No description available.

Lake sediments from inland endoreic (saline) lakes in the semi-arid Ebro Basin, NE Spain have been analysed to provide a history of lake level, vegetation, catchment erosion and anthropogenic activity over the last 10,000 years. Analysis was undertaken for pollen, macrofossils (seeds, Cladocera ephippia, Chironomid head capsules etc), charcoal, geochemistry (total cations/trace metals, sulphate, carbonate & LOI) and sediment composition. Fourteen AMS radiocarbon dates provide dating control. Seven cores were investigated from 4 seasonal playa lakes, I shallow (<1.5m) semi-permanent salt lake, 1 deep (5.0m) permanent salt lake and 1 Medieval-age reservoir. Over 40 surface samples were also taken to investigate modern analogue environments. A review of the use and interpretation of saline lake macrophytes (seeds & pollen), Cladocera and Chironomids in palaeolimnology is provided, with special emphasis on those found in Spanish salt lakes. Taphonomic problems and nearshore-offshore facies were also investigated using a surface sample transect across a small playa lake. A surface sample pollen data set from 30 lakes in the Ebro Basin is presented and the implications for palaeo-interpretation discussed. The sensitivity of the pollen record as a climate indicator is investigated using 6 sites across a climatic gradient from sub-humid to semi-arid. Lake level reconstruction is based on an 8 stage semi-quantitative palaeohydrological model, developed from a surface sample data set from 32 lakes ranging from temporary to permanent, and hypersaline to freshwater. A simple hydrological model for groundwater fed lakes is also discussed which can be used to quantify these palaeohydrological changes. The early Holocene (<9.3-8.6Kyr BP) was characterised by semi-arid extreme continental conditions in the Ebro Basin, with an extensive Juniper thurifera woodland. Lake levels rose to their highest point in the Holocene between 8.6-7.2Kyr BP when evergreen oak and pine forest dominated. This is interrupted by a short recession in lake level between 8.2-7.6Kyr BP. A distinct regional early-Neolithic fire and clearance event occurs between 7.7-7.3Kyr BP. A drop in lake level and development of a monospecific pine forest (P. halepensis) indicates warmer and drier conditions in the mid Holocene (7.2-5.4Kyr BP). Evergreen oak reappears as forest cover declines after 5.4Kyr BP, although this is not marked by any increase in charcoal or cultivation indicators. Low groundwater but moderate lake levels (4.0-2.7Kyr BP) may be linked to high summer storm frequency and low winter rainfall. This coincides with catchment erosion and valley floor alluviation. Lake level rises again significantly between 2.7-1.8Kyr BP during Iberian and Roman times when archaeological evidence indicates a peak in population. Agriculture changes from small scale pastoral to small scale arable without any further decline in woodland cover. A rapid fall in lake level at ca. 1.8Kyr BP is followed by complete forest recovery (P. halepensis) and depopulation, until major deforestation around 1.4Kyr BP marks the arrival of the Visigoths/Arabs and extensive nomadic pastoralism. Intensive grazing pressure or lower temperatures resulted in Juniperus increasing again between 1.4-0.4Kyr BP. This also coincides with a second period of catchment erosion and valley floor alluviation. After ca. 0.4Kyr BP, lake levels have increased along with extensive olive cultivation and the development of modern (irrigated) arable agriculture.

Diss. (sammanfattning) Umeå : Sveriges lantbruksuniv., 2008. / Härtill 4 uppsatser.

This thesis considers some of the main issues surrounding the quantitative models that have been developed to reconstruct vegetation from pollen assemblages. Conducted within a pine dominated woodland, a palynologically difficult landscape, to determine vegetation changes over the late Holocene the results highlight the complexities of undertaking such studies in these contexts. Pollen productivity estimates were calculated from moss samples over the woodland using complete sets and derived subsets to detect influences of sampling design on resultant model output. Differences in the PPE sets were compared using reconstructions from simulation models in comparison to observed vegetation patterns. The results indicate that both parameter calculation and model reconstructions were influenced by the landscape form and composition. Sensitivity of the models to such small variations in parameter values heightens the need for robust data generation and increased investigation to controlling factors on pollen productivity. Performance of the reconstruction models experienced variation with respect to deposition basin size and site specific characteristics. Overall, the regional reconstructions proved to generate more confident estimates of vegetation cover whilst local scale reconstructions were subject to greater variability. Comparison of the quantitative modelling to standard interpretation and the modern analogue approach shows contrasts between the results obtained with respect to limitations associated with each method and the time frames, recent (ca. 100 years) and longer (ca. 3000 years), over which they were applied. Consequently, no one quantitative approach could be identified as being superior as site specific variations were recognised in relation to the most suitable approach. In response, a hierarchical technique is proposed to utilise the benefits of each technique and to obtain detailed information to strengthen interpretations. However, it is stressed study specific constrains that determine the available resources will influence the ability to fully apply this composite approach.

