Wild bees (Hymenoptera: Anthophila) and hoverflies (Diptera: Syrphidae), the two major groups of insect pollinators, are undergoing alarming declines worldwide, including Europe. The lack of accessible and verified spatial and temporal occurrence records currently challenges efforts to understand and mitigate this decline. Here, we compiled datasets from diverse sources, including taxonomists, national experts, public repositories, museum collections, published literature, verified open-access platforms, and aggregated datasets from previous European projects. The collected data were standardised, cleaned and validated by taxonomists and national experts. This collective effort resulted in two databases comprising more than 4.34 million and 1.04 million records for wild bees and hoverflies, respectively. The databases cover 97% of the European bee fauna (2,083 species out of 2,138 recorded in Europe) and 97% of the European hoverfly fauna (886 species out of 913 recorded in Europe). These standardised databases constitute essential resources for future assessments of status and trends, habitat associations, and other research and conservation initiatives to protect and understand wild pollinators on the European continent.

In the Anthropocene, the decline of insect pollinators poses a significant threat to ecosystem services, particularly to wild bee populations essential for plant biodiversity and agricultural productivity. France, with 983 species, hosts one of the most diverse bee faunas in Europe, yet these species face growing pressures from habitat loss, climate change, and intensive agriculture. Addressing this crisis requires robust taxonomic frameworks and efficient species identification methods to support long-term monitoring initiatives such as the European Pollinator Monitoring Scheme, EU-PoMS. DNA barcoding, utilizing the COI-5P gene, has proven effective for species delineation and biodiversity monitoring, particularly in detecting cryptic diversity among genera with large numbers of species such as Andrena, Nomada or Lasioglossum. However, significant gaps remain in reference libraries, particularly for the species from the Mediterranean Basin. To bridge this gap, the CODABEILLES initiative was launched in 2021 to enhance barcode data for the French bee fauna. Initially, only 25% of species had barcodes from French voucher specimens, increasing to 62% when considering voucher specimens from other countries. By 2025, thanks to collaboration with sixteen specialists and institutions, CODABEILLES contributed 1477 reference barcodes, covering approximately 560 species and raising barcode coverage to 82%. When integrating data published under other initiatives over the same period the coverage reaches 94% of the French bee fauna. This dataset significantly enhances species identification accuracy and supports large-scale pollinator monitoring through metabarcoding and environmental DNA approaches. Despite the success of COI-5P barcoding, taxonomic inconsistencies persist, necessitating further integrative research. This study underscores the need for continued collaboration among taxonomists, molecular biologists, and conservationists to refine species classifications and ensure comprehensive reference databases. The improved barcode coverage provided by CODABEILLES paves the way for more accurate DNA-based monitoring of wild bee populations and their ecological interactions, crucial for guiding conservation strategies in the face of ongoing environmental change.

Updated checklist of bees of mainland France (Hymenoptera: Apocrita: Apoidea). - The checklist of bees from metropolitan France is presented here, with an update of the previous checklist published in 1995 which included 865 species. A total of 150 species have been added to this previous checklist, 114 thanks to new distributional records and 36 due to an update of their taxonomic status. In addition, 32 have been removed from the previous list, along with 12 species recently reported in French territory whose presence has either been refuted, deemed doubtful, or requires confirmation. This work results in a list of the 983 confirmed bee species for metropolitan France. This high species richness is related to the high variety of climatic and biogeographic contexts throughout the country. The amount of changes between the previous and the current checklists, most of them related to changes that happened in the past few years, illustrates the importance of keeping our efforts on improving the knowledge of the French bee fauna even today and in the years to come. This update represents an initial step toward supporting these efforts, including the forthcoming red list of French wild bees.

