conditions. Some of the phases of woodland decline correlate strongly with charcoal input suggesting forest destruction by fire.