Paul Roiron

Latest Pliocene pollen and leaf floras from Bernasso palaeolake (Escandorgue Massif, Hérault, France)

Abstract Bernasso palaeocanyon (Herault, France) is in the Escandorgue volcanic massif, south of the Massif Central. The first glacial-interglacial cycles of the Plio-Pleistocene period are recorded in the infilling of this canyon and are rich in macroflora (mainly leaves) and microflora (mainly pollen). Pollen zones I and III represent a steppe environment, in contrast to pollen zone II, a forested one. This study concentrates on pollen zone II for which new pollen spectra and abundant leaves are described owing to new outcrops and a 8 m long drillhole (BN I) through the deposit. Pollen zone II-a poorly illustrates an open oak forest that could correspond to a pioneering phase after a steppe period (pollen zone I). No sampling of the sediment between those yielding pollen zones II-a and II-b was possible. Therefore little is known of the intermediate vegetational phases. Pollen zones II-b to II-d show a diversified mixed temperate forest. Pollen zones II-a to II-d are probably steps in vegetation successions of an entire interglacial period such as the Nogaret interglacial, defined in a neighbouring diatomite deposit of similar age. The macrofloral study is based on 800 samples. Most abundant specimens are Carpinus suborientalis, Parrotia persica, Acer and Carya. The Bernasso macroflora reflects a mesothermic forest similar to the present vegetation south of the Caspian sea. The difference between the dominant genera in the macroflora and microflora leads to an improvement in the interpretation of pollen percentages. There is an under-representation of pollen from Carpinus orientalis, Parrotia persica and Acer sp. and over-representation of Carya minor, Zelkova, Pinus and Tsuga. The Hyrcanian region and to a lesser degree the Euxinian region, serve as models for the Pliocene flora. Compared to present-day Bernasso, the Late Pliocene climate was milder and had more precipitation throughout the year with a reduced decrease during the summer leading to reduced seasonal contrast. The estimated duration for pollen zone II, part of an odd oxygen isotope stage driven by an obliquity cycle (41 ka), is less than 10 ka. The age estimates (based on K/Ar dates, palaeomagnetism and cyclopalynostratigraphy) indicate that Bernasso floras developed during the time interval between ca. 2.16 and 1.96 Ma. Therefore, Bernasso pollen zones II-b to II-d could correlate to part of an oxygen isotope stage between stage 81 and stage 73.

Needle accumulation rate model-based reconstruction of palaeo-tree biomass in the western subalpine Alps

An appropriate bioproxy is required to decipher Holocene tree biomass dynamics from the stand scale in relation to local processes such as disturbance or global climate change. Here we used plant litter collected in traps placed in subalpine forests, and data on the surrounding stands, to develop calibration equations for converting the observed macroremain accumulation rates to tree biomass (basal area) values. The needle accumulation rate (NAR) was modeled for Larix decidua and Pinus cembra. We then used the calibration equation developed from the trapped macroremains to reconstruct past tree biomass for sedimentary Holocene series from two subalpine lakes in the Alps. Our data show that NAR is significantly correlated with basal area. We found a clear overrepresentation of L. decidua NAR compared with its real basal area. This distortion potentially masks the occurrence of P. cembra, another important functional species of subalpine ecosystems, when macroremains are not calibrated. Without calibration, the use of NAR to describe past plant biomass always leads to an overestimation of L. decidua biomass and an underestimation of P. cembra biomass. Several shifts between the dominance of the two species, which were masked when using unadjusted NAR, were apparent and occurred at both sites. By comparing the reconstructed basal areas with fire frequencies, we found that P. cembra biomass accumulation preceded the increase of fire frequency and that fire frequencies superior to 0.0085 fire/yr could induce a long-term loss of resilience of cembra pine forest to the benefit of larch. This results to a slight dominance of Larix biomass from 2500 to 2000 cal. BP until the present day at the two sites. Our results provide increased understanding of tree biomass dynamics associated with specific vegetation phases, and shifts in dominant species, and highlight the needs to understand the causes of these shifts and identify how such processes are related to local environmental conditions.

