Holocene vegetation history of the Sahel: pollen, sedimentological and geochemical data from Jikariya Lake, north-eastern Nigeria

Aim This study aims to separate regional and local controls on Holocene vegetation development and examine how well pollen records reflect climate change in a semi‐arid region. The relative importance of climate and human activity as agents of vegetation change in the Sahel during the late Holocene is also considered. Location Jikariya Lake, an inter‐dune depression in the Manga Grasslands of north‐eastern Nigeria. Methods Pollen and charcoal were used to provide a record of Holocene vegetation history. Palaeoclimate and hydrological changes were reconstructed from sedimentary and geochemical data. Regional and local influences were separated by comparing the evidence obtained from Jikariya Lake with previously published data from the Manga Grasslands. Results The Manga Grasslands experienced a prolonged wet period during the early and mid‐Holocene, during which swamp forest vegetation with Guinean affinities (Alchornea, Syzygium, Uapaca) occupied the inter‐dune depressions. However, variation in the pollen records between sites suggests that their establishment was dependent on conditions being locally favourable, rather than being directly coupled to regional climate. The pollen records from the Manga Grasslands are more consistent in suggesting the colonization of the dunefields by trees associated with Sudanian savanna (Combretaceae, Detarium) c. 8700 cal. yr bp . The Jikariya Lake pollen data are in accordance with the sedimentological and geochemical data from the region in indicating that the onset of arid conditions occurred progressively during the late Holocene (from c. 4700 cal. yr bp ). Abrupt changes in pollen stratigraphy, recorded at other Manga Grasslands sites 3500 cal. yr bp , appear to be the product of the local passing of ecological thresholds. The dunefield vegetation (Sahelian savanna) appears to have been resilient to (or at least palynologically silent regarding) to the climatic variability of the late Holocene. Main conclusions While climate appears to have been the primary control on vegetation development in the Manga Grasslands during the Holocene, local conditions (particularly depression size and sand influx) had a strong influence on the timing of pollen stratigraphic changes. Anthropogenic influences are difficult to detect, even during the late Holocene.     

On the Late Pleistocene and Holocene history of vegetation and human impact in the Ücker valley, north-eastern Germany

A high-resolution Late Pleistocene and Middle to Late Holocene pollen profile of regional significance is presented. The coring site is located in a mire between two lakes. Ober- and Unter-ückersee, in Brandenburg, north-eastern Germany. The study was carried out in an archaeological context. It provides information about the history of vegetation, climate and human impact in the ücker river valley and the surrounding hills, the Uckerm?rker Hügelland. Hence, it is an important contribution for the reconstruction of the past vegetation of this area of Brandenburg. Seven AMS ¹⁴C-dates based on pollen concentrates provide a chronology for the middle Holocene part of the profile. Phases of intensive human activity can be shown from the middle Neolithic times until the Roman Iron Age. Received February 1, 2000 / Accepted January 18, 2001     

Detection of the impact of early Holocene hunter-gatherers on vegetation in the Czech Republic, using multivariate analysis of pollen data

Pollen data from the Czech Republic was used to detect the early Holocene impact of hunter-gatherers on vegetation based on a selection of 19 early Holocene pollen profiles, complemented with archaeological information regarding the intensity of local and regional Mesolithic human habitation. Archaeological evidence was assigned to simple categories reflecting the intensity of habitation and distance from pollen sites. Multivariate methods (PCA and RDA) were used to determine relationships between sites and possible anthropogenic pollen indicators and to test how these indicators relate to the archaeological evidence. In several profiles the pollen signal was influenced by local Mesolithic settlement. Specific pollen types (e.g. Calluna vulgaris, Plantago lanceolata, Solanum and Pteridium aquilinum) were found to be significantly correlated with human activity. The role of settlement proximity to the investigation site, the statistical significance of pollen indicators of human activity, as well as the early occurrence of Corylus avellana and its possible anthropogenic dispersal, are discussed.     