Islands are areas where biodiversity conservation is of the utmost importance and is particularly challenging due to the isolation and vulnerability of animal and plant populations. The coastline of Brittany includes a large number of islands, which vary greatly in size, distance from the mainland, landscape composition and climate. Until recently, virtually nothing was known about the bees on these islands, but a number of studies have been carried out in recent years, allowing an initial assessment to be made. The aim of this article is to provide an overview of the bee fauna of the islands of Brittany, in terms of species richness, species composition and rarity status. In total, we gathered records of 188 wild bee species on 25 continental islands, located on both the north and south coasts of Brittany. For most of the islands, we obtained only occasional data, but a few have benefitted from intensive surveys, with data collected throughout the entire flight period and over several years and in different locations and habitat types. For four islands, we considered that the current knowledge is relatively good: Groix (113 wild bee species), Houat (82 species), Hoedic (64 species) and Ouessant (57 species). In addition to the number of species, this study shows that the islands host many species that are rare at regional or national level. Our results highlight the importance of taking bees into account when managing habitats and defining protected areas in islands, in order to conserve both food resources and nesting sites for these pollinator insects.

Background The spectacular decline in pollinators and their prominent role in pollination of natural and cultivated plants has stimulated research on pollinating insects. Over the last ten years, much ecological research has been carried out on bees, often generating a large volume of specimens and increasing the importance of entomological collections. Here, we present the bee collection of the IMBE laboratory (Marseille, France) after ten years of study of plant-pollinator networks. New information We provide distribution data on 2181 specimens belonging to 246 species of bees, mainly from the Mediterranean Region of France. One of the recorded species, Lasioglossum soror, is classified as "endangered" at the European level, while 68 of the recorded species are currently Data Deficient according to the 2014 Red List of European bees. This dataset contributes to the broader effort to enhance the knowledge of French bee diversity. It aligns with the objectives of the French Pollinator Plan and supports the development of a national Red List. In this context, information about the distribution of wild bees from the Mediterranean Region, which harbours the highest species diversity in mainland France, are of particular importance.

The spectacular decline in pollinators and their prominent role in pollination of natural and cultivated plants has stimulated research on pollinating insects. Over the last ten years, many ecological researches have been carried out on bees, often generating a large volume of specimen capture and increasing the importance of entomological collections. Here we present the bee collection of the IMBE laboratory (Marseille, France), after ten years of study of plant-pollinator networks. We provide distribution data on 2180 specimens belonging to 244 species of bees, mainly from Mediterranean France. Two of the recorded species, Lasioglossum soror and Nomada italica, are classified as "endangered" at the European level, while 44 of the recorded species are currently data deficient following the 2014 European bee red list. The data presented here are a part of a global effort to improve knowledge about the bees of France, within the framework of the French Pollinator Plan, and with the goal of the production of a national red list. Within this framework, bees of the Mediterranean region, where the highest species diversity is found in mainland France, are particularly of interest.

Pollinators play a crucial role in ecosystems globally, ensuring the seed production of most flowering plants. They are threatened by global changes and knowledge of their distribution at the national and continental levels is needed to implement efficient conservation actions, but this knowledge is still fragmented and/or difficult to access. As a step forward, we provide an updated list of around 3000 European bee and hoverfly species, reflecting their current distributional status at the national level (in the form of present, absent, regionally extinct, possibly extinct or non‐native). This work was attainable by incorporating both published and unpublished data, as well as knowledge from a large set of taxonomists and ecologists in both groups. After providing the first National species lists for bees and hoverflies for many countries, we examine the current distributional patterns of these species and designate the countries with highest levels of species richness. We also show that many species are recorded in a single European country, highlighting the importance of articulating European and national conservation strategies. Finally, we discuss how the data provided here can be combined with future trait and Red List data to implement research that will further advance pollinator conservation.

Heatwaves exert disproportionately strong and sometimes irreversible impacts on forest ecosystems. These impacts remain poorly understood at the tree and species level and across large spatial scales. Here, we investigate the effects of the record-breaking 2018 European heatwave on tree growth and tree water status using a collection of high-temporal resolution dendrometer data from 21 species across 53 sites. Relative to the two preceding years, annual stem growth was not consistently reduced by the 2018 heatwave but stems experienced twice the temporary shrinkage due to depletion of water reserves. Conifer species were less capable of rehydrating overnight than broadleaves across gradients of soil and atmospheric drought, suggesting less resilience toward transient stress. In particular, Norway spruce and Scots pine experienced extensive stem dehydration. Our high-resolution dendrometer network was suitable to disentangle the effects of a severe heatwave on tree growth and desiccation at large-spatial scales in situ, and provided insights on which species may be more vulnerable to climate extremes.

