Didier Galop

Modern pollen assemblages from grazed vegetation in the western Pyrenees, France: a numerical tool for more precise reconstruction of past cultural landscapes

Modern pollen assemblages from grazed vegetation in the Pyrenees Mountains (France) were studied with the aim of providing a calibrated model for reconstructing past pastoral activities. The modem analogues were selected to cover the major gradients of grazing pressure and degree of openness. The vegetation was surveyed by means of the synusial integrated method, assessing the structure and the patchiness of the pastoral phytoceonoses. A correlative model (Redundancy analysis) was devised relating 61 modern pollen spectra with 37 explanatory vegetation and land-use variables. It was shown that wooded, open grazed and nitrophilous sites are clearly separated from one another and that the model can be simplified using three relevant vegetation types as explanatory variables: dry heathland, semi-open oak forest and overgrazed community, respectively related to gradients of openness, soil richness and grazing pressure. When reconstructing past pastoral activities with fossil pollen spectra, it is important to consider scale-dependent influences of plant species. Low frequencies of well-dispersed taxa such as Artemisia, Chenopodiaceae, Plantago lanceolata and Plantago majorlmedia must be interpreted with care since they reflect more regional, rather than local, input into the pastoral landscape. In contrast, the simultaneous occurrence of Asteroideae, Cichorioideae, Cirsium-type, Galium-type, Ranunculaceae, Stellaria-type and Potentilla-type pollen is clearly related to grazing on a local scale. Calculation of Davis indices also shows that Cichorioideae, Galium-type and Potentilla-type indicate the very local presence of the corresponding plants. These pastoral plant indicators may have a limited geographical validity, ie, mountainous regions with crystalline bedrock, which may indeed also provide the framework for the application to fossil spectra of the modem pollen/vegetationAand-use models presented here.

Fire frequency and landscape management in the northwestern Pyrenean piedmont, France, since the early Neolithic (8000 cal. BP)

Both quantitative reconstruction of fire frequency from charcoal counts and pollen analysis were undertaken on a 312 cm sediment core from Gabarn peat bog. An 8000 yr cal. BP palaeofire record and vegetation history were established on the basis of nine 14C (AMS) dates. As anthropogenic Inferred Fire Frequency (IFF) has seldom been studied, we test and discuss two different methods of frequency calculation. Our results shows a clear Holocene bipartition at c. 3500—4000 cal. BP characterized by a three times decrease in Mean Fire Interval (MFI): from 7000 to 4000 cal. BP, MFI = 530 yr; from 4000 to 400 cal. BP, MFI = 160 yr. In an Atlantic vegetation context, we hypothesize this fire regime with such episode frequency to be mainly controlled by human activities. This hypothesis is supported by comparisons with other European quantified palaeofire regimes (Swiss Alps, northern Italy) whether they are controlled by climate, man or both. Taking into account the pollen record, we interpret the Gabarn palaeofire record links with human pressure and land use. Our results suggest that the relationship between fire frequency and human pressure is not always linear. Fire frequency could also reflect land-use shifts and changing use of fire within agro-pastoral activities.

Population differentiation of sessile oak at the altitudinal front of migration in the French Pyrenees

To assess the effects of altitude on the level and structure of genetic diversity, a genetic survey was conducted in 12 populations of sessile oak (Quercus petraea) located between 130 and 1660 m in two parallel valleys on the northern side of the Pyrenees Mountains. Genetic diversity was monitored at 16 nuclear microsatellite loci and 5 chloroplast DNA (cpDNA) markers. The cpDNA survey suggested that extant populations in both valleys shared the same source populations from the plain. There was no visible trend of nuclear genetic diversity along altitude, even if indirect estimates of effective population sizes revealed a consistent reduction at higher altitudes. Population differentiation, although low, was mostly present among populations of the same valleys and reached similar levels than differentiation across the range of distribution of sessile oak. Contribution to the overall differentiation in the valleys was mostly due to the genetic divergence of the highest populations and the altitudinal variation of allelic frequencies at a few loci. Bayesian inference of migration between groups of populations showed that gene flow is preferentially unidirectional from lower altitudes in one valley to other groups of populations. Finally, we found evidence of clonal reproduction in high altitude populations. The introgression of Quercus robur and Quercus pubescens was also more frequent at the altitudinal margin suggesting that this mechanism may have contributed to the present migration and adaptation of Q. petraea and may also facilitate its future upslope shift in the context of climate change.

