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As climate model uncertainties remain very large for future rainfall in the Sahel, a multi-centennial perspective is required to assess the situation of current Sahel climate in the context of global warming. We present here the first record of hydroclimatic variability over the past 1600 years in Senegal, obtained from stable oxygen isotope analyses (δ 18 O) in archaeological shell middens from the Saloum Delta. During the preindustrial period, the region was relatively humid, with maximum humidity reached during the period from AD 1500 to AD 1800, referred to as the Little Ice Age. A significant negative link is observed at the centennial scale between global temperature and humidity in the Sahel that is at odds with the expected effects of latitudinal shifts of the intertropical convergence zone during the last millennium. In the context of the past 1600 years, the Western Sahel appears to be experiencing today unprecedented drought conditions. The rapid aridification that started ca. AD 1800 and the recent emergence of Sahel drought from the natural variability point to an anthropogenic forcing of Sahel drying trend. This new long-term perspective suggests that the recovery of Sahel rainfall in the last decade may only result from short-term internal variability, and supports climate models that predict an increase of Sahel drought under future greenhouse climate.

This study presents, for the first time, an environmental reconstruction of a sequence spanning nearly the entire Mediterranean Epipaleolithic (∼22.0–11.9 ka cal. BP). The study is based on a well-dated, high-resolution pollen record recovered from the waterlogged archaeological site Jordan River Dureijat (JRD), located on the banks of Paleolake Hula. JRD's continuous sequence enabled us to build a pollen-based paleoclimate model providing a solid background for the dramatic cultural changes that occurred in the region during this period. Taxonomic identification of the waterlogged wood assemblage collected from JRD was used to fine-tune the paleoenvironmental reconstruction. The chronological framework is based on radiocarbon dating and the typology of archaeological findings. The LGM (∼22–19 ka cal. BP) was found to be the coldest period of the sequence, marked by a distinct decrease in the reconstructed January temperatures of up to 5°C lower than today, while mean annual precipitation was only slightly lower than the present-day average (∼450 vs. 515 mm, respectively). The wettest and warmest period of the record was identified between ∼14.9 and 13.0 ka cal. BP, with maximum values of 545 mm mean annual precipitation reached at ∼14.5 ka cal. BP. This time interval is synchronized with the global warm and moist Bolling-Allerod interstadial as well as with the onset of the Natufian culture and the emergence of sedentism in the Levant. The Younger Dryas began around 12.9 ka cal. BP and was identified as an exceptional period by the JRD sequence with low temperatures and minimal climatic seasonality contrast: an increase in rain contribution during spring, summer, and autumn was documented concurrently with a significant decrease in winter precipitation. The detailed vegetation and climatological reconstruction presented in this study serves as backdrop to seminal events in human history: the transition from small nomadic groups of hunter-gatherers to the sedentary villages of the Natufian, eventually transitioning to the agricultural, complex communities of the Neolithic.

International audience; Lack of constraint on spatial and long-term temporal variability of the El Niño southern Oscillation (ENSO) and its sensitivity to external forcing limit our ability to evaluate climate models and ENSO future projections. Current knowledge of Holocene ENSO variability derived from paleoclimate reconstructions does not separate the role of insolation forcing from internal climate variability. Using an updated synthesis of coral and bivalve monthly resolved records, we build composite records of seasonality and interannual variability in four regions of the tropical Pacific: Eastern Pacific (EP), Central Pacific (CP), Western Pacific (WP) and South West Pacific (SWP). An analysis of the uncertainties due to the sampling of chaotic multidecadal to centennial variability by short records allows for an objective comparison with transient simulations (mid-Holocene to present) performed using four different Earth System models. Sea surface temperature and pseudo-δ18O are used in model-data comparisons to assess the potential influence of hydroclimate change on records. We confirm the significance of the Holocene ENSO minimum (HEM) 3-6ka compared to low frequency unforced modulation of ENSO, with a reduction of ENSO variance of ∼50 % in EP and ∼80 % in CP. The approach suggests that the increasing trend of ENSO since 6ka can be attributed to insolation, while models underestimate ENSO sensitivity to orbital forcing by a factor of 4.7 compared to data, even when accounting for the large multidecadal variability. Precession-induced change in seasonal temperature range is positively linked to ENSO variance in EP and to a lesser extent in other regions, in both models and observations. Our regional approach yields insights into the past spatial expression of ENSO across the tropical Pacific. In the SWP, today under the influence of the South Pacific Convergence Zone (SPCZ), interannual variability was increased by ∼200 % during the HEM, indicating that SPCZ variability is independent from ENSO on millennial time scales.

A new fossil record from the southern Middle Atlas spans continuously the last 25000 years and provides evidence of an increased amount of snow precipitation during the last glacial period and a warm early Holocene with rather dry climate conditions. This environmental reconstruction is based on a multi-proxy approach that integrates pollen, micro-charcoals, grain size and geochemical analysis. During the last glacial period we observe a strong presence of aquatic plants species that today flower during late spring and summer. These occurrences are related to an increased amount of snow precipitation on the surrounding mountains which fed the marsh during the summer season. Although the early Holocene reveals a slight and steady expansion of Mediterranean oaks, the semi-arid Artemisia steppe remained dominant in the landscape until 6.8ka cal BP. Thus, the early Holocene seems to have been less humid than elsewhere in North Africa. The Atlas cedars began to establish around 6ka cal BP. This indicates that the amount of annual rainfall increased after the mid-Holocene. The late Holocene is marked by an increase of fire events, which may be related to a strengthening of the dry season and/or a higher seasonality. Copyright (C) 2016 John Wiley & Sons, Ltd.

The 4.2 ka BP event is defined as a phase of environmental stress characterized by severe and prolonged drought of global extent. The event is recorded from the North Atlantic through Europe to Asia, leading scientists to evoke a 300-yr global mega-drought. Focusing on the Mediterranean and the Near East, this abrupt climate episode radically altered precipitation, with an estimated 30–50 % drop in precipitation in the eastern basin. While many studies reveal similar trends in the northern Mediterranean (from Spain to Turkey and the northern Levant), data from northern Africa and central/southern Levant are more nuanced, suggesting a weaker imprint of this climate shift on the environment and/or different climate patterns. Here, we provide a synthesis of environmental reconstructions for the Levant and show that, while the 4.2 ka BP event also corresponds to a drier period, a different climate pattern emerges in the central/southern Levant, with two dry phases framing a wetter period, suggesting a W-shaped event, particularly well defined by records from the Dead Sea area.

