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The chemical composition of the wood reflects the composition of the soil over which the corresponding tree has developed. Multi-elemental and isotopic signatures, which are characteristic of the soil and underlying rock substrates, are potentially powerful tools for determining wood provenance. These tracers are of special interest for charred archaeological wood because they circumvent some limitations of dendrochronological provenancing linked to tree-ring loss. However, thermal degradation may introduce a significant bias in wood chemical and isotopic analyses. This experimental study focused on the effects of carbonization temperature on three geochemical wood markers: elemental signatures and isotopic signatures of strontium and neodymium (86Sr/87Sr and 143Nd/144Nd, respectively). Wood specimens from a variety of oak trees and stand locations were pyrolyzed at four temperatures (ranging from 200°C to 800°C) and analyzed using ICP-MS and μ-XRF (X-ray fluorescence) spectroscopy for elemental composition and with multiple collection ICP-MS (MC-ICP-MS) for strontium (Sr) and neodymium (Nd) isotope composition. The concentration of mineral nutrients generally increased with temperature, but the magnitude of the enrichment depended on the element, wood compartment (sapwood vs. heartwood), and geological substrate. The concentrations of rubidium, strontium, manganese, magnesium, potassium, and, to a lesser extent, calcium, were minimally affected by temperature, wood compartment, and substrate. The ratios between the concentrations of these elements, as well as the 86Sr/87Sr and 143Nd/144Nd isotope ratios, were stable over the entire temperature range. However, only 86Sr/87Sr and selected elemental ratios (calcium or magnesium normalized to manganese) were successful for site discrimination. Therefore, our multi-tracer approach provides promising new information to determine the provenance of charred archaeological wood.

International audience; Aim Climate change is known to be a driver of changes in forest plant communities and to modify disturbance regimes. We investigated whether forest gaps favoured vegetation adaptation to warmer climates by accelerating the shift of plant communities to a warmer-adapted composition independently of canopy closure linked to natural forest dynamics. Location Temperate and mountainous forests of France. Time period 2002-2018. Major taxa studied Vascular plants. Methods Using floristic surveys conducted in 2002 and 2018 in 139 permanent plots set up in unmanaged forest gaps created by windstorms in 1999, we assessed the plant communities' changes in context of global warming. We also compared gap communities to closed communities inventoried in undisturbed forest. A community temperature index (CTI) and a community light index (CLI) were computed for each floristic survey with species temperature optima and Ellenberg light indicator values, respectively. Results CTI increased significantly in the gaps over the 16 years by 0.11 degrees C/decade on average. During the same period, the CLI decreased, indicating that community thermophilization was not the direct result of an increase in solar radiation linked to gap creation. Models showed that, after canopy recovery, thermophilization was stronger in mountains (+0.54 degrees C) than lowland sites (+0.12 degrees C) compared to undisturbed forests. The difference between former gaps and undisturbed forests resulted from the colonization of warm adapted species and the decline of cold adapted species in gaps. Main conclusions For a given canopy closure, our results show that thermophilization of understorey communities is higher in areas with previous disturbances than in undisturbed forests. By increasing the speed of thermophilization, the disturbance regime plays a key role in the adaptation of forest communities to climate warming. The effects of large-scale disturbances on forest plant composition should therefore not be overlooked, especially since disturbance regime tends to intensify with climate change.

International audience; Aim. Climate warming reshuffles biological assemblages towards less cold-adapted but more warm-adapted species, a process coined thermophilization. However, the velocity at which this process is happening generally lags behind the velocity of climate change, generating a climatic debt the temporal dynamics of which remain misunderstood. Relying on high-resolution time series of vegetation data from a long-term monitoring network of permanent forest plots, we aim at quantifying the temporal dynamics – up to a yearly resolution – of the climatic debt in the understorey of temperate forests before identifying the key determinants that modulate it. Location. France. Time period. 1995–2017. Taxa studied. Vascular plants. Methods. We used the community temperature index (CTI) to produce a time series of understorey plant community thermophilization, which we subsequently compared to a time series of mean annual temperature changes over the same period and for the same sites. The direction and magnitude of the difference (i.e., the climatic debt) was finally analysed using linear mixed-effect models to assess the relative contributions of abiotic and biotic determinants, including forest stand characteristics. Results. We found a significant increase in CTI values over time (0.08–0.09 °C/decade), whereas the velocity of mean annual temperature changes was three times higher over the same period (0.22–0.28 °C/decade). Hence, the climatic debt increased over time and was greater in forest stands with higher basal area or older trees as well as under warmer macroclimate. By contrast, a greater frequency of anthropogenic disturbances decreased the climatic debt, while natural disturbances and herbivory had no impact. Conclusions. Although often overlooked in understanding the climatic debt of forest biodiversity, changes in forest stand characteristics may modulate the climatic debt by locally modifying microclimatic conditions. Notably, the buffering effect of the upper canopy layer implies microclimate dynamics that may provide more time for understorey plant communities to locally adapt.