The European Modern Pollen Database (EMPD) project

Modern pollen samples provide an invaluable research tool for helping to interpret the quaternary fossil pollen record, allowing investigation of the relationship between pollen as the proxy and the environmental parameters such as vegetation, land-use, and climate that the pollen proxy represents. The European Modern Pollen Database (EMPD) is a new initiative within the European Pollen Database (EPD) to establish a publicly accessible repository of modern (surface sample) pollen data. This new database will complement the EPD, which at present holds only fossil sedimentary pollen data. The EMPD is freely available online to the scientific community and currently has information on almost 5,000 pollen samples from throughout the Euro-Siberian and Mediterranean regions, contributed by over 40 individuals and research groups. Here we describe how the EMPD was constructed, the various tables and their fields, problems and errors, quality controls, and continuing efforts to improve the available data.

Hurricanes and climate in the Caribbean during the past 3700 years BP

A multiproxy analysis of lacustrine sediments cored in Grand-Case Pond at Saint-Martin, north of the Lesser Antilles archipelago, reveals three distinct climatic periods for the last 3700 years. From 3700 to ~2500 yr cal. BP and from 1150 yr cal. BP to the present, carbonate mud deposition occurred in connection with pond lowstands. These periods were also punctuated by severe drought events, marked by gypsum laminae, and hurricane landfalls, leading to marine sand inputs into the pond. The intermediate time interval, from 2500 to 1150 yr cal. BP, is typified by black organic mud deposition, suggesting that hypoxic to anoxic conditions prevailed at the pond bottom. These were probably linked with a perennial pond highstand and reflect more uniform and wetter climatic conditions than today. The carbon isotopic composition of the ostracod Perissocytheridea bisulcata shows that the lowest δ13C values are recorded during the hypoxic periods, as a consequence of bacterial recycling of isotopically depleted organic matter. Such a climatic history agrees closely with that documented from other records in the Caribbean area, such as the Cariaco Basin, central coast of Belize or Barbados. By constrast, discrepancies seem to emerge from the comparison between hurricane activity recorded at Saint-Martin on the one hand and Vieques (Puerto Rico) on the other hand. We explain this apparent contradiction by a balance between two distinct storm paths in response to latitudinal shifts of the Intertropical Convergence Zone (ITCZ). Stronger storm activity over the Gulf coast and the inner Caribbean Sea is favoured by a southern position of the ITCZ in connection with dry climatic conditions. Plausible links with the North Atlantic Oscillation (NAO) are also suggested.

Differential human impact and vegetation history in two adjacent Pyrenean valleys in the Ariège basin, southern France, from 3000 B.P. to the present

Detailed palynological studies in two adjoining French Pyrenean valleys, complemented by the study of archives, demonstrate that under similar climatic conditions, the forest history of each valley from the Bronze Age to present time was essentially determined by socio-economical constraints, possibly modified by natural characteristics such as topography. The studies show why the expansion of Fagus (beech) at c. 4000 B.P. was asynchronous on the northern slope of the Pyrenees and emphasize the effects of the human impact on the recent lowering of the tree-line.