Climate Change in Africa: Evidence, Mechanisms, and Impacts, Past and Present; Marrakesh, Morocco, 6–11 November 2017

Concern is growing that global climate change will have widespread impact on the world’s terrestrial ecosystems, but future impacts are imperfectly constrained by ecosystem models and direct observations. All available data, including records of past ecological change, need to be utilized to assess the range of potential future outcomes. Here we show that pervasive ecosystem transformations occurred in response to warming and associated climatic changes during the last glacial-to-interglacial transition, which was of comparable magnitude to climatic change projected to occur in the next 100 to 150 years under high-emission scenarios. We used data from 596 published paleoecological records to examine compositional and structural changes in global terrestrial vegetation since the last glacial period, and to project the magnitude of ecosystem transformations under different emission scenarios in the future. Our results indicate that terrestrial ecosystems are highly sensitive to temperature change, and suggest that without major reductions in greenhouse-gas emissions to the atmosphere (i.e., in line with those targeted in the 2015 Paris Agreement), most terrestrial ecosystems worldwide are at risk of major transformation, with accompanying disruption of ecosystem services and impacts on biodiversity.

In northern Middle Atlas, the Dayet Iffère is located in an area affected by karst and tectonic. After its watershed genesis of middle altitude during the upper Pleistocene, two lacustrine formation were deposed. The detailed sedmentological study as well as the correlations between the different lacustrine formations defined in Dayet Afourgagh and Dayet Agoulmam, and the 14C dating allowed to reconstitute the major stages of the filling evolution of the lake basin and its sedimentary dynamic. The variations of sedimentation are interpreted as climatic fluctuations and evolution of vegetation since upper Soltanien. These results show a complex interaction between sedimentary processes and climatic phenomena that tend to a stability marked by heat, permanent humidity and a fairly dense vegetation cover at the end of the Soltanian, after probably a hot arid to semi-arid episode.

International audience; This study reconstructs and interprets the changing range of Atlas cedar in northern Morocco over the last 9,000 years. A synthesis of fossil pollen records indicated that Atlas cedars occupied a wider range at lower elevations during the mid-Holocene than today. The mid-Holocene geographical expansion reflected low winter temperatures and higher water availability over the whole range of the Rif Mountains relative to modern conditions. A trend of increasing aridity observed after 6,000 years BP progressively reduced the range of Atlas cedar and prompted its migration toward elevations above 1,400 masl. To assess the impact of climate change on cedar populations over the last decades, we performed a transient model simulation for the period between 1960 and 2010. Our simulation showed that the range of Atlas cedar decreased by about 75% over the last 50 years and that the eastern populations of the range in the Rif Mountains were even more threatened by the overall lack of water availability than the western ones. Today, Atlas cedar populations in the Rif Mountains are persisting in restricted and isolated areas (Jbel Kelti, Talassemtane, Jbel Tiziren, Oursane, Tidighine) that we consider to be modern microrefugia. Conservation of these isolated populations is essential for the future survival of the species, preserving polymorphisms and the potential for population recovery under different climatic conditions.

A new record from the heart of the Moroccan Middle Atlas cedar forests spans the last 18 000 years and provides valuable insight into our understanding of the natural vegetation and environmental changes. The approach is based on the study of pollen content, geochemical elements and grain size analysis. The pollen data indicate that the vegetation was dominated by herbaceous plants until 9000 BP. Such open landscape allowed greater soil erosion and an input of chemical elements from the watershed. After 9000 BP, tree cover, mainly oak, increased slightly and was accompanied by a higher taxonomic diversity. However, several steppe elements remain well represented in the area until 5000 BP, which suggests that the climate was rather dry during the first part of the Holocene. After 6000 BP, the climate became more favourable to expansion of the forest ecosystems, including Cedrus atlantica, thereby reducing erosion. A strong reduction of the tree pollen percentages is recorded after 2000 BP, which may be related to increasing human activities during the Roman period. These forest changes are concomitant with an increase of lead and copper concentrations in the record, probably related to Roman metalworking activities.

International audience; AimOur aims were to provide new pollen data for establishing a sub‐continental surface pollen database (East Asian Pollen Database, EAPD) and to study relationships between vegetation and climate.LocationThe sample sites covered most regions of East Asia, including China, Mongolia, the Russian Far East, Vietnam, Cambodia and Thailand.MethodsData quality control procedures were applied, including taxonomic standardization, removal of duplicates, and adjustment of geographical coordinates. Vegetation types and climate parameters were assigned to each sample. Modern pollen distribution maps were drawn using circle scattergrams. The plots of pollen percentages versus climate variables allowed quantitative estimates of climate values. The modern analogue technique (MAT) was used to predict modern biomes and climate parameters.ResultsPollen assemblages extracted from 2858 sites were used to model the geographical distribution of selected taxa and their relationships with climate. For most taxa, the reconstructed range fitted the observed geographical distribution rather well. Arboreal pollen (AP) and Pinus dominated the transition zone between forest and steppe. Use of the MAT revealed that the predicted and observed biomes matched in 71% of the cases. The warm temperate evergreen broadleaf forest had the best agreement between predictions and observations. Climate values reconstructed using MAT were highly correlated with observed values in January temperature. The correlation coefficient of the temperature variables ranged from 0.799 to 0.930 and was as high as 0.939 for precipitation.Main conclusionsThis paper documents a new modern pollen database for East Asia and makes the data readily available. The reconstructed biomes and climate variables are significantly correlated with the observed values, thus demonstrating the utility of the pollen database for future multiscale palaeoenvironmental studies.

International audience; Although it is generally agreed that the Arctic flora is among the youngest and least diverse on Earth, the processes that shaped it are poorly understood. Here we present 50 thousand years (kyr) of Arctic vegetation history, derived from the first large-scale ancient DNA metabarcoding study of circumpolar plant diversity. For this interval we also explore nematode diversity as a proxy for modelling vegetation cover and soil quality, and diets of herbivorous megafaunal mammals, many of which became extinct around 10 kyr bp (before present). For much of the period investigated, Arctic vegetation consisted of dry steppe-tundra dominated by forbs (non-graminoid herbaceous vascular plants). During the Last Glacial Maximum (25-15 kyr bp), diversity declined markedly, although forbs remained dominant. Much changed after 10 kyr bp, with the appearance of moist tundra dominated by woody plants and graminoids. Our analyses indicate that both graminoids and forbs would have featured in megafaunal diets. As such, our findings question the predominance of a Late Quaternary graminoid-dominated Arctic mammoth steppe.

