Philippe Ponel

The climate in Western Europe during the last Glacial/Interglacial cycle derived from pollen and insect remains

Using the pollen sequence of La Grande Pile XX (France), we review problems with the application of transfer functions in paleoclimatic reconstructions. One of them is to find modern analogues for the herbaceous vegetation of the cold periods. We propose a method to distinguish between steppes and tundra vegetations for which the moderns are only partial analogues of the glacial periods. Another method to solve these problems is based on constraining by insect remains. The two methods provide coherent reconstructions. The results are also compared with other paleodata. There is a good correlation with the six cold Heinrich events between 70 and 15 ka B.P. A cooling event during the Eemian period (marked by high percentages of Taxas) at about 125 ka B.P. needs still to be correlated with high resolution ocean and ice cores.

Rissian, Eemian and Würmian Coleoptera assemblages from La Grande Pile (Vosges, France)

Abstract The Grande Pile peat-bog sequence is one of the few west European sites that cover the entire time span of the last major climatic cycle (140,000 years). A recent program of coring has provided material for insect analysis. The aim of this palaeoentomological study is to interpret the environmental and climatic evolution from the end of the Rissian glaciation to the Holocene using subfossil Coleoptera. The studied samples yielded 394 taxa of Coleoptera, half of them identified to species level; 19 of which do not belong to the present-day French fauna. The large number of taxa suggests a wide variety of habitats and provides much detailed palaeoecological evidence for the period studied. The lowermost sediments of the sequence, corresponding to the end of the Rissian glaciation, were deposited under very cold conditions in a tundra environment. This is succeeded by a forest period in which two cool interludes of grassland environment occur. Although these periods are decidedly poor in tree-dependent Coleoptera they do not contain any really cold-adapted taxa. They divide the forest phase into three periods. The first one, corresponding to the Eemian Interglacial, shows an early stage in which the beetle fauna is characterized by species dependent on deciduous trees, a later stage in which this fauna is mixed with many conifer-dependent elements, some of which (e.g. Platypus oxyurus) suggest warmer and perhaps wetter climatic condition than today. The two later woodland periods yielded coleopteran assemblages rather similar to those recorded in the second part of the Eemian, i.e. with both deciduous- and conifer-dependent taxa. There is some evidence to suggest that these two periods were slightly cooler than the Eemian proper. Marked climatic deterioration becomes obvious in the upper half of the sedimentary sequence attributed to the last glacial period (Wurm), with the reappearance of tundra beetle assemblages. Sediment and insect evidence suggest that the climate was extremely cold and continental at La Grande Pile at about 30,000 B.P. A comparison of the insect analysis with previous palynological works enables precise correlation between the results provided by these two independent approaches. However, large numbers of running-water Coleoptera in the forest periods, replaced by standing-water Coleoptera in cold periods, raise questions concerning the lacustrine origin of the sedimentation at La Grande Pile.

Indian summer monsoon variations could have affected the early Holocene woodland expansion in the Near East

Postglacial expansion of deciduous oak woodlands of the Zagros—Anti-Taurus Mountains, a major biome of the Near East, was delayed until the middle Holocene at ~6300 cal. yr BP. The current hypotheses explain this delay as a consequence of a regional aridity during the early Holocene, slow migration rates of forest trees, and/or a long history of land use and agro-pastoralism in this region. In the present paper, support is given to a hypothesis that suggests different precipitation seasonalities during the early Holocene compared with the late Holocene. The oak species of the Zagros—Anti-Taurus Mts, particularly Quercus brantii Lindl., are strongly dependent on spring precipitation for regeneration and are sensitive to a long dry season. Detailed analysis of modern atmospheric circulation patterns in SW Asia during the late spring suggests that the Indian Summer Monsoon (ISM) intensification can modify the amount of late spring and/or early summer rainfall in western/northwestern Iran and eastern Anatolia, which could in turn have controlled the development of the Zagros—Anti-Taurus deciduous oak woodlands. During the early Holocene, the northwestward shift of the Inter-Tropical Convergence Zone (ITCZ) could have displaced the subtropical anticyclonic belt or associated high pressure ridges to the northwest. The latter could, in turn, have prevented the southeastward penetration of low pressure systems originating from the North Atlantic and Black Sea regions. Such atmospheric configuration could have reduced or eliminated the spring precipitation creating a typical Mediterranean continental climate characterized by winter-dominated precipitation. This scenario highlights the complexity of biome response to climate system interactions in transitional climatic and biogeographical regions.