Oaks are dominant forest tree species widely distributed across the northern hemisphere, where they constitute natural resources of economic, ecological, social and historical value. Hybridization and adaptive introgression have long been thought to be major evolutionary drivers of the ecological success of oaks. However, the maintenance of species barriers remains a key question, given the extent of interspecific gene flow. We used a demographically-explicit genome scan approach combining approximate Bayesian computation and backward simulations to scan the genomes of four European white oak species for reproductive barriers. We first confirmed earlier findings of interspecific contact since the last glacial maximum. We then made use of the tremendous genetic variation among these four species (31 million SNPs) to identify genomic regions enriched in SNPs deviating from demographic expectations under a hypothesis of recent secondary contact. The outlier-enriched regions detected were of restricted size and widely distributed, over all the chromosomes. We identified 215 regions, containing 227 oak genes. A Literature-based functional annotation of these genes highlighted important functions driving the reproductive isolation of the four species. These functions included tolerance to biotic and abiotic constraints, and intrinsic mating barriers. The functions of the annotated genes were highly consistent with the ecological preferences of the four species. These genes may, therefore, be considered candidate genes in studies of species responses to past and ongoing environmental changes.

SUMMARY Surveys of ground layer vegetation are a reliable tool for monitoring spatial and temporal variations of the forest environment. In 1991, 47 vegetation plots first sampled in 1972 in a forest of the Lorraine Plain, North-East France, were resampled. This beech–oak forest had both acidic and calcareous soils depending on the thickness of alluvial deposits above the calcareous bedrock. The mean number of species per sample increased from 32 to 39 during this period and the frequency of nitrophilic species increased throughout the forest. On acidic soils, acidophilic species increased in frequency, while on calcareous soils there were no systematic changes. Multivariate statistical analysis clearly distinguished two gradients in this set of vegetation samples: acidity and nitrogen availability of soils. Along the first gradient, a shift of the plots towards a more acidic state occurred during the past 19 years on acidic soils only. Along the second one. a strong eutrophication happened on both acidic and calcareous soils, indicating an enrichment in nitrogen of forest ecosystems. Possible causes of these changes are discussed, namely sylviculture changes, aging of the stands and pollution. Atmospheric nitrogen inputs seem to be the most probable cause of eutrophication.

International audience; Bud-burst and leaf-senescence determine the length of the growing season for deciduous trees and therefore the duration of potential carbon assimilation with consequences on biomass production. In Fagus sylvatica L., leaf phenology depends on both photoperiod and temperature. The future climate is expected to induce more frequent soil water deficits and biotic attacks (possibly resulting in severe defoliation). The aim of the study is to assess whether these constrains may alter leaf phenology. In a common garden, we sowed seeds collected from six beech forests along a small latitudinal gradient (140 km) in North-Eastern France. In 2014, after seven years growth, a rain exclusion was installed above the trees to test how recurrent soil water deficits impacted bud-burst (BB) and leaf-yellowing (LY) over three years. We also analyzed the response of leaf phenology to annual defoliation, aiming at affecting carbon and nitrogen availability in trees. Delayed BB and early LY were observed, reducing the growing season (GS) until 14 days in response to soil water deficit whereas no influence of defoliation was detected. These time lags were not in relation with leaf nitrogen content. In the control treatment, BB occurred earlier and LY later in the northernmost populations than in the southernmost without clear relationships with local climate. A significant treatment x population interaction was observed revealing a plasticity in the leaf phenology response to soil water deficit among populations. These results suggest that beech trees present a genetic differentiation of leaf phenology even within a small latitudinal gradient but that these differentiations could be disrupted by soil water deficit that is predicted to increase in the future.

International audience; Questions: Land use legacies in current forest understorey vegetation, thoroughly studied in temperate regions, were investigated in a Mediterranean context. We tested the effect of three historical variables on current forest plant communities and traits: forest temporal continuity (ancient: forested before 1860, recent: reforested after 1860, and very recent forest: reforested after 1958) and type of land use in 1860 and 1958 (forest, pasture or arable land).Location: The Regional Natural Park of Luberon (southeastern France).Methods: We used a comprehensive vegetation plot database (473 species in 1,429 plots). Species’ response to historical variables was tested with logistic regressions, and the relationship between plant traits and historical variables was analysed with RLQ and fourth‐corner analyses.Results: Among all studied species, 250 responded to forest temporal continuity, 208 to 1860 land use, and 246 to 1958 land use. Species associated with ancient forests were more frequently forest specialists or forest edge species, shade‐tolerant and perennials, while species associated with recent and very recent forests were more frequently annuals, anemochorous and heliophilous species. Species exhibited different traits and ecological preferences according to the type of land use prior to forest: therophytes were more frequent on former arable land while chamaephytes were more frequent on former pasture. Trait responses to 1860 and 1958 land uses were globally consistent.Conclusions: The effect of forest temporal continuity and past land use on forest understorey communities was consistent with other studies in northern Europe or northern America, which suggests that the same ecological processes apply in temperate lowland and Mediterranean regions. This study highlights a succession of plant communities in the long term and different trajectories of succession according to the type of former agricultural use. The long‐term legacies of past land use in current forest plant communities highlight the importance to preserve ancient forests, where typical forest species can be maintained.

International audience; & Key message French forests exhibit the fastest relative changes across Europe. Growing stock increases faster than area,and is greatest in low-stocked private broadleaved forests. Past areal increases and current GS levels show positive effectson GS expansion, with GS increases hence expected to persist.& Context Strong increases in growing stocks (GS) of European forests for decades remain poorly understood and of unknownduration. French forests showing the greatest relative changes across Europe form the investigated case study.& Aims The magnitudes of net area, GS, and GS density (GSD) changes were evaluated across forest categories reflecting forestpolicy and land-use drivers. The roles of forest areal changes, GS and GSD levels on GS changes were investigated.& Methods National Forest Inventory data were used to produce time series of area, GS and GSD across forest categories over1976–2014, and exploratory causal models of GS changes.& Results GS (+ 57%) increased three times faster than area, highlighting an advanced stage in the forest transition. Low-stockedprivate forests exhibited strong changes in GS/GSD, greatest in private broadleaved forests, stressing the contribution of returningforests on abandoned lands. Regression models demonstrated positive effects of both past areal increases and current GS, on GSexpansion.& Conclusion Aerial C-sink in French forests is expected to persist in future decades.