Aim Vegetation dynamics and the competitive interactions involved are assumed to restrict the ability of species to migrate. But in most migration modelling approaches disturbance-driven succession and competition processes are reduced to simple assumptions or are even missing. The aim of this study was to test a combination of a migration model and a dynamic vegetation model to estimate the migration of tree species controlled by climate, environment and local species dynamics such as succession and competition. Location Europe. Methods To estimate the effect of vegetation dynamics on the migration of European beech and Norway spruce, we developed a post-process migration tool (LPJ-CATS). This tool integrates outputs of the migration model CATS and the dynamic vegetation model LPJ-GUESS. The model LPJ-CATS relies on a linear dependency between the dispersal kernel and migration rate and is based on the assumption that competition reduces fecundity. Results Simulating potential migration rates with the CATS model, which does not account for competition and disturbance, resulted in mean Holocene migration rates of 435 +/- 55 and 330 +/- 95 m year(-1) for the two species Picea abies and Fagus sylvatica, respectively. With LPJ-CATS, these mean migration rates were reduced to 250 +/- 75 and 170 +/- 60 m year(-1) for spruce and beech, respectively. Moreover, LPJ-CATS simulated migration pathways of these two species that generally comply well with those documented in the palaeo-records. Main conclusions Our 'hybrid' modelling approach allowed for the simulation of generally realistic Holocene migration rates and pathways of the two study species on a continental scale. It suggests that competition can considerably modify spread rates, but also the magnitude of its effect depends on how close climate conditions are to the niche requirements of a particular species. (Less)

International audience; The Cederberg Mountains (Western Cape Province, South Africa) are located within the Fynbos Biome, which exhibits some of the highest levels of species richness and endemism in the world. The region's post-glacial vegetation history, however, remains largely unknown. Presented here are high resolution pollen and microcharcoal records spanning the last 15,600 years obtained from the De Rif rock hyrax midden from the Driehoek Valley of the central Cederberg. In this region, previous pollen studies have shown muted variability in vegetation community composition during periods of globally marked climatic variability (e.g. the last glacial–interglacial transition). In our record, however, significant changes in vegetation composition are apparent. Most notably, they indicate a shift from ericaceous/restioid fynbos (present from 15,600 to 13,300 cal yr BP) to a brief, but prominent, development of proteoid fynbos at the beginning of the Holocene around 11,200 cal yr BP. This vegetation shift is associated with increased moisture at the site, and coincides with reduced fire frequency as indicated by the microcharcoal record. At 10,400 cal yr BP, there is a marked reduction in Protea-type pollen, which is replaced by thicket, characterised by Dodonaea, which became the dominant arboreal pollen type. This shift was likely the result of a long relatively fire-free period coupled with warmer and wetter climates spanning much of the early Holocene. A brief but marked decrease in water availability around 8500–8000 cal yr BP resulted in the strong decrease of Dodonaea pollen. The vegetation of the mid-to late Holocene is characterised by the increased occurrence of Asteraceae and succulent taxa, suggesting substantially drier conditions. These data give unprecedented insight into the vegetation dynamics across a period of substantial, rapid climate change, and while they confirm the presence of fynbos elements throughout the last 15,600 years, the results highlight significant fluctuations in the vegetation that were triggered by changes in both climate and fire regimes.

International audience; In southeast Africa – a region for which few palaeoenvironmental records are available – the fossil pollen record from the Wonderkrater spring mound has contributed substantially to our understanding of past vegetation change since the Last Glacial Maximum (LGM; 21 ka). Multivariate analysis of the pollen data by Scott and Thackeray (1987) provided environmental reconstructions suggesting relatively mesic LGM conditions, with warm and dry conditions during the early Holocene (11–6 cal kBP). This conforms to predicted patterns of precipitation change in the southern African tropics in response to Northern Hemisphere cooling and or-bital forcing. Subsequent data from the Cold Air Cave speleothems and a sea-surface temperature record from the Mozambique Channel, however, indicate that conditions during the early to mid-Holocene may have been wetter than present in the Wonderkrater region. To explore this question further, we have created a series of botanical–climatological transfer functions based on a combination of modern climate and plant distribution data from southern Africa. Applying these to the Wonderkrater fossil pollen sequence, we have derived quantitative estimates for temperatures during the cold and warm quarters, as well as precipitation during the wet and dry quarters. In addition, a species-selection method based on Bayesian statistics is outlined, which provided a parsimonious choice of likely plant species from what are otherwise taxonomical-ly broad pollen-types. We do not propose that our findings invalidate the previous principal component analyses, but they do have the advantage of being based more clearly on the relationship between modern plant distributions and individual climatic variables. Results indicate that temperatures during both the warm and cold seasons were 6 ± 2 °C colder during the LGM and Younger Dryas, and that rainy season precipitation during the Last Gla-cial Maximum was ~ 50% of that during the mid-Holocene. Our results also imply that changes in precipitation at Wonderkrater generally track changes in Mozambique Channel sea-surface temperatures, with a steady increase following the Younger Dryas to a period of maximum water availability at Wonderkrater ~ 3–7 ka. These findings argue against a dominant role of a shifting Intertropical Convergence Zone in determining long-term environmental trends, and indicate that the northern and southern tropics experienced similar climatic trends during the last 20 kyr.

A high-resolution pollen record obtained from Pingnan County, Fujian province in China, provides new insights into the nature of ecosystem changes and the relative importance of human disturbances during the last 1300 years. Pollen and stable carbon isotope data indicate that prior to about 800 cal BP the study area was covered by a natural forest, dominated by evergreen broad-leaved trees (Castanopsis and Quercus). This primeval vegetation was then progressively replaced by the secondary vegetation after similar to 800 cal BP. Increases of Gramineae pollen since similar to 800 cal BP and a sharp rise in Pinus pollen after similar to 450 cal BP clearly express the expansion of human impacts, reflecting the expansion of farming and the succession of a now-widespread Pinus massoniana after alteration of the primeval vegetation. Taxonomic diversity analysis also shows that the floristic diversity is higher during the period of human disturbances than in the earlier part of the record, a phenomenon that has been observed in temperate pollen records where human activities increased.