This thesis investigates the past extent, structure and dynamics of Mar Lodge Caledonian pine (Pinus sylvestris L.) woodland, near Braemar in the south-eastern Cairngorms. The geographical extent and Holocene history of the Scottish pinewoods are generally understood, but the Mar pinewoods are relatively obscure. This thesis is concerned with the Holocene history of the Mar pinewoods; the timing and reasons for first appearance, the increase in abundance of Pinus to become a dominant species, the spatial extent of the woodland and its structure and form. The investigation includes changes to the woodland assemblage during its fragmentation and disappearance in the late Holocene and possible influences on the woodland from people living in the area. At the heart of this thesis is an understanding of the factors underpinning the ecology of Pinus and the response of the species to competition with other taxa. This is related to the spatial and temporal changes in climate that contribute to the location and development of Pinus in Scotland and Mar Lodge. Areas comparable to Mar Lodge are defined as ‘core areas’ of pine woodland rather than ‘native areas’. This avoids the necessity of considering every short period of colonisation by Pinus in areas distal to large populations. The location, extent, form and behaviour of woodland according to macro sub-fossils and micro sub-fossils is used to define core woodland as those with a long presence of Pinus, often continuing to the present day. Areas with a long history but no extant population are regarded as peripheral areas. This thesis consists of extensive palaeoecological investigations of three peat sequences: from within extant pine woodland (Doire Bhraghad), from just beyond its edge (White Bridge) and from peat with sub-fossil pine stumps located 10km west of the modern range of Pinus (Geldie Lodge). A range of techniques, including loss of mass on ignition and colorimetric light transmission analysis are applied to the peat, but palynological techniques form the basis of the investigation. Stomatal counts are used in conjunction with pollen counts to explore the process of Pinus colonisation, and its increase in abundance to form woodland. Pinus percentage and influx, together with the ratio of arboreal to non-arboreal pollen and the percentage of Empetrum are used to define the density of the woodland canopy. The stability of the Doire Bhraghad assemblage confirms the area as core Pinus woodland. Pinus is present from c. 9600 cal BP and dominates woodland from c. 9150 cal BP. Woodland here is a closed, solely Pinus canopy from c. 8600 until 4000 cal BP. Arrival of Pinus at Geldie Lodge is undated but occurs before c. 7550 cal BP. Woodland is always more open; Pinus is co-dominant with Betula, showing affinity with other peripheral areas. Pinus woodland fragments at all Mar Lodge sites from c. 3900 cal BP, disappearing from Geldie Lodge by c. 2800 cal BP and White Bridge by c. 1900 cal BP. Calluna replaces Pinus as the dominant species at all three sites. The disappearance of Pinus is thought to relate to regional climatic change toward wetter conditions. At Geldie Lodge a prior Coleopteran study suggests Pinus growing on the mire surface to be small and short lived. These may not have been the only trees growing in the area but they perhaps contributed to the major fluctuations in arboreal and non-arboreal pollen. Early canopy fluctuations (c. 7550 to 6000 cal BP) at Geldie Lodge may be related to Mesolithic human activity; there is stronger evidence of human presence from c. 4000 cal BP, possibly including cereal cultivation. Evidence from Doire Bhraghad and White Bridge is indicative only of low intensity grazing activity. It is unlikely that human activity instigated the fragmentation and disappearance of woodland, but may have contributed to the process.

Diss. (sammanfattning) Alnarp : Sveriges lantbruksuniv. / Härtill 7 uppsatser.

No description available.

L’étude de la dynamique végétale et anthropique des zones humides d’Algérie du nord-est, a été menée à partir d’une démarche basée sur la rétro-observation et utilisant la palynologie comme principal outil.Ainsi, l’étude multi-proxy de cinq séquences sédimentaires étayées par 9 datations radiocarbones et l’exploitation de référentiels polliniques contemporains destinés à définir une liste de taxons polliniques indicateurs de l’anthropisation permettent de reconstituer la dynamique de la végétation et de la diversité végétale passée au cours des derniers siècles dans des régions où les données paléobotaniques étaient inexistantes (exception faite pour la Numidie). Les données paléoécologiques acquises permettent d’écrire pour le secteur biogéographique Kabylie-Constantinois-Numidie une histoire de la végétation locale, de la biodiversité passée et de la dynamique environnementale des zones humides. L’ensemble de ces données pouvant être mobilisées dans le cadre de politiques contemporaines de gestion des zones humides, pour la restauration des habitats disparus ou la réintroduction d’espèces localement éteintes. Les résultats acquis, qui documentent pour l’essentiel une période récente ne remontant pas au delà du XVII° siècle, indiquent une activité humaine intense et marquée par le poids de l’agro-pastoralisme mais dont l’impact sur les écosystème et en particulier les mares temporaires est variable selon les secteurs et n’entraine pas nécessairement de dégradation majeures sur les communautés végétales ou leurs capacités de résilience. Dans une optique de gestion conservatoire, cette prise en compte des dynamiques passées des zones humides est fondamentale et peut constituer un outil essentiel pour définir les priorités de conservation. / The plant dynamic and anthropic study of northern Algeria wetlands was lead from an approach based on retro-observation and using palynology as main tool. Thus, the multi-proxy study of five sedimentary sequences supported by 9 radiocarbon dating and exploitation of contemporary pollen referential, devoted for defining a list of pollen taxa indicators of anthropisation, allow us to reconstruct the vegetation dynamics and past plant diversity in the last centuries in areas where paleobotanical data were do not exist (except for Numidia). Paleoecological data acquired allow us to write, for the biogeographical Kabylie-Constantine-Numidia sector, a local vegetation history, past biodiversity and environmental dynamics of wetlands. All these data can be used within contemporary political management of wetlands for missing habitat restoration or for reintroduction of locally extinct species. The results obtained, which document essentially a recent period not back beyond the XVII° century, indicate intense human activity, marked by the weight of agro-pastoralism but the impact on the ecosystem and on particular temporary ponds varies from sectors and does not necessarily lead to a major damages on plant communities and on their resilience. From the perspective of conservation management, the consideration of past wetland dynamics is fundamental and can be an essential tool to define conservation priorities.