International audience; Through the variations in their dimension, density, anatomy or isotopes composition, tree rings have provided invaluable proxies to evaluate past changes in the environment. Whereas long-term records of changes in soil fertility are particularly desired for forest ecosystem studies, the use of the chemical composition of tree rings as potential marker is still controversial. Dendrochemistry has sometimes been considered as a promising approach to study past changes in soil chemistry, whereas some authors stated that element translocations in the wood preclude any possibility of reliable retrospective monitoring. Here, we aimed at testing whether the wood elemental content of fertilized oaks (Quercus petraea) differed from control trees >30 years after a NPKCaMg fertilization and, if so, if the date of fertilization could be retrieved from the ring analysis. The contents in N, Mg, P, K, Ca and Mn were measured for each of the 43 sampled trees and in every ring of the 58-year long chronology with a non-destructive method coupling a Wavelength Dispersive Spectroscope (WDS) with a Scanning Electron Microscope (SEM).The results showed significantly higher contents in Ca and lower contents in Mn in fertilized compared to control trees. However, there was no difference in elemental content between the rings of the fertilized trees built in the 20 years before and those built after fertilization. Thus, whereas the effect of fertilization on increasing ring width was dramatic, immediate and relatively short-lasting, the elemental composition of the entire ring sequence was impacted, precluding the dating of the event. These results question the possibility to reconstruct long-term changes in soil fertility based on dendrochemistry.

International audience; Forest area has dramatically increased since the beginning or middle of the 19th century in European countries. At least half of the forests present today have grown on formerly cultivated lands, pastures or heathlands. However, net forest expansion largely masks a slow but irretrievable erosion of ancient forests. Meanwhile, forest resource harvesting (biomass, litter) has fundamentally changed during the last two centuries, moving from intensive biomass removal to increased growing stocks in different European countries. This article reviews the current knowledge on the long-term legacies of past land use and forest management practices and their effects on the functions, diversity and composition of understory vegetation of current forest ecosystems. First, we define the concepts of forest continuity and ancient forest. Then, based on the French case, we present the advances in historical sources, which make it possible to better reconstruct the change in land use and forest management practices over the last two hundred years. We review how understory plant communities and their traits respond to forest continuity and to different types of former agricultural uses, both at local and landscape scales. We then address three important issues for conservation and management: the conservation value of ancient forests, the impact of forest management on the ecological integrity of ancient forests, and the under-explored legacies of former forest management practices on soil and understory vegetation. Lastly, we propose five main fronts for future research efforts: (a) explore all types of cartographic, written sources and environmental markers; (b) develop modelling approaches to understand how past land use shapes plant communities; (c) better define the conservation value of ancient forests in conservation and management policies; (d) investigate how drivers of global change interact with forest management and land use legacies and (e) explore land use legacies in mountain and Mediterranean socio-ecological systems.

International audience; Soil properties vary spatially according to land use; both because land users have selected specific soil properties for specific land uses, and land uses modify the soil properties. However, permanent environment factors and land-use effects are unlikely to display the exact same spatial patterns. Study of the spatial and historical patterns of distribution of soil properties could help to separate between these two causes. In this aim, we studied 22 forest-grassland interfaces with controlled historical configurations in northeast France. In each land use (forest and grassland), three distances to the edge (edge, periphery and core) and two land-use histories (ancient and recent) were studied.Along forest-grassland interfaces, forests were usually located slightly upslope of grasslands, and mainly because this non-random topographic position the topsoil texture was significantly more silty in forests, and clayey in grasslands. After statistically controlling for the effects of topography and soil texture, we observed two main gradients of variation in soil properties according to the distance-to-edge (acidity in forest and nutrient content in grassland). In forest, pH and Ca dropped from the edges to the peripheries (15 m distance), while in grassland, C, N, P and Na sharply increased from the edges to the cores (25 m distance). These results demonstrate, through the edge effect, the strong influence of the land use on a part of soil properties. Furthermore, less than two centuries after grassland afforestation or deforestation, we observed that soil properties in recent forests and recent grasslands were respectively closer to their current land use than to their former land use. These results demonstrate a rapid change in soil properties after land-use change. However, recent forests and recent grasslands kept a legacy of soil texture from their former land use, respectively. Recent grasslands also kept a lower soil density, N and Na content compared to ancient grasslands.Hence, this study of forest-grassland interfaces show strong and short-scale relationships between land use and soil properties and suggest that they express both original choices of land users for specific soil properties and land-use after-effects. The non-random topographic position of the forest-grassland interfaces indicates a conscious choice of this positioning by the land users, for agronomic reasons. Beyond that, land use, through vegetation composition and management practices, also has a strong impact on soil properties. The fact that land-use changes affect most soil properties after only a few decades confirms the existence of land-use effects over time.

