Europe's lost forests: a pollen-based synthesis for the last 11,000 years.

8000 years ago, prior to Neolithic agriculture, Europe was mostly a wooded continent. Since then, its forest cover has been progressively fragmented, so that today it covers less than half of Europe's land area, in many cases having been cleared to make way for fields and pasture-land. Establishing the origin of Europe's current, more open land-cover mosaic requires a long-term perspective, for which pollen analysis offers a key tool. In this study we utilise and compare three numerical approaches to transforming pollen data into past forest cover, drawing on >1000 14C-dated site records. All reconstructions highlight the different histories of the mixed temperate and the northern boreal forests, with the former declining progressively since ~6000 years ago, linked to forest clearance for agriculture in later prehistory (especially in northwest Europe) and early historic times (e.g. in north central Europe). In contrast, extensive human impact on the needle-leaf forests of northern Europe only becomes detectable in the last two millennia and has left a larger area of forest in place. Forest loss has been a dominant feature of Europe's landscape ecology in the second half of the current interglacial, with consequences for carbon cycling, ecosystem functioning and biodiversity.

Pollen-based quantitative reconstructions of Holocene regional vegetation cover (plant-functional types and land-cover types) in Europe suitable for climate modelling.

We present quantitative reconstructions of regional vegetation cover in north-western Europe, western Europe north of the Alps, and eastern Europe for five time windows in the Holocene [around 6k, 3k, 0.5k, 0.2k, and 0.05k calendar years before present (bp)] at a 1° × 1° spatial scale with the objective of producing vegetation descriptions suitable for climate modelling. The REVEALS model was applied on 636 pollen records from lakes and bogs to reconstruct the past cover of 25 plant taxa grouped into 10 plant-functional types and three land-cover types [evergreen trees, summer-green (deciduous) trees, and open land]. The model corrects for some of the biases in pollen percentages by using pollen productivity estimates and fall speeds of pollen, and by applying simple but robust models of pollen dispersal and deposition. The emerging patterns of tree migration and deforestation between 6k bp and modern time in the REVEALS estimates agree with our general understanding of the vegetation history of Europe based on pollen percentages. However, the degree of anthropogenic deforestation (i.e. cover of cultivated and grazing land) at 3k, 0.5k, and 0.2k bp is significantly higher than deduced from pollen percentages. This is also the case at 6k in some parts of Europe, in particular Britain and Ireland. Furthermore, the relationship between summer-green and evergreen trees, and between individual tree taxa, differs significantly when expressed as pollen percentages or as REVEALS estimates of tree cover. For instance, when Pinus is dominant over Picea as pollen percentages, Picea is dominant over Pinus as REVEALS estimates. These differences play a major role in the reconstruction of European landscapes and for the study of land cover-climate interactions, biodiversity and human resources.

Holocene biomass burning and global dynamics of the carbon cycle.

Fire regimes have changed during the Holocene due to changes in climate, vegetation, and in human practices. Here, we hypothesise that changes in fire regime may have affected the global CO2 concentration in the atmosphere through the Holocene. Our data are based on quantitative reconstructions of biomass burning deduced from stratified charcoal records from Europe, and South-, Central- and North America, and Oceania to test the fire-carbon release hypothesis. In Europe the significant increase of fire activity is dated approximately 6000 cal. yr ago. In north-eastern North America burning activity was greatest before 7500 years ago, very low between 7500-3000 years, and has been increasing since 3000 years ago. In tropical America, the pattern is more complex and apparently latitudinally zonal. Maximum burning occurred in the southern Amazon basin and in Central America during the middle Holocene, and during the last 2000 years in the northern Amazon basin. In Oceania, biomass burning has decreased since a maximum 5000 years ago. Biomass burning has broadly increased in the Northern and Southern hemispheres throughout the second half of the Holocene associated with changes in climate and human practices. Global fire indices parallel the increase of atmospheric CO2 concentration recorded in Antarctic ice cores. Future issues on carbon dynamics relatively to biomass burning are discussed to improve the quantitative reconstructions.