Aim Species distribution models (SDMs) based on current species ranges underestimate the potential distribution when projected in time and/or space. A multi-temporal model calibration approach has been suggested as an alternative, and we evaluate this using 13,000 years of data. Location Europe. Methods We used fossil-based records of presence for Picea abies, Abies alba and Fagus sylvatica and six climatic variables for the period 13,000 to 1000 yr bp. To measure the contribution of each 1000-year time step to the total niche of each species (the niche measured by pooling all the data), we employed a principal components analysis (PCA) calibrated with data over the entire range of possible climates. Then we projected both the total niche and the partial niches from single time frames into the PCA space, and tested if the partial niches were more similar to the total niche than random. Using an ensemble forecasting approach, we calibrated SDMs for each time frame and for the pooled database. We projected each model to current climate and evaluated the results against current pollen data. We also projected all models into the future. Results Niche similarity between the partial and the total-SDMs was almost always statistically significant and increased through time. SDMs calibrated from single time frames gave different results when projected to current climate, providing evidence of a change in the species realized niches through time. Moreover, they predicted limited climate suitability when compared with the total-SDMs. The same results were obtained when projected to future climates. Main conclusions The realized climatic niche of species differed for current and future climates when SDMs were calibrated considering different past climates. Building the niche as an ensemble through time represents a way forward to a better understanding of a species' range and its ecology in a changing climate.

The CARAIB (CARbon Assimilation In the Biosphere) model is used to study the vegetation distribution during the Late Miocene (Tortonian). In this version, the plant classification is specifically adapted to best represent Miocene European vegetation. Compared to other plant classifications used in global models, this adapted classification is more refined, since it is specifically developed for European vegetation and it includes various thermophylous tree types, which were present in Europe during the Miocene. The corresponding climatic tolerance parameters are based on the study of Laurent et al. (Journal of Vegetation Science, 15, 739-746, 2004 ) for the tree types currently present in Europe and on the distribution of analogue species in southeastern Asia and North/Central America for the thermophylous (sub-tropical) trees. The same classification is used to characterize the palaeoflora at the available Late Miocene localities, allowing a model–data comparison at the plant functional type level, rather than at the biome level. The climatic inputs to CARAIB are obtained from the COSMOS atmosphere–ocean general circulation model. The climatic anomalies (Tortonian minus Present) derived from COSMOS are interpolated to a higher spatial resolution before being used in the vegetation model. These anomalies are combined with a modern climatology to produce climatic fields with high spatial resolution (10′ × 10′). This procedure has the advantage of making apparent relief features smaller than the grid cells of the climate model and, hence, makes easier the comparison with local vegetation data, although it does not really improve the quality of the Tortonian climate reconstruction. The new version of CARAIB was run over Europe at this higher spatial resolution. It calculates the potential distribution of 13 different classes of trees (including cold/cool/warm-temperate, sub-tropical and tropical types), together with their cover fractions, net primary productivities and biomasses. The resulting model vegetation distribution reconstructed for the Tortonian is compared to available palaeovegetation and pollen data. Before performing this comparison, the tree taxa present at the various data sites are assigned to one or several model classes, depending on the identification level of the taxa. If several classes are possible for a taxon, only those that can co-exist with the other tree classes identified at the site are retained. This methodology is similar to the co-existence approach used in palaeoclimatic reconstructions based on vegetation data. It narrows the range of tree types present at the various sites, by suppressing in the data the extreme types, such as the cold boreal/temperate and tropical trees. The method allows a comparison with the model simulation on a presence/absence basis. This comparison provides an overall agreement of 53% between the model and the data, when all sites and tree types are considered. The agreement is high (> 85%) for needle-leaved summergreen boreal/temperate cold trees (Larix sp.) and for tropical trees, intermediate (> 40%) for other boreal/temperate cold trees and for needle-leaved evergreen temperate cool trees, broadleaved summergreen temperate cool trees and broadleaved evergreen warm-temperate trees, and poor (

Long-term vegetation studies are needed to better predict the impact of future climate change on vegetation structure and distribution. According to the IPCC scenario, the Mediterranean region is expected to undergo significant climatic variability over the course of this century. Cedrus libani (A. Rich), in particular, is currently distributed in limited areas in the Eastern Mediterranean region, which are expected to be affected by such climate change. In order to predict the impact of future global warming, we have used fossil pollen data and model simulations. Palaeobotanical data show that C. libani has been affected by both climate change and human activities. Populations of C. libani survived in refugial zones when climatic conditions were less favourable and its range extended during periods of more suitable climate conditions. Simulations of its future geographical distribution for the year 2100 using a dynamic vegetation model show that only three areas from Mount Lebanon may allow its survival. These results extrapolated for cedar forests for the entire Eastern Mediterranean region show that forests in Syria are also threatened by future global warming. In southern Turkey, cedar forests seem to be less threatened. These results are expected to help in the long-term conservation of cedar forests in the Near East.

International audience; A borehole core from Lake Ifrah (Middle Atlas, Morocco) provided a unique, continuous record of environmental change spanning the past c. 29,000 years cal BP (29 ka). A study of its organic matter, carbonates and magnetic susceptibility allowed us to reconstruct past climate changes and their impact on the lake's catchment area. The geochemical and pollen data show that the prevailing climate in the Middle Atlas from c. 29 ka to c. 12 ka was cold with a succession of dry and more humid periods. Prior to 24 ka the area surrounding Lake Ifrah enjoyed a relatively wet climate that allowed the survival of rare tree vegetation despite the overall cold conditions. After 12 ka, an increase in primary productivity and arboreal pollen is documented indicating the development of forest vegetation.

Predicting future ecosystems changes is necessary for better managing human resources. Such forecasting requires robust vegetation models which have been tested versus observed field data. Nowadays, it is very common that a simulation model is firstly validated using modern observed data and then tested versus palaeodata. In a sense, ecological data represent the natural laboratory for modelers. Thus, palaeo and actuo-ecological data are key points when dealing with predicting future changes. The present work represents the first step in such data-model comparison approach. Here, we use only modern plants distributions to test the robustness of our ecosystems definitions and use these definitions for testing a dynamic vegetation model. We have defined twenty-nine Bioclimatic affinity groups (BAGs) for 196 dominant plant species including trees, shrubs and herbs in China. These BAGs are characterized by the phenology and the climatic tolerances of the species they include. They are detailed enough to describe all vegetation types in China including the tropical, the subtropical, the temperate and the high altitude (Tibet Plateau) ecosystems. The climatic thresholds of these 29 BAGs were then used to test and validate a global dynamic vegetation model (CARAIB). The simulated BAGs are in good agreement with those observed in China, especially in the Tibetan Plateau and in the subtropical ecosystems. Broadly, all simulated BAGs fit quite well with the modern distribution. However, they all cover larger areas than the observed distributions, especially in the temperate region and in some areas in the northwest and the tropical zone. These discrepancies between simulated and observed distributions are related to the fact that the vegetation models simulate potential distributions. In China during recent decades natural ecosystems, mostly in the temperate zone, have been strongly altered in their species composition and geographical extent by different human activities such as the intense cultivation, deforestation, introduction of fast growing species and grazing.