Oak (Quercus petraea (Matt.) Liebl. and Quercus robur L. grouped), European beech (Fagus sylvatica L.) and hornbeam (Carpinus betulus L.) are three major species of western and central European forests. When conditions are suitable for the three species, silvicultural management often favours oak because of its greater economic interest. Forest managers know that beech and hornbeam are strong competitors for oak during the regeneration phase, but the conditions that influence the relative success of the regeneration of the three species growing in mixture are still poorly characterised. The natural regeneration of the three species 20 years after canopy openings was studied based on 108 study sites established in 2001 in French forests impacted by the windstorms Lothar and Martin in 1999. In spring and summer 2018 and 2019, all saplings over 0.1 m in height were counted, species were identified and diameter at breast height (DBH) was measured for all saplings over 1.30 m. The height of the saplings with the highest and median DBH in each plot was recorded for each species. Mixed models were used to analyse the combined effects of former stand type, distance from the edge of the gap and soil conditions on species presence, sapling abundance, DBH and height. The modelling approach highlighted the preponderant role of the initial seed rain on the presence and sapling density of the three species compared to interspecific competition or distance from the edge. The two latter factors had a secondary effect on sapling DBH and height. Beech and hornbeam saplings were more abundant than oak saplings regardless of soil conditions (on average, 3097, 3063 and 344 saplings ha−1, respectively), suggesting a strong competitive ability of these two species. Oak was present on 22% (43% for hornbeam and 68% for beech) of the studied plots, at a low density but with a height and DBH similar to that of beech or hornbeam. This result highlights the high dissemination capacity of beech and hornbeam, which prevents the establishment of a stand dominated by oak. When seeking to obtain oak-dominated stands in the lowlands of Europe, the abundance of beech and hornbeam can be a limiting factor that could lead to the disappearance of oak from large areas if no silvicultural operations are performed to promote it.

Soil moisture and nutritional characteristics are frequently assessed using plant species and community bioindication, e.g., the Ellenberg system of species indicator values. This method, based on complete inventories of plant species present in plots, is time-consuming, which could prevent its general use for forest or other natural land management. Our aim was to determine the impact of a reduction in the time spent to carry out a floristic inventory on the quality of soil characteristic assessment using plant bioindication. We compared the measurements of soil pH-H2O (pH), organic carbon to total nitrogen ratio (C:N) and base saturation (BS) in the 0–5 cm soil layer of 470 plots with the same variables estimated from floristic inventories of increasing duration, using plant indicator values (IV) from the EcoPlant database. The performance of predictions was evaluated by the square of the linear correlation coefficient between measured and predicted values (R2) and the root mean square error (RMSE) of predictions. The number rather than the percentage of total plot species used for the estimations was determinant for the prediction of soil pH quality. Performance of bioindication of pH, BS and C:N reached the maximum R2 using the first 20–25 species recorded per plot, corresponding to a 14-min-long floristic inventory in comparison to a mean of 28 min spent to carry out a complete floristic inventory. A precision of prediction of 80% of the maximal precision was obtained after 4–5 min (6–12 inventoried species) for the three studied variables. These results are independent of the nutritional capability of the soils and were similar at the national and local scales. In order to estimate soil nutritional resources by plant bioindication, it is feasible to significantly reduce the time spent on floristic inventories and, thus, their cost. This is especially useful when the goal is to map the soil quality for decision-making in forest management.

International audience

Most studies of landscape effects on plants in forests have explored only relatively small landscape scales (size of spatial extent) considering the poor-dispersal ability generally reported for forest plants, or failed to verify confidently that the scales at which landscape is considered best predicts plant patterns. We investigated the effect of landscape composition on response of plant communities according to three scales - 400 ha, 100 ha and 25 ha - in 263 forests in the northern half of France. We hypothesized that landscape composition at the 400-ha scale better predicted plant responses than smaller scales. We built models to compare the effects of each scale on individual species response and plant composition of 1902 700-m2 vegetation plots, considering the shared and pure effects of scales. Only landscape composition at the 400-ha scale showed a critical pure effect on plant composition. Similarly, the 400-ha scale better predicted individual species response. Using a large dataset, we brought evidence that landscape composition further than 100 ha and at least up to 400 ha had more effects on local plant diversity in forests, which means that smaller-scale investigations may miss the influence of landscape on plant patterns. The effects of large spatial scale may reflect the legacies of past landscape or the long-distance dispersal capacity of plants. Our findings call for better consideration of the large-scale effects of landscape on plants both in scientific studies and management plans.

International audience; Understanding how climate and soil hydrology control tree growth is critical to predict the response of Siberian ecosystems to climate change. The general aim of this study was to (i) characterize the soil water budget and identify the factors controlling aspen (Populus tremula L.) radial growth in south-western Siberia, and (ii) assess its potential response to future climate change. Along a gradient of climate and soil hydrological conditions, soil water budgets were reconstructed by modeling at four sites, and dendrochronological analyses were performed. Aspen growth potential was simulated in response to different climate change scenarios represented by shifts in soil water budgets. Simulated soil water budgets varied with climate variables, specifically increased temperature and drier summer combined with varying winter precipitation occurring as snowfall.. We show that plant-available soil water and drainage gradually increased while stress decreased from the warmest and driest (south, forest-steppe zone) site to the coldest and wettest (north, southern taiga zone) site. Aspen radial growth was mainly limited by summer temperature in the north and by summer water deficit in the south. Surprisingly, we did not find clear evidence of snow level impact on radial growth, either positively in the south (water supply and protection against soil freezing) or negatively in the north (water-logging and drainage). In the context of climate change, water stress intensity could increase dramatically in the south inhibiting aspen growth; in those places summer soil water content depends on the refilling that occurs at snow-melt and increasing winter precipitation could alleviate stress levels. Conversely, in the north, aspen growth may mostly benefit from rising temperature.