Late-Holocene climatic variability south of the Alps as recorded by lake-level fluctuations at Lake Ledro, Trentino, Italy

A lake-level record for the late Holocene at Lake Ledro (Trentino, northeastern Italy) is presented. It is based on the sediment and pollen analysis of a 1.75 m high stratigraphic section observed on the southern shore (site Ledro I) and a 3.2 m long sediment core taken from a littoral mire on the southeastern shore (site Ledro II). The chronology is derived from 15 radiocarbon dates and pollen stratigraphy. The late-Holocene composite record established from these two sediment sequences gives evidence of centennial-scale fluctuations with highstands at c. 3400, 2600, 1700, 1200 and 400 cal. BP, in agreement with various palaeohydrological records established in central and northern Italy, as well as north of theAlps. In addition, high lake-level conditions at c. 2000 cal. BP may be the equivalent of stronger river discharge observed at the same time in Central Italy’s rivers. In agreement with the lake-level record of Accesa (Tuscany), the Ledro record also suggests a relatively complex palaeohydrological pattern for the period around 4000 cal. BP. On a millennial scale, sediment hiatuses observed in the lower part of the Ledro I sediment sequence indicate that, except for a highstand occurring just after 7500 cal. BP, lower lake levels generally prevailed rather before c. 4000 cal. BP than afterwards. Finally, the lake-level data obtained at Lake Ledro indicate that the relative continuity of settlements in humid areas of northern Italy during the Bronze Age (in contrast to their general abandonment north of the Alps between c. 3450 and 3150 cal. BP), does not reflect different regional patterns of climatic and palaeohydrological conditions. In contrast, the rise in lake level dated to c. 3400 cal. BP at Ledro appears to coincide with a worldwide climate reversal, observed in both the hemispheres, while palaeoenvironmental and archaeological data collected at Lake Ledro may suggest, as a working hypothesis, a relative emancipation of protohistoric societies from climatic conditions.

Social-ecological systems in the Anthropocene: The need for integrating social and biophysical records at regional scales

Understanding social-ecological system dynamics is a major research priority for sustainable management of landscapes, ecosystems and resources. But the lack of multi-decadal records represents an important gap in information that hinders the development of the research agenda. Without improved information on the long-term and complex interactions between causal factors and responses, it will be difficult to answer key questions about trends, rates of change, tipping points, safe operating spaces and pre-impact conditions. Where available long-term monitored records are too short or lacking, palaeoenvironmental sciences may provide continuous multi-decadal records for an array of ecosystem states, processes and services. Combining these records with conventional sources of historical information from instrumental monitoring records, official statistics and enumerations, remote sensing, archival documents, cartography and archaeology produces an evolutionary framework for reconstructing integrated regional histories. We demonstrate the integrated approach with published case studies from Australia, China, Europe and North America.

A History of Long-Term Human–Environment Interactions in the French Pyrenees Inferred from the Pollen Data

This chapter examines the pollen evidence on human signature in the Pyrenees since the arrival of the first agro-pastoralists in the foothills of the mountains in the Early Neolithic Period. The palaeoecological studies of natural archives such as lakes and peat bogs are used to trace the evidence of human-made mountainous landscapes. This chapter summarizes the palaeoecological data from several research programs. The results show that the “domestication” of the Pyrenees was not a smooth and linear process, but the history of human impact on the mountains is characterized by a succession of phases of varying intensity punctuated by periods of shorter or longer stability and decline.

Explosive eruption of El Chichon volcano (Mexico) disrupted 6th century Maya civilization and contributed to global cooling

A remarkably long period of Northern Hemispheric cooling in the 6th century CE, which disrupted human societies across large parts of the globe, has been attributed to volcanic forcing of climate. A major tropical eruption in 540 CE is thought to have played a key role, but there is no consensus about the source volcano to date. Here, we present evidence for El Chichon in southern Mexico as the most likely candidate, based on a refined reconstruction of the volcano’s eruption history. A new chronological framework, derived from distal tephra deposits and the world’s largest Holocene beach ridge plain along the Gulf of Mexico, enabled us to positively link a major explosive event to a prominent volcanic sulfur spike in bipolar ice core records, dated at 540 CE. We speculate that voluminous tephra fall from the eruption had a severe environmental impact on Maya societies, leading to temporary cultural decline, site abandonment, and migration within the core area of Maya civilization.