Response of the Selle River to climatic modifications during the Lateglacial and Early Holocene (Somme Basin-Northern France)

Abstract Research on Lateglacial sequences from the Selle valley leads to an overview of its evolution in relation to climatic variations between the end of the Weichselian Upper Pleniglacial and the beginning of the Holocene. The first major modification of the fluvial morphology is dated at the Upper Pleniglacial/Lateglacial transition (13,000 14 C-yr BP). At that time, the response to climatic improvement and environmental modifications is marked by downcutting and evolution from a braided river to a transitional river pattern (Bolling infilling in the newly created channels). After a short cold phase recorded in a thin calcareous bed at the top of the Bolling peat attributed to the Older Dryas (Dr. II), the Allerod is characterized by the deposition of organic overbank silts within a large single channel meandering system. In lower slope environments, this period is also marked by slow rates of colluvial accumulation and by the development of upbuilding soils (Allerod soil). On the other hand, the end of the Lateglacial, is characterised by the infilling of the whole valley by fine calcareous overbank silts during the Younger Dryas cold phase (overflow of a large single channel and lateral input of chalk mud). A second major downcutting phase occurs at the beginning of the Holocene at around 10,000 BP, in parallel with another rapid climatic improvement and the renewed spread of vegetation. From a general point of view, the evolution of fluvial environments in the Selle valley is comparable with many other river valleys in NW Europe, showing that fluvial systems react very quickly to climatic variations of short duration (1000 to 100 years). Finally, in the Upper Selle River, incision events occur clearly before the main modifications of the vegetal cover. They are most likely linked to a rapid shift in the balance between water discharge and sediment supply, caused by climate modifications (shift to more temperate and oceanic conditions), and the resulting environmental changes: cessation in aeolian sedimentation, strong reduction of slope processes, permafrost disappearance and soil development.

Middle Pleistocene deposits at La Côte, Val-de-Lans, Isère department, France: plant macrofossil, palynological and fossil insect investigations

plant macrofossils, pollen and spores, and Coleoptera remains were analysed from high altitude, lacustrine, interglacial deposits collected from La Cote, Val-de-Lans, Isere, western French Alps. The investigation concentrated on the second half of the temperate stage (locally called the La Cote Interglacial Stage). Palaeoecological, palaeoenvironmental and quantitative climatic reconstructions for the termination of the interglacial period and the onset of cold conditions are presented. Because the different fossils were affected in varying ways by taphonomic processes they provide a range of complementary data about the palaeoenvironment, and illustrate the importance of multi-disciplinary studies. As conditions became cooler at the end of the temperate stage the lake levels fluctuated, and the waters trophic status changed. The occurrence of Pterocarya and the dominance of Abies support a correlation with the temperate Holsteinian Stage (oxygen isotope stage 11). At the top of the core an interstadial event characterised by Pinus, Picea and Betula is represented. This could have occurred either directly after the La Cote Interglacial Stage or the event may have occurred during the following cold La Bourns Stage after a hiatus. The climate fluctuations represented at the end of the La Gate Interglacial Stage in the Val-de-Lans basin prompt comparisons with the end of the Eemian Stage (Late Pleistocene) and suggest that such oscillations are characteristic for the end of temperate stages. An understanding of the changes represented here aids the evaluation of present trends as we possibly enter the final phases of the Holocene Stage. Sites of this age and located at this altitude are rare in Europe; therefore, it is proposed that the La Cote site should be considered as a high altitude, alpine parastratotype for the Holsteinian Stage in western Europe

River system evolution and environmental changes during the Lateglacial in the Paris Basin (France).

Abstract Lateglacial sequences from the Paris Basin floodplains provide a general overview of the valleys evolution related to climatic changes from the Weichselian Upper Pleniglacial to the beginning of the Holocene. Comparison between morphostratigraphical and palaeobiological data allows discussion of fluvial dynamics and related palaeoenvironmental conditions. The Upper Pleniglacial/Oldest Dryas transition remains poorly documented. It is represented by sands and silts deposited by a braided channel network. The Bolling begins with a significant incision related to a meandering system which is followed by local organic and minerogenic deposition, contemporaneous with vegetation development. The Older Dryas is evident in several sequences. The Allerod appears more stable and the forest extension is accompanied by a thin soil formation on the banks. The Younger Dryas is characterised by a strong infilling of the valleys by calcareous silts. This last sharp event precedes a second major downcutting phase which takes place in the early Postglacial and is followed by a decline in river flow and sediment supply. This evolution reflects a broad regional pattern of fluvial response which illustrates its sensitivity to climatic change. The study of various morphosedimentary contexts shows their influence on the fluvio-dynamic record and bio-proxies which complicates the detection of minor phases.

Palaeoenvironments and cultural landscapes of the last 2000 years reconstructed from pollen and Coleopteran records in the Lower Rhône Valley, southern France:

For the first time, a high-resolution pollen/Coleoptera joint analysis is performed on a late Holocene sedimentary sequence located in the Lower Rhône Valley. 14C dates validated by pollen data show that the bottom of the sequence is contemporaneous with the Greco-Roman period whereas the top is attributed to the present. This sequence yielded very rich pollen and insect assemblages, enabling a detailed reconstruction of the palaeoenvironment succession during the two last millennia around the site itself and more widely in the Arles plain. The very low pollen representation of trees and the near absence of tree-dependent Coleoptera suggest a marked deforestation of the area. The abundance of dung-beetles and nitrophytes is also in keeping with a strong grazing impact throughout the sequence. Three agricultural phases reflecting a growing level of human activities are identified. Phase 1 is contemporaneous with Celto-ligurian, Greek and Roman civilizations in Provence. At this time the forest cover was already largely destroyed, and pastoralism, cultivation of cereals, olives, vines and walnuts, was practised. Phase 2 is contemporaneous with a period spanning the Merovingian time and the Upper Middle Ages. It is characterized by increased agro-pastoral activities, probably related to the establishment of a monastic community at the Montmajour Abbey and to the settlement of farmers on the nearby Castellet hill. The major characteristic of agricultural phase 3 is the very high pollen percentages of Dipsacus fullonum or teasel, which was formerly extensively cultivated for cloth teasing. This early cultivation of an industrial plant, dated at La Calade to the twelfth century, is recorded for the first time in Provence. It may be connected with craft industries performed by monks at Montmajour Abbey. The sedimentological data suggest a succession of two stability phases interrupted by three flood phases. This interpretation agrees both with insect data, the fluctuating abundances of which are certainly connected with the alternation of ground submersion and dry periods, and with pollen data, marked by the impact of the floods upon the marshy veg etation. However, no clear climatic signal is recorded.