International audience; How to move forward if we cannot understand our present from our past? The same applies for the study of ecosystems. Evidence of ecological legacies in temperate post-agricultural forests has been provided on soil physico-chemical properties and understory vegetation richness and composition, which led to distinguish ancient and recent forests. However, no land use legacies dating back more than 50 years have been reported in Mediterranean forests. The definition of ancient and recent forests usually relies on a threshold date, most often provided by historical maps. In France, the Etat-Major map is the most precise, with a relatively high resolution and drawn over the whole country with a standardised method. However, the use of historical maps only for studying land use legacies in forest is questionable in a Mediterranean context characterised by a traditional agro-sylvo-pastoral system. Using a historical ecology approach, our purpose was to examine the legacies of various former land uses on soil and understory vegetation in Mediterranean forests and to compare the relevance of two historical sources: 1860 land use map (map-based PLU) and remnants recorded in the field (in situ PLU remnants). In the Regional Natural Park of Luberon (French Mediterranean area), we inventoried plant communities and analysed soil physico-chemical properties on 100 plots with various past land uses according the Etat-Major map (arable, pasture or forest) and in situ PLU remnants (terrace, stone removal or no remnants). Compared to ancient forest, former arable land hosted more species and had deeper and nutrient-richer soils while former pasture had shallower and nutrient-poorer soils. Similarly, and compared with no remnants, terraces hosted more species and had deeper and nutrient-richer soils whereas stone removal had shallower and nutrient-poorer soils. Understory species composition significantly varied according to map-based PLU and in situ PLU remnants. However, in situ PLU remnants were globally a much better indicator of land use legacies on soil and understory plant composition compared to map-based PLU. We thus confirmed the legacies of past land use on Mediterranean forest soil and understory vegetation. We also stressed that historical ecology should rely on both field evidence and historical maps, particularly in Mediterranean landscapes with a complex history of land uses.

From 1903–1904 to 1988–1989, the two World Wars and sociological factors as rural desertification and changes in land uses mainly explained the decline of black truffle production in the Vaucluse department, which well reflects that of the whole of France. These can be correlated with the annual climatic variations as well as, from 1924–1925 to 1948–1949, the raw production rates of the managed truffle orchard of Pernes-les-Fontaines located in Vaucluse. The two methods used (correlation coefficients and Bayesian functional linear regression with Sparse Step functions) gave consistent results: the main factor explaining the annual variations of truffle production was the summer climatic water deficit of the year n. A general model including the rural exodus and the cumulated climatic water deficit of summer months both allowed to well explain the evolution of truffle production from 1903–1904 to 1988–1989 in the Vaucluse and its huge decrease. During that period, global warming had little effect. However, in the twenty-first century, all the scenarios predict increased summer water stress for the Mediterranean region, which could greatly affect black truffle production.

[Departement_IRSTEA]Territoires [ADD1_IRSTEA]Dynamique et fonctionnement des écosystèmes; International audience; In Boulanger et al. (2018), we investigated the effects of ungulates on forest plant diversity. By suggesting a revisit of our conclusions regarding ecosystem dynamics since the late Pleistocene, Fløjgaard et al. (2018) came to the conclusion that moderate grazing in forest should be a conservation target. Since major points of our paper were mis‐ or over‐ interpreted, we put the record straight on our study system and on the scope of our conclusions. Finally, we advocate for an assessment of the conservation issues of ungulates in forests not only regarding hypothetical and still debated states of past ecosystems but also considering timely challenges for forest ecosystems. In the study by Boulanger et al. (2018), we assessed the role of ungulates' presence on short‐term understory plant dynamics, using a nationwide network composed of paired exclosure‐control plots. We demonstrated that ungulates are key drivers of understory vegetation in managed forests since they alter the richness and abundance of the shrub layer, increase the richness of the herb layer, and favor open habitat plant species. Our results show that local scale mechanisms, here involving indirect facilitation, lead to global dynamics in forest‐ungulate systems. Our conclusions underline that an increase in species richness, often simplistically viewed as a positive change in ecosystems, can alter the community composition and thus require a more subtle interpretation regarding conservation issues. Fløjgaard et al. (2018) questioned them from a macroecological and evolutionary perspective with respect to general nature conservation issues. They argued that an "evolutionary informed baseline" would change our conclusions based on short‐term and experimental features. We need to specify three over‐ or misinterpretations. 1. Although ungulates affect many groups of organisms, depending or not on the vegetation layer, our results were strictly limited to plant species. 2. Our investigations were not restricted to "ungulate grazing" (Fløjgaard et al., 2018), since the ungulate species generally co‐occurring at our study sites are not only obligate grazers (Gordon, 2003): roe deer is a browser, red deer an intermediate grazer-browser, and wild boar a frugivore-omnivore. Moreover, our interpretations included combined effects of different ecological processes in which sympatric forest ungulates are involved, notably herbivory, zoochory, and physical engineering (Persson, Danell, & Bergström, 2000; Wilby, Shachak, & Boeken, 2001). 3. Fløjgaard et al. (2018) argued that our results were conditional on "mainly plantation" forests, in "highly managed landscapes." Our sampling design does not include intensively managed forest plantations isolated in an agricultural landscape matrix, but even‐aged stands mainly issued from natural regeneration, located in forest‐dominated landscapes, and mostly with a long history of forest continuity (Table 1). While Fløjgaard et al. (2018) consider that the landscape context may bias our results, recent independent (Jaroszewicz, Pirożnikow, & Sondej, 2013; Picard, Chevalier, Barrier, Boscardin, & Baltzinger, 2016), but also older studies (von Oheimb, Schmidt, Kriebitzsch, & Ellenberg, 2005; Schmidt, Sommer, Kriebitzsch, Ellenberg, & von Oheimb, 2004) on seed dispersal by wild ungulates suggest that there is no overall effect of the landscape matrix on the traits of the plants dispersed by our three model ungulates; these animals disperse preferentially plants typical of open habitats even in forest‐dominated landscape matrices. These exchanges of views revive the unsolved and current debate on the role of ungulates as drivers of Anthropocene forest dynamics, as potential contributors to forest biodiversity in primary or secondary forests and more globally as dynamic actors of ecosystem functioning through direct, indirect, trophic, and nontrophic cascading effects. More specifically, the openness of Pleistocene forest stands and the primary habitat of light‐demanding species in ancient landscapes remain a matter of discussion (Mitchell, 2005). Consequently, from a conservation point of view, it seems unwise to recommend a uniform "moderate grazing" baseline without stronger scientific evidence and without considering current and future socioeconomic issues (Webster et al., in press).