A Correction to this paper has been published: https://doi.org/10.1038/s41597-021-00851-9.

Annual time-series of the two satellites C-band SAR (Synthetic Aperture Radar) Sentinel-1A and 1B data over five years were used to characterize the phenological cycle of a temperate deciduous forest. Six phenological metrics of the start (SOS), middle (MOS) and end (EOS) of budburst and leaf expansion stage in spring, and the start (SOF), middle (MOF) and end (EOF) of leaf senescence in autumn were extracted using an asymmetric double sigmoid function (ADS) fitted to the time-series of the ratio (VV/VH) of backscattering at co-polarization VV (vertical–vertical) and at cross polarization VH (vertical-horizontal). Phenological metrics were also derived from other four vegetation proxies (Normalized Difference Vegetation Index NDVI time-series from Sentinel-2A and 2B images, and in situ measurements of NDVI measurements, Leaf Area Index LAI and litterfall temporal dynamics). These estimated phenological metrics were compared to phenological observations obtained by visual observations from the ground, achieved using binoculars by three inter-calibrated observers, on a bi-weekly basis during the budburst and weekly during the senescence. We observe a decrease in the backscattering coefficient (σ0) at VH cross polarization during the leaf development and the expansion phase in spring and an increase during the senescence phase, contrary to what is usually observed on various types of crops. In vertical polarization, σ0VV shows very little variation throughout the year. S-1 time-series of VV/VH ratio provide a good description of the seasonal vegetation cycle allowing the estimation of spring and autumn phenological metrics. Estimates provided by VV/VH of budburst dates using MOS criterion differ by approximately 8 days on average (mean average deviation) from phenological observations. During senescence phase, estimates using MOF criterion are later and deviate by about 20 days from phenological observations of leaf senescence while the differences are of the order of 2 to 4 days between the phenological observations and estimates based on in situ NDVI and LAI time-series, respectively. A deviation of about 7 days, comparable to that observed during budburst, is obtained between the estimates of senescence (MOF) from S-1 and those determined from the in situ monitoring of litterfall. While in spring, leaf emergence and expansion described by LAI or NDVI explain the increase of VV/VH (or the decrease of σ0VH), during senescence, S-1 VV/VH is decorrelated from LAI or NDVI and is better explained by litterfall temporal dynamics. This behavior resulted in a hysteresis phenomenon observed on the relationships between VV/VH and NDVI or LAI. For the same LAI or NDVI, the response of VV/VH is different depending on the phenological phase considered. This study shows the high potential offered by Sentinel-1 SAR C-band time-series for the detection of forest phenology, thus overcoming the limitations caused by cloud cover in optical remote sensing of vegetation phenology.