Norway spruce (Picea abies [L.] Karst.) is a broadly distributed European conifer tree whose history has been intensively studied by means of fossil records to infer the location of full-glacial refugia and the main routes of postglacial colonization. Here we use recently compiled fossil pollen data as a template to examine how past demographic events have influenced the species' modern genetic diversity. Variation was assessed in the mitochondrial nad1 gene containing two minisatellite regions. Among the 369 populations (4876 trees) assayed, 28 mitochondrial variants were identified. The patterns of population subdivision superimposed on interpolated fossil pollen distributions indicate that survival in separate refugia and postglacial colonization has led to significant structuring of genetic variation in the southern range of the species. The populations in the northern range, on the other hand, showed a shallow genetic structure consistent with the fossil pollen data, suggesting that the vast northern range was colonized from a single refugium. Although the genetic diversity decreased away from the putative refugia, there were large differences between different colonization routes. In the Alps, the diversity decreased over short distances, probably as a result of population bottlenecks caused by the presence of competing tree species. In northern Europe, the diversity was maintained across large areas, corroborating fossil pollen data in suggesting that colonization took place at high population densities. The genetic diversity increased north of the Carpathians, probably as a result of admixture of expanding populations from two separate refugia.

The geographical distribution of dominant plant species in China was georeferenced and climatic variables were interpolated into all grids. Accordingly, the percentage distributions of principal pollen taxa based on 1860 surface pollen sites in China were selected and the related climate values were interpolated with the same method. The geographical and climatic comparison between the two datasets indicated that the climate threshold of most pollen taxa from surface pollen is coherent with plant distributions. The climatic envelopes of dominant plant are mostly accordant with those of pollen taxa at certain levels. However, some distinct offsets of the climate ranges exist between the two datasets for most pollen taxa identified at family level, such as Ericaceae, Asteraceae, Poaceae and Chenopodiaceae. The present study provides for the first time rich information on temperature and precipitation in relation to pollen and plant distribution based on the datasets on a continental scale useful for global ecological modeling and Quaternary palaeoclimate reconstruction.

The Holocene climate is known to be rather stable although with few abrupt changes that lasted few decades. The present study is related the climate changes and their environmental impacts during the last 6000 years from a fossil record collected in the Middle Atlas, Morocco. Reconstruction of three climate variables (January temperature (Tjan), annual precipitation (Pann) and a precipitation seasonal index (SI)) was based on pollen data and analyzed various bio and geo-chemical elements. Then we evaluated the relationships between all the environmental variables. Climate over the last 6000 years was rather stable with a smooth trend of aridity towards the present. Tjan has varied within about 2 °C range and Pann within less than 100 mm yr−1. Despite such overall climate stability, after ca. 3750 cal BP some important changes were observe in the ecosystem composition, the carbon isotopic contents of organic matter in lake sediments (δ13C), the total organic carbon and nitrogen amount and the carbon to nitrogen ratio (C / N). These environmental changes are related to the transition in the conifer forest between the Atlas cedar, which expanded after 3750 cal BP, and the pine forest. These vegetation changes have impacted the sedimentation type and composition into the lake. Between 5500 and 5000 cal BP an abrupt change is recorded in all bio and geo-chemical indicators as well as in the pollen data. The multi-proxy analysis, taking into account the climate variables, tends to indicate that it was mainly a decrease in temperature without a significant change in the overall amount of precipitation. In summary, the present study confirms the overall climate stability over the last 6000 years and highlights the presence of short and abrupt climate events.

Summary We present here a review of the recolonisation of the Atlantic oakwoods following the end of the last glacial period. The study is based on two independent data sources: palaeoecological and phylogeographical data. The spread of oak is examined at two scales: (1) continental, allowing a consideration of the location of glacial refugia and the broad outlines of the migration, (2) the Atlantic coastal region, in order to establish the specific history of the Atlantic oakwoods. Climatic and human controls on the timing, speed and pattern of spread are considered, in particular, the conditions of the early Holocene period during which the majority of the recolonisation took place.

In this paper we reconstruct the location of the last glacial refugia and postglacial spread of Abies throughout Europe based on combined pollen and macrofossil data. More than 208 pollen sequences available in the European Pollen Database (EPD) and 38 macrofossil sites are used to produce distribution maps encompassing a time span between 38000 and 5500 years B.P. The investigation excludes more recent periods, because these could be strongly influenced by human impact. The pollen data presented here confirm long-lasting refugial areas such as southern Italy and Greece already described in previous studies. The combined pollen/macrofossil dataset identifies the Pyrenees as a further important refugium. In addition the pollen data indicate potential refugia in south-east France and north-west Italy. Possible migration tracks of Abies are discussed by comparing the palaeobotanical evidence with isozyme studies on gene markers of recent fir populations.

Question: How to refine simulations based on a global vegetation model in order to apply it to regional scale? Location: Europe from 35° N to 71° N and 25° W to 70° E. Methods: Geographical ranges of European plants were georeferenced and used with monthly mean climatic data (diurnal temperature ranges, ground frost frequencies, precipitation, relative humidity, rain frequencies, amount of sunshine hours and temperature) and growing degree days to infer climatic boundaries for 320 taxa. We performed a discriminant analysis to define their potential geographic ranges. Hierarchical clustering was computed on potential ranges. Results: Clustering provided 25 Bioclimatic Affinity Groups (BAG) of plants consisting of 13 tree, seven shrub and five herb groups. These BAGs are characterized by different geographical ranges and climatic tolerances and requirements. Conclusion: The use of monthly data instead of annual values improved the prediction of potential distribution ranges and highlighted the impo...