International audience; Charcoal analysis aims to study different aspects of forest management, techno-economical choices and their specific impact on past landscapes, as well as the impact of climatic events. However, at the present time, charcoal analysis is generally limited to the study of a list of taxa and their relative frequency, as the methods usually employed in dendrochronology to characterize past woodland, based on long tree-ring series, are not suitable for anthracological material. Today, the new challenge for charcoal analysis is thus to develop adapted dendrological tools. In this context, the aim of the ANR DENDRAC project “Development of dendrometrical tools applied to anthracology: study of the interactions between Man, resources and environments” was to characterize modern-day wood stands in accordance with historical woodland practices and convert dendroecological data into parameters adapted to charcoal analysis. The purpose of this study is to define the dendrological features with the help of the anthracological tools without explaining the observed differences between the sampled stands (given the stational variability, age and regeneration modes). The first step consisted in creating dendro-anthracological tools based on morpho-anatomical criteria that help to characterize growth, distinguish heartwood from sapwood and evaluate charcoal-pith distance. The second step involves characterizing three modern-day wood stands (coppice under standard, high forest and young stand formed by a mixture of seeded and coppice trees), defined by their structure, stand density and regeneration modes, using dendrological data measured on fresh wood material and modelled into anthracological data with the dendro-anthracological tools. In this way, anthracological types were defined for each wood stand, forming anthraco-typological models, which area useful for the interpretation of archaeological charcoal assemblages. Finally, an anthracological key is proposed to sort archaeological charcoal fragments in anthraco-groups before data processing.

National audience

[Departement_IRSTEA]Territoires [ADD1_IRSTEA]Dynamique et fonctionnement des écosystèmes; International audience; Large wild ungulates are a major biotic factor shaping plant communities. They influence species abundance and occurrence directly by herbivory and plant dispersal, or indirectly by modifying plant-plant interactions and through soil disturbance. In forest ecosystems, researchers' attention has been mainly focused on deer overabundance. Far less is known about the effects on understory plant dynamics and diversity of wild ungulates where their abundance is maintained at lower levels to mitigate impacts on tree regeneration. We used vegetation data collected over 10 years on 82 pairs of exclosure (excluding ungulates) and control plots located in a nation-wide forest monitoring network (Renecofor). We report the effects of ungulate exclusion on (i) plant species richness and ecological characteristics, (ii) and cover percentage of herbaceous and shrub layers. We also analyzed the response of these variables along gradients of ungulate abundance, based on hunting statistics, for wild boar (Sus scrofa), red deer (Cervus elaphus) and roe deer (Capreolus capreolus). Outside the exclosures, forest ungulates maintained higher species richness in the herbaceous layer (+15%), while the shrub layer was 17% less rich, and the plant communities became more light-demanding. Inside the exclosures, shrub cover increased, often to the benefit of bramble (Rubus fruticosus agg.). Ungulates tend to favour ruderal, hemerobic, epizoochorous and non-forest species. Among plots, the magnitude of vegetation changes was proportional to deer abundance. We conclude that ungulates, through the control of the shrub layer, indirectly increase herbaceous plant species richness by increasing light reaching the ground. However, this increase is detrimental to the peculiarity of forest plant communities and contributes to a landscape-level biotic homogenization. Even at population density levels considered to be harmless for overall plant species richness, ungulates remain a conservation issue for plant community composition.

Nous testons ici la faisabilite d’estimer la repartition passee d’une espece vegetale, en l’occurrence le hetre, a l’aide de la repartition des toponymes actuels dont l’etymologie fait reference a cette espece. Cette recherche a necessite la mise en commun de competences en agronomie, geomatique, linguistique et toponymie. Elle a montre la faisabilite de l’approche, ainsi que ses limites. Les toponymes se sont reveles une source de connaissances precieuse (plus de 6 100 toponymes lies au hetre ont ete identifies) mais delicate, qu’il est pertinent d’exploiter en tant qu’indices de repartition d’un phenomene passe.