Direct experimental evidence for a negative heat capacity in the liquid-to-gas phase transition in hydrogen cluster ions: backbending of the caloric curve.

By selecting specific decay reactions in high-energy collisions (60 keV/amu) of hydrogen cluster ions with a helium target (utilizing event-by-event data of a recently developed multicoincidence experiment) and by deriving corresponding temperatures for these microcanonical cluster ensembles (analyzing respective fragment distributions), we are able to construct caloric curves for H+3(H2)(m) cluster ions (6

Probing the liquid-to-gas phase transition in a cluster via a caloric curve.

High-energy collisions ( 60 keV/amu) of hydrogen cluster ions with a helium target have been completely analyzed on an event-by-event basis. By selecting specific decay reactions we can start after the energizing collision with a microcanonical cluster ion ensemble of fixed excitation energy and we derive corresponding temperatures of the decaying cluster ions. The relation between the temperature and the excitation energy (caloric curve) exhibits the typical prerequisites of a first-order phase transition in a finite system, in the present case signaling the transition from a bound cluster to the gas phase.

Event-by-event analysis of collision-induced cluster-ion fragmentation: sequential monomer evaporation versus fission reactions.

The most abundant decay channels have been studied quantitatively for high-energy (60 keV/amu) cluster ions H (3) (+)(H (2))(m = 1-14) colliding with He atoms employing a recently developed multicoincidence technique for the simultaneous detection of the correlated fragments on an event-by-event basis. This allows us to identify decay reactions and their underlying decay mechanisms responsible for the occurrence of the U-shaped fragmentation pattern.

Total, partial, and electron-capture cross sections for ionization of water vapor by 20-150 keV protons.

We present experimental results for proton ionization of water molecules based on a novel event by event analysis of the different ions produced (and lost). We are able to obtain mass analyzed product ion signals (e.g., H2O+, OH+, O+, O++, H+) in coincidence with the projectile analyzed after the collision, i.e., either being H+, neutral H after single electron capture during the ionization event, or H- after double electron capture. After proper calibration we are thus able to determine a complete set of cross sections for the ionization of a molecular target by protons including the total and the partial cross sections and in addition also the direct ionization and the electron capture cross sections.

[The assessment of long-term memory and semantic knowledge]. / L'évaluation de la mémoire du passé lointain et des connaissances sémantiques.

Following a previous review about the different components of memory (Eustache et al., Revue Neurologique, 1998), this paper is devoted to the evaluation of both autobiographical and semantic memory. An original method to analyse autobiographical memory is proposed. The different tasks used for the analysis of semantic memory are detailed with a particular emphasis given to the category -specific semantic impairments.

[Naming impairment for man-made objects in a case of herpes encephalitis]. / Trouble de la dénomination pour les objets manufacturés dans un cas d'encéphalite herpétique.

We report the naming performances of a 25 year-old woman with a left internal and inferior temporal lesion caused by herpes encephalitis who showed a preferential impairment for naming man-made objects. Evidence for category-specific effect was provided by a stepwise logistic regression using 171 pictures characterized by several parameters (words frequency, diversity of responses, length, name agreement, majoritary response, familiarity, visual complexity and canonicity). Analyses were realized over a 5 month period. Methodological considerations, anatomic correlations and arguments suggesting lexical access or semantic storage disturbance are discussed.

[Clinical assessment of dysarthria: presentation and validation of a method]. / Evaluation clinique de la dysarthrie: présentation et validation d'une méthode.

We adapted in French the Frenchay Dysarthria Assessment (FDA) developed by P. Enderby in 1983. This tool quantitatively evaluates the organs involved in speech and provides a measurement of intelligibility. Productions of normal subjects were analyzed. Reproductibility of data (correlation and interobserver concordance) was high in 18 dysarthric patients. A study performed in 100 dysarthric patients corresponding to 4 types of dysarthria (spastic, ataxic, hypokinetic and mixte) showed that dysarthria resulted from a global impairment of organs implied in speech, rather than one specific organ. The reduction in the intelligibility score was related to organ impairment.