Aim This paper presents a probabilistic method for the characterization of pollen taxa using attributes, and for the reconstitution of past biomes. The probabilities are calculated on the basis of European floristic and pollen databases sufficiently large and exhaustive to provide robust estimates. Location The analysis is based on data from approximately 1000 sites throughout Europe. Method We use all the pollen data from the European Pollen Database (EPD), which contains about 50 000 pollen assemblages distributed across Europe and covering the period from the Last Glacial Maximum to the present. Using existing floras, each pollen taxon has been characterized by allocating one or more modes of several attributes, chosen according to the biogeography and phenology of the taxon. With this information, conditional probabilities are defined, representing the chance of a given attribute mode occurring in a given pollen spectrum, when the taxa assemblage is known. The concept of co-occurrence is used to provide a greater amount of information to compensate for difficulties in the identification of pollen grains, allowing a better interpretation when there is little diversity in the pollen assemblage. Results The method has been validated using a dataset of modern samples against existing methods of biome classification and remote sensing data. An application is proposed in which the new method is used to produce biomes for pollen data 6000 years ago. This confirms previous results showing an extension of the deciduous forest to the north, east and south, explained by milder winters in western and northern Europe, and cooler and wetter climate in the Mediterranean region. Conclusion The results show the new method to be efficient, reliable and flexible and to be an improvement over the previous method of biomization. They will be used to test simulations of earth system models running on periods with climate significantly different from the present day, enabling a robust test of the validity of applying these models to the future.

During the last two decades, numerous studies applied to various continental deposits have highly improved the knowledge of environmental changes in Western Europe during the last climatic cycles. Here we review a set of available data, and try to correlate and compare the three long lacustrine sequences from France (La Grande Pile, Les Echets and Le Velay) with other west European discontinuous limnic deposits, fluvial systems and lœss accumulations. Limnic sequences provide the best records of the last Interglacial and Early Glacial (ca. 125–75 kyr) allowing a clear picture of environmental changes during this interval. Nevertheless, there are divergent interpretations on the timing and climate regime of the last Interglacial. During the last Glacial, in the North Atlantic deep-sea cores and Greenland ice cores, short-term abrupt climatic fluctuations (Bond events, Dansgaard–Oeschger events) which are poorly or partly reflected on the continent have been recognised. The classical subdivision in a Lower (ca. 75–55 kyr) (very cold), Middle (ca. 55–29 kyr) (cold) and Upper Pleniglacial (ca. 29–15 kyr) (very cold) is confirmed both by limnic and terrestrial sequences. In the Rhine valley, north-eastern France, Belgium and the Netherlands, subcontinuous lœss accumulation, river systems and associated periglacial features provide quantitative climate reconstructions that are compared with those obtained from limnic sequences. Interstadial events may be correlated with the major warm oscillations of the GRIP core. During the Upper Pleniglacial, no clear vegetation changes are apparent from lacustrine pollen sequences, whereas thick lœss accumulations have registered a succession of climatic changes. The timing of the Lateglacial warming is now well documented from rare annually laminated lake sediments.

The geographic distribution throughout Europe of each of 32 chloroplast DNA variants belonging to eight white oak species sampled from 2613 populations is presented. Clear-cut geographic patterns were revealed by the survey. These distributions, together with the available palynological information, were used to infer colonisation routes out of the glacial period refugia. In western Europe in particular, movements out of the Iberian and the Italian Peninsulas can be clearly identified. Separate refugia are also present in eastern Balkans, whereas further west in this peninsula similarities with Italy were evident. Movements resulting in the exchange of haplotypes between refugia both during the present interglacial and probably also during earlier glacial cycles were therefore inferred. The consequences of these past exchanges is that phylogenetically divergent haplotypes have sometimes followed very similar colonisation routes, limiting somewhat the phylogeographic structure. Cases of geographic disjunction in the present-day distribution of haplotypes are also apparent and could have been induced by the existence of rapid climatic changes at the end of the glacial period (specifically the Younger Dryas cold period), which resulted in range restriction following an early warm period during which oak first expanded from its primary refugia. This cold phase was followed by a new period of expansion at the outset of the Holocene, involving in some cases ‘secondary’ refugia. It is expected that these short climate oscillations would have led to a partial reshuffling of haplotype distribution. Early association between haplotypes and oak species are also suggested by the data, although extensive introgression among species has ultimately largely blurred the pattern. This implies that colonisation routes may have been initially constrained by the ecological characteristics of the species hosting each chloroplast variant. We suggest for instance that two oak species distributed in the north of the Iberian Peninsula ( Quercus petraea and Q. pubescens ) are recent post-glacial immigrants there. When considered together, conclusions on the location of glacial period refugia and the colonisation routes derived from molecular information and fossil pollen data appear to be both largely compatible and complementary.

Several methods currently exist to quantitatively reconstruct palaeoclimatic variables from fossil botanical data. Of these, pdf-based (probability density functions) methods have proven valuable as they can be applied to a wide range of plants assemblages. Most commonly applied to fossil pollen data, their performance, however, can be limited by the taxonomic resolution of the pollen data, as many species may belong to a given pollen-type. Consequently, the climate information associated with different species cannot sometimes not be precisely identified, resulting less accurate reconstructions. This can become particularly problematic in regions of high biodiversity. In this paper, we propose a novel pdf-based method that takes into account the different climatic requirements of each species constituting the broader pollen-type. Pdfs are fitted in two successive steps, with parametric pdfs fitted first for each species, and then a combination of those individual species pdfs into a broader single pdf to represent the pollen-type as a unit. A climate value for the pollen assemblage is estimated from the likelihood function obtained after the multiplication of the pollen-type pdfs, with each being weighted according to its pollen percentage. To test the robustness of the method, we have applied the method to southern Africa as a regional case study, and reconstructed a suite of climatic variables based on extensive botanical data derived from herbarium collections. The reconstructions proved to be accurate for both temperature and precipitation. Predictable exceptions were areas that experience conditions at the extremes of the regional climatic spectra. Importantly, the accuracy of the reconstructed values is independent from the vegetation type where the method is applied or the number of species used. The method used in this study is publicly available in a software package entitled CREST (Climate REconstruction SofTware) and will provide the opportunity to reconstruct reliable quantitative estimates of climatic variables even in areas with high geographical and botanical diversity.