A palaeoecological investigation into the role of fire and human activity in the development of montane grasslands in East Africa

Human activity has been widely implicated in the origin and expansion of montane grasslands in East Africa, yet little palaeoecological evidence exists to test whether these grasslands are natural or secondary. Pollen and charcoal data derived from two Holocene records in the Eastern Arc mountains of Tanzania are used as a case study to investigate the supposed secondary nature of montane grasslands in Africa. Fossil pollen data are used to detect vegetation change, and charcoal analysis is used to reconstruct fire history. The pollen data are characterised by stable proportions of local taxa suggesting permanence of grasslands throughout the past ~13,000 years. Recent increases in fire adapted taxa such as Morella point towards the development of a grassland/forest patch mosaic possibly associated with burning. However, robust evidence of human activity is absent from the records, which may be attributed to the late human occupation of the mountains. The records indicate long-term persistence of grasslands which, coupled with a lack of evidence of human activity, suggests that these grasslands are not secondary. These data support the hypothesis that grasslands are an ancient and primary component of montane vegetation in Africa, but that they experienced some expansion during the late Holocene as a result of changing fire regime.     

Vegetational change in the Balearic Islands (Spain) during the Holocene

New information about the vegetational history of the Balearic Islands during part of the Holocene derives from the results of a pollen study of a 20‐metre‐deep core from Cala Galdana on the SW coast of Minorca.

The lower part of the pollen diagram at the beginning of the Atlantic Period records significant quantities of pollen of Corylus and also local taxa indicating swamp vegetation. In the middle part, Corylus is greatly reduced, AP percentages decrease appreciably and Olea and Ericaceae reach important values, while Plantago Poaceae and Cerealia increase significantly. In the upper part, a rise in Chenopodiaceae occurs, during which a slight increase of the arboreal taxa takes place with greater dryness. Most recently, vegetation changes reflect human activity.     

Holocene vegetation and climate change from near Lake Pedder, south-west Tasmania, Australia

Aim To use surface pollen and vegetation relationships to aid the interpretation of a Holocene pollen record. Location South‐west Tasmania, Australia. Methods A survey was undertaken of surface‐pollen samples from the major regional vegetation types: alpine, rain forest and moorland. Relationships between vegetation type and surface‐pollen representation were analysed using twinspan classification and ordination. A core was retrieved from moorland vegetation, and interpretation of the fossil pollen sequence was aided using relationships detected in our surface‐pollen analysis. Results Regional vegetation types are reflected in the pollen rain of south‐west Tasmania, despite the over‐representation of important rain forest tree species in samples from non‐forest sites. twinspan classification of the surface‐pollen samples identified the following indicator pollen taxa for each vegetation type: Astelia alpina (alpine); Lagarostrobos franklinii (rain forest); Leptospermum and Melaleuca (moorland). Detrended correspondence analysis of the surface‐pollen samples clearly separates samples from each vegetation type. Correlation of the ordination axes with environmental data identified a dominant temperature/altitudinal gradient in the surface‐pollen data (R = 0.852/0.844). Application of the results of the surface‐pollen analysis to the fossil sequence revealed that fire‐promoted moorland has dominated the local environment around the core site for the entire Holocene. Changes in fossil pollen composition also suggest that temperatures increased through the Late Glacial to peak in the mid‐Holocene and declined thereafter, a trend consistent with other sites in the region. Main conclusions Pollen spectra can successfully be used to predict local vegetation in south‐west Tasmania. At least this part of inland south‐west Tasmania has remained forest‐free throughout the Holocene, conflicting with the dominant palaeoecological paradigm of a mid‐Holocene dominated by rain forest. A comparison with pollen records from moorland vegetation across the region suggests that fire‐promoted moorland has dominated the landscape since the Late Glacial. We suggest that burning by people through the Late Glacial (if not earlier) facilitated the spread of moorland throughout the region, greatly restricting the expansion of rain forest. The continued influence of fire throughout the Holocene in this perennially wet landscape argues for a revision of the dominant human‐occupation model that depicts an abandonment of the interior of south‐west Tasmania in the Late Glacial in response to the expansion of rain forest.     