Towards the reconstruction of the Holocene vegetation history of lower Provence : two new pollen profiles from Marais des Baux

Two new14C-dated Holocene pollen profiles from Marais des Baux, Bouches-du-Rhône, France, are presented. The record begins in the Younger Dryas, when the vegetation consisted mainly of grasses and mugwort (Artemisia). The Preboreal was marked by a transitory expansion of pine forests and was followed by the establishment of a rich deciduous oak-forest that included hazel (Corylus) and elm (Ulmus). During the Boreal, hazel played a dominant role within the oak-forest. The oak forests, which includedQuercus ilex, achieved a major expansion during the Atlantic period. The Subboreal was characterised by the regional establishment of, firstly, fir (Abies) and then beech (Fagus). The spread and expansion of beech coincides with the first clear evidence for farming. Agricultural activities brought about the decline of deciduous oak-forest. During the Subatlantic, forests in the vicinity of Marais des Baux were cleared for farming. Cereal growing, which included rye cultivation, was of considerable importance. Three noteworthy characteristics that serve to differentiate the Holocene vegetation history of the low-lying Provence region from other French regions are as follows: 1) the early establishment (from the onset of Preboreal) of low altitude mixed forest; 2) the expansion during the Subboreal of fir and beech in low altitude areas with a Mediterranean climate and, 3) the exceptional taxonomic richness of the pollen assemblages (120 identified taxa) and the presence of borealalpine and Euro-Siberian taxa that no longer exist in Lower Provence.

Colonial seabirds change beetle assemblages on a Mediterranean island

Abstract Island communities are very sensitive to disturbances. Such disturbances include, in particular, pressure from colonial seabird colonies. Seabirds are a major ecological factor driving both species assemblage patterns and community dynamics of plants on islands. However, very little is known about the response of insect assemblages to seabirds, despite the important ecological and functional role of insects within all ecosystems. Here we aimed to assess the response of beetle communities to the influence of a Yellow-legged gull (Larus cachinnans) colony on a small Mediterranean island. The study was conducted on Bagaud island, which is a fully protected reserve within Port-Cros National Park (France), where the yellow-legged gulls are the most densely concentrated. The experiment was designed on a 12-plot transect extending from a low gull-induceddisturbance area to the highly disturbed centre of the colony. Beetle communities were sampled three times during spring and autumn 2001. Beetle patterns across the gradient were analyzed with respect to species ordination, species richness, abundance, and biomass. A total of 255 beetle specimens from 28 species and 15 families were collected. Surprisingly, species richness and the abundance of beetles were not significantly affected by gulls. However, ordination of beetle assemblages showed that there was a marked change in species composition along the gradient of gull influence. The gull colony also affected distribution of feeding-types of beetles. Tenebrionidae species, in particular, seemed to draw strong benefit from such disturbance. Tenebrionidae species, which are polyphagous, markedly increased at the expense of phytophagous species, which decreased. Collected species were likely to be found in other, gull-free environments and were not strictly endemic to Mediterranean islands. However, some species did present particular conservation interests.

Impact of anthropogenic disturbances on beetle communities of French Mediterranean coastal dunes

In coastal dunes, influenced by anthropogenic activities such as tourism, it is important to determine the relative influence of environmental factors at different spatial scales to evaluate the sensitivity of local communities to disturbances. We analyzed beetle communities of 14 dunes of the French Mediterranean coast: four in the relatively preserved Camargue area, and ten in the Var department, where tourism is intensive. Beetle communities were studied three times in early spring using sand sampling. Species-environment relationships were evaluated at the regional, landscape and local scale using redundancy analysis (RDA) and variability partitioning. About 28 species were identified, of which 15 were sand-specialist species, which accounted for more than 93% of total abundance. The beetle communities of Camargue were significantly different from those of the Var department owing to the pullulation of a Tenebrionid species (Trachyscelis aphodioides Latr.) in the Var, except for one restored dune where the community was very similar to those of Camargue. Our results showed no longitudinal gradient between the two regions. Local factors (dune height, preservation and disturbance index) significantly explained most of the variation in the dominance of T. aphodioides, while some other local factors were important for other psammophilous species. This study also suggests that dune beetle communities are strongly affected on beaches intensively managed for tourism, but beetles are still abundant in much disturbed sites.