International audience

International audience; Written sources and archaeological evidence suggest that coppicing was a common practice in past woodland management. Depending mainly on the length of rotations, coppices provided wood products of various sizes, and coppice-wood has been identified in fuel-wood remains as well as in timber studies. Assigning the origin of the wood analyzed to coppice is based on observation of “typical growth patterns”: an even-age structure and a rapid decrease in ring-width with age are used nowadays. However, the wide variety of coppice practices and the variability observed in living-tree analogs make it difficult to draw definitive conclusions. To contribute to improving coppice-wood identification, the present study analyzed differences in growth and tree-ring anatomy between living sessile oaks from a mixed stand of coppiced and seeded trees.Stems were compared based on ring-width, early- and late-wood widths, number and size of the earlywood vessels, and tissue proportions measured at different heights. The growth of coppiced trees was found to be faster than that of seeded trees, in height at cambial ages between 3 and 5 years and in diameter at 5–8 years. A quantitative anatomy study showed that tree rings from coppice shoots had smaller and more numerous vessels per unit surface area and a weaker hydraulic conductivity. Earlywood width, which can be acquired on archaeological wood much more easily than vessel surface, was significantly greater in the sample of seeded trees. Linear discriminant analysis performed on the data used to model earlywood width (leave-one-out procedure) correctly classified 77% of coppice and 54% of seeded trees when the radius exceeded 1.66 cm and offers promising perspectives for dendro-anthracology and dendrochronology. Growth and anatomical differences between coppiced and seeded trees mixed in the same stand were observed while other sources of variability (site condition, competition, species) were constrained.

Large-scale tree distribution changes have received considerable attention but underlying demo-genetic mechanisms are less well documented. We used a diachronic approach to track species shifts in a mixed oak stand (Quercus petraea-Quercus robur) at a fine spatiotemporal scale. Species assignment was made using single nucleotide polymorphism (SNP) fingerprints employing clustering and parentage analysis. Mating patterns and reproductive success were assessed by parentage analysis. Plot-based inventories of soil parameters and sapling densities provided ecological and demographic information, respectively. Sapling density and reproductive success was higher in Q. petraea than in Q. robur, and were correlated with a spatial expansion of Q. petraea (50% to 67% of the area). Admixed trees resulting from hybridization and backcrossing between the two species were more frequent under the Q. robur canopy. We suspect that species' differential responses to ongoing environmental changes and interspecific competition are the predominant factors accounting for the recruitment success of Q. petraea, while human interference, differential reproduction and hybridization (and backcrossings) are probably of more limited importance. We anticipate in mixed Q. petraea-Q. robur stands, under current ongoing environmental change, that these processes will be enhanced, at least in the western part of the distribution of the two species.

[Departement_IRSTEA]Territoires [TR1_IRSTEA]SEDYVIN; International audience; Delineating ancient woodlands, characterised as woodlands that have subsisted continuously for a long period, requires the use of maps. When such a study is undertaken over a large area, a comprehensive examination of all existing documentation is not feasible. A single cartographic collection should be chosen for the whole area. Two sources are clearly the most suitable in France: the Napoleonic Cadastre [Land Registry], and the Etat-Major [Ordnance Survey] maps, both of which were implemented at a date close to that of the French historical minimum forest area. The work presented here compares the two sources in order to evaluate their respective advantages and disadvantages not only for mapping ancient woodlands but also, more broadly, for establishing a comprehensive historical land-cover map, including forests, pastures, meadows, croplands, vineyards and built areas.; La délimitation de forêts dites anciennes, caractérisées par une longue continuité temporelle de l’état boisé, impose le recours à des sources cartographiques. Quand un tel travail est entrepris sur une vaste surface, l’examen systématique de toute la documentation existante est exclu, et il faut alors définir un unique corpus cartographique qui puisse faire référence sur la totalité du territoire étudié. Deux sources s’imposent alors comme étant les plus adaptées : le cadastre dit napoléonien, et la carte d’état-major, tous deux en général réalisés à une date proche du minimum historique forestier français. Les travaux ici présentés confrontent ces deux sources pour en évaluer les avantages et inconvénients réciproques, non seulement pour la cartographie des forêts anciennes mais aussi, plus largement, pour la construction de la carte de l’ensemble des occupations passées du sol, incluant forêts, pâtures, prairies, cultures, vignes et bâti

Based upon the historical data—obtained from the French National Forest Inventory—on the tree species’ productivities, assimilated to be a measure of return on investment, as well as on their variances as sources of risk, we apply the portfolio selection theory in order to optimize the species distributions in France. We thus determine the optimal return-risk combinations of tree species and map them per administrative department. We also estimate the resistance of optimal portfolios using the species’ probabilities of presence. Our results show that greater weights in the optimal portfolios match with higher probabilities of presence, implying that foresters have incentives to invest in the most resilient species.

International audience

Questions What are the patterns of plant communities in terms of richness and floristic composition along stable forest–grassland interfaces? Are there specific species at the edge and/or specialist species transgressions between adjacent habitats? How does edge displacement following land-use change alter distance-to-edge plant diversity patterns? What are the relative influences of the edge effect and the edge displacement in forests and grasslands? Location Forests and grasslands in northeast France. Methods Floristic surveys were conducted in three types of forest–grassland interface, which can be stable or the result of edge displacements due to afforestation or deforestation. The sample comprised a total of 132 plots in 22 forest–grassland interfaces. Point-biserial correlation coefficients were used to classify the species into several groups in stable interfaces: forest, edge or grassland specialists and generalists. Using LMMs and Tukey's HSD tests, the total species richness and that of each species group were compared between the plot positions (i.e. distance-to-edge) and between the stable interfaces and cases of afforestation and deforestation. To evaluate the relative influence of the edge effect (plot position) and edge displacement (afforestation/deforestation) on plant community composition, CCAs and variation partitionings were performed. Results The largest difference in both plant community richness and composition was found between the forest and grassland edges. The highest species richness was found at the grassland edges. In addition to a high number of generalist species, a mixture of forest and grassland specialist species were predominant at the edges, and the forest specialists were almost the only transgressive species. Afforestation interfaces showed an extinction debt of grassland and edge specialist species and a colonization credit of forest specialists in recent forests. The effects of edge displacement were larger than those of the edge effect in forests, and the opposite was observed in the grasslands. Conclusions Forest and grassland plant communities differ strongly even over very short distances. However, the edges host a large number of forest and grassland specialist species, which explain higher species richness than in adjacent habitats. This results from interactive effects of distance-to-edge and edge displacement following land-use change.