The vegetational history of the northern Apennines, Italy: information from three new sequences and a review of Regional vegetational change

Abstract. The results of pollen analysis and radiocarbon dating are presented from three northern Apennine sequences; Lago Padule in northern Tuscany and Lago Pratignano and Ospitale in the Emilia-Romagnan Apennines. This is the first detailed pollen stratigraphic information from sites in Emilia-Romagna and north Tuscany and extends eastwards the area from which information on vegetational history is available. The sequence from Lago Padule is one of the most complete Holocene records known from the northern Apennine region. Lago Pratignano has the deepest sequence of organic sediments (1544 cm) and the fastest rates of sediment accumulation (up to 28 cm per 100 years) providing the highest resolution record for the mid to late Holocene periods in the region. High rates of sedimentation have also occurred at Ospitale where organic sediments are 780 cm deep and began to form at approximately 5500 bp. The record from Lago Padule is compared with Holocene records from two nearby sites and a series of Regional Pollen Assemblage Zones is defined for the eastern area of the northern Apennines. The main features of vegetational change identified are: (i) a‘pioneer’phase of rapid forest development during the early Holocene followed by the establishment of an upper forest belt dominated by Abies, and a belt of mixed deciduous forest at lower altitudes; (ii) the appearance and rapid expansion of Fagus between approximately 5200 bp and 2900 bp forming a mixed Abies-Fagus association in the upper forest belt; and (iii) the overall reduction of forest cover, and dominance of Fagus in the arboreal vegetation from around 2900 bp. The scheme of Regional PAZs for the eastern area is used as a framework for the review of pollen stratigraphic information and radiocarbon dates from other sites in the northern Apennine region. Characteristics of pollen records which can be identified in sequences from across the region are identified and the chronology of similar changes in pollen stratigraphy is examined. The scheme of four regional PAZs for the Holocene period is shown to be valid for the entire northern Apennine region. The examination of a series of pollen records shows that Fagus appeared earlier in the western than the eastern part of the region during the mid Holocene and became dominant in the northern Apennine forests post 3000 bp. The impact of anthropogenic activity and climatic change on the spread and development of Fagus are discussed. The palynological evidence which is now available from the northern Apennines is compared with information for the region shown in the‘European pollen maps’of Huntley & Birks (1983). This study provides an updated review of the representation of different tree taxa in Holocene pollen records from the northern Apennines and illustrates the role of the northern Apennines as a refugium for trees during the Wurmian Lateglacial.     

Protracted drought during the late Holocene in the Lacandon rain forest,Mexico

A 3.4 m core was obtained for paleoecological analysis from Naja Lake in the Lacandon region of southeastern Mexico. This is the first study of the Lacandon area aimed at reconstructing late Holocene environmental history. The basal section of the core yielded an AMS date of 2020 ¹⁴C years b.p. The Naja pollen record shows that the lower montane rain forest characterized by Moraceae, Mimosoideae, Leguminosae and Combretaceae/Melastomataceae, coexisted with a pine-oak forest throughout the late Holocene. No Zea mays pollen was found during routine pollen counts, but the presence of both secondary pollen taxa and abundant charcoal particles suggest some degree of regional human impact. A marked increase in Pinus pollen, together with a reduction in lower montane rain forest taxa, is interpreted as evidence for a strong, protracted drought from 1260 to 730 ¹⁴C years b.p.     

Holocene forest development in the central Scandes Mountains, Sweden

Pollen analyses of sediment cores from two small lakes within the boreal forest in the central Scandes Mountains help to elucidate the Holocene forest dynamics of the region. Analyses of pore/pollen grain diameter ratios of Alnus grains indicate the early Holocene presence of Alnus glutinosa in the study area. The results are discussed in conjunction with available pollen records to evaluate the importance of thermophilous trees during the early Holocene and to deduce the regional spread of Picea abies. Corylus avellana, Alnus glutinosa and Ulmus glabra were probably common constituents of the early Holocene forest. Tilia cordata may have occurred there as a rare tree. Pollen stratigraphies from the region do not indicate the occurrence of Quercus robur. The regional spread of Picea abies can be separated into two phases: a mid-Holocene establishment or first expansion of small outpost populations and a late-Holocene population expansion. The mid-Holocene shift in vegetation composition may have been caused by changes in the westerly airflow.     