Reliable phenological observations are needed to quantify the impact of climate change on tree phenology. Ground observations remain a prime source of phenological data, but their accuracy and precision have not been systematically quantified. The high subjectivity of ground phenological observations affects their accuracy, and the high within‐population variability of tree phenology affects their precision. The magnitude of those effects is unknown to date. We first explored the inter‐observer variability in the timing of bud development and leaf senescence in trees using a unique dataset of seven observer inter‐calibration sessions. Then, using tree phenological data collected in three European forests (n = 2,346 observations for budburst, n = 539 for leaf senescence), we quantified how the ‘observer uncertainty’ (accuracy of the observations) and the ‘population sampling uncertainty’ (precision of the observations) combine to affect the estimates of the budburst and the leaf senescence dates. The median observer uncertainty was 8 days for budburst (BBCH = 7) and 15 days for leaf senescence (BBCH = 95). As expected, the population sampling uncertainty decreased with increasing sample size, and was about 6 days for budburst and 10 days for leaf senescence for a sample of 10 individuals monitored per population (corresponding to the median sample size in the phenological literature). As a whole, the overall uncertainty of phenological observations could reach up to 2 weeks for budburst and 1 month for leaf senescence. Synthesis. This paper quantifies for the first time the accuracy and precision of ground phenological observations in forest trees and as such offers tables to estimate the uncertainty of phenological data. We show that reliable estimates of budburst and leaf senescence require three times (n = 30) to two times (n = 20) larger sample sizes as compared to sample sizes usually considered in phenological studies. We further call for an increased effort of observer inter‐calibration, required to increase the accuracy of phenological observations. These recommendations reduce the uncertainty of phenological data, thereby improving the estimation of phenological trends over time, the response of phenology to temperature or the inference of phenological model parameters.

First mention of Nomada barcelonensis Cockerell, 1917 for France (Hymenoptera: Apidae: Nomadinae) . - The authors relate here the discovery within Mediterranean fringe of metropolitan France, in the Var department, of a species of Nomada so far only known from Spain: Nomada barcelonensis Cockerell,1917. The ecology, biology and morphological description allowing its determination are presented as well as the conditions of capture of the specimen.

Tree phenology is a major driver of forest–atmosphere mass and energy exchanges. Yet, tree phenology has rarely been monitored in a consistent way throughout the life of a flux-tower site. Here, we used seasonal time series of ground-based NDVI (Normalized Difference Vegetation Index), RGB camera GCC (greenness chromatic coordinate), broadband NDVI, LAI (leaf area index), fAPAR (fraction of absorbed photosynthetic active radiation), CC (canopy closure), fRvis (fraction of reflected radiation) and GPP (gross primary productivity) to predict six phenological markers detecting the start, middle and end of budburst and of leaf senescence in a temperate deciduous forest using an asymmetric double sigmoid function (ADS) fitted to the time series. We compared them to observations of budburst and leaf senescence achieved by field phenologists over a 13-year period. GCC, NDVI and CC captured the interannual variability of spring phenology very well (R2>0.80) and provided the best estimates of the observed budburst dates, with a mean absolute deviation (MAD) of less than 4 d. For the CC and GCC methods, mid-amplitude (50 %) threshold dates during spring phenological transition agreed well with the observed phenological dates. For the NDVI-based method, on average, the mean observed date coincides with the date when NDVI reaches 25 % of its amplitude of annual variation. For the other methods, MAD ranges from 6 to 17 d. The ADS method used to derive the phenological markers provides the most biased estimates for the GPP and GCC. During the leaf senescence stage, NDVI- and CC-derived dates correlated significantly with observed dates (R2=0.63 and 0.80 for NDVI and CC, respectively), with an MAD of less than 7 d. Our results show that proximal-sensing methods can be used to derive robust phenological metrics. They can be used to retrieve long-term phenological series at eddy covariance (EC) flux measurement sites and help interpret the interannual variability and trends of mass and energy exchanges.

On the identity of Coelioxys coturnix Pérez 1884 (Hymenoptera - Megachilidae). - Coelioxys coturnix Pérez 1884 is an uncommon species whose male identification remains uncertain or difficult with available publications. A study of the material contained in the MNHN collections and material lent by M. Schwarz permitted us to confirm some of the Pérez and Dusmet’s described diagnostic features and to find new ones. Those morphological features are illustrated and included in a key to make easier the distinction between C. coturnix and close species.