Les flores du bassin lacustre de Rubielos de Mora. Nouvelles données sur les conditions climatiques au Miocène inférieur dans la région de Teruel (Espagne)

Abstract The stratigraphie and floristic studies of two sections in the lacustrine deposits of the Miocene basin of Rubielos de Mora increase our knowledge of palaeoenvironmental and palaeoclimatic conditions and specify the biochronology of these sites. The lowlands are inhabited by a swampy, or lacustrine, vegetation ( Botryococcus, Sparganium, Potamogeton , Taxodiaceae, Myrica, Nyssa… ), whereas the uplands are covered by a Zelkova mesophilous forest with other temperate elements ( Acer, Betula, Carya… ). The scarcity of thermophilous taxa in this vegetation indicates that the climatic conditions were not the warmest in the Miocene. The rodents faunas of this basin suggest a Ramblian-basal Aragonian age (Lower Miocene).

Subalpine Vegetation Dynamics in the Southern French Alps during the Holocene: Evidence from Plant Imprints and Charcoal Preserved in Travertine Sequences

Abstract In the Aigue Agnelle Valley (Queyras, southern French Alps), between 2200 and 2300 m a.s.l., several travertine deposits are present. Some, containing leaf imprints and pine cones, have been dated back to the early Holocene. Others containing charcoal fragments and dating back to the middle Holocene have also been found. The study of the plant imprints and charcoal within these travertines allowed us to reconstruct the vegetation dynamics of this valley. During the early Holocene (9800 B.P.), Pinus uncinata (mountain pine) was the most common tree. It was gradually replaced by Pinus cembra (arrola pine) in association with Betula (birch) and Vaccinium sp. (berry), probably as a result of climatic warming (ca. 7600 B.P.). Since ca. 5600 B.P., Pinus cembra seems to have regressed in correlation with the development of Larix decidua/Picea abies (larch/spruce) as a consequence of fire events related to climatic and/or anthropogenic factors.

Paléoenvironnements au pléistocene moyen dans la Vallée du Tarn: La formation travertineuse de la Rouquette (Creissels-Aveyron)

Middle Pleistocene paleoenvironments in the Tarn valley: the travertine formation of la Rouquette (Creissels-Aveyron). The site of la Rouquette (near Millau) reveals a paleothalweg filled by colluvia submitted by a fersiallitic pedogenesis and travertine formations ≥350,000 years old (230Th/234U). Paleoecologic informations reveal closed and humid temperate forest conditions with both mediterranean and altitude influences, indicate an Interglacial of Middle Quaternary age.

A new, isolated and endangered relict population of dwarf pine (Pinus mugo Turra) in the northwestern Alps.

Dwarf pines were discovered in 2004 during a paleoecological survey in the Mont Cenis massif (Savoy, France). These dwarf pines are the sole natural and spontaneous population in the NW French Alps of Pinus mugo Turra, ssp. mughus (Scop.) O. Schwarz. The population, fragile in light of the individual numbers, is currently isolated, but likely results from populations that would have covered larger areas during the Lateglacial or the early-Holocene, from the SW Alps (France) toward the Mont Cenis, throughout the Susa valley (Italy). With a fragmented distribution area of dwarf pine, the future of the Mont Cenis population seems altered due to important necroses observed on the topmost part of pine crowns, except for individuals that do not grow in the local ski station area. We stress the need for a conservation program to preserve this natural population, the sole known in the NW French Alps.

Les travertins à empreintes, témoins de la paléobiodiversité végétale

De nombreux systemes travertineux fossilisent des restes vegetaux sous formes d’empreintes. Leur identification au niveau specifique permet de definir la vegetation qui se developpait localement. Differents exemples decrits dans cet article montrent l’interet de ces depots a empreintes pour comprendre l’histoire passee de certaines especes ligneuses ou apporter des informations sur l’evolution des paleoenvironnements holocenes.

Environments and societies of small Caucasus (Armenia) in the light of the Quaternary climatic changes and landscape mutations

(1) Laboratoire Méditerranéen de Préhistoire Europe Afrique, UMR 6636, Aix-en-Provence, France (2) Department of Cartography and Geomorphology , Yerevan State University, Armenia (3) Centre de Bio-Archéologie et d’Ecologie, UMR 5059, Montpellier, France (4) Institute of Botany, National Academy of Sciences of the Republic of Armenia (5) UMR 5125 PEPS, Université Lyon 1, Bt Géode, Lyon Cedex, France (6) Maison de l’Orient, UMR 5133 Archéorient, Lyon, France (7) UMR 5808, Institut de Préhistoire et de Géologie du Quaternaire, Bordeaux, France (8) Institute of Archaeology and Ethnography, National Academy of Sciences of the Republic of Armenia.