Forest response to climate changes in Atlantic Equatorial Africa during the last 4000 years BP and inheritance on the modern landscapes

This review paper synthesizes the recent published palaeoecological results obtained in Atlantic Equatorial Africa (ECOFIT program) on the history of forest ecosystems and inferred climate changes during the past 4000 years. Evidence are mainly provided by pollen analysis carried out at nine sites from Congo, Cameroon and Ghana, locally supported by macroflora remains, phytoliths, diatoms, δ¹³C and mineralogical data. At all the sites, except Lake Bosumtwi (Ghana), following a large expansion of rain and mesophilous forests until 3000 years BP , a major change is registered, affecting floristic composition, structure and geographical distribution. According to the hydrological sensitivity of the different sites, local openings of the forests with development of heliophilous formations and/or isolated enclosed savannas are observed at the most humid sites; complete disappearance of forested formations at the driest. The agreement between pollen records, hydrological and hydrobiological data definitely demonstrates that an arid event has been the primary driving factor of this change and is responsable for the main features of the modern landscapes in Atlantic Equatorial Africa. Moreover, the most recent palaeoecological data obtained in Congo (Lake Sinnda), indicate that this Late Holocene increasing aridity was of longer duration, from 4000 to 1300 years BP , and more progressive than previously inferred. A new expansion of forests is locally detected c. 900–600 BP despite increased human impact.     

Vegetation changes and human occupation in the Patagonian steppe, Argentina, during the late Holocene

Vegetation changes during the late Holocene are interpreted from four fossil pollen sequences from two caves at the Los Toldos archaeological locality, Santa Cruz province, Argentina. Taphonomic processes are particularly taken into account in order to analyze the effects on the fossil pollen records of biotic factors such as human occupation and animals, and abiotic ones such as volcanic ash fall. Fossil pollen assemblages are interpreted using local modern pollen data. The main vegetation change occurred at ca. 3750 uncal b.p., when a shrub steppe of Asteraceae subf. Asteroideae with Schinus, Ephedra frustillata and a high proportion of grasses was replaced by a shrub steppe of Colliguaja integerrima and Asteraceae subf. Asteroideae. This change is synchronous with an archaeological record change and could be related either to moderate climatic variations or the effects of ash fall on the environment. Plant communities similar to the present-day ones were established in the Los Toldos area from ca. 3750 uncal b.p.     

A late Holocene pollen diagram from the Megaris,Greece, giving possible evidence for cultivation of<Emphasis Type="Italic"> Ceratonia siliqua</Emphasis> L. during the last 2000 years

A late Holocene pollen profile from the Megaris on the eastern Gulf of Corinth shows a vegetation which was strongly influenced by human impact throughout. A Pistacia-Phillyrea maquis, which is reflected in the older parts of the profile, changed later to a more degraded vegetation type. In the uppermost part Pinus dominates the pollen spectrum. A continuous record of Ceratonia siliqua pollen older than cal a.d. 100 is of special interest.     

Earliest Holocene vegetation history and island biogeography of the Isle of Man, British Isles