Phenological cameras have been used over a decade for identifying plant phenological markers (budburst, leaf senescence) and more generally the greenness dynamics of forest canopies. The analysis is usually carried out over the full camera field of view, with no particular analysis of the variability of phenological markers among trees. Here we show that images produced by phenological cameras can be used to quantify the within-population variability of budburst (WPVbb) in temperate deciduous forests. Using seven site-years of image analyses, we report a strong correlation (r(2) = 0.97) between the WPVbb determined with a phenological camera and its quantification through ground observation. We show that WPVbb varies strongly (by a factor of 4) from year to year in a given population and that those variations are linked with temperature conditions during the budburst period, with colder springs associated to a higher differentiation of budburst (higher WPVbb) among trees. Deploying our approach at the continental scale, i.e., throughout phenological cameras networks, would improve the understanding of the spatial (across populations) and temporal (across years) variations of WPVbb, which have strong implications on forest functioning, tree fitness and phenological modelling.

The impact of atmospheric reactive nitrogen (Nr) deposition on carbon (C) sequestration in soils and biomass of unfertilized, natural, semi-natural and forest ecosystems has been much debated. Many previous results of this dC∕dN response were based on changes in carbon stocks from periodical soil and ecosystem inventories, associated with estimates of Nr deposition obtained from large-scale chemical transport models. This study and a companion paper (Flechard et al., 2020) strive to reduce uncertainties of N effects on C sequestration by linking multi-annual gross and net ecosystem productivity estimates from 40 eddy covariance flux towers across Europe to local measurement-based estimates of dry and wet Nr deposition from a dedicated collocated monitoring network. To identify possible ecological drivers and processes affecting the interplay between C and Nr inputs and losses, these data were also combined with in situ flux measurements of NO, N2O and CH4 fluxes; soil NO3- leaching sampling; and results of soil incubation experiments for N and greenhouse gas (GHG) emissions, as well as surveys of available data from online databases and from the literature, together with forest ecosystem (BASFOR) modelling. Multi-year averages of net ecosystem productivity (NEP) in forests ranged from −70 to 826 g C m−2 yr−1 at total wet + dry inorganic Nr deposition rates (Ndep) of 0.3 to 4.3 g N m−2 yr−1 and from −4 to 361 g C m−2 yr−1 at Ndep rates of 0.1 to 3.1 g N m−2 yr−1 in short semi-natural vegetation (moorlands, wetlands and unfertilized extensively managed grasslands). The GHG budgets of the forests were strongly dominated by CO2 exchange, while CH4 and N2O exchange comprised a larger proportion of the GHG balance in short semi-natural vegetation. Uncertainties in elemental budgets were much larger for nitrogen than carbon, especially at sites with elevated Ndep where Nr leaching losses were also very large, and compounded by the lack of reliable data on organic nitrogen and N2 losses by denitrification. Nitrogen losses in the form of NO, N2O and especially NO3- were on average 27 % (range 6 %–54 %) of Ndep at sites with Ndep < 1 g N m−2 yr−1 versus 65 % (range 35 %–85 %) for Ndep > 3 g N m−2 yr−1. Such large levels of Nr loss likely indicate that different stages of N saturation occurred at a number of sites. The joint analysis of the C and N budgets provided further hints that N saturation could be detected in altered patterns of forest growth. Net ecosystem productivity increased with Nr deposition up to 2–2.5 g N m−2 yr−1, with large scatter associated with a wide range in carbon sequestration efficiency (CSE, defined as the NEP ∕ GPP ratio). At elevated Ndep levels (> 2.5 g N m−2 yr−1), where inorganic Nr losses were also increasingly large, NEP levelled off and then decreased. The apparent increase in NEP at low to intermediate Ndep levels was partly the result of geographical cross-correlations between Ndep and climate, indicating that the actual mean dC∕dN response at individual sites was significantly lower than would be suggested by a simple, straightforward regression of NEP vs. Ndep.