The atmospheric CO2 content is expected to continue to increase and probably induce warming at the global scale during the next century. The impact of such an increase will affect the composition and distribution of ecosystems on the same scale. To predict the integrated whole-ecosystem response to the CO2 increase in the Mediterranean region we used a vegetation biogeochemical model. This model (BIOME3) integrates monthly temperature and precipitation, some soil characteristics, cloudiness and CO2 concentration as inputs to simulate the vegetation in terms of biomes. First we demonstrate the ability of the model to simulate past vegetation when tested versus pollen data. Second we use the vegetation model for different climate scenarios and report results of future changes in the Mediterranean vegetation. These simulations indicate that an increase of the atmospheric CO2 to 500 ppmv, jointly with an increase of about 2 °C of the mean annual temperature, as simulated by several atmospheric general circulation models, should be accompanied by a severe reduction (more than 30%) of the present annual precipitation to change significantly the present vegetation surrounding the Mediterranean. When precipitation is maintained at its present-day level, an evergreen forest spreads in the eastern Mediterranean and a conifer forest in Turkey. In NW Africa, a woody xerophytic vegetation occupies a more extensive territory than today and replaces part of the present steppe area.

International audience; Pollen data from 18,000 C-14 yr sp were compiled in order to reconstruct biome distributions at the last glacial maximum in southern Europe and Africa. Biome reconstructions were made using the objective biomization method applied to pollen counts using a complete list of dryland taxa wherever possible. Consistent and major differences from present-day biomes are shown. F orest and xerophytic woods/scrub were replaced by steppe, both in the Mediterranean region and in southern Africa, except in south-western Cape Province where fynbos (xerophytic scrub) persisted. Sites in the tropical highlands, characterized today by evergreen forest, were dominated by steppe and/or xerophytic vegetation (cf. today's Ericaceous belt and Afroalpine grass land) at the last glacial maximum. Available data from the tropical lowlands are sparse but suggest that the modern tropical rain forest was largely replaced by tropical seasonal forest while the modern seasonal or dry forests were encroached on by savanna or steppe. Montane forest elements descended to lower elevations than today.

Using a climatic calibration based on the scores of the plant functional types (PFTs) calculated for 1245 surface pollen spectra, the climate at 6 ka BP has been reconstructed for a set of 116 pollen spectra from the former Soviet Union and Mongolia. The results are presented as maps of climatic anomalies and maps of probability classes showing the significance of these differences from the modern climate. The reconstructed patterns are spatially coherent, but have confidence levels that vary from region to region, due to the often-large error ranges. At 6 ka, the winters were more than 2oC warmer than today north of 50oN, with a high significance east of the Urals. Summers were also more than 2oC warmer than today with a high level of confidence north of the Polar Circle and in central Mongolia. In the mid-latitudes of Siberia, in northern Kazakhstan and around the Black and the Caspian seas, 6 ka summers were significantly cooler than today. The reconstructed moisture availability (ratio of actual to equilibrium evapotranspiration) was more than 10% higher than today in the Ukraine, southern Russia and northern Mongolia, and more than 10% lower than today in central Mongolia. This pattern corresponds partly with that of the water budget (annual precipitation minus evaporation) reconstructed from lake level records. © 1999 Elsevier Science B.V. All rights reserved.

An objective method for the assignment of pollen spectra to appropriate biomes has been published recently. The aim of this paper is to improve the distinction between warm and cool steppes, thus refining vegetation and climate reconstruction, particularly during the Last Glacial Maximum. A set of modern pollen spectra from the Mediterranean and Kazakhstan regions, dominated today by open vegetation types, has been analysed statistically in order to relate pollen taxa abundances to warm acid cool grass/shrub plant functional types (PFTs). A statistical test using modern pollen data shows that the method is able to distinguish between cool and warm steppe biomes with a high degree of confidence. The method has been applied to two fossil pollen records. The results of this exercise showed that cool steppe dominated in central Greece between 18 000 and 13 000 yr BP, while in western Iran the vegetation was at the boundary between cool and warm steppes. These vegetation types were replaced by warm mixed forest in Greece and warm steppe in Iran after that time span. (C) 1998 John Wiley & Sons, Ltd.

Here we investigate the processes leading to high organic content and high pollen concentration in pelagic marine sediments. Three marine cores near the base of the Nile River cone display the classical Quaternary sequence of sapropels and hemipelagic muds. Large variations in total pollen concentration, as well as in percentage composition of the pollen assemblage are clearly linked to the two lithological types. All pollen types have much higher concentration in sapropels than in muds, by 3 or 4 orders of magnitude. Within sapropels, the percentages of Gymnosperms (Pinus and Cedrus) pollen and Pteridophyte spores, are very low and the pollen spectrum is dominated by various Angiosperms. These variations in total pollen concentration as well as in percentages cannot be accounted for by variations in pollen production, or in efficiency of transport, because they similarly involve pollen of different areas and climates, transported to the sea by different means. The cause for these variations can only be a difference in preservation of pollen. Preservation is good in sapropels for all pollen types, but generally poor in muds. We believe that sapropels were deposited under reducing bottom waters which allowed a better preservation of the organic matter including pollen.

Pollen spectra from three eastern Mediterranean cores have been used to document the paleoclimates of the Levantine Basin borderlands over the last 250 kyr to establish the relationship between this regional climate data set and the global climate as recorded by foraminiferal δ18O and to compare it with proximal land pollen records. Core MD 84 642 with eight sapropels covers the last two climatic cycles up to the early Holocene, MD 84 627 with four sapropels goes back to 125 kyr, and MD 84 629 with one sapropel covers the last 70 kyr. The sedimentation rate decreases from core 629, located at the shallowest depth beneath the Nile River plume, to cores 627 and 642. During the interglacials defined by a low 18O/16O ratio, the abundance of tree pollen is maximum and points to an optimum Mediterranean climate with greatest humidity, including some summer rainfall. During glacial maxima, with highest 18O/16O ratio, the pollen abundance is high for steppe and semidesert plants and low for trees, indicating a definitely more arid, more continental, and probably colder climate. The variations of pollen abundance occur in phase with those of the foraminifer δ18O record. This signifies that the regional climate of the Levantine Basin borderlands had the same temporal pattern as the global ice volume documented by the ice volume curve.

International audience; 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 modem analogues for the herbaceous vegetation of the cold periods. We propose a method to distinguish between steppes and tundra vegetations for which the modems 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 Taxus) at about 125 ka B.P. needs still to be correlated with high resolution ocean and ice cores.