Aim To present radiocarbon dated early Holocene pollen analytical data from two sites on the northern plain of the Isle of Man and to discuss the implications of the vegetation history in relation to severance of the island from the British Isles and to identify further evidence for divergent biogeographical development previously exemplified by the survival and apparent dwarfism of late glacial Megaloceros giganteus (Giant Deer). Location The Isle of Man, British Isles. Methods Pollen analysis and AMS radiocarbon dating of late glacial to early Holocene lake sequences at Pollies and Curragh‐y‐Cowle on the northern plain of the Isle of Man. Results The pollen data indicate a prolonged period of pre‐woodland vegetation after the late Glacial/Holocene transition, which lasted for most of the first post‐glacial millennium. This persistence of pre‐forest environments meant that the expansion of Betula woodland occurred later in this part of the Isle of Man than in adjacent areas of Britain and Ireland. Conclusions The Isle of Man, in the northern Irish Sea, was isolated from Britain during the late Glacial period perhaps explaining the delayed arrival of tree species. Delayed rise of the Holocene forest compared with surrounding regions probably reflects severance of the land‐bridge with Cumbria, but also could be a function of climate changes during the early Holocene and local environmental conditions. Late survival and the dwarfism of the Megaloceros giganteus (Giant Deer) fauna is another example of biogeographical divergence during the early Holocene/late Glacial of the Isle of Man. The delayed afforestation and absence of human hunters in the Manx early Holocene offers a permissive environmental context for the as yet unproven survival of Megaloceros into the early Holocene.     

Late Pleistocene and Holocene pollen stratigraphy at Lago di Vico, central Italy

A new pollen record from Lago di Vico (core V1) provides fundamental new information towards reconstruction of flora and vegetation history in central Italy during the last 90 000 years. The chronological framework is secured by seventeen AMS¹⁴C dates, one⁴⁰Ar/³⁹Ar date and tephra analyses. At the base of the pollen record, i.e. shortly after the⁴⁰Ar/³⁹Ar date 87 000±7000 B.P., three phases with significant expansion of trees are recorded in close succession. These forest phases, which stratigraphically correspond to St Germain II (and Ognon?) and precede pleniglacial steppe vegetation, are designated by the local names Etruria I, Etruria II and Etruria III. During the pleniglacial, a number of fluctuations of angiosperm mesophilous trees suggest the presence of tree refugia in the area. The lowest pollen concentration values are recorded at ca. 22 000 B.P. which corresponds with other pollen records from the region. The late-glacial is characterized by an expansion in the arboreal pollen curves that is less pronounced, however, than in other pollen profiles from Italy. The Holocene part of the profile is consistently dominated by deciduous oak pollen. No major changes in arboreal pollen composition are recorded but several marked and sudden declines of the tree pollen concentration suggest that the forest cover underwent dramatic changes. Clear evidence for human impact is recorded only when cultivated crops became important which dates to ca. 2630±95 B.P.     

Plant landscape and land use at the Neolithic lake settlement of Dispilió (Macedonia,northern Greece)

The Neolithic settlement of Dispilió (lake Orestiás, northern Greece) is a unique site due to its continual inhabitation from the Middle Neolithic (5400 BC) to the Chalcolithic (3600 BC) and its exceptional location at the shore of Lake Orestiás (also known as Lake Kastoria). The plant landscape shaping of the area has been examined by correlating pollen and non-pollen palynomorphs from both on-site and off-site records. The examined pollen profiles bear concrete evidence of agricultural activities and land use in the area. The local pollen assemblages identified, each of them corresponding either to a different kind or intensity of exploitation of natural resources, display the diachronic evolution of the cultural landscape during more than 2000 years of human activity. The successive phases of intense human impact on vegetation patterns are in good accordance with the periods of major constructing activities described by the archaeological study of the Dispilió settlement. Finally, the differences on palynomorph accumulation pathways of the examined records made possible the distinction between local and “regional” plant landscapes and related human activities.     

Late Quaternary paleoecology from fossil beetle communities in the Awatere Valley, South Island, New Zealand