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Les influences respectives de l’anthropisation et de la variabilité climatique sur l’histoire de la végétation méditerranéenne sont difficiles à différencier et peuvent être variables d’une région à une autre. Ce travail de recherche a pour objectif de mieux caractériser l’influence des populations humaines et de la variabilité climatique sur la mise en place des environnements du nord-ouest de la Méditerranée (i) en apportant une contribution inédite à l’étude de l’histoire de la végétation de cette région et (ii) en développant de nouveaux outils de traitement des données paléo-environnementales. Pour cela, deux nouvelles séquences polliniques à haute résolution temporelle situées dans le Languedoc (France) et dans la région de Murcie (Espagne) ont été acquises. Elles couvrent respectivement les 7800 et 6500 dernières années. Dans le Languedoc, la végétation est dominée par des taxons plutôt mésophiles pendant la majeure partie de la séquence, notamment le hêtre qui forme des forêts à basse latitude en zone méditerranéenne. Ce dernier régresse sous l’effet d’une aridification croissante du climat, combinée à des crises d’aridités centennales. D’un autre côté, la végétation sclérophylle méditerranéenne s’installe progressivement depuis le Néolithique en lien avec une anthropisation croissante. Dans la région de Murcie, l’impact du climat sur la végétation est plus équivoque, c’est l’impact de l’Homme qui est le plus nettement visible. Les formations arbusitives et pionnières montrent clairement des phases de développement et de régression reliées aux variations de l’anthropisation du territoire. D’autre part, un travail de calibration du signal pollinique par rapport à la végétation a été initié. Le modèle de transport des grains de pollen, REVEALS, a été adapté aux environnements de dépôts côtiers tels que ceux étudiés dans cette thèse. De plus, des données en vue de la quantification de la production pollinique de douze des principaux taxons méditerranéens ont été collectées et traitées. Pour finir, l’analyse spectrale de séries temporelles paléoclimatiques a permis de caractériser l’influence de l’activité solaire, de la circulation thermohaline atlantique et de la variabilité climatique tropicale sur le climat du nord-ouest de la Méditerranée. La variabilité spatiale du signal climatique à l’Holocène en Méditerranée a également été discutée grâce à une remise en contexte des résultats de cette thèse à l’échelle de l’ensemble du bassin Méditerranéen. / Holocene climate fluctuations and human activities since the Neolithic have shaped present-day Mediterranean environments. Separating anthropogenic effects from climatic impacts to better understand Mediterranean paleoenvironmental changes over the last several millennia remains a challenging issue. This work aims to characterize the influence of human activities and past climate variability over the development of north western Mediterranean environments by (i) providing new data about the vegetation history of this region and (ii) developing new tools for paleoenvironmental data processing. Two high-resolution pollen sequences from Languedoc (France) and the Murcia region (Spain) are presented, covering the last 7800 and 6500 years, respectively. In Languedoc, the past vegetation is dominated by mesophilous forests during most of the sequence, in particular beech forests growing at low altitude within the Mediterranean area. However, recurrent abrupt climate changes, the late Holocene aridity trend, and human deforestation caused beech forests to decline. On the other hand, evergreen Mediterranean vegetation has developed gradually since the Neolithic due to the increasing human impact. In the Murcia region, the influence of past climate variability on the environment is less obvious. Changes in human activities are clearly driving most of the observed vegetation changes. Shrubs and pioneer plants show spread and decline phases alternatively in relation to archeological and historical records. Work to adapt pollen based land-cover reconstruction methods developed in northern Europe to the Mediterranean area was also initiated. REVEALS model of pollen dispersal and deposition was adapted to coastal sedimentary basins such as those studied in this PhD. However, to apply such pollen based land-cover reconstruction methods, pollen productivity estimates are needed. Thus, the data necessary to quantify the pollen productivity of 12 Mediterranean plant taxa were collected and processed. Finally, spectral analysis of paleoclimate time series using wavelets allowed us to characterize the influence of solar variability, the Atlantic thermohaline circulation, and tropical climate variability on the past climate of the north-western Mediterranean. The spatial variability of past climate changes in the Mediterranean is also highlighted by comparing our results obtained for the north western Mediterranean with paleoclimate data from the whole Mediterranean basin.