Past climates provide a testing bed for the predictive ability of general circulation models. A number of studies have been performed for periods where the climate forcings are relatively different from the present and there is a good coverage of data. For one of these periods, the mid-Holocene (6 ka before present), models and data show a good match over northern Europe, but disagree over the south, where the data show cooler summers and winters and more humid conditions. Understanding the reasons for this disagreement is important given the expected vulnerability of the region under scenarios of future change. We present here a set of different past climate scenarios and sensitivity studies with a global vegetation model in order to try and understand this disagreement. The results show that the vegetation changes can be explained by a combination of both increased precipitation, and a reduction in the length of the growing season, controlled by a reduction in winter temperatures. The matching simulated circulation patterns support the hypothesis of increased westerly flow over this region.

Continuous pollen and isotopic records were established for core BAN 84 09 GC retrieved from the anoxic Bannock Basin in the Eastern Mediterranean. On the basis of two 14C dates, they document the palaeoclimate between about 25.7 ka B.P. and 5.2 ka B.P. in the northern borderlands of the Ionian Basin. The upper half of the core has been redeposited. The isotopic record displays a correlation with pollen percentages that is strong and positive for Artemisia (sage-brush) and negative for Quercus (oak). The last glacial maximum and the deglaciation are identified by these combined taxa, together with Chenopodiaceae. The glacial maximum around 18 ka B.P. (which has elsewhere been dated from 20 to 15 ka B.P.) has pollen percentages that are high for Artemisia and low for Quercus. The climate in the pollen source area was arid, cold in winter, briefly warm in summer and sustained the vegetation of a semi-desert. The onset of deglaciation after 18 ka B.P. coincides with that of the decline in Artemisia pollen percentage. However, this decline does not indicate reduced aridity, because it is accompanied by a pollen percentage rise of the even more arid herbs Chenopodiaceae and Ephedra. Throughout the deglaciation from 18 to 11 ka B.P., the aridity progressively increases, culminating at 11 ka B.P. This trend is briefly interrupted by a more humid event, shown by a peak in Artemisia pollen percentage and a smaller peak in oak; these two peaks are coeval with the Bolling-Allerod chronozone (13-11 ka B.P.). Maximum aridity occurs during the Younger Dryas chronozone (11-10 ka B.P.). Afterwards, the oak pollen percentage begins a steady increase, and its maximum value is coeval with the lowest isotopic value, dated at 8760 ± 170 yr B.P. This period was one of high moisture, warm summers, and, according to altitude, mild to cool winters. This climate sustained forests that were Mediterranean in the lowlands and warm temperate in the uplands. A high pollen concentration is observed during this period and reveals the presence of sapropel S1, which is otherwise unrecognizable in this entirely black core. During the following period between 8760 ± 170 and 5200 yr B.P., the δ180 reverts to slightly higher values and the Quercus pollen percentage decreases, while the pollen percentage of the wetter Ostrya, the oriental hornbeam, increases. The high pollen concentration during the deposition of sapropel S1 cannot have been caused by increased pollen input into the sea, this pollen being wind-borne, nor by increased pollen production for all taxa, both trees and herbs. We conclude that it is entirely due to increased preservation of this allochtonous organic material by the deep anoxia of the bottom water, below a thick anoxic water column. The coincidence of sapropel deposition with warm and humid local climate as well as with the second global meltwater pulse suggests that the cessation of bottom-water ventilation was due to decreased surface water density, resulting from less saline incoming Atlantic surface water, increased local runoff, and warmer winters.

International audience; La séquence pollinique du Velay a permis d'y préciser les variations du climat au cours des 450 derniers millénaires et témoigne de la très grande complexité des quatre derniers cycles climatiques. Cet enregistrement est confronté avec deux séquences plus anciennes d'Italie du Nord, celle de Leffe au Pléistocène ancien, qui s'achève vers 1 Ma, et celle de Piànico-Sèllere, qui débute vers –800 ka. Il en ressort que l'amplitude et le rythme des cycles ont radicalement changé entre –1 Ma et –800 ka. Aux oscillations relativement courtes de faible amplitude, avec des interglaciaires très humides et de glaciaires peu marqués, du Pléistocène ancien font suite des alternances beaucoup plus abruptes entre glaciaires froids et secs et interglaciaires à climats proches de l'Actuel. Les cycles de 100 000 ans s'installent. Ce basculement correspond à une phase majeure d'extinction de taxons forestiers hérités du Tertiaire.

The Mediterranean Basin is expected to be more strongly affected by ongoing global climate change than most other regions of the earth. Given the magnitude of forecasted trends, there are great concerns for the particularly rich biodiversity found in the region. Studies of the consequences of past climate shifts on biodiversity represent one of the best sources of data to validate models of the ecological and evolutionary consequences of future changes. Here we review recent findings from palaeoecology, phylogeography and climate change research to (1) explore possible antecedents of the predicted climate warming in the younger geological history of the Mediterranean Basin, (2) assess how tree populations have reacted to them, and (3) evaluate the significance of the evolutionary heritage that is at stake. A major question of our retrospective approach is whether Quaternary tree extinctions took place primarily during glacial or during interglacial episodes. Available data are scanty and somewhat conflicting. In contrast, abundant phylogeographic evidence clearly indicates that the bulk of genetic diversity in European temperate tree species is almost invariably located in the southernmost part of their range. Long-term persistence of isolated populations have been common phenomena in the Mediterranean, to the point that the current genetic structure in this area probably often reflects population divergence that pre-dates the onset of the Mediterranean climate in the Pliocene. In particular, Tertiary migrations into the Mediterranean of tree taxa originating from Asia seem to have left their footprints in the current genetic structure in these slowly evolving organisms. Moreover, phylogeographic studies point to heterogeneous rates of molecular evolution across lineages that are inversely related with their stability. We conclude that relict tree populations in the Mediterranean Basin represent an evolutionary heritage of disproportionate significance for the conservation of European plant biodiversity.

Data on the genetic structure of tree and shrub populations on the continental scale have accumulated dramatically over the past decade. However, our ability to make inferences on the impact of the last ice age still depends crucially on the availability of informative palaeoecological data. This is well illustrated by the results from a recent project, during which new pollen fossil maps were established and the variation in chloroplast DNA was studied in 22 European species of trees and shrubs. Species exhibit very different levels of genetic variation between and within populations, and obviously went through very different histories after Ice Ages. However, when palaeoecological data are non-informative, inferences on past history are difficult to draw from entirely genetic data. On the other hand, as illustrated by a study in ponderosa pine, when we can infer the species' history with some certainty, coalescent simulations can be used and new hypotheses can be tested.