Aim The research aim is to reconstruct last glacial maximum (LGM) and Holocene vegetation history and ecology from fossil beetle assemblages. Location The LGM and Holocene sites are located in the Awatere Valley, which lies in the tectonically active Marlborough Region in the north east of the South Island of New Zealand. Methods Beetle fossils were extracted from silty organic sediment using the standard kerosene flotation method. Fossils were identified by comparisons made to modern species based on morphology and surface features. The ecology and distribution of modern analogues are extrapolated to reconstruct the fossil environment. Results One hundred and forty‐five beetle species belonging to 33 families were identified. The LGM fossil fauna showed the local vegetation was characterized by a forest patch surrounded by an open tussock/grassland landscape. This Nothofagus (southern beech) forest persisted at the site until mid‐Holocene when it was replaced by a podocarp forest that contained high beetle diversity. Herbivores dominate in the early stage of this zone, indicating a relatively new forest environment. Later in the Holocene, the fauna is dominated by detritivores indicating an older more established forest. The late Holocene is characterized by low diversity and the absence of forest species. This fauna indicates that by 500 years ago, the forest was absent and is associated with an almost compete loss of beetle biodiversity. Main conclusions The fossil beetles provide a unique perspective into the past environment in the Awatere Valley on a local scale. The reconstruction supports regional pollen interpretations of Holocene vegetation by identifying a specific forest patch. Fossil beetles are thus a valuable local proxy for vegetation reconstructions.     

The late Holocene palaeoecological sequence of Serranía de las Villuercas (southern Meseta,western Spain)

New pollen results and radiocarbon dating from a valley mire in south-western Spain are presented. This is a region where few palaeoecological records have been preserved and the sequence yields important new palaeobotanical evidence for the late Holocene. The landscape is shown as having been largely open woodland, but more wooded than at present. The vegetation history of the last four millennia in these montane territories of south-western Iberia is discussed in the light of anthropogenic indicators, archaeological and documentary archives; fire incidence and climate change. Alnus is the predominant pollen type, although a decline is noted during the last couple of centuries. Its presence is connected with local topography behaving as a phreatophyte, that is, a plant which obtains a significant amount of water from the zone of saturated soil. A framework is also provided for the age and ecological dynamics of some major woodland taxa—Betula, Corylus, Ilex, evergreen and deciduous oaks, Ericaceae and Pinus. In addition, the natural status of several pollen taxa and local trends in biodiversity are discussed. We consider that the results of our work will have important implications for the understanding of the vegetation history in a floristically very rich area, with a noticeable diversity of woody taxa, and a relatively well preserved ecosystem structure.     

Pugillo Di Licheni Dell'Abissinia E Dell'Eritrea

Abstract

The long pollen sequences from four volcanic lakes of the Lazio région are presented in order to outline the history of flora and vegetation on the Tyrrhenian side of Central Italy during the last hundred thousand years. The four long pollen records correlate satisfactorily with each other and reflect climatic changes at least at regional scale. Particular attention is paid to the development of arboreal vegetation during the last glacial. The local name “Lazio Complex” is given to the seven main fluctuations of trees of the Pleniglacial (from about 60,000 to about 30,000 years B.P.). The history of Zelkova, Abies, Picea, Fagus, Corylus, Ulmus, Carpinus betulus, Tilia in central Italy is outlined.     

Mid- and late-Holocene vegetation history,climate and human impact in the forest-steppe ecotone of European Russia: new data and a regional synthesis

Appropriate management of contemporary environments requires knowledge of their long-term history. We use palaeoecological data to explore how contemporary forest-steppe environments have been shaped by climate change and human impacts through the Holocene using the western Mid-Russian Upland as a case-study. Our paper presents new reconstructions of Mid- and Late Holocene climate, vegetation dynamics and local environmental change based on pollen, plant macrofossil and testate amoeba records from a site at Selikhovo (Mid-Russian Upland, Russia). Eutrophic fen vegetation dominated by Phragmites australis developed around 6800 cal year BP and has been resilient to episodes of local burning and variable input of mineral material through the Holocene. New and previously-published data show that the boundary between broadleaf forest and steppe occupied a similar position to present during the period 7000–4800 cal year BP, despite a warmer and drier climate, but shifted to the south following climate cooling and an increase in precipitation from 4800–2500 cal year BP. A subsequent decline in woodland cover was caused by both climate change and human impacts, with human activity becoming increasingly significant over the last two millennia. Prior to major human disturbance (about 1700 cal year BP) the landscape was dominated by mixed broadleaf-pine forests with some spruce covering about 60 % of the study area. Our results emphasize the variability of steppe-forest habitats over long time periods and the need to consider human impacts and climate change when setting targets for habitat conservation.