Questions How did past land use and conifer plantation affect understorey plant communities? What plant traits explain understorey vegetation response to agricultural past land use and coniferous plantation? Location Forest of Orleans (50 000 ha), Loiret, north-central France. Methods Canopy cover, herb layer composition, litter and soil properties were measured in 80 100 m2 plots sampled in plantations of Pinus sylvestris or P. nigra vs natural regenerations of Quercus petraea and Q. robur along a gradient of forest continuity (using historical maps and aerial photos from 1840, 1949 and 2006). We related 15 plant traits to past land use and tree species using RLQ and fourth-corner analyses. Results The magnitude of past land use effect largely exceeded that of coniferous plantation. Post-agricultural forests, even 150 yr after afforestation, differed from ancient forests in soil properties (thinner humus layer, higher P content, higher pH and lower C/N ratio) and plant traits. Ancient forests hosted more forest core species, stress-tolerant, competitive species and bryophytes, but fewer ruderals, annuals/biennials, shrubs and trees and nutrient-demanding species, and had lower SLA and higher LDMC. Conifer plantations had a thicker humus layer, lower pH and higher C/N ratio than deciduous forests, and hosted more light-demanding species but less forest core species. Importantly, differences in soil and plant traits between conifer plantations and naturally regenerated deciduous stands were discernible in both recent and ancient forests, indicating that tree species lastingly influence ecosystem functioning. Conclusions Past land use and coniferous plantation resulted in different understorey plant communities and traits under pine plantations and naturally regenerated oak stands. These differences were driven through soil acidification, litter decomposition rate, light conditions, canopy development, soil disturbance, stand management and dispersal and recruitment limitations. Coniferous plantations slowed down the recovery of post-agricultural forests to ancient deciduous forest conditions. Applying natural regeneration and favouring native deciduous tree species thus helps recreate or maintain ancient forest plant communities.

[Departement_IRSTEA]Territoires [ADD1_IRSTEA]Dynamiques spatiales d'anthropisation [ADD2_IRSTEA]Dynamique et fonctionnement des écosystèmes; International audience; Context Land use and land cover (LULC) change is a major part of environmental change. Understanding its long-term causes is a major issue in landscape ecology.Objectives Our aim was to characterise LULC transitions since 1860 and assess the respective and changing effects of biophysical and socioeconomic drivers on forest, arable land and pasture in 1860, 1958 and 2010, and of biophysical, socioeconomic and distance from pre-existing forest on forest recovery for the two time intervals.Methods We assessed LULC transitions by superimposing 1860, 1958 and 2010 LULCs using a regular grid of 1 9 1 km points, in a French Mediterranean landscape (195,413 ha). We tested the effects of drivers using logistic regressions, and quantified pure and joint effects by deviance partitioning.Results Over the whole period, the three main LULCs were spatially structured according to land accessibility and soil productivity. LULC was driven more by socioeconomic than biophysical drivers in 1860, but the pattern was reversed in 2010. A widespread forest recovery mainly occurred on steeper slopes, far from houses and close to pre-existing forest, due to traditional practice abandonment. Forest recovery was better explained by biophysical than by socioeconomic drivers and was more dependent on distance from pre-existing forest between 1958 and 2010.Conclusions: Our results showed a shift in drivers of LULC and forest recovery over the last 150 years. Contrary to temperate regions, the set-aside of agricultural practices on difficult land has strengthened the link between biophysical drivers and LULC distribution over the last

Deer populations have dramatically increased over the last decades in Western Europe and their browsing has affected forest vegetation, especially plant community composition. High deer browsing pressure may threaten forest ecosystems and needs to be assessed over the long run. However, few studies to date have addressed the long-term impact of deer on forest regeneration. During one regeneration phase, we assessed the impact of deer ( Cervus elaphus L. and Capreolus capreolus L.) browsing on mixed silver fir ( Abies alba Mill.)/Norway spruce ( Picea abies L. H. Karst.) stands in the Vosges Mountains in North-eastern France. For both tree species, we measured seedling and sapling density, height and diameter in 28 paired fenced – unfenced plots distributed over two sites that had been fenced 27 years ago, for 10 and 23 years respectively. We demonstrated that the presence of deer decreased the density, height and diameter of silver fir saplings, while it increased the height of Norway spruce saplings. We also noticed that the effect of fencing was very different depending on fencing duration, and that even 10 years of fencing led to changes that were still visible 17 years later. Our results confirm that deer browsing has a long-term impact on the regeneration of silver fir. Furthermore, they suggest that deer browsing may cause a species substitution, with Norway spruce gradually replacing silver fir. Such a trend would have an impact on the ecological and economical value of these forests. How browsing impacts the forest’s ability to adapt to global warming should also be considered, since browsing might impede the implementation of management policies designed to address this issue.