Abstract. Tree phenology is a major driver of forest-atmosphere mass and energy exchanges. Yet tree phenology has historically not been recorded at flux measurement sites. Here, we used seasonal time-series of ground-based NDVI (Normalized Difference Vegetation Index), RGB camera GCC (Greenness Chromatic Coordinate), broad-band NDVI, LAI (Leaf Area Index), fAPAR (fraction of Absorbed Photosynthetic Active Radiation), CC (Canopy Closure), fRvis (fraction of Reflected Radiation) and GPP (Gross Primary Productivity) to predict six phenological markers detecting the start, middle and end of budburst and of leaf senescence in a temperate deciduous forest. We compared them to observations of budburst and leaf senescence achieved by field phenologists over a 13-year period. GCC, NDVI and CC captured very well the interannual variability of spring phenology (R2 \u003e 0.80) and provided the best estimates of the observed budburst dates, with a mean absolute deviation (MAD) less than 4 days. For the CC and GCC methods, mid-amplitude (50 %) threshold dates during spring phenological transition agreed well with the observed phenological dates. For the NDVI-based method, on average, the mean observed date coincides with the date when NDVI reaches 25 % of its amplitude of annual variation. For the other methods, MAD ranges from 6 to 17 days. GPP provides the most biased estimates. During the leaf senescence stage, NDVI- and CC-derived dates correlated significantly with observed dates (R2 = 0.63 and 0.80 for NDVI and CC, respectively), with MAD less than 7 days. Our results show that proximal sensing methods can be used to derive robust phenological metrics. They can be used to retrieve long-term phenological series at flux measurement sites and help interpret the interannual variability and trends of mass and energy exchanges.

We assembled homogenized long-term time series, up to 19 years, of measurements of net ecosystem exchange of CO2 (NEE) and its partitioning between gross primary production (GPP) and respiration (R-eco) for five different ecosystems representing the main plant functional types (PFTs) in France. Part of these data was analyzed to determine the influence of the main environmental variables on carbon fluxes between temperate ecosystems and the atmosphere, and to investigate the temporal patterns of their variations. A multi-temporal statistical analysis of the time series was conducted using random forest (RF) and wavelet coherence approaches. The RF analysis showed that, in all ecosystems, the incident solar radiation was highly correlated with GPP and that GPP was better correlated with the temporal variations of NEE than R-eco. The air temperature was the second most important driver in ecosystems with seasonal foliage, i.e., deciduous forest, cropland and grassland; whereas variables related to air or soil drought were prominent in evergreen forest sites. The environmental control on CO2 fluxes was tighter at high frequency suggesting an increased resilience to environmental variations at longer time spans. The spectral analysis performed on three of the five sites selected revealed contrasting temporal patterns of the cross-coherence between CO2 fluxes and climate variables among ecosystems; these were related to the respective PFT, management and soil conditions. In all PFTs, the power spectrum of GPP was well correlated with NEE and clearly different from R-eco. The spectral correlation analysis showed that the canopy phenology and disturbance regime condition the spectral correlation patterns of GPP and R-eco with the soil moisture and atmospheric vapour deficit.

Preliminary list of the bees of the Franche-Comté region (Hymenoptera, Anthophila). - This work synthesizes the knowledge of Hymenoptera Anthophila of our region, with the aim to establish the first list of species to assess regional biodiversity. Begun in 2016, it summarizes historical data contained in the collections of the Besançon Natural History Muséum, and extends to other data obtained throughout decades by multiple naturalist associations (OPIE-FC, CBNFC-ORI, CEN-FC, Réserves Naturelles…), educational institutions (LEGTA de Mancy et Montmorot, Lons-le Saunier, Jura), independent consultancy firms (ECOJURA Environnement-Insectes) and targeted contemporary research. Specific determinations were verified and validated in collaboration with several specialists, such as David Genoud, Éric Dufrêne, Matthieu Aubert and Christophe Praz, to whom we would like to express here our gratitude. The present work shows the presence of 275 species from the former Franche-Comté region : 189 from the Doubs, 55 from the Haute-Saône, 226 from the Jura and 1 from the Territoire de Belfort. This synthesis will certainly become quickly obsolete, after analysis of collections not yet studied and more recent inventories. Nevertheless, it aims to encourage entomologists to prospect, collect and identify specimens to improve knowledge and enable the implementation of a conservation strategy for our wild bees. In the future, this works could be extended to the new region of Bourgogne - Franche-Comté.